Citation
Sediment and light requirements for four species of native submerged macrophytes occuring in Florida lakes

Material Information

Title:
Sediment and light requirements for four species of native submerged macrophytes occuring in Florida lakes
Creator:
Hopson-Fernandes, Margaret Sherrie
Publication Date:
Language:
English
Physical Description:
xvii, 247 leaves : ill. ; 29 cm.

Subjects

Subjects / Keywords:
Biomass ( jstor )
Chara ( jstor )
Epiphytes ( jstor )
Lakes ( jstor )
Macrophytes ( jstor )
Nutrients ( jstor )
Plant growth ( jstor )
Plants ( jstor )
Sediments ( jstor )
Species ( jstor )
Dissertations, Academic -- Environmental Engineering Sciences -- UF ( lcsh )
Environmental Engineering Sciences thesis, Ph. D ( lcsh )
Genre:
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 2005.
Bibliography:
Includes bibliographical references.
General Note:
Printout.
General Note:
Vita.
Statement of Responsibility:
by Margaret Sherrie Hopson-Fernandes.

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
Copyright [name of dissertation author]. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Resource Identifier:
003320037 ( ALEPH )
AA00004681_00001 ( sobekcm )
770716200 ( OCLC )

Downloads

This item has the following downloads:


Full Text









SEDIMENT AND LIGHT REQUIREMENTS OF FOUR SPECIES OF NATIVE
SUBMERGED MACROPHYTES OCCURRING IN FLORIDA LAKES













By

MARGARET SHERRIE HOPSON-FERNANDES


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY


UNIVERSITY OF FLORIDA


2005
















To my family Carlos, Eddie, Maria, Mom and Daddy for your undying support
and willingness to help no matter what needed to be done. We did it!













ACKNOWLEDGMENTS

I would like to express my gratitude to all of the people who helped me to reach

this incredible goal. My sincere thanks go to Dr. Koopman for his guidance,

encouragement and genuine commitment to education. I appreciate his continued

patience and flexibility in working with a student "not living locally." His comprehensive

reviews of the dissertation also proved invaluable. I am indebted to Dr. Phlips for always

encouraging me to strive to find ecological explanations and for his generosity in sharing

so many thought-provoking ideas with me. He also provided invaluable assistance in

securing funding for this project. Dr. Sutton gave me a key to his laboratory, his fabulous

growth tank facilities and his supply shed before I had any funding in place. Thanks to

his generosity, I was able to begin my research in a timely fashion. I also appreciate his

willingness to accommodate my research needs by making space and supplies available

to me throughout my program. I extend many thanks to Dr. Montague for encouraging

me to view conventional ecological issues from alternative perspectives.

I am very honored to have been a GAANN Fellow. I am grateful for the

opportunity given to me by the United States Department of Education in association

with the University of Florida Department of Environmental Engineering Sciences. My

sincere thanks go to Dr. J .J. Warwick for his commitment to the advancement of the

academic careers of students in his department. I am also very privileged to have received

a Supplemental Retention Award from the UF Office of Graduate Minority Programs.








Funding for this research was provided by a grant awarded to the Department of

Fisheries and Aquatic Sciences, University of Florida, by the City of Lakeland Lakes

Program. Special thanks go to Mr. Gene Medley and Mr. Bal Sukrah and the personnel

from the City of Lakeland Lakes and Stormwater and Construction and Maintenance

Divisions for providing logistical and field support in Lake Hollingsworth. Dr. Gabe

Vargo (Marine Science Laboratory, University of South Florida) generously offered the

use of his facilities and equipment for field and laboratory research. I am indebted to Ms.

Joanne Korvick of the University of Florida, Ft. Lauderdale Research and Education

Center (UF FLREC) for her friendship, expert advice on field-related issues and

willingness to lend assistance in the field. Mr. Frank Nazario also provided valuable field

support at the UF FLREC. I greatly appreciate the assistance of Ms. Merrie Beth Neely

(Marine Science Laboratory, University of South Florida) for her help with the

macrophyte chlorophyll a analyses. Many thanks go to Dr. H. J. Grimshaw (South

Florida Water Management District) for his generous exchange of ideas during the

development of the experimental design for the light experiment. He also graciously lent

me a light probe. Mr. Dan Mahon analyzed sediment samples for organic matter content

and subsamples for epiphyte chlorophyll a for one culture period at the laboratory at the

City of Lakeland Carl W. Dicks Wastewater Reclamation Facility. Thanks go to Dr.

Vernon Vandiver for helping me "see the light" about some problems with the

experimental design in my first light experiment. Dr. Chuck Cichra (Department of

Fisheries and Aquatic Sciences, University of Florida) helped me to understand the wild

world of SAS. His help proved invaluable. Dr. Cornell provided statistical guidance.

Sediment nutrient analyses were performed by the Analytical Research Laboratory of the








Soil and Water Science Department, University of Florida, Gainesville. Mr. Matt Phillips,

of the Florida Fish and Wildlife Conservation Commission, graciously allowed me to use

the drying oven at his facility. Many warm thanks go to the Environmental Engineering

Office staff, especially Ms. Berdenia Monroe, Ms. Barbi Barber and Ms. Hoa Dinh for all

of the kindness that they bestowed upon me. I am also indebted to the Fisheries and

Aquatic Sciences Office staff, especially Ms. Jennifer Hermelbracht and to Ms. Bobbi

Godwin (Center for Aquatic and Invasive Plants) for all of their assistance over the years.













TABLE OF CONTENTS


ACKNOW LEDGM ENTS ...............................................................................................iii

LIST OF TABLES ....................................................................................................... viii

LIST OF FIGURES ...................................................................................................... xii

ABSTRACT................................................................................................................. xvi

CHAPTER

1. INTRODUCTION ...................................... .............................................. I

Background Inform ation.................................................................................
Statem ent of Purpose................................................................................... 3
Hypotheses................................................................................................... 4

2. LITERATURE REVIEW ...................................... ................................. 6

Background Inform ation.............................................................................. 6
Lake Restoration Techniques....................................................................... 7
Algal Biom ass Control M ethods.................................................................. 8
M acrophyte Biom ass Control M ethods ........................................................ 11
Aeration and Sedim ent Rem oval ............................................................... 12
Revegetation Projects in Lake Restoration................................................ 14
M acrophyte Species Selection................................................................... 20
Description of Study M acrophytes ............................................................ 22
Subm erged M acrophyte Biology ............................................................... 24
Environmental Factors Controlling Production ......................................... 29
The Role of Light in Submerged Macrophyte Growth.............................. 30
The Role of Sediments in Macrophyte Nutritional Ecology ..................... 32
Culturing Subm erged M acrophytes ........................................................... 35
Epiphytic Algae ......................................................................................... 36
The M acrophyte-Epiphyte Complex.......................................................... 39
M ethods for Investigating Epiphytic Algae............................................... 42








3. COMPARISON OF THE GROWTH OF FOUR SPECIES OF NATIVE
SUBMERGED MACROPHYTES ON INORGANIC SEDIMENTS FROM A
SHALLOW URBAN FLORIDA LAKE ...................................................... 48
Introduction and Literature Review ..................................................... 48
Materials and Methods......................................................................... 55
R esults.................................................................................................. 64
Discussion............................................................................................ 80
Conclusions.......................................................................................... 93

4. LIGHT REQUIREMENTS OF FOUR SPECIES OF NATIVE SUBMERSED
MACROPHYTES: IMPLICATIONS FOR THE RESTORATION OF
SHALLOW EUTROPHIC LAKES 1. ASSESSMENT FOR MATURE
PLA N TS .................................................................................................. 123
Introduction........................................................................................ 123
Materials and Methods....................................................................... 126
R esults................................................................................................ 132
D discussion .......................................................................................... 139
Conclusions........................................................................................ 144

5. LIGHT REQUIREMENTS OF FOUR SPECIES OF NATIVE
SUBMERSED MACROPHYTES: IMPLICATIONS FOR THE
RESTORATION OF SHALLOW EUTROPHIC LAKES 2. ASSESSMENT
FOR PROPAGULE PLANTS ................................................................. 166
Introduction........................................................................................ 166
Materials and Methods....................................................................... 169
R esults................................................................................................ 174
D discussion .......................................................................................... 181
Conclusions........................................................................................ 184

6. SUMMARY AND CONCLUSIONS ...................................................... 214

APPEN D IX ................................................................................................................ 217

LITERATURE CITED.............................................................................................. 221

BIOGRAPHICAL SKETCH..................................................................................... 247













LIST OF TABLES


Table

3-1: Organic matter content and pH of sediments from the preliminary survey............ 95

3-2: Organic matter, pH and selected macro- and micronutrient composition of sediments
from the four study stations and control sediments ..................................................... 96

3-3: Temperature and irradiance during the three culture periods............................... 97

3-4: Spring culture period 30 April to 29 June 2001. Results of analysis of variance to
investigate the effect of sediment source, plant type and the interaction between these two
factors on m acrophyte growth. ..................................................................................... 97

3-5: Spring culture period 30 April to 29 June 2001. Dry weight of study macrophytes
cultured on sediments collected from the four study stations in Lake Hollingsworth and
on artificial sedim ents .................................................................................................. 98

3-6: Stepwise multiple regression analysis results using macrophyte biomass as the
dependent variable, sediment macro- and micronutrient concentrations and epiphyte
biomass as the independent variables ....................................................................99-100

3-7. Spring culture period 30 April to 29 June 2001. Results of analysis of variance to
investigate the effect of sediment source, plant type and the interaction between these two
factors on macrophyte root:shoot ratios..................................................................... 101

3-8: Summer culture period 20 July to 21 September 2001. Results of analysis of
variance to investigate the effect of sediment source, plant type and the interaction
between these two factors on macrophyte biomass ................................................... 101

3-9: Summer culture period 20 July to 21 September 2001. Dry weight of study
macrophytes cultured on sediments collected from the four study stations in Lake
Hollingsworth and on artificial sediments ................................................................. 102

3-10: Summer culture period 20 July to 21 September 2001. Results of analysis of
variance to investigate the effect of sediment source, plant type and the interaction
between these two factors on macrophyte root:shoot ratios ...................................... 103








3-11: Winter culture period 19 December 2001 to 22 February 2002. Results of analysis
of variance to investigate the effect of sediment source, plant type and the interaction
between these two factors on macrophyte biomass ................................................... 103

3-12: Winter culture period 19 December 2001 to 22 February 2002. Dry weight of
study macrophytes cultured on sediments collected from the four study stations in Lake
Hollingsworth and on artificial sediments ................................................................. 104

3-13: Winter culture period 19 December 2001 to 22 February 2002. Results of analysis
of variance to investigate the effect of sediment source, plant type and the interaction
between these two factors on macrophyte root:shoot ratios ...................................... 105

3-14: Results of analysis of variance of pooled total macrophyte biomass of all species
combined produced during the summer and winter culture period to investigate the effect
of culture period, sediment type, plant type and the interaction between the factors... 105

3-15: Differences among the study species in the pooled mean biomass produced during
the summer and winter culture periods...................................................................... 106

3-16: Differences within the study species in the pooled mean biomass produced during
the summer and winter culture periods...................................................................... 107

3-17: Results of analysis of variance of pooled macrophyte root:shoot ratios from the
summer and winter culture period (n=--90) to investigate the effect of culture period,
sediment source, plant type and the interaction between the factors......................... 108

3-18: Differences in the pooled mean root:shoot ratios among the study species........ 108

3-19: Differences within macrophyte species in the pooled mean root:shoot ratios
produced during the summer and winter culture periods........................................... 109

3-20: Results of analysis of variance of pooled epiphyte biomass from the summer and
winter culture periods to investigate the effect of culture period, sediment source, plant
type and the interaction between the factors.............................................................. 109

3-21: Differences in epiphyte biomass occurring in the summer and winter culture
periods (n=30)............................................................................................................. 110

3-22: Differences in epiphyte biomass occurring in the summer and winter culture
periods on each host macrophyte species (n=1 8) ......................................................... 111

3-23: Differences in mean pooled epiphyte biomass (n=30) occurring in the summer and
winter culture periods on each host macrophyte species at the study stations .......... 112

3-24: Differences in mean epiphyte biomass (n=60) occurring at each station during the
summer and winter culture periods............................................................................ 113








3-25: Results of the use of simple regression analysis to evaluate the relative significance
of each sediment characteristic on the pooled mean biomass of all species combined
(total) (n=120) and each individual species (n=30) during the summer and winter culture
periods........................................................................................................................... 113

3-26: Results of the use of simple regression analysis to evaluate the relative significance
of light and water temperature on the pooled mean composite biomass of all species
(n=120) and each individual species (n=30) during the summer and winter culture
periods........................................................................................................................... 114

3-27: Stepwise multiple regression analysis results using pooled macrophyte biomass
produced during the summer and winter culture periods (n=120 for total biomass of all
species combined and n=30 for each individual species) .......................................... 115

4-1: Temperature and irradiance during the three culture periods............................. 146

4-2: Experiment 1: Estimated average instantaneous, daily and total photosynthetic flux
density (PPFD) received over the period 22 August to 16 September 2001 ............. 147

4-3: Results of analysis of net growth (g dry weight per pot per culture period) of above-
ground macrophyte biomass produced in Experiment 1 using GLM procedures ....... 148

4-4: Experiment 2: Estimated average instantaneous, daily and total photosynthetic flux
density (PPFD) received over the period 25 February to 13 April 2002 ................... 148

4-5: Results of analysis of net growth (g dry weight per pot per culture period) of total
macrophyte biomass (above plus below ground biomass) in Experiment 2 using GLM
procedures (SAS Institute Inc. 1999-2001). ............................................................... 149

4-6: Root:shoot ratios for Experiment 2. Values are the means calculated for three culture
containers per macrophyte species per treatment group followed by the standard
deviation........................................................................................................................ 149

4-7: Experiment 3: Estimated average instantaneous, daily and total PPFD received over
the culture period (CP) 16 July to 31 August 2002 ................................................... 150

4-8: Results of analysis of net growth (g dry weight per pot per culture period) of total
macrophyte biomass (above plus below ground biomass) in Experiment 3 using GLM
procedures (SAS Institute Inc. 1999-2001) ............................................................... 150

4-9: Root:shoot ratios for Experiment 3. Values are the means calculated for three culture
containers per macrophyte species per treatment group followed by the standard
deviation........................................................................................................................ 151

Table 4-10: Selected field observations and experimental conclusions concerning the
light requirements of several species of submersed macrophytes ............................. 152









Table 4-11: A comparison of the seasonal light levels at which there was zero net growth
of the study species .................................................................................................... 153

5-1: Temperature and irradiance during the three culture periods............................. 186

5-2: Experiment 1: Estimated average instantaneous, daily and total photosynthetic
photon flux density (PPFD) received over the period 27 April to 14 July 2002.......... 187

5-3: Results of within species analysis of net growth (g dry weight per pot per culture
period) of total macrophyte biomass (above- plus below-ground biomass) in Experiment
1 using GLM procedures (SAS Institute Inc. 1999-2001)......................................... 187

5-4: Within species comparisons of root:shoot ratios for Experiment 1 .......... 188

5-5. Comparisons among species of root:shoot ratios for Experiment 1..................... 188

5-6: Experiment 2: Estimated average instantaneous, daily and total photosynthetic
photon flux density (PPFD) received over the period 21 April to 7 June 2003............ 189

5-7: Results of within- species analysis of net growth (g dry weight per pot per culture
period) of total macrophyte biomass (above plus below ground biomass) in Experiment 2
using GLM procedures (SAS Institute Inc. 1999-2001)............................................ 189

5-8: Experiment 3: Estimated average instantaneous, daily and total photosynthetic
photon flux density (PPFD) received over the period 28 June to 02 August 2003 ..... 190

5-9: Results of analysis of net growth (g dry weight per pot per culture period) of total
macrophyte biomass (above plus below ground biomass) in Experiment 3 using GLM
procedures (SAS Institute Inc. 1999-2001) ............................................................... 190

5-10: Selected field observations and experimental conclusions concerning the light
requirements of several species of submersed macrophytes...................................... 191

5-11: A comparison of the seasonal variation in light levels at which there was zero net
growth of the study species........................................................................................ 192













LIST OF FIGURES

Figure 2-1. Najas guadelupensis is a pioneer species in the Najadaceae.................... 44

Figure 2-2: Chara spp. are macroalgae........................................................................ 45

Figure 2-3: Potamogeton illinoensis is a Florida native perennial with broad lanceolate
leaves............................................................................................................................... 46

Figure 2-4: Vallisneria americana is a perennial with broad ribbonlike leaves .......... 47

Figure 3-1: Map of Lake Hollingsworth showing the location of the four study stations -
B D F and H ............................................................................................................ 116

Figure 3-2: A diagrammatic sketch of the distribution of 7.6-L nursery containers in the
experim ental tanks ..................................................................................................... 117

Figure 3-3: Biomass produced by Najas and Potamogeton during the spring culture
period .......................... ............................................................................................. 118

Figure 3-4: A comparison of the mean biomass produced by each plant species when
grown in sediments from stations: B, D, F and H and controls for each of the three culture
periods ........................................................................................................................... 119

Figure 3-5: A comparison of the average number of individual plants produced by each
species when grown in the six sediments .................................................................. 120

Figure 3-6: Ratio of root:shoot biomass for the four study species in the spring, summer
and winter culture periods.......................................................................................... 121

Figure 3-7: Epiphyte biomass occurring on the study plants..................................... 122

Figure 4-1: Experimental set-up for mature plant light requirements Experiments 1, 2 and
3 and propagule plant light requirements Experiment 1............................................ 154

Figure 4-2: Experiment 1: Graphical interpretation of the net growth of Najas
guadelupensis in response to the percent incident PAR at the water surface............ 155

Figure 4-3: Experiment 1: Graphical interpretation of the net growth of Potamogeton
illinoensis in response to the percent incident PAR at the water surface .................. 156








Figure 4-4: Experiment 1: Graphical interpretation of the net growth of Vallisneria
americana in response to the percent incident PAR at the water surface.................. 157

Figure 4-5: Experiment 2: Graphical interpretation of the net growth of Najas
guadelupensis in response to the percent incident PAR at the water surface............ 158

Figure 4-6: Experiment 2: Graphical interpretation of the net growth of Potamogeton
illinoensis in response to the percent incident PAR at the water surface .................. 159

Figure 4-7: Experiment 2: Graphical interpretation of the net growth of Chara sp in
response to the percent incident PAR at the water surface ........................................ 160

Figure 4-8: Experiment 3: Graphical interpretation of the net growth of Najas
guadelupensis in response to the percent incident PAR at the water surface............ 161

Figure 4-9: Experiment 3: Graphical interpretation of the net growth of Potamogeton
illinoensis in response to the percent incident PAR at the water surface .................. 162

Figure 4-10: Experiment 3: Graphical interpretation of the net growth of Vallisneria
americana in response to the percent incident PAR at the water surface.................. 163

Figure 4-11: Experiment 3: Graphical interpretation of the net growth of Chara sp. in
response to the percent incident PAR at the water surface........................................ 164

Figure 4-12: Mature plant light requirements experiment: Among species comparisons of
macrophyte chlorophyll a measured for each of the study plants ............................. 165

Figure 5-1: Propagule light requirements Experiment 1: Linear regression of PAR at the
air-water interface versus the net growth (g dry weight per container per 78 days) of
Najas guadelupensis. .................................................................................................. 193

Figure 5-2: Propagule light requirements Experiment 1: Linear regression of mid-water
PAR, measured at the sediment-water interface, versus the net growth (g dry weight per
container per 78 days) of Najas guadelupensis ......................................................... 194

Figure 5-3: Propagule light requirements Experiment 1: Linear regression of PAR at the
air-water interface versus the net growth (g dry weight per container per 78 days) of P.
illinoensis. ..................................................................................................................... 195

Figure 5-4: Propagule light requirements Experiment 1: Linear regression of mid-water
PAR measured at the sediment-water interface versus the net growth (g dry weight per
container per 78 days) of P. illinoensis...................................................................... 196

Figure 5-5: Propagule light requirements Experiment 1: Linear regression of PAR at the
air-water interface versus the net growth (g dry weight per container per 78 days) of V.
americana .................................................................................................................... 197









Figure 5-6: Propagule light requirements Experiment 1: Linear regression of mid-water
PAR, measured at the sediment-water interface, versus the net growth (g dry weight per
container per 78 days) of V americana ..................................................................... 198

Figure 5-7: Propagule light requirements Experiment 1: Linear regression of PAR at the
air-water interface versus the net growth (g dry weight per container per 78 days) of
Chara sp........................................................................................................................ 199

Figure 5-8: Propagule light requirements Experiment 1: Linear regression of mid-water
PAR, measured at the sediment-water interface, versus the net growth (g dry weight per
container per 78 days) of Chara sp.............................................................................200

Figure 5-9: Propagule light requirements Experiment 2: Linear regression of PAR at the
air-water interface versus the net growth (g dry weight per container per 48 days) of V.
am ericana. .................................................................................................................... 201

Figure 5-10: Propagule light requirements Experiment 2: Linear regression of mid-water
PAR, measured at the sediment-water interface, versus the net growth (g dry weight per
container per 48 days) of V americana ..................................................................... 202

Figure 5-11: Propagule light requirements Experiment 2: Linear regression of PAR at the
air-water interface versus the net growth (g dry weight per container per 48 days) of P.
illinoensis .....................................................................................................................203

Figure 5-12: Propagule light requirements Experiment 2: Linear regression of mid-water
PAR, measured at the sediment-water interface, versus the net growth (g dry weight per
container per 48 days) of P. illinoensis...................................................................... 204

Figure 5-13: Propagule light requirements Experiment 2: Linear regression of PAR at the
air-water interface versus net growth (g dry weight per container per 48 days) of Chara
sp................................................................................................................................... 205

Figure 5-14: Propagule light requirements Experiment 2: Linear regression of mid-water
PAR, measured at the sediment-water interface, versus net growth (g dry weight per
container per 48 days) of Chara sp............................................................................ 206

Figure 5-15: Propagule light requirements Experiment 3: Linear regression of PAR at the
air-water interface versus the net growth (g dry weight per container per 35 days) of V.
am ericana .................................................................................................................... 207

Figure 5-16: Propagule light requirements Experiment 3: Linear regression of mid-water
PAR, measured at the sediment-water interface, versus the net growth (g dry weight per
container per 35 days) of V. americana ..................................................................... 208








Figure 5-17: Propagule light requirements Experiment 3: Linear regression of PAR at the
air-water interface versus the net growth (g dry weight per container per 35 days) of P.
illinoensis. Outlying data points were excluded from analysis and are indicated in the
figure as open circles. ................................................................................................. 209

Figure 5-18: Propagule light requirements Experiment 3: Linear regression of mid-water
PAR, measured at the sediment-water interface, versus the net growth (g dry weight per
container per 35 days) of P. illinoensis......................................................................... 210

Figure 5-19: Propagule light requirements Experiment 3: Linear regression of PAR at the
air-water interface versus the net growth (g dry weight per container per 35 days) of
Chara sp........................................................................................................................211

Figure 5-20: Propagule light requirements Experiment 3: Linear regression of mid-water
PAR, measured at the sediment-water interface, versus the net growth (g dry weight per
container per 35 days) of Chara sp............................................................................ 212

Figure 5-21: Among species comparisons of macrophyte chlorophyll a produced during
propagule plant light requirements Experiment 1 (4/27 to 7/14/02).......................... 213













Abstract of Dissertation Presented to the Graduate School
Of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

SEDIMENT AND LIGHT REQUIREMENTS OF FOUR SPECIES OF NATIVE
SUBMERGED MACROPHYTES OCCURRING IN FLORIDA LAKES

By

Margaret Sherrie Hopson-Fernandes

May 2005

Chair: Ben Koopman, Ph.D.
Cochair: Edward J. Phlips, Ph.D.
Major Department: Environmental Engineering Sciences

The purpose of this research was to investigate sediment and light growth

requirements, two key factors in the establishment of native submersed macrophytes in

shallow eutrophic Florida lakes. The study plants were Najas guadelupensis,

Potamogeton illinoensis, Vallisneria americana and Chara sp., all Florida native

submerged species commonly occurring state-wide. The selected species exhibited a

variety of morphometries and life histories. The results will be of value to lake managers

for use in the development of a more systematic approach to the establishment of diverse

communities of desirable native species.

This study was divided into two main objectives. In Objective 1, the study species

were cultured outdoors in growth tanks in south Florida for three separate 9-week culture

periods on inorganic sediments collected three different times from four littoral stations

in Lake Hollingsworth and on artificial control sediments. The results suggested that the








inorganic sediments collected from Lake Hollingsworth had sufficient nutrient levels to

support the growth of the study species. The findings further indicated that late spring

was the ideal time to introduce plant propagules into restored systems. Submerged

macrophyte growth in this study appeared to be most significantly affected by a

combination of factors including light, water temperature and sediment nutrients.

In Objective 2, shade cloth was used to establish four light treatment groups in an

outdoor growth tank in south Florida. The light requirements of mature plants and

vegetative propagules were investigated during three culture periods for each group. The

photosynthetic photon flux density (PPFD) for no net growth of mature plants ranged

from 14 to 416 pmol photons s'l m-2 (2 to 50% incident irradiance). The PPFD for no net

growth of propagules ranged from 25 to 183 pmol photons s"' m"2 (3 to 22% incident

irradiance). V americana exhibited the lowest minimum light requirement for growth, 2

to 18% incident irradiance. Propagules of P. illinoensis and V americana had higher light

requirements as compared with mature plants. Both mature and propagule plants

exhibited the greatest capability for growth at low light levels during the summer culture

periods.


xvii













CHAPTER 1
INTRODUCTION

Background Information

Submersed macrophytes are important ecological components of aquatic

systems. These primary producers provide excellent habitat for epiphytes (Cattanco

and Kalff 1980, Wetzel 1999b), invertebrates (Soszka 1975, Wetzel 2001), fish

(Wiley et al. 1984) and a variety of other aquatic organisms (van der Velde 1987).

Aquatic macrophytes also play a critical role in the nutrient dynamics of aquatic

ecosystems (Carpenter and Lodge 1986).

Macrophyte growth is affected by a variety of abiotic and biotic factors

including light availability, water depth, nutrient availability and sediment

composition (Spence 1967, Canfield et al. 1983, Chambers and Kalff 1987). Biotic

factors such as the degree of colonization by epiphytes (Sand-Jensen and Borum

1984, Sand-Jensen 1990), competition with phytoplankton (Fitzgerald 1969, Allen

1971) and inter-specific competition (McCreary 1991) also impact macrophyte

production. Herbivory and grazing often play an integral role in macrophyte

community dynamics in many systems (cf. Lodge 1991). There is currently

considerable evidence that indicates that light (Canfield et al. 1985, Duarte and Kalff

1986, Kalff 2002) and sediment physical and nutrient composition (Barko and Smart

1986, Short 1987, Barko et al. 1991) are among the most significant abiotic factors

controlling submersed macrophyte growth.








Realization of the pivotal role that submersed macrophytes play in

determining the alternative stable state of shallow productive lakes and ponds (cf.

Moss 1990, Scheffer et al. 1993, Donnabaum et al. 1999) has led to an increased

interest in the nutritional ecology of submersed macrophytes. However, a review of

the literature indicates that, to date, little research has been done on the sediment and

light requirements for growth of submersed macrophytes especially species native to

subtropical and tropical climes. Information on the growth requirements of native

submersed macrophytes will be of particular value to lake managers for use in the

development of a more systematic approach to the establishment of desirable aquatic

vegetation in restored systems.

Natural sediments investigated in this study were collected from Lake

Hollingsworth. Lake Hollingsworth is a 144 ha shallow (Znen= 1.2 m) (City of

Lakeland 1988-2000) urban lake located in central Florida (28001'30", 810 56'45")

(Figure 3-1). The lake is a solution basin roughly circular in shape with a mean depth

of 1.2 m (Lake Hollingsworth Diagnostic Feasibility Study 1994). Water inputs to the

lake are in the form of rainfall, groundwater seepage, stormwater runoff and inputs

from Lakes Morton and Homey. Groundwater recharge contributes up to 85% of the

total water budget for the lake (Romie 1994). Surface drainage flows southeast into

Lake Bentley. Paleolimnological study indicated that Lake Hollingsworth is naturally

eutrophic (Brenner et al. 1995). This is probably due to the fact that the lake lies in

the Bartow Embayment division of the Central Lakes District where the underlying

bedrock consists of the phosphatic sands and clays of the Bone Valley region of

Central Florida (Canfield and Hoyer 1992). During the course of the study, Lake








Hollingsworth was being restored using whole-lake dredging in order to remove a

layer of flocculent organic measuring up to 15 feet in thickness in some areas of the

lake. The lake is a highly valued resource, serving as the site for a variety of social,

educational and recreational activities for the City of Lakeland and the surrounding

community. The lake also supports sustenance, commercial and sport fisheries.

Statement of Purpose

The goal of this research was to investigate two key factors in the

establishment of native submersed macrophytes in shallow eutrophic urban Florida

lakes: sediment and light growth requirements. This study was divided into two main

objectives. The first objective was to investigate the effect of sediment chemical

composition on the growth of four species of native submersed macrophytes: Najas

guadalupensis (Sprengel) Magnus., Potamogeton illinoensis Morong., Vallisneria

americana Michaux and Chara sp. Objective two was to investigate the amount of

photosynthetically active radiation (PAR) required for the survival and growth of the

four study species. In Objective 1, plants were cultured outdoors in growth tanks in

south Florida for three separate 9-week culture periods on sand sediments collected

three different times from four littoral stations in Lake Hollingsworth. In Objective 2,

shade cloth was used to establish four light treatment groups in an outdoor growth

tank in south Florida. Mature macrophytes were cultured on artificial sediments

during three separate culture periods, one approximately 4 weeks in length and the

other two approximately 7 weeks in length. The light requirements of macrophyte

propagules grown on artificial sediments were also evaluated during three separate








culture periods. This research will provide valuable information for use in the

establishment of desirable native submerged macrophytes in lake restoration projects.

Hypotheses

Experiment 1: Effects of Sediment on Macrophyte Growth

The experimental procedure was designed to test several hypotheses based

upon findings from the literature and previous experience. The first was that there

would be spatial variation in the organic matter and nutrient content of the littoral

sediments in Lake Hollingsworth. I also anticipated that N. guadelupensis, P.

illinoensis and Chara sp., the canopy-forming, erect species, would produce greater

biomass in sediments with higher nutrient levels while net growth of V americana, a

rosette species, would be inversely related to sediment nutrient content. Based upon

my personal experience growing stock cultures of the study plants, I expected to

observe differences in growth rate among the species such that N. guadelupensis

would be the fastest grower followed by P. illinoensis, V. americana and lastly Chara

sp. I further expected the growth rate of Chara sp to be positively related to

increasing culture period length. I anticipated that N. guadalupensis, V americana

and Chara sp. would produce the greatest biomass during the summer months while

growth of P. illinoensis, a species with a range distribution that stretches into more

temperate regions, would be stimulated by the cooler temperatures of the winter

months. Finally, I hypothesized that sediments collected from the littoral zone of

Lake Hollingsworth would have sufficient quantities of sediment nutrients to support

the growth of N. guadalupensis, P. illinoensis, V americana and Chara sp. when

grown in the experimental growth tanks used in this study.








Experiment 2: Effects of Light on Macrophyte Growth

The procedure used in the first part of Experiment 2 was designed to test

several hypotheses reagrding the light requirements of mature plants of the study

species. The first hypothesis was that N. guadelupensis and Chara sp. would exhibit

the highest light requirements for net growth due to self-shading due to the habit and

growth strategies of these species. I anticipated that V. americana would exhibit the

lowest light requirement for net growth among the study species, approximately 4%

incident irradiance. Based upon the literature, I expected the PPFD for no net growth

of P. illinoensis and N. guadelupensis to be approximately 11% and 15% incident

irradiance, respectively. I anticipated PPFD for no net growth of Chara sp. to range

between 4 and 20% incident irradiance. I further expected to observe photoinhibition

in those species that are either canopy-formers or have an erect habit, N.

guadelupensis, P. illinoensis and Chara sp., at light levels > 26.2% incident

irradiance.

The procedure used in the second part of Experiment 2 was designed to test

several hypotheses regarding the light requirements of vegetative propagule plants of

the study species. First, I hypothesized that plants grown from propagules would have

higher light requirements than mature plants of the same species. I anticipated that V

americana would exhibit the greatest capability for growth in low levels of light. I

further expected that plants grown from propagules would not become photoinhibited

during the course of each culture period.













CHAPTER 2
LITERATURE REVIEW

Background Information

A review of the literature indicates that little is known about the macrophytes

that are often an integral component in the ecosystem processes of shallow productive

lakes and ponds concentrated in subtropical to tropical climates. With the exception

of some limited studies (i.e. Denny 1972b, 1973, Finlayson et al. 1980, Geddes 1984,

Roijackers and Verstraelen 1988, Limon et al. 1989, Mitchell 1989, Schriver et al.

1995), most limnological research has been conducted in deepwater oligotrophic to

mesotrophic systems located in temperate climes. Much of the limited research in

shallow systems has been conducted in Denmark (e.g. Finlayson et al. 1980,

Roijackers and Verstraelen 1988, Schriver et al. 1995) and other temperate climes

(Donnabaum et al. 1999). Most of the research to date on the autotrophic component

of lacustrine systems has been conducted on the phytoplankton occurring in

deepwater temperate lakes. The majority of the research that has been conducted on

macrophytes occurring in subtropical to tropical climes has been focused either on

emergent vegetation or on nuisance exotic species such as hydrilla (Pieterse 1981,

Barko 1982, Steward 1984, Barko and Smart 1986, Sutton 1990, 1993, Sutton et al.

1992, Sutton and Portier 1995, Sutton and Latham 1996).

The emerging interest in using macrophytes in lake restoration projects has

identified the need for more information on the growth requirements of submerged








aquatics especially native species occurring in subtropical to tropical climates

(Nichols 1991, Smart 1996). This information will be very useful to lake managers

conducting restoration projects which include a littoral zone enhancement component.

Lake Restoration Techniques

Restoration can be defined as the action of returning an ecosystem to a former

condition following degradation caused by some kind of disturbance. A typical lake

restoration project would begin with the elimination or significant reduction of

anthropogenic nutrient loading and include a land restoration and management

program (Cooke et al. 1993). It might also include the manipulation of the structure of

the fish community, reestablishment of native plant communities, and restoration of

wetland areas in the watershed. The objective of the typical lake restoration project is

to return the system to a long-term steady state condition similar to its pre-disturbance

condition and in accord with reasonably attainable conditions, as dictated by the

characteristics of the ecological region (Cooke et al. 1993). Prior to the

implementation of any lake restoration initiative, a diagnosis and feasibility study

should be conducted. Cooke et al. (1993) provide a comprehensive discussion of the

components and procedures for the development of diagnosis and feasibility studies.

The purpose of such studies is to evaluate the current status of the lake, determine the

severity of the problem, and use the results to propose the most suitable restoration

technique. Proposed techniques should be cost efficient while still permitting

attainment of water quality goals.

Lake restoration methods are divisible into four groups depending upon their

primary objective: 1) to control algal biomass, 2) to control macrophyte biomass, 3)








to alleviate oxygen problems and 4) to remove sediment. These methods are

described in the following.

Algal Biomass Control Methods

A variety of mechanical and chemical methods are used to control algal

biomass in surface waters. The first step in the control of algal biomass is the

reduction of nutrient loading to the system (Cooke et al. 1993, Hosper 1998,

Anadotter et al. 1999, Jeppesen et al. 1999, Phillips et al. 1999, Van der Molen and

Portielje 1999, Robertson et al. 2000, Sondergaard et al. 2000b, Barbieri and Simona

2001). This can be done using a variety of Best Management Practices (BMPs) in the

watershed (Cooke et al. 1993, Robertson et al. 2000), mechanical devices such as

CDS units to screen out debris and large particulate matter in inflows, enhancement

of wetlands in the watershed and/or physical diversion, or re-meandering of inflows

(Annadotter et al. 1999, Jeppesen et al. 1999, Robertson et al. 2000). Chemical

solutions include aluminum sulfate (alum) injection systems installed in stormwater

pipes and improved treatment of wastewater inflows (Anadotter et al. 1999,

Donnabaum et al. 1999). After ensuring the quality of the water entering the system,

the next step is to minimize internal loading of sediment nutrients, especially

phosphorus. Internal loading can be a significant source of nutrient input to a lake,

especially in shallow lakes with a long fetch (Maciena and Soballe 1990). Various

methods can be used to decrease internal loading including the more traditional

approach of alum application (Cooke et al. 1993, Anon 1996, Robertson et al. 2000,

Rydin et al. 2000) or sediment oxidation through enhanced nitrification (Donnabaum

et al. 1999). Some more recent experiments have been conducted to investigate other








chemical alternatives for sediment phosphorus inactivation, including hypolimnetic

nitrate dosing and gypsum application to sediments. Sondergaard et al. (2000a)

concluded that hypolimnetic nitrate dosing is a potential restoration technique for use

in deepwater lakes in which internal loading is a problem. Salonen and Varjo (2000)

determined that the application of gypsum to sediments to control nutrient release had

potential value as a restoration technique. In their evaluation of the most commonly

used restoration techniques in Danish lakes, Sondergaard et al. (2000b) concluded

that hypolimnetic oxidation can be used to reduce internal phosphorus loading.

Copper sulfate, a traditional method used to lower the algal standing crop in lakes, is

used infrequently in contemporary restoration projects due, in part, to detrimental

environmental impacts (Cooke et al. 1993).

There are also a variety of mechanical methods for lake restoration. Dilution

with low-nutrient water and subsequent flushing of nutrients and algal biomass is a

method that can be applied in the absence of external control of inflows to the lake

(Hosper 1999). Other mechanical restoration methods include withdrawal of nutrient-

rich hypolimnetic waters and aeration (Lindenschmidt and Hamblin 1997). Biological

control methods involving food web manipulations are also options for decreasing

algal biomass in systems. Numerous studies have documented the successful use of

biomanipulation as a lake restoration strategy (Shapiro 1990, Perrow et al. 1995,

Drenner and Hambright 1999, Jeppesen et al 1999, Robertson et al. 2000,

Sondergaard et al. 2000b). Kairesalo et al. (1999) discuss the necessary components

of a successful biomanipulation plan for use in system restoration.








Each of the aforementioned methods has its associated advantages and

disadvantages. Some methods are considerably more costly than others. Flushing, for

example, is a very effective technique, but is highly dependent on the availability of

water in the area (Cooke et al. 1993). Remediation time and sustainability are other

factors that must be considered when choosing a restoration method. McQueen

(1998) discusses some of the challenges managers face in the use of biomanipulation.

Alum has a very rapid and dramatic effect on water quality that can last two to five

years or more (Smeltzer 1990, Anon 1996). However, the longevity of the positive

effects of alum application on water quality vary from system to system and in many

systems alum reapplication is required on a yearly basis in order to maintain desired

water quality levels (Dr. Harvey Harper, President of Environmental Research and

Design, personal observation). Conversely, biomanipulation of systems is an

inexpensive method that can yield sustainable results (Drenner and Hambright 1999).

Positive impacts of this method may not become apparent for several years, however.

Another very important consideration is the impact of each method on ecosystem

health. For example, little is known to date about the long-term ecological effects of

alum on lakes especially on invertebrate populations (Smeltzer 1990, Cooke et al.

1993). Other studies (e.g. Neville 1985, Ramamoorthy 1988) have documented the

lethal effects of aluminum salts in fish. Copper sulfate addition also has a detrimental

effect on the ecology of aquatic systems (Cooke et al. 1993). Moss (1999) made a

comprehensive comparison of the ecological implications associated with some of the

more commonly used lake restoration methods.








Macrophyte Biomass Control Methods

Managers currently have a variety of chemical, physical and biological

methods available to them for the control of macrophyte biomass in lake systems.

Chemical methods involve the use of herbicides. Smith (1995) successfully used

Sonar in the restoration of Long Lake, Washington. The results of this study indicated

that the active ingredient in Sonar, fluoridone, targets exotic species; native species

exhibited less sensitivity to the herbicide. Physical methods for macrophyte control

include preventative measures, hand and mechanical harvesting, water level

drawdown, lake stage manipulations, sediment covers and surface shading. Cooke et

al. (1993) discussed the limitations of the use of preventative measures as a

macrophyte control technique. Carter et al. (1994) reported significant reductions in

macrophyte biomass when they used plastic sheets in several manmade lakes in

Australia.

The escalating problem with proliferation of exotic macrophyte species,

especially in Florida and other southeastern states, in combination with a growing

dissatisfaction with chemical and mechanical methods, has resulted in intense

research into and development of biological controls for aquatic vegetation (Cooke et

al. 1993). Biological controls currently being used in lake systems include

phytophagous insects and fish, plant pathogens (e.g. fungi and viruses) and

allelopathy. Painter and McCabe (1988) documented the successful use of the moth

Acentria nivea to control milfoil in certain Ontario lakes. Crosson (1992) reported

that a weevil, Euhrychiopsis lecontei, and A. nivea together were probably

responsible for declines in milfoil biomass in several Vermont lakes. Other studies








(e.g. Haag and Habeck 1991) suggest that an integration of chemical and biological

methods is the most effective means by which to control aquatic macrophytes. One of

the most commonly used phytophagous fish is the grass carp, or white amur

(Ctenopharyngodon idella (Val.)). The popularity of the use of grass carp is due to

the relatively low cost and long term results associated with the use of this control

agent (Cooke et al. 1993). However, introduction of carp into systems often results in

total eradication of all submerged plants (e.g. Mitchell 1980, Shireman et al. 1985),

suggesting that the viability of the use of carp in macrophyte control is highly

dependent upon the management goal.

As with algal biomass control methods, the management techniques employed

to control macrophyte biomass have associated advantages and disadvantages. Cooke

et al. (1993) provide a thorough discussion of the positive and negative effects of the

use of the various macrophyte control methods and include case studies.

Aeration and Sediment Removal

The two remaining categories of lake restoration methodologies are aeration

and sediment removal. Cooke et al. (1993) refer to these two categories as "multiple

benefit treatments." Aeration of lakes can be achieved through hypolimnetic aeration

and artificial circulation. Ashley and Hall (1990) define hypolimnetic aeration as a

management technique designed to prevent anoxic conditions in the hypolimnion and

the problems associated with anoxic hypolimnea. Potential benefits associated with

the use of this method include oxygenation of the hypolimnion without causing an

increase in temperature or de-stratification, increased habitat for aerobic organisms,

and a decrease in internal phosphorus loading, due to the establishment of aerobic








conditions at the sediment-water interface (Cooke et al. 1993). The objective of

artificial circulation is complete turnover of the lake. Benefits associated with

artificial circulation include an increase in habitat for aerobic organisms, a potential

decrease in internal phosphorus loading, and a possible decrease in algal biomass by

increasing the depth to which phytoplankton are mixed in the water column (Cooke et

al. 1993).

Sediment removal is a multipurpose restoration method. Objectives for the use

of sediment removal include increasing the mean depth of the system, reduction of

internal loading, removal of toxic substances, and mechanical control of aquatic

macrophytes. Disadvantages include sediment resuspension during removal, release

of sediment-bound toxic substances, destruction and degradation of habitat of benthic

organisms, and the need for a disposal location for dredged sediments (Cooke et al.

1993). There are two methods by which sediment can be removed from a lake: lake

drawdown followed by excavation with a bulldozer and sediment removal using a

dredge.

Sediment removal is a frequently used management technique that has

recently been used in a variety of different systems (Bengtsson et al. 1975, Kelly et al.

1994, Annadotter et al. 1999). At the beginning of the present study, hydraulic

dredging was being used in Lake Hollingsworth to remove 2.7 million cubic meters

of flocculent organic sediment. A rapid dewatering process patented by the Florida

Institute of Phosphate Research (FIPR) was used to facilitate disposal of dredged

sediments (Patel 1995). The project in Lake Hollingsworth represents the first field-

testing of this dewatering process. Dredging was halted at approximately 60%








completion to prevent an unplanned drawdown due to drought conditions in the

region. Post-dredge measurements of water quality parameters, including chlorophyll

a, indicate that the removal of sediment is reducing water column nutrients in the

system (Dan Mahone, City of Lakeland Wastewater Chemist, personal

communication).

Numerous researchers have concluded that successful restoration of their

systems required a combination of restoration techniques (Hulon 1994, Kelly et al.

1994, Annadotter et al. 1999, Phillips et al. 1999, Robertson et al. 2000). Restoration

of Delavan Lake, Wisconsin, was conducted in three phases: 1) limiting external

loading using BMPs in the watershed, enhancing an existing wetland, and diverting

inflows, 2) reducing internal P loading using alum inactivation and carp removal, and

3) biomanipulation of the fish population (Robertson et al. 2000). Phillips et al.

(1999) discuss the variety of restoration techniques used in the Norfolk Broads over a

25-year period.

Revegetation Projects in Lake Restoration

The littoral zone habitat enhancement component of restoration projects in

shallow subtropical to tropical eutrophic lakes often includes the establishment of

diverse communities of native submerged macrophytes. As more research is

conducted in shallow lake systems, researchers are beginning to recognize the

importance of aquatic macrophytes in ecosystem processes. Macrophytes are a key

component of most restoration projects involving shallow lakes due to their pivotal

role in determining community dominance. Numerous studies have identified the

existence of multiple alternative stable states in ecosystems (May 1977, 1981, Hosper








1994, Timms and Moss 1984, Scheffer 1990, Scheffer et al. 1993). Hosper (1994),

Timms and Moss (1984), Scheffer et al. (1993) and Donnabaum et al. (1999) identify

two alternative stable states in their study systems: a clear one dominated by aquatic

macrophytes and a turbid one dominated by phytoplankton. Moss (1990) emphasized

the importance of biomanipulation in the prevention of a shift to an undesired stable

state following lake restoration. Scheffer (1990) discusses the use of simple models to

identify the existence of alternate stable states in lakes.

Various studies have attempted to elucidate the mechanisms) that control the

alternation between dominance by macrophytes and phytoplankton. Some studies

suggest that the stabilizing effect of submerged macrophytes on sediments reduces

internal loading during sediment resuspension events (Carpenter and Lodge 1986,

Sondergaard and Moss 1998) thereby reducing the nutrients available for

phytoplankton uptake. Barko and James (1998) suggested that submerged

macrophytes serve as a sink for phosphorus and thus exert positive effects on water

quality in lacustrine systems. Zimba et al. (1995) used chemical composition data in

conjunction with GIS areal estimates to determine the amount of bound nutrients

within the submersed macrophyte communities occurring in Lake Okeechobee in

1990 and 1991. They concluded that 117 metric tons of phosphorus were bound in the

tissues of submersed macrophytes present in the lake in 1990. This number increased

to 125 metric tons in 1991. The results of their study indicated that nutrients were

sequestered by the five species studied in the following order (from the greatest to the

least extent): Vallisneria americana> Hydrilla verticillata>> Potamogeton

illinoenesis>> Chara sp. > Najas guadelupensis. Several studies (e.g. Timms and








Moss 1984, Schriver et al. 1995, Jeppesen et al. 1997) have indicated that the effect

of aquatic macrophytes on the food web in shallow lakes may reduce the turbidity of

the whole system. Landers (1982), Wetzel (1983) and Carpenter and Lodge (1986)

concluded that aquatic macrophytes and their associated epiphytes also play an

important role in littoral and littoral:pelagic nutrient cycling. Moss (1998) discussed

the role of macrophytes in limiting phytoplankton productivity via production of

allelopathic substances. Carpenter and Lodge (1986) presented a thorough discussion

of the effects of submerged macrophytes on ecosystem processes. Using Charisma, a

simulation model, to describe the growth of Chara aspera, van Nes et al. (2002)

concluded that the effect of water clarity on aquatic plant growth is the most

important factor affecting the stable state equilibria of shallow lakes. Similarly, a

positive relationship between water transparency and macrophyte percent volume

infested (PVI) in excess of 30%, irregardless of water column nutrient concentrations

has been identified in several empirical studies conducted in tropical and temperate

systems (Canfield et al.1984, Jeppesen et al. 1990, Canfield and Hoyer 1992).

There are other additional benefits associated with native submerged

macrophyte communities. Submerged macrophytes are a vital component of the

aquatic ecosystem (Wetzel 1983). This is especially true of shallow highly productive

subtropical to tropical systems. From an ecological point of view, these primary

producers provide habitat for zooplankton (Soszka 1975, Timms and Moss 1984,

Winfield 1986, Diehl 1988, Schriver et al. 1995), epiphytes (Cattaneo and Kalff

1980), fish (Wiley et al. 1984, Engel 1985, Killgore et al. 1989) and a variety of other

aquatic organisms (van der Velde 1987). Schriver et al. (1995) concluded that fish








predation on zooplanktivores decreased with increasing PVI of macrophytes

especially when PVI exceeds 15-20%. They discussed the positive implications of

these refugia for zooplankton in the control of phytoplankton. From a management

perspective, several studies (Smart and Barko 1989, McCreary et al. 1991, Barko et

al. 1991 and Smart et al. 1994) have indicated that some native submerged species are

highly competitive and may offer protection from invasion by weedy exotic species.

V americana outcompeted Hydrilla at low light levels in reciprocal replacement

series studies conducted by Smart and Barko (1989). The results of the same study

indicated that Vallisneria exhibits better growth on fertile sediments as compared to

Hydrilla. The introduction of Eleocharis coloradoensis reduced new growth in a

variety of submerged species including Hydrilla verticillata and Myriophyllum

spicatum in an additive study conducted by Yeo and Thurston (1984). Diverse

communities of native submersed macrophytes typically produce less biomass than

monotypic stands of exotic weedy species. In many native species, the growth form

concentrates the majority of the plant biomass beneath the water surface.

Accordingly, native submersed aquatics provide enhanced habitat with fewer of the

management problems such as interference with recreation, navigation, water supply

and hydropower generation and access to the water typically associated with exotic

macrophyte species. Smart and Doyle (1995), Van et al. (1976) and Haller and Sutton

(1975) discuss the adaptations that often make exotics superior competitors,

especially in disturbed areas, as compared to native species. Filling this niche with

desirable native species is essential in order to avoid exchanging one management

challenge for another (Smart et al. 1996).








Despite the rising popularity of littoral zone enhancement projects, there

remains a need for the development of a systematic approach for establishing and

maintaining submerged macrophyte communities that can be used with more

widespread success in lacustrine systems (Nichols 1991, Phillips et al. 1999). The

most common approach to littoral zone development is the introduction of

monocultures of a submerged aquatic species planted on 1-m centers. For example, in

Florida, Vallisneria is the plant most often used in revegetation projects due to its

availability and relative ease in planting (personal observation: results of informal

survey of lake managers around the state). Planting monocultures can often lead to

frustrating results such as invasion by a faster-growing exotic species (Smart and

Doyle 1995). For this reason, the common practice of planting only monospecific

stands of Vallisneria should be avoided. Certainly, the positive characteristics of

Vallisneria make it a highly desirable species for use in restoration efforts. Vallisneria

provides forage for waterfowl and refuge for juvenile fish. Studies have also shown

that it has relatively low light requirements as compared to other species (Carter and

Rybicki 1985, Smart and Barko 1989, this study) thus potentially making it a good

candidate for growth in turbid waters. The growth habit of this macrophyte also

concentrates biomass below the water column. However, in their 1975 study, Haller

and Sutton concluded that Vallisneria is not a strong competitor against Hydrilla.

Although both species are members of the Hydrocharitaceae family, differences in

their growth structure render Hydrilla the superior competitor in most cases. Hydrilla

forms a dense canopy at the water surface and reduces light penetration by 95% in the

first 0.3 m of the water column (Haller and Sutton 1975). Vallisneria communities








produce less biomass, which is concentrated below the water surface so that light

penetration is similar to that of open water. Hydrilla exhibits faster growth than

Vallisneria. Haller and Sutton (1975) determined that Vallisneria invests energy in

the production of large quantities of nonphotosynthetic biomass that would appear to

negate any advantage of its greater leaf area index as compared to Hydrilla. The

difference in biomass production is also attributable to differences in reproductive

strategy. Haller and Sutton (1975) determined that the production of millions of

meristematic tissues per hectare by Hydrilla is a highly competitive strategy.

McCreary (1991) characterized hydrilla and Vallisneria americana as exhibiting

guerilla and phalanyx growth strategies, respectively. She proposed the use of V

americana in combination with an equally robust native canopy-forming phalanyx

species in order to outcompete Hydrilla. In conclusion, use of a variety of species

with a diverse array of reproductive and growth strategies appears to be the most

likely way to avoid colonization of troublesome weedy exotics.

Research being conducted by the Army Corps of Engineers Aquatic Plant

Control Research Program has led to the development of a new revegetation method

that they refer to as the "founder colony" approach (sensu Smart et al. 1998). The key

to this approach is to treat submerged macrophytes introduced into the system much

as one would treat fish i.e., close monitoring, habitat modification and restocking are

provided, on a continuing basis, as necessary. Use of the founder colony approach has

yielded successful results in reservoirs and natural lakes in several states including

Texas, Oklahoma, Kansas, Alabama and New York (Smart et al. 1996, Smart et al.

1998). Establishment of diverse communities of native submerged aquatic plants in








these systems resulted in improved water quality, enhanced fish habitat and

prevention of invasion by weedy exotics. These results indicate the potential for the

successful use of the founder colony approach in a wide variety of lake systems.

Smart et al. (1996) suggested the use of preliminary investigations of selected

environmental characteristics including sediment suitability to evaluate the viability

of a location as submerged macrophyte habitat.

Macrophyte Species Selection

Establishment of diverse submersed macrophyte communities should be a

fundamental goal of lake restoration projects. In order to accomplish this goal, species

selected for lake restoration should include both annuals (pioneer species) and

perennials and r- and K-selected species. In an ecological sense, lakes in which

restoration methods have been recently used to improve water quality are disturbed

environments. In addition, submersed aquatic plant communities are often absent

from such systems for up to many years prior to restoration primarily due to

insufficient light availability for sustained growth. Natural systems recover in a

predictable ecological succession following a disturbance that destroys the plant

community at a given site. The first colonizers are r-selected pioneer species that

exhibit rapid increases in biomass and produce large quantities of widely dispersed

propagule material (Stearns 1977). These characteristics allow pioneer species to

rapidly colonize available niches. Pioneer species also modify the localized

environment in a variety of ways. These species promote stability and conditions

favorable for subsequent establishment of perennials including increased

sedimentation that creates more shallow areas suitable for macrophyte growth








(Carpenter 1981), increased water clarity due to decreased turbidity (Carpenter and

Lodge 1986), decreased algal populations due to reduction in water column nutrients

(Kufel and Ozimek 1994) and/or modifications in the aquatic food web (Schriver et

al. 1995). Eventually, the system enters a more advanced state of succession, and

perennial species dominate the community composition. The life history of perennials

includes a longer life span and increased accumulation of energy reserves which

results in slower growth as compared to that of pioneer species. However, the growth

strategy of perennials makes these species more resistant to subsequent disturbance as

compared to pioneer species (Grime 1979, Sheldon 1986). An additional advantage

associated with the establishment of pioneer species is that these plants produce

extensive seed banks that permit rapid recolonization following any future

disturbance that might set the community back to an earlier successional stage (van

der Valk 1981, Sheldon 1986). The plasticity in response to environmental

perturbation conferred to macrophyte communities by the combined life strategies of

annual and perennial species in diverse communities is probably of pivotal

importance in the maintenance of some shallow eutrophic systems in the macrophyte-

dominated stable state. Community diversity is a fundamental aspect of the founder

colony approach. Smart et al. (1996) discussed the importance of selecting a variety

of species, both annuals and perennials, r-selected and K-selected species as an

important initial step in the use of this method.

Several criteria were used to select the macrophyte species investigated in this

study. Initially, selection was determined by the need to identify Florida native

submersed macrophytes with a wide distribution and for which propagule material is








readily available. In addition, a mix of annual and perennial species was selected in

order to maximize the potential for establishment of viable, self-sustaining

communities of SAV capable of out-competing exotic species in restored lakes.

Finally, plants were selected based on their relative value as habitat for fish and other

aquatic organisms, resistance to herbivory and relative potential positive impact on

the water quality of the lake.

Description of Study Macrophytes

Four species were selected using the aforementioned criteria Najas

guadelupensis (Spreng.) Magnus), Potamogeton illinoensis Merong, Vallisneria

americana Michx.) and Chara sp.

Annuals Najas guadelupensis and Chara sp., both summer annuals, are

excellent pioneer species. N. guadalupensis is often the primary colonizer in areas of

disturbance (i.e. abandoned fish nests, boat trails and in areas previously not

colonized by submersed macrophytes (Lawson 1991, Hopson-Femandes personal

observation). N. guadalupensis expansion is due to prolific seed production, drought

tolerance and ability to colonize by vegetative fragmentation and subsequent

adventitious root formation. N. guadalupensis exhibits a decumbent habit with very

slender, sparsely branched stems with numerous finely dissected (2 cm long and 1.2

mm wide) leaves (Westerdahl and Getsinger 1988) (Figure 2.1). In nature, N.

guadalupensis forms monospecific stands (defined as those in which a single species

contributes greater than 90% of the total biomass).

There are 35 species of Chara occurring in the United States (Figure 2.2). The

majority of the species are dioecious. Reproduction also occurs via fragmentation.








Chara sp. typically occur at shallow depths but have been found at depths greater

than 10 m. Some recent studies (e.g. Blindow 1991, Kufel and Ozimek 1994, Kufel

and Kufel 2002) found that Chara may play an important role in improving water

quality due to its storage capacity and ability to colonize shallow lakes previously

dominated by phytoplankton. In a study conducted in Lake Okeechobee, Steinman et

al. (2002) observed high Chara biomass over a wide range of light levels.

Charophytes were also the first submerged macrophytes to re-establish following a

managed recession of the lake. Kufel and Kufel (2002) discuss additional positive

effects of Chara growth in systems including relatively slower decomposition rates

and lower contributions of sediment-derived nitrogen and phosphorus to the water

column upon decomposition as compared to rooted vascular plants.

Perennials-P. illinoensis, a native perennial in the Potamogetonaceae, is a

common inhabitant of many Florida lakes. As compared to the other macrophytes

included in this study, P. illinoensis has slightly thicker stems and broad, flat

lanceolate leaves measuring 15 cm long by 6 cm wide (Westerdahl and Getsinger

1988) (Figure 2.3). The growth form of this plant involves the production of elongate

stems which typically extend to the water surface. The majority of the elodeid (sensu

Hutchinson 1975) leaves are concentrated in the photic zone. P. illinoensis exhibits

low biomass density (cf. Duarte and Kalff 1990). Members of the Potamogetonaceae

propogate vegetatively via budding from underground rhizomes. The formation of

tubers, structures in which the plant sequesters carbohydrate reserves, is critical to the

germination and early development of young plants (Hodgson 1966).








V americana, a perennial native in the Hydrocharitaceae, exhibits a growth

form that is dissimilar to that of the other study plants (Figure 2.4). V americana

grows as rosettes of elongate, ribbon-like leaves, measuring up to 2 m in length by ca.

3 cm in width (Westerdahl and Getsinger 1988) which arise from a stoloniferous

rootstock. Each rosette usually gives rise to several stolons which in turn produce

multiple rosettes. The root systems may allow V americana to exploit sediment

nutrient reserves that are unavailable to other rooted macrophyte species (Titus and

Stephens 1983). Titus and Stephens (1983) also observed that V americana is

capable of altering its growth pattern in response to the presence of other plant

species. Vallisneria propagates by seeds and by the production of vegetative

propagules. Vallisneria concentrates biomass lower in the water column as compared

to canopy-forming species and exhibits median biomass density (sensu Duarte and

Kalff 1990).

Submerged Macrophyte Biology

According to the classification scheme for aquatic macrophytes developed by

Arber (1920) and Sculthorpe (1967) submerged macrophytes are those aquatic plants

which are rooted in the sediment. This is a heterogeneous group of plants composed

of filamentous algae (e.g. Cladophora), certain macroalgae (e.g. Chara and Nitella)

numerous mosses, a few nonvascular macrophytes and approximately 20 families of

vascular macrophytes (Wetzel 2001). There is considerable evidence that aquatic

angiosperms originated on land. Wetzel (2001) discusses the fact that adaptation and

specialization in aquatic macrophytes lags behind colonization of the aquatic habitat.








He uses this phenomenon to explain the presence of nonfunctional vestigial structures

such as cuticles and stomates in many submerged macrophyte groups.

Life in the aquatic environment has, however, resulted in the development of salient

morphological and physiological features in submerged macrophytes. Submerged

macrophytes do not require a dominant erect axis; there is a reduction in the

lignification of plant tissues and sclerenchyma and collenchyma are rarely present

even in vascular tissues. There is no evidence of secondary growth or cambial

development (Sculthorpe 1967, Wetzel 2001). In many species the vascular strands

are condensed resulting in central lacunae. Submerged macrophytes also exhibit

adaptations to low light availability similar to those displayed by terrestrial shade

plants including a very thin cuticle, thin leaves (1-3 cell layers thick) and high

numbers of chloroplasts in epidermal tissue. Leaves tend to be much more divided,

resulting in much greater surface-to-volume ratios, than in terrestrial plants. Leaf

morphology maximizes exposure to light and to dissolved gases and nutrients in the

water column (Wetzel 2001). Many submerged macrophytes exhibit extreme

heterophylly, often on the same stem or petiole. Submerged macrophytes can be

divided into two groups based upon their growth form as determined by differences in

apical organization: an abbreviated axis producing a rosette of radical leaves or an

elongated flexuous stem with an abundance of leaves and rooted from the nodes

(Sculthorpe 1967). The different growth forms are determined by differences in apical

organization.

Vegetative and clonal reproduction are the primary mechanisms for

propagation and dispersal of submerged macrophytes. Although sexual reproduction








has been retained, vegetative reproduction plays a far more important role in the life

history of hydrophytes. Submerged macrophytes propagate vegetatively via

fragmentation, horizontal expansion by rhizomes, stolons, runners, and tubers and via

the production of specialized organs such as turions (winter buds). Most species

produce aerial, insect or wind-pollinated flowers, although there are some examples

of hydrophily (water-pollinated flowers) (e.g. the Najadales and many genera in the

Hydrocharitaceae) (Sculthorpe 1967). Cox (1993) determined that hydrophily occurs

in < 5% of aquatic species.

Additional morphological and physiological adaptations are necessary to

permit the flow of gases required to minimize the toxic effects of the byproducts of

anaerobic fermentation in aquatic sediments and to sustain photosynthetic and

respiratory metabolic processes (Wetzel 2001). Metabolically significant gases move

throughout the plant body through large intercellular spaces and cortical gas spaces in

roots and shoots. Internal lacunae make up a large portion of the total plant volume

(often > 70%) (Wetzel 2001). A temporal difference in the production of oxygen

during photosynthesis and subsequent release to the environment creates an internal

positive pressure (Hartmann and Brown 1967, Sorrell 1991). This internal pressure

plays a significant role in the internal mass flow of gases throughout the plant body.

Sorrell and Dromgoole (1989) determined that large portions of the oxygen stored in

the lacunae were used in respiratory metabolism without affecting the surrounding

water. Moeslund et al. (1981) concluded that, although oxygen to water exchange

increases with increasing current, oxygen concentrations in the surrounding water do

not reflect the entire amount of oxygen produced during photosynthesis. This








tendency to "stockpile" oxygen prompted Wetzel (2001) to suggest caution in the use

of oxygen evolution experiments as a quantitative indicator of macrophyte

photosynthesis. Much of the oxygen produced during photosynthesis is transported to

the roots and diffuses into the microrhizosphere (Sand-Jensen et al. 1982, Zhang et al.

1998) where it forms an oxidized layer immediately around the root and is utilized by

microaerophyllic bacteria.

There is increasing evidence that inorganic carbon availability may be the

most significant factor limiting aquatic macrophyte growth in some systems. The

diffusion rate of gases in water is four orders of magnitude slower than in air.

Submerged organs are also surrounded by a stagnant boundary layer that can be from

several mm to cm thick (Wetzel 2001) that further impedes gas diffusion into the

plant. In order to survive the challenges posed by carbon acquisition in the aquatic

environment, submerged macrophytes have evolved several adaptations that facilitate

uptake, conservation and recycling of carbon. Morphological modifications to stems,

leaves and petioles that facilitate absorption of dissolved gases include an extremely

thin cuticle, highly reduced mesophyll tissue, concentration of photosynthetic

pigments in the epidermis and thin tissues (1 to 3 cells thick). Once inside the plant

body, large intercellular lacunae facilitate internal diffusion of gases to all plant

organs. Most submerged species exhibit C3-Calvin-type photosynthesis with high

rates of photorespiration (Wetzel 2001). Additional carbon sources for hydrophytes

include the CO2 produced during photorespiration and cellular respiration. Some

softwater species also take up CO2 from sediments (Wetzel 2001). Kimber et al.

(1999) concluded from isotope tests that the majority of the carbon fixed in








Vallisneria was sediment-derived. Some aquatic angiosperms occupying carbon-poor

systems photosynthesize via crassulacean acid metabolism (CAM) (e.g. Vallisneria).

These CAM plants assimilate CO2 at night and store it as malate for use in

photosynthesis during the light hours.

Submerged macrophytes have developed two basic strategies for carbon

assimilation in the aquatic environment (cf. reviews of Maberly and Spence 1983,

Madsen and Sand-Jensen 1991). Some species depend primarily to exclusively on

CO2 for their carbon source (Wetzel 1969, Van et al. 1976, Moeller 1978b, Kadono

1980) while others utilize bicarbonate (Raven 1970, Prins et al. 1980, Beer and

Wetzel 1981, Lucas 1983). Obligate CO2 species are restricted to locales with

sufficient levels of carbon dioxide to support their growth. Since bicarbonate often

occurs in higher concentrations in natural waters as compared to carbon dioxide,

uptake of bicarbonate would appear to be an advantageous adaptation (Wetzel 2001).

This mechanism has been documented in many macroalgae, and in mosses and

submerged angiosperms (Ruttner 1947, 1948, 1960, Bain and Proctor 1980). Raven

and Lucas (1985) and Eighmy et al. (1991) discuss the energetic costs associated with

the use of bicarbonate as the carbon source for photosynthesis. Many submerged

species exhibit low CO2 compensation points and relatively high productivity (Wetzel

2001).

Submerged macrophytes occurring in lakes inhabit the littoral zone in the area

extending from the shoreline to the depth at which light becomes limiting. Submerged

macrophytes colonize all depths of the photic zone of lakes (Wetzel 2001). Vascular

angiosperms can occur up to depths of approximately 10 m while nonvascular








macrophytes (e.g. macroalgae) can be found growing up to the littoral-pelagic

interface. McCreary (1991) provides a thorough review of the competitive causes for

the zonation of macrophyte distribution characteristic of littoral areas.

Environmental Factors Controlling Production

Studies that have addressed the dynamics of submerged macrophyte

communities suggest that macrophyte production is influenced by a variety of abiotic

and biotic environmental factors. Among these factors are light availability (Van et al.

1976, Barko and Smart 1981b, Duarte and Kalff 1986, Chambers 1987a, Chambers

and Kalff 1987, Canfield and Hoyer 1988b, Hough and Fornwall 1988, Goldsborough

and Kemp 1988, Chambers and Prepas 1990, Grimshaw et al. 2002), sediment

composition and nutrients (Sculthorpe 1967, Barko and Smart 1983, Short 1987,

Barko and Smart 1986, Barko et al. 1991), water transparency and depth (Spence

1967, Canfield et al. 1985, Scheffer et al. 1992), nutrient availability (Spence 1967,

Chambers and Kalff 1987b, Canfield and Hoyer 1988b, Hough and Fornwall 1988,

Lauridsen et al. 1993) and temperature (Barko and Smart 1981b). Wind events were

also found to have a significant effect on macrophyte production in the shallow lake

studied by Lauridsen et al. (1993). Sculthorpe (1967) identified light intensity and

quality, the nature of the substrate and turbulence as the most significant

environmental factors determining the distribution of communities, species and

growth forms of submerged macrophytes.

The effects of various biotic factors on macrophyte growth have been the

topic of additional studies. Sand-Jensen and Borum (1984) and Sand-Jensen (1990)

observed a negative relationship between macrophyte growth and the degree of light








attenuation by the epiphytes. In his 1971 study, Allen described the "antagonism"

(sensu Fitzgerald 1969) between macrophytes, epiphytes, and phytoplankton

competing for available light and nutrients within aquatic systems. In many systems,

grazing also plays an integral role in macrophyte community dynamics (Wetzel 1983,

Cattaneo 1990, Lauridsen et al. 1993). Lodge (1991) reviewed the literature on the

effects of herbivory on freshwater macrophytes.

A variety of studies have reported species-specific responses of macrophytes

to their environment (Spence 1964, Van et al. 1976, Chambers and Kalff 1987b,

Hough and Fornwall 1988, Chambers and Prepas 1990, Scheffer et al. 1992, Spencer

et al. 2000, Cenzato and Ganf 2001). Scheffer et al. (1992), for example, documented

a differential response in two species of P. illinoensis to changes in water depth in the

study system. Spencer et al. (2000) reported species-specific differences in the

number of degree-days required for emergence of vegetative propagules of three

submerged species. Changing environmental conditions often result in shifts in

dominance among competing species within macrophyte communities.

The Role of Light in Submerged Macrophyte Growth

Numerous studies have identified light availability as one of the most

significant factors controlling macrophyte production in aquatic systems (Duarte and

Kalff 1986, Canfield et al. 1985, Barko et al. 1986, Smith and Barko 1990). Various

studies have investigated the impact of light attenuation on submerged macrophyte

productivity (Carter and Rybicki 1990, Duarte 1991, Dunton 1994, Goodman et al.

1995, Masini et al. 1995, Zimmerman et al. 1995, Livingston et al. 1998). The

classification scheme Gessner (1955) developed for submerged macrophytes based on








their physiological adaptations to light availability indicates the extreme plasticity and

adaptability of submerged macrophytes to the highly variable underwater light

environment. The adaptation types include strictly shade adapted requiring low light

intensities, strictly light adapted and requiring high light intensities, shade adapted but

exhibiting optimum photosynthesis at intermediate light levels, etc. Van et al. (1976)

and Kenworthy and Fonseca (1996) reported species-specific differences in minimum

light requirements. All submerged angiosperms are shade plants (Wetzel 2001).

Spencer and Bowes (1990) determined that light saturation for photosynthesis ranges

from 10-50% full sunlight. Van et al. (1976) reported photosynthetic rates less than

5% of those achieved by terrestrial plants at atmospheric levels of CO2 for three

species of submerged aquatic macrophytes. They attributed this to low activities of

the carboxylation enzymes. Goldsborough and Kemp (1988) investigated the

response and recovery of Potamogeton perfoliatus to experimentally induced shade

during a 17-day treatment period followed by a 16-day "recovery" period. During the

treatment period, plants responded by increasing photosynthetic pigments and

producing elongate stems, thinning lower leaves and canopy formation at the surface.

Plants showed significant recovery 10 days after removal of light treatments. The

results of their study indicated that the study species requires a minimum of 11% full

sunlight in order to survive and grow. Other investigations of photosynthetic capacity

and compensation points indicated considerable variation among submerged

macrophytes (Wetzel 2001). Light compensation points often occur at 1-3% full

sunlight (Wilkinson 1963, Spence 1982, Bowes et al. 1977, Moeller 1980). Kimber et

al. (1995) reported that tuber production in Vallisneria americana ceased at light








levels less than 5% of ambient sunlight. They discussed the implications of these

results for vallisneria growth in relation to light attenuation by turbidity in their study

system. Dennison (1987) discussed the use of photosynthesis vs. irradiance curves

together with diurnal light curves to predict growth responses to changes in light

regime (Dennison and Alberte 1985), seasonal growth patterns and the maximum

depth of colonization for Zostera marina. Carter et al. (1996) reported an 11 -fold

increase and a 38-fold increase in total biomass of V. americana americana in lighted

cages in the Chesapeake Bay and the Potomac River. Plants exposed to increased

light levels were more robust and fewer in number as compared to controls.

The Role of Sediments in Macrophyte Nutritional Ecology

The function of roots in submersed macrophytes, especially in angiosperms,

has been subject to debate (Wetzel 2001). After much research (reviewed in Gessner

1959, Wetzel 1964, Sculthorpe 1967, Hutchinson 1975), two theories were proposed:

a) the function of roots was strictly to anchor the plant and b) the roots function in

nutrient absorption from the substrate. Considerable recent research has now

confirmed that the primary function of the root systems in aquatic macrophytes is to

assimilate nutrients from the sediment (Barko and Smart 1986, Short 1987, Barko et

al. 1991, Wetzel 2001). A positive absorptive capacity is present in the roots that

facilitates uptake of sediment nutrients. Most submerged species obtain the majority

of their nutrient requirements from the interstitial water of the sediments, where

nutrients are present at much greater concentrations than in the water column.

Shannon (1953) determined that absorptive capacity of the roots is enhanced by the

presence of root hairs. Many species also exhibit symbiotic relationships with








vesicular-arbuscular micorrhyzae (Sondergaard and Laegaard 1977, Tanner and

Clayton 1985, Wetzel and van der Valk 1996). The mechanism for assimilation of

sediment nutrients the solubilization and mobilization of soil nutrients by secreted

organic acids- utilized by terrestrial plants is thought to be the same in submerged

plants (Wetzel 2001).

Researchers first became aware of the influence of sediment composition on

the productivity and distribution of submerged macrophytes almost one century ago

(Pond 1905, Pearsall 1920, Misra 1938). Subsequent studies conducted in a wide

variety of aquatic systems have confirmed that sediment composition exerts a

significant effect on submerged macrophyte growth (Moeller 1975, Anderson 1978,

Sand-Jensen and Sondergaard 1979, Kiorboe 1980, Danell and Sjoberg 1982,

Wheeler and Giller 1982, Barko and Smart 1983, Barko and Smart 1986, Barko et al.

1991, Livingston et al. 1998). Barko et al. (1991) reported that nitrogen, phosphorus,

iron, manganese and micronutrients are taken up from the sediment. Calcium,

magnesium, sodium, potassium, sulfate and chloride are assimilated from the water

column. The majority of research into the plant available sediment nutrients has been

conducted on phosphorus and nitrogen. Of this literature, most has focused on

phosphorus (Barko et al. (1991). As a result of the large exchangeable pool of

phosphorus in most lake sediments, phosphorus is rarely the limiting factor in

hydrophyte growth (Wetzel 2001). Of the limited information available on the

relative contributions of sediment and open water to the nitrogen economy of

submerged aquatics, several studies indicate that nitrogen can be assimilated from

both the sediment and the open-water (Nichols and Keeney 1976, Short and McRoy








1984). These isotope studies concluded that nitrogen uptake rates were positively

correlated with concentration and that the study macrophytes preferred ammonium to

nitrate for uptake. Nichols and Keeney (1976) reported that, since sediment

ammonium concentrations are typically much greater than water column

concentrations, sediment is probably the major source of nitrogen. There are

relatively few documented cases of inorganic nutrient limitation in submerged aquatic

macrophytes (Anderson and Kalff 1986, Barko et al. 1986). Barko and Smart (1983)

concluded that sediment organic matter can greatly inhibit the growth of submerged

macrophytes. Refractory organic matter appeared to have a longer-lasting inhibitory

effect as compared to labile organic matter. Barko and Smart (1983) attributed this

inhibition to the presence of high concentrations of soluble organic compounds in the

interstitial water produced during anaerobic decomposition. In a later study involving

the growth of Hydrilla and Myriophyllum on 40 different sediments collected from 17

North American lakes, Barko and Smart (1986) concluded that sediment density

rather than organic matter content was most influential in regulating plant growth.

They identified a significant relationship between macrophyte growth, nutrition and

sediment density. Short (1987) reviewed the effects of sediment nutrients on

seagrasses and concluded that seagrass production is strongly correlated with nutrient

availability. He cites examples of how differences in the geochemistry of systems can

result in either phosphorus or nitrogen limitation and concludes. He concludes that

sediment geochemistry is the most significant factor controlling seagrass growth.

Rybicki and Carter (1986) reported better growth of Vallisneria americana on

silty clay than on sand. Barko and Smart (1986) had similar results. They found that








Hydrilla and Myriophyllum exhibited poor growth on highly organic sediments and

on sands. The results of fertilization studies indicated that macrophyte growth

limitation on these substrates was due to nutrient deficiencies. Amendment of sand

substrates with fertilizer has been used in many studies to circumvent problems with

nutrient limitation when using sand substrates (c.f. Sutton 1985, 1993, 1996). Denny

(1972b) reported species-specific responses to sediment composition and nutrient

concentrations. Barko and Smart (1983) identified the difficulty in separating the

effects of sediment nutrient availability from other sediment characteristics as one of

the greatest challenges associated with investigations of the relationship between

sediment composition and macrophyte growth.

Culturing Submerged Macrophytes

Early attempts to culture submerged macrophytes were complicated by the

misconception that macrophyte nutrient requirements were water-derived (c.f. Bourn

1932, Sculthorpe 1967) and that roots functioned simply as organs of attachment (c.f.

Brown 1913, Den Hartog and Segal 1964). Further complicating the effort to culture

submerged macrophytes was the use of culture media developed for macrophytic

algae (e.g. (Pringsheim and Pringsheim 1962, Forsberg 1965) and for hydroponic

growth of terrestrial plants (Hoagland and Amon 1938). The realization of the

importance of sediment nutrient acquisition in submerged aquatics by researchers

such as Denny (1980) has resulted in significant advances in the culture of submerged

macrophytes. Smart and Barko (1985), and Smart et al. (1996, 1998) provide a

thorough discussion of culturing submerged aquatic plant species native to

subtropical climes. Smart and Barko (1985) discuss the nutrient requirements of








submerged aquatics relative to the uptake mechanism (i.e. sediment- versus water-

derived).

One of the challenges to conducting investigations of submerged macrophytes

is the autocorrelation of environmental factors. Spence (1991) discussed the difficulty

separating the effects of light and sediment composition on macrophyte growth poses

for researchers. A plausible solution to this dilemma is the use of growth chambers

located in ambient conditions. The use of growth chambers allows researchers to

manipulate one variable and determine its effect in an otherwise controlled

environment. Many studies investigating submerged macrophytes have been

conducted in outdoor growth tanks (Sutton 1985, Short 1987, Sutton et al. 1992,

Sutton and Portier 1995, Kimber et al. 1999, Spencer et al. 2000, Grimshaw et al.

2002). Grimshaw et al.(2002) used differing numbers of shade cloth layers to

determine the response of several species of submerged aquatic macrophytes to

differing light availability in the aquatic environment. Short (1987) used experimental

mesocosms to investigate sediment nutrient effects on seagrass growth. Barko and

Smart (1986) used large outdoor growth tanks to investigate sediment-related

mechanisms of growth limitation in submerged macrophytes. Macrophyte growth

studies in this experiment were conducted in large outdoor tanks (6.2 m in length by

3-1 m in width by 0.9 m in height filled with pond water to a depth of 0.8 m). Pond

water was the water source and was exchanged daily.

Epiphytic Algae

Aquatic epiphytes are defined as those organisms that attach to aquatic

macrophytes (Wetzel 1983). The "epiphytic community" associated with aquatic








macrophytes is composed of autotrophs and heterotrophs cohabitating in a matrix of

detritus and mineral elements (Sand-Jensen et al. 1989). The autotrophic component

includes epiphytic algae. This study focused on the algal component of the epiphytic

community associated with the submerged macrophytes occurring in the experimental

tanks. From this point forward, the term epiphyte will be used to refer to the algal

component only.

Epiphytes are an integral component of the autotrophic community within

many aquatic systems. Cattaneo and Kalff (1980) reported that epiphytes can play a

significant role in the total primary production of macrophyte beds (up to 62%), a role

which may have been underestimated in previous studies of other systems (Wetzel

1964, Adams et al. 1974). Burkholder and Wetzel (1989a) determined that, as much

as 70-85% of the total carbon produced in littoral systems may be a direct by-product

of epiphyte metabolism. Stable isotope analyses suggest the importance of attached

algae as a source of carbon and nitrogen for higher trophic levels in some marine

systems (Sullivan and Moncrieff 1990).

Epiphyte growth is influenced by a variety of environmental factors. The

epiphytic microenvironment-the metabolizing macrophyte-is an unstable one

responding rapidly to variations in the host due to grazing pressure, age, changing

nutrient status and light availability (Allanson 1973). Several studies (Cattaneo and

Kalff 1979, Cattaneo and Kalff 1980, Rogers and Breen 1983, Borum 1987,

Burkholder and Wetzel 1989a and Lalonde -and Downing 1991) have reported a

correlation between macrophyte growth form and epiphyte colonization rates and

maximum attainable biomass.








The literature also suggests that epiphyte biomass is affected by a variety of

additional environmental factors. Wetzel (1964) reported a positive correlation

between temperature and epiphyte biomass. Several studies (Fox et al 1969, Phillips

et al 1978, Cattaneo and Kalff 1980) have identified a positive relationship between

epiphyte biomass and increasing water depth. This relationship may be due to

decreased wave activity at greater water depths (Fox et al. 1969), decreased grazing

pressure (Cattaneo 1990) or perhaps to a combination of both. Cattaneo (1990)

concluded that increased grazing pressure contributed to a sudden decline in epiphyte

biomass in Lake Memphremagog, Canada. Epiphyte communities are highly

susceptible to loss due to scouring caused by heavy precipitation and strong wind

events (Sand-Jensen 1983, Wetzel 1983, Kairesalo 1984, Sand-Jensen et al. 1989.)

Tete et al. (1978) presented a thorough discussion of the influence of water flow rates

on attached organisms in their 1978 review paper. High epiphytic biomass has also

been related to high light (Wetzel 1964, Pieczynska and Szczepanska 1966, Gons

1982) and nutrient availability (Straskraba and Pieczynska 1970, Phillips et al. 1978,

Cattaneo and Kalff 1980). In studies in different lacustrine systems, Shelden and

Boylen (1975), Tai and Hodgkiss (1975) and Hooper-Reid and Robinson (1978)

correlated decreased epiphyte biomass with nutrient deficiency. Cattaneo and Kalff

(1980) reported a strong correlation between phosphorus and epiphyte production

suggesting that phosphorus may be the growth-limiting nutrient for epiphytes.

Raschke (1993) observed that increased phosphorus loading in the Everglades

National Park stimulated diatom growth. Davis et al. (1990) defined a significant

relationship between light availability and phosphorus uptake by epiphytes.








Within aquatic communities, competition between autotrophs for resources

has a significant effect on the composition and dynamics of the epiphyte community.

In their 1971 and 1984 studies respectively, Allen and Sand-Jensen and Borum

reported the same phenomenon that Fitzgerald (1969) described as an "antagonistic"

relationship between macrophytes, epiphytes and phytoplankton. Other researchers

have investigated the effect of competition for light (Sand-Jensen and Borum 1984,

Sand-Jensen 1990) and nutrients (Sondergaard and Sand-Jensen 1978) upon the

composition and dynamics of the epiphyte community. Rapid nutrient and CO2

uptake rates make planktonic autotrophs more successful than their attached

competitors for nutrients in the water column (Sondergaard and Sand-Jensen 1978).

Competition for water column nutrients is typically greatest between pelagic and

epiphytic autotrophs, as rooted submerged macrophytes derive most of their nutrient

requirements from the sediment (Sondergaard and Sand-Jensen 1978, Barko and

Smart 1981a, Barko et al. 1991). Several studies (Wetzel et al. 1985, Rattray et al.

1991, Kimber et al. 1999) have suggested that submerged macrophytes may also

utilize sediment-derived CO2 under certain field conditions.

The Macrophyte-Epiphyte Complex

Submerged aquatic macrophytes and associated epiphytic algal communities

are keystone components of lacustrine ecosystems with significant macrophyte

populations (Wetzel 1983, Wetzel 2001, Kalff 2002). Several studies (Wetzel 1983,

Moeller et al. 1988, Burkholder and Wetzel 1989a) have concluded that the high rates

of productivity within the littoral zone of macrophyte-dominated lakes are due

primarily to the presence of this primary producer complex. Aquatic macrophytes








also provide critical habitat for a variety of organisms consumed by higher trophic

levels including epiphytes, invertebrates and bacteria (Soszka 1975, Cattaneo and

Kalff 1980, Wiley et al. 1984, van der Velde 1987). The surfaces available for

attachment of microorganisms are considerable; submerged vegetation provided a 5-

fold increase in colonizable surface area in the system investigated by Moeller et al.

(1988). Howard-Williams and Allanson (1981) reported a 30-fold increase of surface

area in P. illinoensis communities in their study system.

Submerged macrophytes and associated epiphytes play a critical role in the

nutrient dynamics of macrophyte-dominated systems (Cattaneo and Kalff 1980,

Carpenter and Lodge 1986, Burkholder and Wetzel 1989b). Various studies

(Carignan and Kalff 1980, Barko and Smart 1981 a, Canfield et al. 1983) have

indicated the importance of aquatic macrophytes in improving water quality in

nutrient-rich systems by a variety of mechanisms including sequestering nutrients

(e.g. nitrogen and phosphorus) in tissues. [See section entitled Revegetation Projects

in Lake Restoration for a discussion of the significance of macrophytes in the stable

state equilibria in shallow lakes.] In his study in Lake Okeechobee, Zimba determined

that over 110 metric tons of phosphorus were bound in macrophyte tissue during the

study period. Landers (1982) and Carpenter and Lodge (1986) discussed the

importance of the role that nutrient release by senescing macrophytes plays in the

cycling of nutrients within aquatic systems.

Additional research has been done on the role of epiphytes in nutrient cycling.

Several studies have documented the transfer of nutrients from living macrophyte

tissue to the epiphyte community (Wetzel and Penhale 1979, Moeller et al. 1988).








Other investigators (Riber et al. 1983, Carlton and Wetzel 1988, Moeller et al. 1988,

Burkholder et al. 1990) observed direct nutrient uptake from the water column by the

epiphyte community. Zimba (1995) determined that approximately 84% of the total

phosphorus removed form the water column by the macrophyte:epiphyte complex in

Lake Okeechobee was bound in the epiphytes colonizing submerged macrophytes.

Howard-Williams (1981) discussed the implications of subsequent sedimentation of

senescent epiphytic biomass as a critical water-to-sediment vector in sediment-to-

water nutrient exchange.

Despite the ecological importance of the macrophyte:epiphyte complex, the

dynamics of the relationship between epiphytes and macrophyte hosts are poorly

understood (Allen 1971, Cattaneo and Kalff 1980, Wetzel 1983, Burkholder and

Wetzel 1989b).Some researchers describe this relationship as a mutual symbiosis in

which nutrient exchange is on going between epiphytes and host (Brezonik et al.

1979). Other studies have concluded that the epiphyte:macrophyte relationship is best

described as a type of parasitismm" in which the epiphytes sap nutrients being pumped

from the sediments by the macrophyte host (Harlin 1975, Moeller et al. 1988,

Burkholder and Wetzel 1990, Burkholder et al. 1990). Sand-Jensen and Borum

(1984) and Sand-Jensen (1990) describe the role that epiphytes can play in host light

exclusion. Rogers and Breen (1981) identified a "necrotrophic" relationship in which

epiphytes played a critical role in the initial decomposition of leaf tissue in a P.

illinoensis species. Other investigators have described the relationship as a neutral

one in which the role of the macrophyte is primarily one of physical support

(Cattaneo and Kalff 1978, Carignan and Kalff 1982). However, the results of these








latter studies indicated the presence of nutrient transfer. Investigations that have

documented host-specific algal assemblages (Godward 1934, Prowse 1959, Blindow

1987) and differing epiphyte productivity levels as a function of host plant (Cattaneo

and Kalff 1980) suggest that there is some degree of interaction between epiphytes

and their hosts. In their study of phosphorus transfer between N. guadalupensis

flexilis and associated epiphytes, Burkholder and Wetzel (1989b) concluded that there

is a probable correlation between epiphytes and their microenvironment.

Methods for Investigating Epiphytic Algae

The relative lack of information on epiphytes and their relationship to their

macrophyte hosts is due in large part to the degree of effort involved in the collection

and preparation of these organisms for study (Hickman 1971, Main 1973). Several

different processing methods are available for use by researchers investigating

epiphyte community composition. The first method entails the use of artificial

substrates. Many studies have been conducted on algal colonization of artificial

substrates (Allen 1971, Brown 1976, Siver 1977, Hooper-Reid and Robinson 1978,

Cattaneo and Kalff 1979, Fontaine and Nigh 1983, Fairchild and Lowe 1984,

Burkholder and Wetzel 1989b). Other research has indicated that this attempt to

simplify the experimental design of epiphyte studies often yields communities that

are not comparable to those occurring on natural substrates (Castenholz 1960,

Sladeckova 1962, Tippet 1970, Brown 1976).

Another approach involves examination of the plant surface using scanning electron

microscopy (SEM) (Allanson 1973, Sieburth et al 1974, Burkholder and Wetzel

1989b). There are several disadvantages associated with the use of SEM as the








primary investigative tool. SEM is a relatively expensive technique. In addition, for

many studies, sample storage time required for transport to the laboratory would

render epiphyte samples physiologically nonviable.

A third possible technique for investigating epiphytes uses an acid digestion

method to allow quantification of the total diatom component present on the natural

substrate (Cattaneo and Kalff 1979). This method excludes nondiatomaceous

components of the epiphytic flora. It also renders impossible comparison of the

percent living versus dead component.

Many studies have identified mechanical removal of the attached algae from

living macrophytes as the most effective way to address the community composition

as well as the physiological state and activities of epiphytes (Sladeckova 1962, Gough

and Woelkerling 1976, Cattaneo and Kalff 1980, Kairesalo 1980, Fairchild and Lowe

1984, Tanaka et al. 1984, Goldsborough and Robinson 1985, Moeller et al. 1988,

Sand-Jensen

et al. 1989, Goldsborough and Hickman 1991, Zimba and Hopson 1997). Mechanical

removal was the method used in this study.























Ws guod nluiw
Southern naid


WAS, Caumr fh fA4.A Ptom
nwersy of R COlshwk. 19M


Figure 2-1: Najas guadelupensis is a pioneer species in the Najadaceae.





















































WAS Char ftr Mare ltink



Figure 2-2: Chara spp. are macroalgae.


n$pp.
UWkWW














PotamoSgew wimsts
Ulnois pOadwoed


FAS. Carw fm Aqume Pm
Uanite*y ofFlord, OFsmmnea. 1W
Figure 2-3: Potamogeton illinoensis is a Florida native perennial with broad
lanceolate leaves.






47












Tapqass


A& COrn Or AWnd ra"


Figure 2-4: Vallisneria americana is a perennial with broad ribbonlike leaves.













CHAPTER 3
COMPARISON OF THE GROWTH OF FOUR SPECIES OF NATIVE
SUBMERGED MACROPHYTES ON INORGANIC SEDIMENTS FROM A
SHALLOW URBAN FLORIDA LAKE

Introduction and Literature Review

The role of submersed macrophyte roots as organs for physical attachment to

the substrate versus absorption of sediment nutrients has been the subject of

considerable historical debate (reviewed in Gessner 1959, Wetzel 1964, Sculthorpe

1967, Hutchinson 1975, Wetzel 2001). More recent research has confirmed that the

primary function of the root systems is to assimilate nutrients from the sediment

(Barko and Smart 1986, Short 1987, Barko and Smart 1991, Wetzel 2001). The roots

take up nutrients primarily from the interstitial water of the sediments, where

nutrients are present at much greater concentrations than in the water column.

Shannon (1955) determined that the absorptive capacity of the roots is enhanced by

the presence of root hairs. Many species also exhibit symbiotic relationships with

vesicular-arbuscular micorrhyzae (Sondergaard and Laegaard 1977, Tanner and

Clayton 1985, Wetzel and van der Valk 1996). The mechanism for assimilation of

sediment nutrients is believed to be the same as that used by terrestrial plants the

solubilization and mobilization of soil nutrients by secreted organic acids (Wetzel

2001). Although macroalgae typically obtain nutrients through foliar absorption from

the water column rather than by rhizoidal structures (Wetzel 1983), uptake of

phosphorus from sediment has been documented in some Charophytes (Littlefield and








Forsberg 1965). Littlefield and Forsberg (1965) observed that Chara absorbed

sediment phosphorus through the rhizoid from where it was translocated to other parts

of the plant.

Researchers have been aware of the influence of sediment physical

composition on the productivity and distribution of submerged macrophytes since the

early 1900's (cf. Pond 1905, Pearsall 1920, Misra 1938). The results of numerous

more recent studies conducted in a wide variety of aquatic systems have confirmed

that sediment composition exerts a significant effect on submerged macrophyte

growth (Moeller 1975, Anderson 1978, Sand-Jensen and Sondergaard 1979, Kiorboe

1980, Danell and Sjoberg 1982, Wheeler and Giller 1982, Barko and Smart 1983,

Barko and Smart 1986, Barko et al. 1991, Livingston et al. 1998). Barko and Smart

(1983) concluded that sediment organic matter can greatly inhibit the growth of

submerged macrophytes. Their results further suggested that refractory organic matter

appeared to have a longer-lasting inhibitory effect as compared to labile organic

matter. They attributed this inhibition to the presence of high concentrations of

soluble organic compounds in the interstitial water produced during anaerobic

decomposition. Rybicki and Carter (1986) reported better growth of Vallisneria

americana on silty clay than on sand. Barko and Smart (1986) found similarly that

Hydrilla and Myriophyllum exhibited poor growth on sands and on highly organic

sediments. They identified the effect of long diffusion distances associated with low

densities as the cause of the growth response to organic sediments.

Other investigations have been focused on the effect of sediment chemical

composition on rooted submersed macrophyte growth. Barko et al. (1991) reported








that nitrogen, phosphorus, iron, manganese and micronutrients are taken up from the

sediment whereas calcium, magnesium, sodium, potassium, sulfate and chloride are

assimilated from the water column. The majority of research into sediment macro-

and micronutrients has been conducted on phosphorus and nitrogen. Of this literature,

most has focused on phosphorus (Barko et al. 1991). As a result of the large

exchangeable pool of phosphorus present in the sediments of most lakes, phosphorus

is rarely the limiting factor in submersed macrophyte growth (Wetzel 2001).

Literature available on the nitrogen economy of submerged aquatics is limited in

comparison. Several isotope studies indicated that nitrogen can be assimilated from

both the sediment and the open-water (Nichols and Keeney 1976, Short and McRoy

1984). The results of these studies suggested that nitrogen uptake rates were

positively correlated with concentration and that ammonium was the preferred form

of nitrogen for uptake. Nichols and Keeney (1976) suggested that, since sediment

ammonium concentrations are typically much greater than water column

concentrations, sediment is probably the major source of nitrogen for rooted

submersed plants. Fertilization studies conducted in freshwater systems indicated that

nitrogen limitation of submersed macrophyte growth may occur in some sediments

(Anderson and Kalff 1986, Duarte and Kalff 1988, Moeller et al. 1988).

There are relatively few documented cases of inorganic nutrient limitation in

submerged aquatic macrophytes (Anderson and Kalff 1986, Barko et al. 1986). Short

(1987) reviewed the effects of sediment nutrients on seagrasses and concluded that

seagrass production is strongly correlated with nutrient availability. He cites

examples of how differences in the geochemistry of systems can result in either








phosphorus or nitrogen limitation. He concluded that sediment geochemistry is the

most significant factor controlling nutrient limitation of seagrass growth. The results

of fertilization studies conducted by Barko and Smart (1986) indicated that

macrophyte growth limitation on both sand and organic substrates was due to nutrient

deficiencies. Many studies have used fertilizer amendments to circumvent problems

with nutrient limitation when using sand substrates (c.f. Moeller 1983, Sutton 1985,

1993, Sutton and Latham 1996, this study).

There is still considerable controversy, however, as to the relative importance

of sediment chemical and physical composition in macrophyte nutrition (Sculthorpe

1967, Haslam 1978, Denny 1980, Barko and Smart 1986). Barko and Smart (1983)

identified the difficulty in separating the effects of sediment nutrient availability from

other sediment characteristics as one of the greatest challenges associated with

investigations of the relationship between sediment composition and macrophyte

growth. Additional studies have indicated that macrophyte growth is significantly

impacted by the combined effects of sediment nutrient composition and physical

characteristics. In a study involving the growth of Hydrilla and Myriophyllum on 40

different sediments collected from 17 North American lakes, Barko and Smart (1986)

identified a significant relationship between macrophyte growth, nutrition and

sediment density. Their results suggested that sediment density is more influential

than organic matter content in regulating plant growth.

The results of several studies have suggested that differences in sediment

composition may play a significant role in determining species composition within

rooted submersed macrophyte communities. Denny (1972) reported species-specific








responses to sediment composition and nutrient concentrations in a growth study that

he conducted in concrete ponds. Denny explained these variations in growth response

in terms of differences in anatomy and morphology that in turn affected sediment

nutrient uptake among the study species. Barko and Smart (1980, 1981, 1986)

observed similar species-specific variations in growth response to sediment fertility in

several laboratory studies. Chambers (1987) observed a shift in community

composition along a natural gradient in Lake Memphremagog such that the

percentage of erect and canopy-forming species decreased and rosette and bottom-

dwelling species increased with decreasing sediment fertility. See Barko et al. (1991)

for a comprehensive review of the ecological implications of variations in sediment

composition on submersed macrophyte communities and littoral ecosystem processes.

In their guide for establishing SAV, Smart and Barko (1996) suggested the

importance of the use of preliminary investigations of sediment composition to

evaluate the viability of a location as habitat for colonization by a diverse community

of submerged macrophytes.

A review of the literature indicated a paucity of information on the

relationship between sediment composition and submersed macrophyte growth. Of

the limited body of research on the macrophyte-sediment relationship, most studies

have been focused on nuisance exotic species such as Hydrilla and Myriophyllum.

Very little information has been published on the sediment requirements of desirable

native submerged species. The objective of this study was to compare the growth of

four species of Florida native submerged macrophytes with varied life histories in

inorganic sediments from Lake Hollingsworth. The findings should contribute vital








information on the growth habits of native submerged macrophytes and will be of

value to lake managers for use in the development of a systematic approach to the

establishment of diverse communities of desirable aquatic vegetation in restored

Florida lakes.

The experimental procedure was designed to test several hypotheses based

upon findings from the literature and previous experience. The first was that there

would be spatial variation in the organic matter and nutrient content of the littoral

sediments in Lake Hollingsworth. I also anticipated that Nguadelupensis, P.

illinoensis and Chara sp., the canopy-forming, erect species, would produce greater

biomass in sediments with higher nutrient levels while net growth of V. americana, a

rosette species, would be inversely related to sediment nutrient content. Based upon

my personal experience growing stock cultures of the study plants, I expected to

observe differences in growth rate among the species such that N. guadelupensis

would be the fastest grower followed by P. illinoensis, V. americana and lastly Chara

sp. I further expected the growth rate of Chara sp to be positively related to

increasing culture period length. I anticipated that N. guadalupensis, V americana

and Chara sp. would produce the greatest biomass during the summer months while

growth of P. illinoensis, a species with a range distribution that stretches into more

temperate regions, would be stimulated by the cooler temperatures of the winter

months. Finally, I hypothesized that sediments collected from the littoral zone of

Lake Hollingsworth would have sufficient quantities of sediment nutrients to support

the growth of N. guadalupensis, P. illinoensis, V americana and Chara sp. when

grown in the experimental growth tanks used in this study.








The study was limited to sediments with low organic matter content to avoid

growth inhibition previously associated with high organic matter concentrations (c.f.

Barko and Smart 1983, 1986, 1991). Submerged macrophyte species were selected on

the basis of several criteria. Initially, species selection was determined by the need to

identify Florida native submersed macrophytes for which propagule material is

widely available. In addition, a mix of annual and perennial species was selected in

order to maximize the potential for establishing viable, self-sustaining communities

of SAV capable of out-competing exotic species in restored lakes. Finally,

macrophytes were selected based on their relative value as habitat for fish and other

aquatic organisms, resistance to herbivory and relative potential positive impact on

the water quality of the lake.

Four species were identified using the aforementioned selection criteria -

Najas guadelupensis (Spreng.) Magnus, Potamogeton illinoensis Merong.,

Vallisneria americana Michaux) and Chara sp. (Refer to the Description of Study

Macrophytes section in Chapter 2 for a detailed description of the study species.) N.

guadalupensis and Chara sp. were selected for inclusion in this study for several

reasons. Both N. guadalupensis and Chara are pioneer annual species that expand and

rapidly cover the sediment with a carpet of vegetation hence filling a niche that would

otherwise be ideal habitat for invasion by an exotic weedy species such as Hydrilla.

In addition, the increased surface area provided by the finely dissected "leaf'

architecture characteristic of both of these native plants makes these macrophytes

excellent habitat for fish-food organisms and refugia for juvenile fishes (Engel 1985).

V americana and P. illinoensis are perennials.








Managed introduction of these four species should result in the establishment

of diverse communities that can maintain restored lakes in a macrophyte-dominated

stable state. The combination of growth strategies exhibited by these annuals and

perennials should make the community relatively resistant to short-term

environmental perturbations. Plasticity in the response of the community to changes

in water depth and light regime is essential in shallow eutrophic lakes that experience

frequent resuspension events and are susceptible to water level fluctuations caused by

seasons of heavy rainfall or drought. A combination of growth strategies also

improves the chances of the managed community to out-compete exotic species by

eliminating available niche space.

Materials and Methods

Site Description

Lake Hollingsworth is a 144 ha shallow (zmean= 1.2 m) (City of Lakeland

1988-2000) urban lake located in central Florida (28001'30", 81* 56'45") (Figure 3-

1). The lake is a solution basin roughly circular in shape with a mean depth of 1.2 m

(Lake Hollingsworth Diagnostic Feasibility Study 1994). Water inputs to the lake are

in the form of rainfall, groundwater seepage, stormwater runoff and inputs from

Lakes Morton and Homey. Groundwater recharge contributes up to 85% of the total

water budget for the lake (SWFWMD 1994 Section II). Surface drainage flows

southeast into Lake Bentley. Paleolimnological study indicated that Lake

Hollingsworth is naturally eutrophic (Brenner et al., 1995). This is probably due to

the fact that the lake lies in the Bartow Embayment division of the Central Lakes

District where the underlying bedrock consists of the phosphatic sands and clays of








the Bone Valley region of Central Florida (Canfield and Hoyer 1992). In the early

1990's, the results of a Diagnostic Feasibility Study conducted on the lake indicated

that Lake Hollingsworth was in an advanced state of aging with estimated

sedimentation rates of approximately 30 cm in 20 years. The result of years of

sedimentation was a layer of flocculent organic sediments measuring up to 4.6 m in

thickness in some areas of the lake. The recommendation of the study was to restore

Lake Hollingsworth using the method of whole lake hydraulic dredging. Dredging

was commenced in 1999 and was halted before completion due to complications from

drought conditions during the dredging period. Post-dredge monitoring efforts

indicate a dramatic improvement in water quality in the lake. The lake is a highly

valued resource, serving as the site for a variety of social, educational and

recreational activities for the City of Lakeland and the surrounding community. The

lake also supports sustenance, commercial and sport fisheries.

Sediment Survey

A survey study was conducted to screen the littoral sediments of Lake

Hollingsworth in order to identify any possible locations at which sediment

characteristics, such as flocculance or relatively high organic matter content, could

inhibit submersed macrophyte growth. Lake Hollingsworth is a shallow, highly

productive lake with the potential for highly variable organic sediment distribution. In

their 1996 study of the variability of sediment distribution in shallow Florida lakes,

Whitmore et al. (1996) indicated the importance of using systematic mapping to

locate optimal coring sites. A grid was superimposed on the bathymetric map of the

lake to identify sampling stations distributed to ensure equal area coverage of the








littoral region (Hakanson 1981). The bathymetric map was drawn on April 13. The

convention, when using the grid method, is that stations can either be located within

the space between the lines or at the intersection of lines. In this study, stations were

located within the spaces between the lines. The sampling grid identified twelve

littoral stations occurring along the 2 ft (0.8 m) contour line. Four of the grid stations

did not cover the 2 ft (0.8 m) contour line and were disregarded. Eighty centimeters

was selected as the optimum planting depth based on several considerations. It has

been previously determined that maximum depth of colonization for most submerged

macrophyte species in shallow eutrophic lakes similar to Lake Hollingsworth is 1 m. I

observed a significant decrease in the biomass of the study species at lake levels

above 1 m in Lake Okeechobee (Hopson 1995). Final lake stage in Lake

Hollingsworth at completion of the restoration project was subject to fluctuation. In

addition, increased turbidity in the system was expected to accompany the whole-lake

dredging being conducted at the time of this study. The goal of this study was to

provide practical information for use by managers in the lake. Therefore, I decided

that planting at 0.8 m would allow for fluctuations in lake stage while ensuring that

submerged macrophytes would have sufficient depth for growth while still having

sufficient available light. The eight grid stations included in the survey were lettered

from A to H, proceeding in a counterclockwise direction (Figure 3-1). Stations on the

grid were 0.45 km apart, on the average. Coordinates of station locations were

determined using a Trimble CDSI GPS unit.

Triplicate sediment samples were collected from each station using the

sediment coring device described by Sutton (1982). Samples were stored in Ziplock








bags and transported in a dark cooler. Samples were air-dried for at least 72 hours and

then dried to constant weight in a forced-air drying oven at 60 *C (Hakanson and

Jansson 1983). Dried samples were homogenized and deflocculated in a hammer mill.

Samples were then further homogenized using a clockwise layering method, weighed

and separated into subsamples for nutrient, pH and organic matter analysis. The pH of

the samples was determined by scooping 20 cm3 of the dried, homogenized sediments

into plastic cups. Samples were hydrated by adding 40 mL of deionized water.

Samples were then stirred thoroughly and allowed to settle for a minimum of 30

minutes. All samples were processed within 2 hours. A calibrated Orion Research

model 601A/digital IONALYZER was used to measure the sample pH. A standard

was used as the last sample in each batch to verify the accuracy of the ionalyzer.

Organic matter content was determined as weight loss on ignition (LOI) at 5500 C in

a muffle furnace (Hakanson and Jansson 1983). The results of this survey study were

used to select four stations that appeared to provide the most suitable habitat for

submersed macrophytes among the eight survey stations. Sediment samples from

the stations selected for the growth study (B, D, F and H) were analyzed for the

plant macro- and micronutrients P, K, Ca, Mg, Zn, Mn, Cu, Al, Na, Fe, Cl', NH4 and

NO3. All samples were extracted using Mehlich-1 extractant and analyzed by

inductively coupled argon plasma (ICAP) spectroscopy (Southern Region

Information and Exchange Group on Soil Testing and Plant Analyses 1983).

Sediment Collection and Processing

Three sediment cores from each of the four selected stations were collected

and loaded into twelve 7.6 L polyethylene nursery containers. Containers were








covered with plastic wrap to prevent drying of sediments during transport. Holes were

punched in the plastic wrap to allow for oxygen transfer. Sediments were transported

to the University of Florida Fort Lauderdale Research and Education Center (FLREC)

(260 05'N and 800 14'W) and submerged within 24 hours of collection. The results of

the analyses performed on samples collected during the preliminary survey were used

to describe the sediment pH, organic matter content and concentration of selected

macro- and micronutrients.

Experimental Environment and Procedures

Plants were grown outdoors at the FLREC in concrete tanks (6.2 m L x 31 m

W x 0.9 m H) on natural and artificial sediments. Pond water (Steward 1984) flows

into the tanks at the surface of one end and out from a drainpipe at the other at a rate

providing one volume exchange every 24 hr. Plants were exposed to natural daylight.

Water temperature was measured using maximum/minimum thermometers placed 30

cm below the surface of the water. Readings were taken 5 days a week at

approximately 3:00 P.M. each day.

Total irradiance (400-1100 nm) (W m-2) was measured by a LICOR LI200SZ

pyrometer. These data were sampled every 3.75 min and reported as 15-min averages

by a data logger. Total irradiance was converted to photosynthetically active radiation

(PAR) (400-700 nm) assuming that PAR is approximately 45% of total irradiance

(Baker and Froiun 1987). PAR in W m"2 was converted to photosynthetic photon flux

density (PPFD) units (ji mol photons s -1 m-2) using a multiplier of 4.6 (see Table 3 in

Thimijan and Heins 1983). The mean incident PPFD for the photic portion of an

experimental period was found by averaging the nonzero fluxes. Accumulated PAR








was found by multiplying the mean incident PPFD by the length of the photic period

for the experiment.

A total of 20 treatment groups (4 species x 4 sediment samples plus the

control) were tested in each culture period. Three 7.6 L containers were planted for

each treatment group, with four propagules per culture container, for a total n = 12

plants per treatment group and an overall total of 60 containers. Plant propagules

were obtained from stock cultures maintained at the FLREC. Propagules were

harvested from similarly aged, actively growing stock plants. Apical cuttings of N.

guadalupensis 20 cm in length were planted to a depth of 23 nodes. Apical cuttings

of P. illinoensis were planted to a depth of> 2 nodes. Propagules of V americana

growing on rhizomes were planted to a depth such that the rhizome was submerged

just beneath the sediment surface but the basal rosette was not covered. Apical

cuttings of Chara sp. 20 cm in length were planted to a depth of> 3 cm. Apical

cuttings and rosettes were collected at the beginning of each culture period to give at

least ten representative initial samples for each species. Each sample was dried at 60

C to constant weight (Hakanson 1981). Mean g dry weight at the time of planting

was calculated for each species.

The total of 60 culture containers was divided equally into two groups of 30.

Each group, containing representatives of each treatment group and plant type, was

placed into a separate tank. A random numbers table was used to arrange culture

containers in four rows within each tank, parallel to the flow of water (Figure 3-2.)

All species were submerged in 0.8 m of water. The study was conducted over three

culture periods from 30 April to 29 June 2001 (Spring Culture Period), 20 July to 21








September 2001 (Summer Culture Period) and 19 December 01 to 22 February 02

(Winter Culture Period). Culture period length in each experiment (approximately 9

weeks) was adequate for the development of treatment-related differences in growth

but minimized tissue deterioration associated with senescence. In a similar study

conducted at the FLREC using sand media amended with controlled-release

fertilizers, including Osmocote, to culture Hydrilla verticillata, a submersed

macrophyte, Sutton and Latham (1996) documented statistical differences in growth

after 8 weeks. (See Figure 1.1 of Sutton and Latham (1996) for a presentation of

biomass data.)

The control group consisted of plants grown in a medium of coarse builders'

sand amended with 15-9-12 (N:P:K) Osmocote Southern Formula, a commercially

available fertilizer. Osmocote is manufactured by Grace Sierra Horticulture Products

Company, Milpitas, CA. This fertilizer is formulated to slow-release in soil over an 8-

9 month period with increased rates of nutrient release at temperatures > 21 C

(Harbaugh and Wilfret 1981). Fertilizer was added at a rate of 40 g per pot for N.

guadalupensis and P. illinoensis and 15 g for V. americana and Chara (Dr. David

Sutton, UF FLREC, personal communication).

In the spring culture period, the activity of the herbivorous moth Paraponyx

diminutalis Snellen apparently caused a significant reduction in the above-sediment

biomass of N. guadalupensis and P. illinoensis. The total loss in N. guadalupensis

and P. illinoensis above-sediment biomass due to herbivore damage was estimated to

be approximately 50% (Figure 3-3). This estimate was made based upon field

estimates of biomass loss in conjunction with trends in root:shoot ratios for N.








guadalupensis observed in the summer and winter culture periods. The estimated loss

fits within the range of loss reported in the literature. Estimated total biomass values

for N. guadalupensis and P. illinoensis were then obtained by adding the calculated

loss to the actual total biomass values measured for each species. These estimated

values were used in subsequent statistical analyses involving the growth of N.

guadalupensis and P. illinoensis in the spring culture period. An emulsifiable

concentrate of malathion (0,0-dimethyl dithiophosphate of diethyl mercaptosuccinate)

was used to achieve a dosing concentration of 1.0 mg/L in order to control herbivore

activity during the summer and winter culture periods.

Tanks were dosed biweekly with a concentrate of Malathion (0,O-dimethyl

dithiophosphate ofdiethyl mercaptosuccinate) to an initial concentration of 1.0 ppm

in the summer and winter culture periods. Dosing was initiated when plant shoots

reached the water surface in order to control the feeding activity of the herbivorous

moth, Parapoynix diminutalis Snellen.

Plants were harvested and separated into above-sediment biomass (shoots)

and below-sediment biomass (roots) at the end of each culture period. The length of

each experiment (9 weeks) was adequate for the development of treatment related

differences in growth, while minimizing tissue deterioration associated with

senescence. Total number of plants harvested per pot was recorded for all species in

the spring culture period. (It was determined during this first harvest that the brittle

nature ofN. guadalupensis and Chara stems made it very difficult to get a

reproducible assessment of the number of plants of these two genera. Therefore, the

average number of harvested plants per pot was quantified only for V americana and








P. illinoensis in the summer and winter culture periods.) Plant material was dried to

constant weight (Hakanson 1981) at 600 C in a forced-air drying oven and dry

weights were measured. Macrophyte growth was measured as the change in dry

weight of plant biomass, after correction for epiphyte biomass (explained below),

since planting of propagule material. From this point forward, the term biomass will

be used to refer to total plant biomass (shoots + roots).

Epiphyte biomass was removed from the macrophytes at the time of harvest.

In the spring culture period, macrophyte material was washed gently with pond water

in order to remove sediment, debris and epiphytic algae. In the summer and winter

culture period, the mechanical removal technique described by Zimba and Hopson

(1997) was used to separate epiphytic biomass from macrophyte biomass. (See

Appendix A for a more detailed discussion of the method used.) A subsample of the

resultant suspension containing the epiphytes was concentrated onto a glass fiber

filter (0.7-pm porosity) and chlorophyll a and phaeophytin a were determined in

accordance with Standard Methods (SM 10200 H) (A.P.H.A. 1995). All epiphyte data

collected were normalized to host plant dry weight. Chlorophyll a values corrected

for phaeophytin a were used as a correction factor to determine total macrophyte

yield. More rigorous efforts were also made in the summer and winter culture periods

to use mechanical removal methods to maintain the tanks relatively free of both

epiphytic and floating algae.

Statistical Analysis of Results

Sediment chemical composition, macrophyte biomass and ratios of root

biomass to shoot biomass were analyzed using the general linear model (GLM)








procedure of Statistical Analysis System (SAS) for personal computers (SAS Institute

1999-2001). Tukey's studentized range distribution test (HSD) procedure was used

for means separation to investigate differences in the pH, organic matter and nutrient

contents of the sediment and among and within species differences in macrophyte

biomass and root:shoot ratios.

Regression analysis (SAS Institute, 1999-2001) was used to identify those

sediment characteristics that had a significant effect on macrophyte growth. Sediment

nutrients, pH and organic matter content and light and water temperature were used as

the independent variables and macrophyte biomass was used as the dependent

variable Stepwise multiple regression analysis was used to further evaluate the

association between macrophyte biomass production and those environmental factors

identified as significant. In an effort to improve the models, sediment calcium,

magnesium, potassium and sodium were excluded from analysis on the basis that

numerous studies have shown that the water column is the primary source of these

nutrients for submersed macrophytes. Data transformation was used to reduce

variance as necessary.

Results

Sediment Survey

The results of the preliminary sediment survey study of Lake Hollingsworth

littoral sediments revealed significant differences in sediment organic matter content

and pH among the survey stations (Table 3-1). (See Figure 3-1 for a map of the

survey study stations). Organic matter content (%) ranged from 0.38% at station B to








39.18% at station E. Station G sediments also had a high organic matter content

(34.96%). The pH varied from a low of 5.4 at station B to a high of 8.0 at station F.

Four stations were selected that appeared to provide the most suitable habitat

for submersed macrophytes among the eight survey stations (Figure 3-1). Study

station selection criteria included low organic matter content, absence of flocculent

sediment layer and protection from boat traffic. Comparison among the survey

stations indicated differences in the relative amount of boat traffic in the different

lake regions. Stations A and E were located in the path of two water ski courses in the

lake. Consequently, these stations were eliminated due to heavy boat traffic that

would be damaging to macrophyte communities. B, C, D, F and H were relatively

protected from boat traffic. Stations B,D,F and H appeared to have the optimum

combination of low organic matter, absence of flocculent layer and minimal

perturbation. In my opinion, these locations had the best potential, dependent upon

chemical composition, to be sites for the successful establishment of founder colonies

of the study species.

Chemical Composition of Study Sediments

Differences in pH, percent organic matter and macro- and micronutrient

contents were apparent among the sediments (Table 3-2). The lake sediments were

more alkaline than the control sediments with the exception of sediment from Station

B, which exhibited the lowest mean pH, 5.4 (Table 3-2). Organic matter contents of

the natural sediments ranged from 0.42 to 1.08%, with Station D having the lowest

percentage and Station F the highest percentage. Sediment from Station F also

contained significantly higher calcium contents (5617 mgKg'") than the other








sediments. Magnesium, phosphorus, manganese and sodium levels were significantly

greater at Station F and in the controls than in the other sediments. There were no

significant differences in the content of these elements in the other sediments. Zinc

was present at significantly highest levels in sediments from Station F and lowest in

sediments from Station D. Control sediments dosed with 40 g of fertilizer (controls

for N. guadalupensis and P. illinoensis) contained significantly greater levels of

copper, potassium and chloride ion as compared with the other sediments. There were

no significant differences in copper, potassium and chloride ion among the remaining

sediments. No significant differences in manganese content were observed among the

sediments. Aluminum content was lowest in sediments from Site D. Iron, ammonium

and nitrate were detected in significantly greater amounts in the control sediments as

compared with the lake sediments. A comparison of the relative iron contents

observed in the control sediments to the amounts contributed by the Osmocote

indicated the presence of iron in the sand used to create the control sediments. The

iron content measured in the control sediments amended with 15 g of Osmocote were

unexpectedly high relative to the those controls amended with 40 g of fertilizer. This

may have resulted in levels of iron that were inhibitory to some species.

Temperature and Irradiance during the Culture Periods

As shown in Table 3-3, the highest average daily water temperature was

recorded during the summer culture period (29.6 C) while the lowest average daily

water temperature was recorded during the winter culture period (21.2*C). The mean

incident PAR were greatest during the spring culture period (806 pmol s"1 m"2) and

least during the winter culture period (624 pmol s1' m'2). Photoperiod was longest








during the spring (13.8L: 10.2D) and shortest during the winter culture period

(11L:13D).

Effects of Sediment on Macrophyte Production

Spring culture period (30 April to 29 June 2001)

Analysis of variance of pooled total macrophyte biomass (n = 60) produced

during the spring culture period using GLM procedures (SAS Institute 1999-2001)

indicated highly significant differences due to plant type (Table 3-4). (Note that total

biomass values for N. guadalupensis and P. illinoensis were corrected for losses due

to herbivory. Refer to the Materials and Methods section for a description of the

method used to estimate the corrected values.) There were no significant differences

in total biomass due to sediment source or to the interaction between sediment source

and plant type. Means separation using Tukey's HSD method indicated that there

were no significant differences in biomass production among species in Site D, Site

F, and control sediments (a = 0.05). V americana produced significantly less

biomass than the other species in Site B and Site H sediments. N. guadalupensis and

Chara sp. produced greater biomass in the control sediments and most of the natural

sediments than P. illinoensis and V americana (Table 3-5). V. americana exhibited

the slowest growth of all species in all but one sediment. Within species comparisons

indicated that N. guadalupensis and Chara sp. produced produced greatest mean total

biomass in control sediments (16.4 and 16.9 g DWT, respectively) (Figure 3-34). N.

guadalupensis growth was slowest in Site H sediments (11.0 g DWT). Chara sp.

accrued the least biomass in Site B sediments (4.1 g DWT). P. illinoensis produced

greatest mean biomass in Site F sediments (9.9 g DWT) and least biomass in Site D








sediments (6.0 g DWT). V americana production was greatest (6.8 g DWT) on Site

D sediments and lowest in Site B (2.3 g DWT). Analysis of variance using the GLM

Procedure (SAS Institute 1999-2001) indicated that there were no statistically

significant differences in macrophyte growth within species in response to sediment

type (Figure 3-4a).

Comparison of the mean number of individual plants produced by each

species indicated that P. illinoensis produced more plants than the other species in

most of the sediments (Figure 3-5a). As a general trend, all species produced the least

number of individual plants on Site B sediments. Note that herbivory had a negative

effect on the total number of plants counted and probably resulted in a significant

underestimate of the total number of plants of N. guadalupensis and P. illinoensis.

Simple regression analysis used to investigate the relationship between

macrophyte biomass production and sediment chemical composition suggested that

sediment pH, OM and macro- and micro-nutrients had relatively little effect on

macrophyte growth in the spring culture period (Table 3-6). The only significant

relationship was between aluminum and N. guadalupensis biomass. There were no

other significant relationships.

Root: shoot ratios produced by all species in response to all sediments were

less than 1 (Figure 3-6a). Analysis of variance of macrophyte root:shoot ratios using

GLM procedures (SAS Institute 1999-2001) indicated highly significant differences

in total root:shoot ratios due to plant type (P <.0001) (Table 3-7). There were no

significant differences due to sediment source or to the interaction between sediment

source and plant type. There were differences among and within the study species. V.








americana allocated energy for the production of greater relative amounts of root

biomass in all sediment types as compared with the other species. These differences

were statistically significant in Site B, Site D and Site H sediments. N. guadalupensis

ratios were significantly lower than that of the other species in Station D sediments.

Within species comparisons suggested that N. guadalupensis and V. americana

allocated relatively more resources to root production in Station B sediments as

compared with the other sediments. In the case of N. guadalupensis, the difference

was statistically significant. P. illinoensis and V americana root:shoot ratios were

lowest in response to the control sediments.

Summer culture period (20 July to 21 September 2001)

Analysis of variance of pooled total macrophyte biomass (n = 60) produced

during the summer culture period using GLM procedures (SAS Institute 1999-2001)

indicated that sediment and plant type had a highly significant effect on macrophyte

biomass production (P <.0001) (Table 3-8). The interaction between these two factors

was not significant. Means separation using Tukey's HSD Procedure suggested that

there were significant differences among and within macrophyte species in response

to sediment type (a = 0.05). N. guadalupensis produced significantly higher biomass

on all natural sediments as compared to the other species (Table 3-9). Chara sp.

exhibited the slowest relative growth in response to all sediments. This difference was

statistically significant for growth in Site B and Site D sediments. N. guadalupensis

and P. illinoensis exhibited more rapid growth in all sediments as compared to V

americana and Chara sp.. There were no significant differences in growth among

macrophytes in response to the control sediments. Within species comparisons








suggested that all species exhibited the slowest growth in Site B sediments. This

difference was statistically significant for V. americana (18.6 g DWT) and Chara sp.

(3.8 g DWT) (Figure 3-4b). V americana produced statistically greatest biomass in

control, Site D and Site F sediments (44.4,41 and 28 g DWT). N. guadalupensis and

P. illinoensis produced greatest biomass in control sediments, however, these

differences were not found to be statistically significant (56.5 and 21 g DWT,

respectively). Although Chara sp. growth was best in control sediments, there were

no statistical differences in the biomass produced in control, Site F, Site H and Site D

sediments.

V americana produced a greater number of individual plants per pot on all

sediments as compared with P. illinoensis (Figure 3-5b). V. americana exhibited the

greatest increase in total number of plants in response to Site D sediments while the

greatest increase in number of P. illinoensis plants was observed on control

sediments.

The results of simple regression analyses of macrophyte biomass and

sediment chemical components indicated that there were species-specific differences

in response to sediment pH, OM, macro- and micro-nutrients and epiphyte biomass in

this culture period (Table 3-6). Sediment phosphorus, copper, manganese, iron,

ammonium, nitrate, magnesium, potassium, sodium, chloride and epiphyte biomass

had highly significant (P < .0001) effects on total macrophyte biomass (n = 60) while

aluminum had a significant effect on total biomass. Models with P. illinoensis

biomass and phosphorus, copper, manganese, iron, ammonium, nitrate, potassium,

sodium and chloride were all significant. Iron, ammonium, nitrate, and potassium








were all found to have significant effects on V americana biomass. Aluminum had a

highly significant effect (P < .0001) on biomass while copper was only slightly

significant. A significant negative relationship was observed between Chara sp.

biomass and epiphyte biomass. None of the models with N. guadalupensis biomass

gave significant results.

The results of stepwise multiple regression analyses using a composite of the

biomasses of all species (n=60) and the biomass of each individual species (n=15) as

the response and the significant factors as the predictors also indicated species-related

differences (Table 3-6). Total biomass was most significantly affected by copper (P <

0.0002) and ammonium (P < 0.0149). Biomass and ammonium were negatively

related. Epiphyte biomass was the most significant predictor of Chara sp. biomass

accumulation. Epiphyte biomass had a negative effect on Chara sp. biomass.

Root: shoot ratios produced by all species in response to all sediment types

were less than 1 (Figure 3-6b). Analysis of variance of macrophyte root:shoot ratios

using GLM procedures (SAS Institute 1999-2001) indicated differences in total

pooled (n = 60) root:shoot ratios due to plant type (P <.0033) (Table 3-10), There

were no significant differences due to sediment source or to the interaction between

sediment source and plant type. There were differences among and within the study

species (Figure 3-6b). V americana and P. illinoensis produced significantly greater

root:shoot ratios on Site B and Site H sediments versus N. guadalupensis. There were

no other species-specific responses to any of the other sediment types. Within species

comparisons suggested that root:shoot ratios for N. guadalupensis were slightly

greater on Site H and Site C sediments. P. illinoensis ratios were greatest on Site B,








Site H and control sediments while V americana produced the greatest mean ratio in

response to Site B sediments.

GLM analysis of epiphyte biomass (g/g host DWT) indicated significant

differences due to sediment source (P < 0.01) and highly significant host-specific

differences (P <.0001). Epiphyte biomass on Chara sp. was greatest in Site B

sediments. There were no other host-specific differences. Comparisons among

species indicated that in control and Site D sediments, Chara sp. and P. illinoensis

exhibited higher epiphyte biomass than V americana and N. guadalupensis. There

were no differences among the macrophytes in Site B, Site F or Site H sediments.

Winter culture period (19 December 2001 to 22 February 2002)

Analysis of variance of the composite macrophyte biomass (n = 60) produced

during the winter culture period using GLM procedures (SAS Institute 1999-2001)

suggested that plant type had a highly significant while sediment type had a

significant effect on macrophyte biomass production (P <.0001 and P < 0.0004,

respectively) (Table 3-11). The interaction between the two factors was slightly

significant. Means separation using Tukey's HSD Procedure suggested that there

were significant differences among and within macrophyte species in response to

sediment type (a = 0.05) (Figure 3-4c).

P. illinoensis and N. guadalupensis exhibited greater growth in all sediments as

compared with V americana and Chara sp. (Table 3-12). V americana biomass was

lower than that produced by the other species in all sediments. P. illinoensis biomass

was significantly greater than that of the other species in Site B, Site D, Site H and

control sediments. Within species comparisons indicated that N. guadalupensis








growth was significantly best in Sites F, C and H sediments. P. illinoensis accrued

greatest biomass in control and Site H sediments, however, there were no significant

differences in the biomass produced in any sediment type. Although V americana

exhibited the greatest growth on Site H sediments (12.9 g DWT), differences in

response to the different sediment types was minimal. Chara sp. accrued significantly

greatest biomass on control sediments (21.3 g DWT) and lowest biomass in Site B

(8.2 g DWT) and Site D sediments (7.3 g DWT) (Table 3-12).

There were species-specific differences in macrophyte biomass production in

response to sediment chemical composition. The results of simple regression analyses

of macrophyte biomass using sediment pH, OM and macro- and micro-nutrients as

predictors indicated a highly significant relationship (p < .0001) between phosphorus,

copper, manganese, ammonium, nitrate, magnesium, potassium, sodium and chloride

and composite macrophyte biomass of all species (n = 60) (Table 3-6). Iron had a

significant effect on composite biomass. Models with N. guadalupensis biomass

indicated highly significant relationships with organic matter, zinc and magnesium,

significant relationships with phosphorus and manganese and slightly significant

relationships with calcium and sodium. None of the models with V americana

biomass gave significant results. Chara sp. biomass was highly related (p < .0001) to

phosphorus, copper, manganese, iron, ammonium, nitrate, magnesium, potassium and

sodium.

P. illinoensis produced a greater average number of individual plants per pot

than V americana in all sediments (Figure 3-6c). P. illinoensis exhibited the greatest

increase in mean number of plants per pot in control sediments. There were no








obvious differences in the number of plants produced by V americana in response to

any of the sediments.

Root: shoot ratios produced by all species in response to all sediment types

were less than 1 (Figure 3-6c). Graphical analyses indicated that P. illinoensis and V

americana produced greatest root:shoot biomass on all sediments. Comparisons

within species suggested that N. guadalupensis ratios were greatest on Site D

sediments. P. illinoensis produced greatest ratios in response to Site B and Site F

sediments. V americana produced considerably more root biomass in comparison to

shoot biomass in Site H sediments. Analysis of variance of macrophyte root:shoot

ratios using GLM procedures (SAS Institute 1999-2001) indicated differences in total

root:shoot ratios due to plant type( P < 0.0004) (Table 3-13). There were no

significant differences due to sediment source or to the interaction between sediment

source and plant type. Among species comparisons indicated that P. illinoensis and V

americana produced significantly greater ratios than N. guadalupensis on Site B and

Site F sediments. There were no significant differences among species on any of the

other sediment types. Within species comparisons indicated that there were no

statistical differences in macrophyte root:shoot response to sediment type.

The results of GLM analysis of the data indicated that there were no

significant host-specific differences in epiphytic biomass (g/g host dry weight) during

the winter culture period. There were no differences in epiphyte biomass due to

sediment source or the interaction between sediment source and plant type.








Identification of General Trends

Graphical analysis of the data indicated differences in macrophyte biomass

production among the three culture periods (Figure 3-4). Overall, greatest plant

growth occurred during the summer culture period. Comparisons among species

indicated that N. guadalupensis produced the greatest biomass of all study species

when grown in lake sediments in spring and in all sediments in summer. P. illinoensis

exhibited the greatest growth among the species on four of the five sediment types

during the winter growing period. Differences in biomass production within

macrophyte species were also observed. The results suggest that N. guadalupensis, V.

americana and Chara sp. grew best during the summer culture period. P. illinoensis

produced greatest biomass during and grew equally well in the summer and winter

culture periods. With the exception of V americana at station H, there was relatively

little difference in the biomass production of V americana and Chara sp. during the

spring and winter culture periods.

Overall trends in macrophyte growth in response to different sediment types

were also observed. Generally, greatest macrophyte biomass accumulation during all

culture periods occurred in control sediments. Site F and Site H were apparently the

most suitable natural substrates for macrophyte growth. Station B sediments

supported the least biomass production among the species over the three culture

periods.

Macrophyte biomass data collected during the summer and winter culture

period were pooled and statistically analyzed as a randomized complete block design

where culture periods were considered blocks. Data collected during the spring








culture period were not included in this statistical analysis. (Refer to the Materials and

Methods section for an explanation.) Analysis of the data using GLM procedures

(SAS Institute 1999-2001) indicated highly significant differences in total pooled

macrophyte biomass due to culture period, sediment source, plant type and the

interaction between culture period and plant type (P < .0001 for all) (Table 3-14). A

weak interaction was also noted for culture period and sediment source (P < 0.0142).

No interaction was observed for sediment source and plant type or for all three effects

together. There were significant differences in biomass among and between the study

species (a = 0.05). Means separation using Tukey's HSD Method indicated that N.

guadalupensis produced significantly greater biomass on F sediments as compared to

the other species (Table 3-15). N. guadalupensis and P. illinoensis biomass was

significantly greater on Station B and Station H sediments as compared to that of V

americana and Chara sp.. V americana response on control sediments was

significantly less than that of the other species. There were no significant differences

in growth among the species when grown on Station D sediments. Within species

analysis of the variance in biomass indicated that Chara sp. produced significantly

greatest biomass in the control sediments Table 3-16). However, it should be noted

that there was only a slight difference between Chara sp. biomass produced in control

and Site F, Site H and Site D sediments. P. illinoensis produced greatest biomass in

control and Site H sediments. No significant differences were noted in the response of

N. guadalupensis and V americana biomass production to different sediments.

Further investigation of the effect of culture period on macrophyte biomass indicated

that N. guadalupensis produced significantly greater biomass during the summer








culture period followed by P. illinoensis and V americana with statistically equal

summer biomass. Chara sp. produced the least summer biomass. P. illinoensis

produced the greatest biomass during the winter culture period while Chara sp. and

V americana exhibited the least amount of growth.

A comparison of the mean number of individual plants produced per pot by

each plant type indicated differences among species and within species during

different culture periods (Figure 3-5). P. illinoensis produced greater numbers of

plants in the winter than in the spring and summer culture periods. A considerably

greater number of V americana plants per pot was measured for the summer culture

period than for the other culture periods.

Comparison of the root:shoot biomass produced indicated values < 1 for all

species during all culture periods (Figure 3-6). V americana produced considerably

greater root:shoot ratios in the spring as compared to the summer and winter culture

periods when ratios were fairly similar. These findings may have been due to

reduction of shoot material by herbivores. Ratios for P. illinoensis were higher in the

winter and spring than in the summer culture period. Similar root:shoot ratios were

observed for N. guadalupensis in the summer and winter culture periods. Slightly

higher ratios in the spring culture period were probably skewed by an underestimate

of shoot biomass due to herbivore damage.

Statistical analysis of pooled root:shoot ratios (n = 120) observed during the

summer and winter culture periods using GLM procedures (SAS Institute 1999-2001)

suggested highly significant species-specific differences in root:shoot biomass (P

<.0001) and a weak interaction between culture period and plant type (Table 3-17).








Further analysis indicated significant differences among plant types such that

root:shoot biomass ratios for P. illinoensis and V americana were greater on Station

B and Station F sediments as compared to N. guadalupensis (Table 3-18). There were

no significant differences on any of the other sediments. V. americana root:shoot

ratios were greater during the summer culture period as compared to the other species

(P < 0.0032) while V. americana and P. illinoensis root:shoot biomass was

significantly greater than that ofN. guadalupensis during the winter culture period (P

< 0.0004). Within species comparisons indicated that P. illinoensis produced

significantly greater root biomass on Site B sediments and lowest root:shoot ratios on

control sediments (Table 3-19). Sediment source did not appear to have a significant

effect on the amount of below-sediment biomass produced by N. guadalupensis and

V. americana during the summer and winter culture periods.

Results of analysis of pooled epiphyte data from the summer and winter

culture periods (n=120) using the GLM procedure indicated that culture period had a

highly significant effect (P < .0001) on epiphyte biomass (Table 3-20). Neither

sediment source, host macrophyte species or any interactions among the factors were

significant. Means separation using Tukey's HSD Test indicated that the epiphytic

biomass occurring on all four species was significantly greater in the winter than in

the summer culture period (Table 3-21). Generally, greater epiphyte biomass was

associated with Chara sp. and N. guadalupensis on all sediments, however none of

these differences were statistically significant (Table 3-22). Similarly, there were no

significant differences in the epiphyte biomass occurring within host species on any

sediment type (Table 3-23). There was no apparent relationship between epiphyte








biomass and sediment source during either the summer or the winter culture period

(Table 3-24).

Effects of Sediment, Temperature, Light and Epiphytes on Macrophyte
Production

Simple regression models revealed differences in macrophyte growth response

to sediment characteristics, light, water temperature and epiphyte biomass during the

summer and winter culture periods. Results from the spring culture period were not

included due to the unquantifiable effects of herbivory on shoot biomass in the study

species. The results suggested that sediment ammonium and nitrate had a highly

significant effect on total pooled (summer and winter culture period) macrophyte

biomass (n = 120) (p < .0001) (Table 3-25). Magnesium had a significant effect on

total pooled (n = 120) and pooled N. guadalupensis biomass (n = 30). No other

models with sediment nutrients and N. guadalupensis biomass were significant.

Pooled P. illinoensis (n = 30) biomass was significantly related to phosphorus,

copper, manganese, aluminum, iron, ammonium, nitrate, magnesium, potassium,

sodium, and chloride. None of the models with pooled V americana biomass (n = 30)

and sediment nutrients were significant. Sediment phosphorus, copper, manganese,

iron, ammonium, nitrate, magnesium, potassium and sodium were all significantly

related to pooled Chara sp. biomass (n = 30).

Additional simple regression models using pooled summer and winter

biomass also indicated that light, water temperature and epiphyte biomass had

significant effects on the growth of the study species (Table 3-26). Models relating

pooled total biomass (n = 120) and biomass of N. guadalupensis and V americana








separately (n =30) suggested that total PAR (pmol photons m'2 per CP), mean

instantaneous PAR (pmol photons m-2 s-1) and water temperature had a highly

significant (p < .0001) effect on biomass production in all cases. None of the models

with pooled Chara sp. biomass (n = 30) and pooled P. illinoensis biomass (n = 30)

were significant.

Stepwise multiple regression analyses conducted using pooled summer and

winter macrophyte biomass as the dependent variable and the significant sediment

nutrients and climatic factors identified using simple regression analyses as the

independent variables indicated macrophyte growth in this study was affected by a

combination of factors. Total pooled biomass (n = 120) was most significantly

affected by nitrate, total PAR per culture period and ammonium (Table 3-27). The

data indicated species-related differences in response to the independent variables. N.

guadalupensis and V. americana biomass exhibited a strong positive relationship with

water temperature. Water temperature explained almost 50% of the variation in N.

guadalupensis biomass and over 64% of the variation in V americana production.

The results suggested that P. illinoensis growth was positively correlated with

sediment copper content and negatively correlated with sediment iron content.

Collectively, these two predictors explained over 44% of the variation in the biomass

of this species. There was a significant positive relationship between Chara sp.

growth and sediment phosphorus content.

Discussion

The results of the sediment survey conducted at the beginning of this study

confirmed the hypothesis that that there would be spatial variation in the organic








matter content of the littoral sediments in Lake Hollingsworth. Organic matter content

in the sediment samples ranged from 0.38% to 39.18% (Table 3-1). Sediment pH

values also ranged from 5.4 to 8.0. In their 1996 study of seven shallow productive

Florida lakes including Lake Hollingsworth, Whitmore et al. identified the presence

of highly variable sediment organic matter content. They attributed the lack of

uniform organic buildup in their study lakes to frequent mixing, lack of thermal

stratification and warm temperatures resulting in the breakdown of organic material.

They identified three types of organic sediment distribution patterns: uniform

distribution, distribution to deeper areas, and distribution to peripheral areas and

embayments where the type of distribution pattern greatly depends on lake

bathymetry. The highly variable nature of organic sediment composition in their

study lakes led these researchers to conclude that systematic sediment mapping

surveys are necessary to characterize the sediments in shallow "wind-stressed"

productive lakes such as Lake Hollingsworth. The findings suggested the importance

of beginning revegetation projects in Florida lakes with a preliminary investigation of

sediment chemical composition.

The findings of the sediment survey conducted in this study made it possible

to identify sites around the lake that were not only relatively protected from

anthropogenic disturbance but that had organic matter contents that were not

inhibitory to plant growth. Having this type of "background information" on a system

should facilitate site selection for planting in revegetation projects. I believe that the

study stations selected in this study should provide highly suitable habitat for the








establishment of founder colonies (sensu Smart et al. 1996) of the study species in

Lake Hollingsworth.

Analyses of sediment chemical composition corroborated the hypothesis that

there would be spatial variation in the nutrient content of the littoral sediments in

Lake Hollingsworth. The study sediments varied in pH, organic matter and nutrient

content (Table 3-2). Natural sediments, with the exception of Site B sediments, were

more alkaline than control sediments. Although organic matter contents were not

available for the control sediments, low organic matter contents are typical for sand

sediments. Therefore, even though the organic content of Site F sediments (1.08%)

was significantly greater than that of the other natural sediments, the limited range of

values made it difficult to identify any effects on macrophyte growth due to sediment

organic content. Calcium content in Site F sediments was significantly greater than

that of the other sediments (5617 mgKg'1). In my opinion, this value was high

probably due to the presence of shell or pebble material in the analytical sample that

was not thoroughly homogenized during processing. Control, Site F and Site H

sediments all exhibited relatively high levels of phosphorus, zinc, copper, manganese

and iron as compared with Site B and Site D sediments. Ammonium and nitrate were

present in significantly greater amounts in the control sediments. Although there were

significant differences in the content of some other nutrients in the sediments, i.e.

potassium and magnesium, the literature indicates that these nutrients are primarily

derived by submersed macrophytes from the water column (reviewed in Barko et al.

1991). Sutton (1990) observed similar chemical composition in sediments collected








from Lake Okeechobee. Sediment nutrient analyses in his study were conducted using

the same procedure as was used in this study.

Light and temperature data gathered throughout the study indicated climatic

variations among the culture periods. Highest average daily water temperature

occurred during the summer culture period. Lowest water temperatures were

observed during the winter. Despite low winter temperatures, average water

temperatures were sufficient to meet the minimum requirement during each culture

period for nutrient release by the Osmocote fertilizer used to amend the control

sediments. Harbaugh and Wilfret (1981) determined that release rates of Osmocote

are temperature-dependent and increase at temperatures above 21 C. Sutton and

Latham (1996) measured minimum average water temperatures equal to or greater

than 21 C during a growth study conducted at the FLREC using sand media amended

with Osmocote. Based upon these water temperatures, they concluded that release

rates remained high enough to maintain sufficient sediment concentrations of

phosphorus, ammonium and nitrate during the winter culture period. Photoperiod was

longest in spring and shortest in winter. Average PAR values showed a similar trend.

These findings are probably best explained by the fact that partly cloudy days are the

norm in South Florida. Relatively lower average PAR values in summer compared to

spring are probably due in part to afternoon thunderstorms that result in 100% cloud

cover during parts of most summer afternoons.

Biomass data collected in this study indicted that macrophyte growth and

sediment nutrient content were positively related. Greatest biomass production

occurred on control sediments probably due to the presence of significantly greater




Full Text

PAGE 1

SEDIMENT AND LIGHT REQUIREMENTS OF FOUR SPECIES OF NATIVE SUBMERGED MACROPHYTES OCCURRING IN FLORIDA LAKES By MARGARET SHERRIE HOPSON-FERNANDES A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2005

PAGE 2

To my family Carlos, Eddie, Maria, Mom and Daddy for your undying support and willingness to help no matter what needed to be done. We did it!

PAGE 3

ACKNOWLEDGMENTS I would like to express my gratitude to all of the people who helped me to reach this incredible goal. My sincere thanks go to Dr. Koopman for his guidance, encouragement and genuine commitment to education. I appreciate his continued patience and flexibility in working with a student "not living locally." His comprehensive reviews of the dissertation also proved invaluable. I am indebted to Dr. Phlips for always encouraging me to strive to find ecological explanations and for his generosity in sharing so many thought-provoking ideas with me. He also provided invaluable assistance in securing funding for this project. Dr. Sutton gave me a key to his laboratory, his fabulous growth tank facilities and his supply shed before I had any funding in place. Thanks to his generosity, I was able to begin my research in a timely fashion. I also appreciate his willingness to accommodate my research needs by making space and supplies available to me throughout my program. I extend many thanks to Dr. Montague for encouraging me to view conventional ecological issues from alternative perspectives. I am very honored to have been a GAANN Fellow. I am grateful for the opportunity given to me by the United States Department of Education in association with the University of Florida Department of Environmental Engineering Sciences. My sincere thanks go to Dr. J .J. Warwick for his commitment to the advancement of the academic careers of students in his department. I am also very privileged to have received a Supplemental Retention Award from the UF Office of Graduate Minority Programs. lll

PAGE 4

Funding for this research was provided by a grant awarded to the Department of Fisheries and Aquatic Sciences, University of Florida, by the City of Lakeland Lakes Program. Special thanks go to Mr. Gene Medley and Mr. Bal Sukrah and the personnel from the City of Lakeland Lakes and Stonnwater and Construction and Maintenance Divisions for providing logistical and field support in Lake Hollingsworth. Dr. Gabe Vargo (Marine Science Laboratory, University of South Florida) generously offered the use of his facilities and equipment for field and laboratory research. I am indebted to Ms. Joanne Korvick of the University of Florida, Ft. Lauderdale Research and Education Center (UF FLREC) for her friendship, expert advice on field-related issues and willingness to lend assistance in the field. Mr. Frank Nazario also provided valuable field support at the UF FLREC I greatly appreciate the assistance of Ms. Merrie Beth Neely (Marine Science Laboratory, University of South Florida) for her help with the macrophyte chlorophyll a analyses. Many thanks go to Dr. H J Grimshaw (South Florida Water Management District) for his generous exchange of ideas during the development of the experimental design for the light experiment. He also graciously lent me a light probe. Mr. Dan Mahon analyzed sediment samples for organic matter content and subsamples for epiphyte chlorophyll a for one culture period at the laboratory at the City of Lakeland Carl W. Dicks Wastewater Reclamation Facility. Thanks go to Dr. Vernon Vandiver for helping me "see the light" about some problems with the experimental design in my first light experiment. Dr. Chuck Cichra (Department of Fisheries and Aquatic Sciences, University of Florida) helped me to understand the wild world of SAS. His help proved invaluable. Dr. Cornell provided statistical guidance. Sediment nutrient analyses were performed by the Analytical Research Laboratory of the lV

PAGE 5

Soil and Water Science Department, University of Florida, Gainesville Mr. Matt Phillips, of the Florida Fish and Wildlife Conservation Commission, graciously allowed me to use the drying oven at his facility Many warm thanks go to the Environmental Engineering Office staff, especially Ms. Berdenia Monroe, Ms. Barbi Barber and Ms. Hoa Dinh for all of the kindness that they bestowed upon me. I am also indebted to the Fisheries and Aquatic Sciences Office staff, especially Ms. Jennifer Hermelbracht and to Ms. Bobbi Godwin (Center for Aquatic and Invasive Plants) for all of their assistance over the years V

PAGE 6

TABLE OF CONTENTS ACKNOWLEDGMENTS ............................................................................................... iii I LIST OF TABLES ......................................................................................................... viii LIST OF FIGURES ...... ................................................................... .. .......... ... ............... xii ABSTRACT ..... ..... ................ ...... ............... ..... ................. ........................................... xvi CHAPTER 1. INTRODUCTION ............... .......................... .... ............................................ 1 Background Information ................................................................................. 1 Statement of Purpose .............................................. ............................ .......... 3 Hypotheses ...... ... ........................................................... ................................. 4 2. LITERATURE REVIEW ............................................................................... 6 Background Information ..................... ...... ................ ..... ...................... .... ... ... 6 Lake Restoration Techniques .................................................................. ....... 7 Algal Biomass Control Methods ........................................................... ... ....... 8 Macrophyte Biomass Control Methods ..................... .. ................................. 11 Aeration and Sediment Removal .................................................................. 12 Revegetation Projects in Lake Restoration .. ...................... ......................... 14 Macrophyte Species Selection ........... .... ..................................................... 20 Description of Study Macrophytes ............................................................... 22 Submerged Macrophyte Biology ......................................... .. ...... ............... 24 Environmental Factors Controlling Production ....................................... .... 29 The Role of Light in Submerged Macrophyte Growth ................................. 30 The Role of Sediments in Macrophyte Nutritional Ecology ........................ 32 Culturing Submerged Macrophytes .... ..... ...................... .......................... ..... 35 Epiphytic Algae .................. ................................... ........ ... .......................... 36 The Macrophyte-Epiphyte Complex .......... ..... ................... ...... .......... . ......... 39 Methods for Investigating Epiphytic Algae ...... .. ............ .................... .... ..... 42 VI

PAGE 7

3. COMPARISON OF THE GROWTH OF FOUR SPECIES OF NATNE SUBMERGED MACROPHYTES ON INORGANIC SEDIMENTS FROM A SHALLOW URBAN FLORIDA LAKE .................................... ................. 48 Introduction and Literature Review ........................................................ 48 Materials and Methods ............................................................................ 55 Results ......................................... ........................................................... 64 Discussion ............................................................................................... 80 Conclusions ....................................... ..................................................... 93 4 LIGHT REQUIREMENTS OF FOUR SPECIES OF NATNE SUBMERSED MACROPHYTES: IMPLICATIONS FOR THE RESTORATION OF SHALLOW EUTROPHIC LAKES 1. ASSESSMENT FOR MATURE PLANTS ......................................................................................... ........... 123 Introduction ....................... ..... .. ................ ....................................... .... 123 Materials and Methods .. .... .... .... .......................................................... 126 Results ...................................................................................... ............. 132 Discussion .............................................. .... ..... ........... ... ........... ........ .. ... 139 Conclusions ..... .................................. .............. ...................... ... .......... 144 5. LIGHT REQUIREMENTS OF FOUR SPECIES OF NATNE SUBMERSED MACROPHYTES : IMPLICATIONS FOR THE RESTORATION OF SHALLOW EUTROPHIC LAKES 2. ASSESSMENT FOR PROPAGULE PLANTS ............. ....................................................... 166 Introduction ......................... .. .................. ........ ..................................... 166 Materials and Methods ..................................................... .................. . 169 Results .. .. ..... ........................................ . ..... ..... ....... .... .... ...... .............. 174 Discussion ........ .......... ............................................. ........................... 181 Conclusions ................................................. .. ........ .... .................. .... ..... 184 6. SUMMARY AND CONCLUSIONS ........... .... ....................... ............ ....... 214 APPENDIX ........ ...... ...... .......... .. . ....... ... ................... ........... .. ................................... 217 LITERATURE CITED ........ ................. ......... .... .................... ............ ........ ............ .... 221 BIOGRAPHICAL SKETCH ... ... .... ............ ................................................... ........... 247 Vll

PAGE 8

LIST OF TABLES 3-1: Organic matter content and pH of sediments from the preliminary survey ............ 95 3-2: Organic matter, pH and selected macroand micronutrient composition of sediments from the four study stations and control sediments ..... .... .... ........ .......................... ... ...... 96 3-3: Temperature and irradiance during the three culture periods .................................. 97 3-4: Spring culture period-30 April to 29 June 2001. Results of analysis of variance to investigate the effect of sediment source, plant type and the interaction between these two factors on macrophyte growth ............................................ ................. ......................... 97 3-5: Spring culture period 30 April to 29 June 2001. Dry weight of study macrophytes cultured on sediments collected from the four study stations in Lake Hollingsworth and on artificial sediments ............... .... .......................... ....................................................... 98 3-6: Stepwise multiple regression analysis results using macrophyte biomass as the dependent variable, sediment macroand micronutrient concentrations and epiphyte biomass as the independent variables ........ ............................................................. 99-100 3-7. Spring culture period 30 April to 29 June 2001. Results of analysis of variance to investigate the effect of sediment source, plant type and the interaction between these two factors on macrophyte root:shoot ratios .... ......... ..... ... ...... ......................................... 101 3 -8: Summer culture period 20 July to 21 September 2001. Results of analysis of variance to investigate the effect of sediment source, plant type and the interaction between these two factors on macrophyte biomass .... ... .... ................ .. ..... .. ........... .... ... 101 3-9: Summer culture period 20 July to 21 September 2001. Dry weight of study macrophytes cultured on sediments collected from the four study stations in Lake Hollingsworth and on artificial sediments ........ .... ...................................................... 102 3-10: Summer culture period 20 July to 21 September 2001. Results of analysis of variance to investigate the effect of sediment source, plant type and the interaction between these two factors on macrophyte root:shoot ratios ........... ... ......... .... ... ........... 103 I Vlll

PAGE 9

3-11: Winter culture period-19 December 2001 to 22 February 2002. Results of analysis of variance to investigate the effect of sediment source, plant type and the interaction between these two factors on macrophyte biomass ...................................................... 103 3-12: Winter culture period-19 December 2001 to 22 February 2002. Dry weight of study macrophytes cultured on sediments collected from the four study stations in Lake Hollingsworth and on artificial sediments .................................................................... 104 3-13: Winter culture period 19 December 2001 to 22 February 2002. Results of analysis of variance to investigate the effect of sediment source, plant type and the interaction between these two factors on macrophyte root:shoot ratios .................................... ..... 105 3-14: Results of analysis of variance of pooled total macrophyte biomass of all species combined produced during the summer and winter culture period to investigate the effect of culture period, sediment type, plant type and the interaction between the factors ... 105 3-15: Differences among the study species in the pooled mean biomass produced during the summer and winter culture periods ................... ...... ................ . ....... ....................... 106 3-16: Differences within the study species in the pooled mean biomass produced during the summer and winter culture periods ....................... . ............ .................. ........... ... ... 107 3-17: Results of analysis of variance of pooled macrophyte root:shoot ratios from the summer and winter culture period (n=90) to investigate the effect of culture period, sediment source, plant type and the interaction between the factors ................. .......... 108 3-18: Differences in the pooled mean root:shoot ratios among the study species ........ 108 3-19: Differences within macrophyte species in the pooled mean root:shoot ratios produced during the summer and winter culture periods ...... ....................................... 109 3-20: Results of analysis of variance of pooled epiphyte biomass from the summer and winter culture periods to investigate the effect of culture period, sediment source, plant type and the interaction between the factors ........ ................. ...................................... 109 I 3-21: Differences in epiphyte biomass occurring in the summer and winter culture periods (n= 30) .................................... ....... ..... .... .......... ..... ......................................... 110 I 3-22: Differences in epiphyte biomass occurring in the summer and winter culture periods on each host macrophyte species (n=18) ......................................................... 111 3-23: Differences in mean pooled epiphyte biomass (n = 30) occurring in the summer and winter culture periods on each host macrophyte species at the study stations ............. 112 3 24: Differences in mean epiphyte biomass (n =6 0) occurring at each station during the summer an.d winter culture periods ............................................. .... ...... ..... ... ............... 113 IX

PAGE 10

3-25: Results of the use of simple regression analysis to evaluate the relative significance of each sediment characteristic on the pooled mean biomass of all species combined (total) (n=120) and each individual species (n=30) during the summer and winter culture periods .......................................................................................... ........................ ....... 113 3-26: Results of the use of simple regression analysis to evaluate the relative significance of light and water temperature on the pooled mean composite biomass of all species (n=120) and each individual species (n=30) during the summer and winter culture periods ........................................................................................................................... 114 3-27: Stepwise multiple regression analysis results using pooled macrophyte biomass produced during the summer and winter culture periods (n=l20 for total biomass of all species combined and n=30 for each individual species) ............................................. 115 4-1: Temperature and irradiance during the three culture periods ................................ 146 4-2: Experiment 1: Estimated average instantaneous, daily and total photosynthetic flux density (PPFD) received over the period 22 August to 16 September 2001. ............... 147 4-3: Results of analysis of net growth (g dry weight per pot per culture period) of aboveground macrophyte biomass produced in Experiment 1 using GLM procedures ........ 148 4-4: Experiment 2: Estimated average instantaneous, daily and total photosynthetic flux density (PPFD) received over the period 25 February to 13 April 2002 ...................... 148 4-5: Results of analysis of net growth (g dry weight per pot per culture period) of total macrophyte biomass (above plus below ground biomass) in Experiment 2 using GLM procedures (SAS Institute Inc. 1999-2001) .................................................................. 149 4-6: Root:shoot ratios for Experiment 2. Values are the means calculated for three culture containers per macrophyte species per treatment group followed by the standard deviation ............... ............................. .. .................................... .......... ......................... 149 4-7: Experiment 3: Estimated average instantaneous, daily and total PPFD received over the culture period (CP) 16 July to 31 August 2002 ...................................................... 150 4-8: Results of analysis of net growth (g dry weight per pot per culture period) of total macrophyte biomass (above plus below ground biomass) in Experiment 3 using GLM procedures (SAS Institute Inc. 1999-2001) ....... .......................................................... 150 4-9: Root:shoot ratios for Experiment 3. Values are the means calculated for three culture containers per macrophyte species per treatment group followed by the standard deviation ........................................................................................... ............................ 151 Table 4-10: Selected field observations and experimental conclusions concerning the light requirements of several species of submersed macrophytes ................................ 152 X

PAGE 11

Table 4-11: A comparison of the seasonal light levels at which there was zero net growth of the study species ........................................................................ ......................... .... 153 5-1: Temperature and irradiance during the three culture periods ................................ 186 5-2: Experiment 1: Estimated average instantaneous, daily and total photosynthetic photon flux density (PPFD) received over the period 27 April to 14 July 2002 .......... 187 5-3: Results of within species analysis of net growth (g dry weight per pot per culture period) of total macrophyte biomass (aboveplus below-ground biomass) in Experiment 1 using GLM procedures (SAS Institute Inc. 1999-2001) ............................................ 187 5-4: Within species comparisons of root:shoot ratios for Experiment 1 ................. .... 188 5-5. Comparisons among species of root:shoot ratios for Experiment 1 ................. . ... 188 5-6: Experiment 2: Estimated average instantaneous, daily and total photosynthetic photon flux density (PPFD) received over the period 21 April to 7 June 2003 ............ 189 5-7: Results of withinspecies analysis of net growth (g dry weight per pot per culture period) of total macrophyte biomass (above plus below ground biomass) in Experiment 2 using GLM procedures (SAS Institute Inc. 1999-2001) ............ .... ......... ..................... 189 5-8: Experiment 3: Estimated average instantaneous, daily and total photosynthetic photon flux density (PPFD) received over the period 28 June to 02 August 2003 ...... 190 5-9: Results of analysis of net growth (g dry weight per pot per culture period) of total macrophyte biomass (above plus below ground biomass) in Experiment 3 using GLM procedures (SAS Institute Inc. 1999-2001) .................................................................. 190 5-10: Selected field observations and experimental conclusions concerning the light requirements of several species of submersed macrophytes ............. ... ......................... 191 5-11: A comparison of the seasonal variation in light levels at which there was zero net growth of the study species . .... ........ . ....... ............. ................... ... ... ... ...... .... ....... ....... 192 XI

PAGE 12

LIST OF FIGURES Figure 2-1. Najas guadelupensis is a pioneer species in the Najadaceae .... .............. .... 44 Figure 2-2: Chara spp. are macroalgae .................................................................... ...... 45 Figure 2-3: Potamogeton illinoensis is a Florida native perennial with broad lanceolate leaves ............................ .. .......... ..... .... ....................... .. ................... ... ... ................ .... .... 46 Figure 2-4: Vallisneria americana is a perennial with broad ribbonlike leaves ... .... .... 47 Figure 3-1: Map of Lake Hollingsworth showing the location of the four study stations B, D, F and H ..... ............................... . ... .............. .... ......................... .. . . .. ................ 116 Figure 3-2: A diagrammatic sketch of the distribution of7. 6-L nursery containers in the experimental tanks ................... . .... ............. ........... .................... ... .. ..... .... ...... . ...... .. 11 7 Figure 3-3: Biomass produced by Najas and Potamogeton during the spring culture period ..... ........... .... ...... .......... ....... .... . . ..... ........ ...... ...... .... .... ..... .............. . .... ... 118 Figure 3-4: A comparison of the mean biomass produced by each plant species when grown in sediments from stations : B, D, F and Hand controls for each of the three culture periods ........ ........ ................. ............. . ...... .......... ...... .... .......... ............ ... ......... ... 119 Figure 3-5: A comparison of the average number of individual plants produced by each species when grown in the six sediments ... ............... ..... ............. . .. .... . ... ... . .... ... ... 120 Figure 3-6: Ratio ofroot:shoot biomass for the four study species in the spring, summer and winter culture periods ..... .......... . .... ............ .............. ................ ... .............. ....... . 121 Figure 3-7: Epiphyte biomass occurring on the study plants ..... .. .... .. ... .... ... .... ........ .. 122 Figure 4-1: Experimental set-up for mature plant light requirements Experiments 1 2 and 3 and propagule plant light requirements Experiment I. ....... ...... . . . ........ . ............. . 154 Figure 4-2: Experiment 1: Graphical interpretation of the net growth of Najas guadelupensis in response to the percent incident PAR at the water surface ........... ... 155 Figure 4-3: Experiment 1 : Graphical interpretation of the net growth o f Potamog e ton illinoensis in r e spons e to the p e rc e nt incident PAR a t the water surfa ce ..... ............ ... 1 5 6 XU

PAGE 13

Figure 4-4: Experiment 1: Graphical interpretation of the net growth of Vallisneria americana in response to the percent incident PAR at the water surface ... . . ... ...... . ... 157 Figure 4-5: Experiment 2: Graphical interpretation of the net growth of Najas guadelupensis in response to the percent incident PAR at the water surface ............. . 158 Figure 4-6: Experiment 2: Graphical interpretation of the net growth of Potamogeton illinoensis in response to the percent incident PAR at the water surface ............. ....... 159 Figure 47: Experiment 2: Graphical interpretation of the net growth of Chara sp in response to the percent incident PAR at the water surface ....... ... ................... ............. 160 Figure 4-8: Experiment 3: Graphical interpretation of the net growth of Najas guadelupensis in response to the percent incident PAR at the water surface ............... 161 Figure 4-9: Experiment 3: Graphical interpretation of the net growth of Potamogeton illinoensis in response to the percent incident PAR at the water surface ........ ..... ........ 162 Figure 4-10: Experiment 3: Graphical interpretation of the net growth of Vallisneria americana in response to the percent incident PAR at the water surface ..................... 163 Figure 4-11: Experiment 3: Graphical interpretation of the net growth of Chara sp. in response to the percent incident PAR at the water surface .. ... . ... ...... .. ........... . .... ....... 164 Figure 4-12: Mature plant light requirements experiment: Among species comparisons of macrophyte chlorophyll a measured for each of the study plants .. .. ............. ............. 165 Figure 5-1: Propagule light requirements Experiment 1: Linear regression of PAR at the air-water interface versus the net growth (g dry weight per container per 78 days) of Najas guadelupensis .................................................................................................... 193 Figure 5-2: Propagule light requirements Experiment 1: Linear regression of mid-water PAR, measured at the sediment-water interface, versus the net growth (g dry weight per container per 78 days) of Najas guadelupensis ............................................................ 194 Figure 5-3: Propagule light requirements Experiment 1: Linear regression of PAR at the air-water interface versus the net growth (g dry weight per container per 78 days) of P. illinoensis . ......... .............. ................... .......... ..... ..... ..... ............................ ............... .... 195 Figure 5 -4: Propagule light requirements Experiment 1 : Linear regression of mid-water PAR measured at the sediment-water interface versus the net growth (g dry weight per container per 78 days) of P. il/inoensis ......................................................................... 196 Figure 5-5: Propagule light requirements Experiment 1: Linear regression of PAR at the air-water interface versus the net growth (g dry weight per container per 78 days) of V. americana ... ....... ..... ... ......... ...................................................... ......... ....... ...... .... ....... 197 Xlll

PAGE 14

Figure 5-6: Propagule light requirements Experiment 1: Linear regression of mid-water PAR, measured at the sediment-water interface, versus the net growth (g dry weight per container per 78 days) of V. americana ....................................................................... 198 Figure 5-7: Propagule light requirements Experiment 1: Linear regression of PAR at the air-water interface versus the net growth (g dry weight per container per 78 days) of Chara sp ....................................................... ................. ............ . ... .. ................. .... .... 199 Figure 5-8: Propagule light requirements Experiment 1: Linear regression of mid-water PAR, measured at the sediment-water interface, versus the net growth (g dry weight per container per 78 days) of Chara sp ......................... .. .................................. ................ 200 Figure 5-9: Propagule light requirements Experiment 2: Linear regression of PAR at the air-water interface versus the net growth (g dry weight per container per 48 days) of V. americana .......................................................................... ............. ........................... 201 Figure 5-10: Propagule light requirements Experiment 2: Linear regression of mid-water PAR, measured at the sediment-water interface, versus the net growth (g dry weight per container per 48 days) of V. americana ....................................................................... 202 Figure 5-11: Propagule light requirements Experiment 2: Linear regression of PAR at the air-water interface versus the net growth (g dry weight per container per 48 days) of P illinoensis .............................................. ........................................ ............................. 203 Figure 5-12: Propagule light requirements Experiment 2: Linear regression of mid-water PAR, measured at the sediment-water interface, versus the net growth (g dry weight per container per 48 days) of P. illinoensis ......................................................................... 204 Figure 5-13: Propagule light requirements Experiment 2 : Linear regression of PAR at the air-water interface versus net growth (g dry weight per container per 48 days) of Chara sp ............. ............. ... . ............... ... .... ... ... ...... . ..... . ........ ................ ... ........................ 205 Figure 5-14: Propagule light requirements Experiment 2: Linear regression of mid-water PAR, measured at the sediment-water interface, versus net growth (g dry weight per container per 48 days) of Chara sp ............ ............................................. .. .... .............. 206 Figure 5-15: Propagule light requirements Experiment 3: Linear regression of PAR at th e air water interface versus the net growth (g dry weight per container per 35 days) of V. americana . . ..... ... ... ..... .. ...... ........ ....... ... ..... . ... ...... .. ......... ; ... . . ........... ... ... .......... ...... 207 Figure 5-16: Propagule light requirements Experiment 3 : Linear regression of mid-water PAR, measured at the sediment-water interface, versus the net growth (g dry weight per container per 35 days) of V. americana .... .. ........ .... .... ..... ............... .......... ............ ....... 2 08 I I XlV

PAGE 15

Figure 5-17: Propagule light requirements Experiment 3: Linear regression of PAR at the air-water interface versus the net growth (g dry weight per container per 35 days) of P. illinoensis. Outlying data points were excluded from analysis and are indicated in the figure as open circles ... .. ....... .. .. .. .... .............................................. ... ........................... 209 Figure 5-18: Propagule light requirements Experiment 3: Linear regression of mid-water PAR, measured at the sediment-water interface, versus the net growth (g dry weight per container per 35 days) of P. illinoensis ... ........................ ...................... ... ....... ............ 210 Figure 5-19: Propagule light requirements Experiment 3: Linear regression of PAR at the air-water interface versus the net growth (g dry weight per container per 35 days) of Chara sp ......................................................................................... ... ......................... .. 211 Figure 5-20: Propagule light requirements Experiment 3: Linear regression of mid-water PAR, measured at the sediment-water interface, versus the net growth (g dry weight per container per 35 days) of Chara sp .............. ..... .. ......................................................... 212 Figure 5-21: Among species comparisons ofmacrophyte chlorophyll a produced during propagule plant light requirements Experiment 1 ( 4/27 to 7 /14/02) .... ........................ 213 xv

PAGE 16

Abstract of Dissertation Presented to the Graduate School Of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy SEDIMENT AND LIGHT REQUIREMENTS OF FOUR SPECIES OF NATIVE SUBMERGED MACROPHYTES OCCURRING IN FLORIDA LAKES By Margaret Sherrie Hopson-Fernandes May 2005 Chair: Ben Koopman, Ph.D. Cochair: Edward J. Phlips, Ph.D. Major Department: Environmental Engineering Sciences The purpose of this research was to investigate sediment and light growth requirements, two key factors in the establishment of native submersed macrophytes in shallow eutrophic Florida lakes. The study plants were Najas guadelupensis, Potamogeton illinoensis Vallisneria americana and Chara sp., all Florida native submerged species commonly occurring state-wide. The selected species exhibited a variety of morphometries and life histories. The results will be of value to lake managers for use in the development of a more systematic approach to the establishment of diverse communities of desirable native species This study was divided into two main objectives. In Objective 1 the study species were cultured outdoors in growth tanks in south Florida for three separate 9-week culture periods on inorganic sediments collected three different times from four littoral stations in Lake Hollin gsw orth and on artificial control sediments. The results suggested that the XVI

PAGE 17

inorganic sediments collected from Lake Hollingsworth had sufficient nutrient levels to support the growth of the study species. The findings further indicated that late spring was the ideal time to introduce plant propagules into restored systems. Submerged macrophyte growth in this study appeared to be most significantly affected by a combination of factors including light water temperature and sediment nutrients. In Objective 2 shade cloth was used to establish four light treatment groups in an outdoor growth tank in south Florida. The light requirements of mature plants and vegetative propagules were investigated during three culture periods for each group. The photosynthetic photon flux density (PPFD) for no net growth of mature plants ranged from 14 to 416 mol photons s-1 m -2 (2 to 50% incident irradiance). The PPFD for no net growth of propagules ranged from 25 to 183 mol photons s -1 m -2 (3 to 22% incident irradiance ). V. americana exhibited the lowest minimum light requirement for growth 2 to 18% incident irradiance Propagules of P. illinoensis and V. americana had higher light requirements as compared with mature plants. Both mature and propagule plants exhibited the greatest capability for growth at low light levels during the summer culture periods. xvii

PAGE 18

CHAPTER 1 INTRODUCTION Background Information Submersed macrophytes are important ecological components of aquatic systems. These primary producers provide excellent habitat for epiphytes (Cattaneo and Kalff 1980, Wetzel 1999b ), invertebrates (Soszka 1975, Wetzel 2001 ), fish (Wiley et al. 1984) and a variety of other aquatic organisms (van der Velde 1987). Aquatic macrophytes also play a critical role in the nutrient dynamics of aquatic ecosystems (Carpenter and Lodge 1986) Macrophyte growth is affected by a variety of abiotic and biotic factors including light availability, water depth, nutrient availability and sediment composition (Spence 1967, Canfield et al. 1983, Chambers and Kalff 1987). Biotic factors such as the degree of colonization by epiphytes (Sand-Jensen and Borum 1984, Sand-Jensen 1990), competition with phytoplankton (Fitzgerald 1969, Allen 1971) and inter-specific competition (McCreary 1991) also impact macrophyte production. Herbivory and grazing often play an integral role in macrophyte community dynamics in many systems (cf. Lodge 1991). There is currently considerable evidence that indicates that light (Canfield et al. 1985 Duarte and Kalff 1986, Kalff 2002) and sediment physical and nutrient composition (Barko and Smart 1986, Short 1987, Barko et al. 1991) are among the most significant abiotic factors controlling submersed macrophyte growth. 1

PAGE 19

Realization of the pivotal role that submersed macrophytes play in determining the alternative stable state of shallow productive lakes and ponds ( cf. Moss 1990, Scheffer et al. 1993, Donnabaum et al. 1999) has led to an increased interest in the nutritional ecology of submersed macrophytes. However, a review of the literature indicates that, to date, little research has been done on the sediment and light requirements for growth of submersed macrophytes especially species native to subtropical and tropical climes. Information on the growth requirements of native submersed macrophytes will be of particular value to lake managers for use in the development of a more systematic approach to the establishment of desirable aquatic vegetation in restored systems. 2 Natural sediments investigated in this study were collected from Lake Hollingsworth. Lake Hollingsworth is a 144 ha shallow (Zmean= 1.2 m) (City of Lakeland 1988-2000) urban lake located in central Florida (28 '30", 81 56'45") (Figure 3-1 ). The lake is a solution basin roughly circular in shape with a mean depth of 1.2 m (Lake Hollingsworth Diagnostic Feasibility Study 1994). Water inputs to the lake are in the form of rainfall, groundwater seepage, stormwater runoff and inputs from Lakes Morton and Homey. Groundwater recharge contributes up to 85% of the total water budget for the lake (Romie 1994). Surface drainage flows southeast into Lake Bentley. Paleolimnological study indicated that Lake Hollingsworth is naturally eutrophic (Brenner et al. 1995). This is probably due to the fact that the lake lies in the Bartow Embayment division of the Central Lakes District where the underlying bedrock consists of the phosphatic sands and clays of the Bone Valley region of Central Florida (Canfield and Hoyer 1992). During the course of the study, Lake

PAGE 20

Hollingsworth was being restored using whole-lake dredging in order to remove a layer of flocculent organic measuring up to 15 feet in thickness in some areas of the lake. The lake is a highly valued resource, serving as the site for a variety of social, educational and recreational activities for the City of Lakeland and the surrounding community. The lake also supports sustenance, commercial and sport fisheries. Statement of Purpose 3 The goal of this research was to investigate two key factors in the establishment of native submersed macrophytes in shallow eutrophic urban Florida lakes: sediment and light growth requirements. This study was divided into two main objectives. The first objective was to investigate the effect of sediment chemical composition on the growth of four species of native submersed macrophytes: Najas guadalupensis (Sprengel) Magnus., Potamogeton illinoensis Morong., Vallisneria americana Michaux and Chara sp. Objective two was to investigate the amount of photosynthetically active radiation (PAR) required for the survival and growth of the four study species. In Objective 1, plants were cultured outdoors in growth tanks in south Florida for three separate 9-week culture periods on sand sediments collected three different times from four littoral stations in Lake Hollingsworth. In Objective 2, shade cloth was used to establish four light treatment groups in an outdoor growth tank in south Florida Mature macrophytes were cultured on artificial sediments during three separate culture periods, one approximately 4 weeks in length and the other two approximately 7 weeks in length. The light requirements of macrophyte propagules grown on artificial sediments were also evaluated during three separate

PAGE 21

4 culture periods. This research will provide valuable information for use in the establishment of desirable native submerged macrophytes in lake restoration projects. Hypotheses Experiment 1: Effects of Sediment on Macrophyte Growth The experimental procedure was designed to test several hypotheses based upon findings from the literature and previous experience The first was that there would be spatial variation in the organic matter and nutrient content of the littoral sediments in Lake Hollingsworth. I also anticipated that N guadelupensis P illinoensis and Chara sp. the canopy-forming erect species would produce greater biomass in sediments with higher nutrient levels while net growth of V. americana, a rosette species would be inversely related to sediment nutrient content. Based upon my personal experience growing stock cultures of the study plants I expected to observe differences in growth rate among the species such that N guadelupensis would be the fastest grower followed by P illinoensis V. americana and lastly Chara sp. I further e x pected the growth rate of Chara sp to be positively related to increasing culture period length I anticipated that N guadalupensis V. americana and Chara sp. would produce the greatest biomass during the summer months while growth of P. illinoensis a species with a range distribution that stretches into more temperate regions would be stimulated by the cooler temperatures of the winter months. Finally I hypothesized that sediments collected from the littoral zone of Lake Hollingsworth would have sufficient quantities of sediment nutrients to support the growth of N guadalupensis P illinoensis V. americana and Chara sp. when grown in the e x perimental growth tanks used in this study

PAGE 22

5 Experiment 2: Effects of Light on Macrophyte Growth The procedure used in the first part of Experiment 2 was designed to test several hypotheses reagrding the light requirements of mature plants of the study species. The first hypothesis was that N guadelupensis and Chara sp. would exhibit the highest light requirements for net growth due to self-shading due to the habit and growth strategies of these species. I anticipated that V. americana would exhibit the lowest light requirement for net growth among the study species, approximately 4% incident irradiance. Based upon the literature, I expected the PPFD for no net growth of P. illinoensis and N. guadelupensis to be approximately 11 % and 15% incident irradiance, respectively. I anticipated PPFD for no net growth of Chara sp. to range between 4 and 20% incident irradiance. I further expected to observe photoinhibition in those species that are either canopy-formers or have an erect habit, N guadelupensis, P. illinoensis and Chara sp., at light levels> 26.2% incident irradiance. The procedure used in the second part of Experiment 2 was designed to test several hypotheses regarding the light requirements of vegetative propagule plants of the study species. First, I hypothesized that plants grown from propagules would have higher light requirements than mature plants of the same species. I anticipated that V. americana would exhibit the greatest capability for growth in low levels of light. I further expected that plants grown from propagules would not become photoinhibited during the course of each culture period.

PAGE 23

CHAPTER2 LITERATURE REVIEW Background Information A review of the literature indicates that little is known about the macrophytes that are often an integral component in the ecosystem processes of shallow productive lakes and ponds concentrated in subtropical to tropical climates. With the exception of some limited studies (i e Denny 1972b 1973, Finlayson et al. 1980, Geddes 1984, Roijackers and Verstraelen 1988, Limon et al. 1989 Mitchell 1989 Schriver et al. 1995), most lirnnological research has been conducted in deepwater oligotrophic to mesotrophic systems located in temperate climes. Much of the limited research in shallow systems has been conducted in Denmark ( e.g. Finlayson et al. 1980 Roijackers and V e rstraelen 1988 Schriver et al 1995) and other temperate climes (Donnabaum et al. 1999). Most of the research to date on the autotrophic component of lacustrine systems has been conducted on the phytoplankton occurring in deepwater temperate lakes The majority of the research that has been conducted on macrophytes occurring in subtropical to tropical climes has been focused either on emergent vegetation or on nuisance e x otic species such as hydrilla (Pieterse 1981 Barko 1982, Stew ar d 1984, Barko and Smart 1986, Sutton 1990 199 3, Sutton et al. 1992 Sutton and Portier 1995 Sutton and Latham 1996) The emergin g interest in usin g m a crophytes in lak e restoration proj e cts has id e ntifi e d the n ee d for mor e inform a tion on the growth re quirem e n ts of s ubmer ge d 6

PAGE 24

7 aquatics especially native species occurring in subtropical to tropical climates (Nichols 1991 Smart 1996). This information will be very useful to lake managers conducting restoration projects which include a littoral zone enhancement component. Lake Restoration Techniques Restoration can be defined as the action of returning an ecosystem to a former condition following degradation caused by some kind of disturbance. A typical lake restoration project would begin with the elimination or significant reduction of anthropogenic nutrient loading and include a lana'restoration and management program (Cooke et al. 1993). It might also include the manipulation of the structure of the fish community, reestablishment of native plant communities, and restoration of wetland areas in the watershed. The objective of the typical lake restoration project is to return the system to a long-term steady state condition similar to its pre-disturbance condition and in accord with reasonably attainable conditions, as dictated by the characteristics of the ecological region (Cooke et al. 1993). Prior to the implementation of any lake restoration initiative, a diagnosis and feasibility study should be conducted Cooke et al. (1993) provide a comprehensive discussion of the components and procedures for the development of diagnosis and feasibility studies. The purpose of such studies is to evaluate the current status of the lake determine the severity of the problem and use the results to propose the most suitable restoration technique Proposed techniques should be cost efficient while still p e rmittin g attainment of water quality goals. Lake restoration methods are divisible into four groups depending upon their primary objectiv e : 1) to control al g al biomass 2 ) to control macrophyte biomass 3 )

PAGE 25

to alleviate oxygen problems and 4) to remove sediment. These methods are described in the following. Algal Biomass Control Methods 8 A variety of mechanical and chemical methods are used to control algal biomass in surface waters. The first step in the control of algal biomass is the reduction of nutrient loading to the system (Cooke et al. 1993 Hosper 1998, Anadotter et al. 1999 Jeppesen et al.1999 Phillips et al. 1999, Van der Molen and Portielje 1999, Robertson et al. 2000, Sondergaard et al. 2000b Barbieri and Simona 2001). This can be done using a variety of Best Management Practices (BMPs) in the watershed (Cooke et al. 1993, Robertson et al. 2000) mechanical devices such as CDS units to screen out debris and large particulate matter in inflows enhancement of wetlands in the watershed and/or physical diversion or re-meandering of inflows (Annadotter et al. 1999 Jeppesen et al 1999, Robertson et al. 2000). Chemical solutions include aluminum sulfate (alum) injection systems installed in stormwater pipes and improved treatment of wastewater inflows (Anadotter et al. 1999 Donnabaum et al. 1999). After ensuring the quality of the water entering the system the next step is to minimize internal loading of sediment nutrients especially phosphorus. Internal loading can be a significant source of nutrient input to a lake especially in shallow lakes with a long fetch (Maciena and Soballe 1990) Various methods can be us e d to decreas e internal loading includin g the more traditional approach of alum application (Cooke et al. 1993 Anon 1996 Robertson e t al. 2 000 Rydin et al. 2000) or sediment o x idation through enhanced nitrification (Donnabaum e t al. 1999). Som e mor e rec ent exp e rim e nts have b ee n conducted to inve stigate oth e r

PAGE 26

9 chemical alternatives for sediment phosphorus inactivation, including hypolimnetic nitrate dosing and gypsum application to sediments. Sondergaard et al. (2000a) concluded that hypolimnetic nitrate dosing is a potential restoration technique for use in deepwater lakes in which internal loading is a problem. Salonen and Varjo (2000) determined that the application of gypsum to sediments to control nutrient release had potential value as a restoration technique. In their evaluation of the most commonly used restoration techniques in Danish lakes, Sondergaard et al. (2000b) concluded that hypolimnetic oxidation can be used to reduce internal phosphorus loading. Copper sulfate, a traditional method used to lower the algal standing crop in lakes, is used infrequently in contemporary restoration projects due, in part, to detrimental environmental impacts (Cooke et al. 1993). There are also a variety of mechanical methods for lake restoration. Dilution with low-nutrient water and subsequent flushing of nutrients and algal biomass is a method that can be applied in the absence of external control of inflows to the lake (Hosper 1999). Other mechanical restoration methods include withdrawal of nutrient rich hypolimnetic waters and aeration (Lindenschmidt and Hamblin 1997). Biological control methods involving food web manipulations are also options for decreasing algal biomass in systems. Numerous studies have documented the successful use of biomanipulation as a lake restoration strategy (Shapiro 1990, Perrow et al. 1995, Drenner and Hambright 1999, Jeppesen et al 1999, Robertson et al. 2000, Sondergaard et al. 2000b ). Kairesalo et al. ( 1999) discuss the necessary components of a successful biomanipulation plan for use in system restoration.

PAGE 27

10 Each of the aforementioned methods has its associated advantages and disadvantages. Some methods are considerably more costly than others. Flushing for example, is a very effective technique, but is highly dependent on the availability of water in the area (Cooke et al. 1993). Remediation time and sustainability are other factors that must be considered when choosing a restoration method. McQueen (1998) discusses some of the challenges managers face in the use ofbiomanipulation. Alum has a very rapid and dramatic effect on water quality that can last two to five years or more (Smeltzer 1990, Anon 1996). However the longevity of the positive effects of alum application on water quality vary from system to system and in many systems alum reapplication is required on a yearly basis in order to maintain desired water quality levels (Dr. Harvey Harper, President of Environmental Research and Design personal observation). Conversely, biomanipulation of systems is an inexpensive method that can yield sustainable results (Drenner and Hambright 1999) Positive impacts of this method may not become apparent for several years however. Another very important consideration is the impact of each method on ecosystem health. For example little is known to date about the long-term ecological effects of alum on lakes especially on invertebrate populations (Smeltzer 1990 Cooke et al 1993). Other studies (e.g. Neville 1985 Ramamoorthy 1988) have documented the lethal effects of aluminum salts in fish. Copper sulfate addition also has a detrimental effect on the ecolo g y of aquatic systems (Cooke et al. 1 993). Moss ( 1 9 99) made a comprehensive comparison of the ecological implications associated w i th some of the more commonly used lake restoration methods

PAGE 28

11 Macrophyte Biomass Control Methods Managers currently have a variety of chemical, physical and biological methods available to them for the control of macrophyte biomass in lake systems. Chemical methods involve the use of herbicides. Smith (1995) successfully used Sonar in the restoration of Long Lake, Washington. The results of this study indicated that the active ingredient in Sonar, fluoridone, targets exotic species; native species exhibited less sensitivity to the herbicide. Physical methods for macrophyte control include preventative measures, hand and mechanical harvesting, water level drawdown, lake stage manipulations, sediment covers and surface shading. Cooke et al. (1993) discussed the limitations of the use of preventative measures as a macrophyte control technique. Carter et al. ( 1994) reported significant reductions in macrophyte biomass when they used plastic sheets in several manmade lakes in Australia. The escalating problem with proliferation of exotic macrophyte species, especially in Florida and other southeastern states, in combination with a growing dissatisfaction with chemical and mechanical methods has resulted in intense research into and development of biological controls for aquatic vegetation (Cooke et al. 1993). Biological controls currently being used in lake systems include phytophagous insects and fish, plant pathogens (e.g. fungi and viruses) and allelopathy. Painter and McCabe (1988) documented the successful us e of the moth Acentria nivea to control milfoil in certain Ontario lakes Crosson (1992) reported that a weevil Euhrychiopsis lecontei and A nivea together were probably responsible for declines in milfoil biomass in several Vermont lak es. Other studies

PAGE 29

12 ( e.g. Haag and Habeck 1991) suggest that an integration of chemical and biological methods is the most effective means by which to control aquatic macrophytes. One of the most commonly used phytophagous fish is the grass carp, or white amur (Ctenopharyngodon idella (Val.)). The popularity of the use of grass carp is due to the relatively low cost and long term results associated with the use of this control agent (Cooke et al. 1993). However, introduction of carp into systems often results in total eradication of all submerged plants ( e.g. Mitchell 1980, Shireman et al. 1985), suggesting that the viability of the use of carp in macrophyte control is highly dependent upon the management goal. As with algal biomass control methods, the management techniques employed to control macrophyte biomass have associated advantages and disadvantages. Cooke et al. ( 1993) provide a thorough discussion of the positive and negative effects of the use of the various macrophyte control methods and include case studies. Aeration and Sediment Removal The two remaining categories of lake restoration methodologies are aeration and sediment removal. Cooke et al. (1993) refer to these two categories as multiple benefit treatments ." Aeration of lakes can be achieved through hypolirnnetic aeration and artificial circulation. Ashley and Hall (1990) define hypolimnetic aeration as a management technique designed to prevent anoxic conditions in the hypolimnion and the problems associated with ano x ic hypolirnnea Potential benefits as soc i a t ed with the use of this method include oxygenation of the hypolimnion without causing an increase in temperature or de-stratification, increased habitat for aerobic organisms and a decrease in internal phosphorus loading due to the establishm e nt o f a erobic

PAGE 30

13 conditions at the sediment-water interface (Cooke et al. 1993). The objective of artificial circulation is complete turnover of the lake. Benefits associated with artificial circulation include an increase in habitat for aerobic organisms, a potential decrease in internal phosphorus loading and a possible decrease in algal biomass by increasing the depth to which phytoplankton are mixed in the water column ( Cooke et al. 1993). Sediment removal is a multipurpose restoration method. Objectives for the use of sediment removal include increasing the mean depth of the system reduction of internal loading, removal of toxic substances, and mechanical control of aquatic macrophytes. Disadvantages include sediment resuspension during removal release of sediment-bound toxic substances destruction and degradation of habitat ofbenthic organisms and the need for a disposal location for dredged sediments (Cooke et al. 1993). There are two methods by which sediment can be removed from a lake: lake drawdown followed by excavation with a bulldozer and sediment remo v al using a dredge. Sediment removal is a frequentl y used management technique that has recently been us e d in a variety of different systems (Bengtsson et al. 19 7 5 Kelly et al. 1994, Annadotter et al. 1999). At the beginning of the present study hydraulic dredging was being used in Lake Hollingsworth to remove 2. 7 million cubic meters o f flocculent org anic sediment. A rapid dewaterin g process patented by the F lorida Institute of Phosphate Research (FIPR) was used to facilitate disposal of dredged sediments (Patel 1995) The project in Lake Hollingsworth represents the first field testin g of this d e w a terin g proc e s s. Dre d g ing was halted at approxim a t el y 60 %

PAGE 31

14 completion to prevent an unplanned drawdown due to drought conditions in the region. Post-dredge measurements of water quality parameters, including chlorophyll a, indicate that the removal of sediment is reducing water column nutrients in the system (Dan Mahone, City of Lakeland Wastewater Chemist, personal communication). Numerous researchers have concluded that successful restoration of their systems required a combination of restoration techniques (Hulon 1994, Kelly et al. 1994, Annadotter et al. 1999, Phillips et al. 1999, Robertson et al. 2000) Restoration of Delavan Lake, Wisconsin, was conducted in three phases: 1) limiting external loading using BMPs in the watershed, enhancing an existing wetland, and diverting inflows, 2) reducing internal P loading using alum inactivation and carp removal, and 3) biomanipulation of the fish population (Robertson et al. 2000). Phillips et al. (1999) discuss the variety of restoration techniques used in the Norfolk Broads over a 25-year period. Revegetation Projects in Lake Restoration The littoral zone habitat enhancement component of restoration projects in shallow subtropical to tropical eutrophic lakes often includes the establishment of diverse communities of native submerged macrophytes. As more research is conducted in shallow lake systems, researchers are beginning to recognize the importance of aquatic macrophytes in ecosystem processes. Macrophytes are a key component of most restoration projects involving shallow lakes due to their pivotal role in determining community dominance. Numerous studies have identified the existence of multiple alternative stable states in ecosystems (May 19 77, 1981, Hosper

PAGE 32

15 1994, Timms and Moss 1984, Scheffer 1990, Scheffer et al. 1993). Hosper (1994), Timms and Moss (1984), Scheffer et al. (1993) and Donnabaum et al. (1999) 1identify two alternative stable states in their study systems: a clear one dominated by aquatic macrophytes and a turbid one dominated by phytoplankton. Moss ( 1990) emphasized the importance ofbiomanipulation in the prevention of a shift to an undesired stable state following lake restoration. Scheffer (1990) discusses the use of simple models to identify the existence of alternate stable states in lakes. Various studies have attempted to elucidate the mechanism(s) that control the alternation between dominance by macrophytes and phytoplankton. Some studies suggest that the stabilizing effect of submerged macrophytes on sediments reduces internal loading during sediment resuspension events (Carpenter and Lodge 1986, Sondergaard and Moss 1998) thereby reducing the nutrients available for phytoplankton uptake. Barko and James (1998) suggested that submerged macrophytes serve as a sink for phosphorus and thus exert positive effects on water quality in lacustrine systems. Zimba et al. (1995) used chemical composition data in conjunction with GIS areal estimates to determine the amount of bound nutrients within the submersed macrophyte communities occurring in Lake Okeechobee in 1990 and 1991. They concluded that 117 metric tons of phosphorus were bound in the tissues of submersed macrophytes present in the lake in 1990. This number increased to 125 metric tons in 1991. The results of their study indicated that nutrients were sequestered by the five species studied in the following order (from the greatest to the least extent): Val/isneria americana> Hydrilla verticillata>> Potamog eton illinoenesis>> C hara sp. > Najas guadelupensis. Several studies (e.g. Timms and

PAGE 33

16 Moss 1984 Schriver et al. 1995 Jeppesen et al 1997) have indicated that the effect of aquatic macrophytes on the food web in shallow lakes may reduce the turbidity of the whole system. Landers (1982) Wetzel (1983) and Carpenter and Lodge (1986) concluded that aquatic macrophytes and their associated epiphytes also play an important role in littoral and littoral:pelagic nutrient cycling. Moss (1998) discussed the role of macrophytes in limiting phytoplankton productivity via production of allelopathic substances. Carpenter and Lodge (1986) presented a thorough discussion of the effects of submerged macrophytes on ecosystem processes. Using Charisma, a simulation model to describe the growth of Chara aspera van Nes et al. (2002) concluded that the effect of water clarity on aquatic plant growth is the most important factor affecting the stable state equilibria of shallow lakes. Similarly a positive relationship between water transparency and macrophyte percent volume infested (PVI) in excess of 30% irregardless of water column nutrient concentrations has been identified in several empirical studies conducted in tropical and temperate systems (Canfield et al.1984 Jeppesen et al. 1990 Canfield and Hoyer 1992) There are other additional benefits associated with native submerged macrophyte communities. Submerged macrophytes are a vital component of the aquatic ecosystem (Wetzel 1983) This is especially true of shallow highly productive subtropical to tropical systems. From an ecological point of view these primary producers provide habitat for zooplankton (Soszka 1975 Timms and Moss 1984 Winfield 1986, Diehl 1988 Schri v er et al. 1995) epiphytes (Cattaneo and Kalff 1980) fish (Wiley et al 1984 Engel 1985 Killgore et al 1989) and a v ariety of other aquatic organisms (v an der V elde 1987) Schriver et al. (1995) concluded that fish

PAGE 34

17 predation on zooplanktivores decreased with increasing PVI of macrophytes especially when PVI exceeds 15-20%. They discussed the positive implications of these refugia for zooplankton in the control of phytoplankton. From a management perspective, several studies (Smart and Barko 1989, McCreary et al. 1991, Barko et al. 1991 and Smart et al. 1994) have indicated that some native submerged species are highly competitive and may offer protection from invasion by weedy exotic species. V. americana outcompeted Hydrilla at low light levels in reciprocal replacement series studies conducted by Smart and Barko (1989). The results of the same study indicated that Vallisneria exhibits better growth on fertile sediments as compared to Hydrilla. The introduction of Eleocharis coloradoensis reduced new growth in a variety of submerged species including Hydrilla verticillata and Myriophyllum spicatum in an additive study conducted by Yeo and Thurston (1984). Diverse communities of native submersed macrophytes typically produce less biomass than monotypic stands of exotic weedy species. In many native species, the growth form concentrates the majority of the plant biomass beneath the water surface. Accordingly native submersed aquatics provide enhanced habitat with fewer of the management problems such as interference with recreation navigation w~ter supply and hydropower generation and access to the water typically associated with exotic macrophyte species. Smart and Doyle (1995), Van et al. (1976) and Haller and Sutton (1975) discuss the adaptations that often make exotics superior competitors, especially in disturbed areas, as compared to native species. Filling this niche with desirable native species is essential in order to avoid exchanging one management challenge for another (Smart et al. 1996)

PAGE 35

18 Despite the rising popularity of littoral zone enhancement projects, there remains a need for the development of a systematic approach for establishing and maintaining submerged macrophyte communities that can be used with more widespread success in lacustrine systems (Nichols 1991, Phillips et al. 1999). The most common approach to littoral zone development is the introduction of monocultures of a submerged aquatic species planted on 1-m centers For example, in Florida, Val/isneria is the plant most often used in revegetation projects due to its availability and relative ease in planting (personal observation: results of informal survey of lake managers around the state). Planting monocultures can often lead to frustrating results such as invasion by a faster-growing exotic species (Smart and Doyle 1995). For this reason, the common practice of planting only monospecific stands of Val/isneria should be avoided. Certainly, the positive characteristics of Vallisneria make it a highly desirable species for use in restoration efforts. Vallisneria provides forage for waterfowl and refuge for juvenile fish. Studies have also shown that it has relatively low light requirements as compared to other species (Carter and Rybicki 1985 Smart and Barko 1989, this study) thus potentially making it a good candidate for growth in turbid waters. The growth habit of this macrophyte also concentrates biomass below the water column. However, in their 1975 study, Haller and Sutton concluded that Vallisneria is not a strong competitor against Hydri/la. Although both species are members of the Hydrocharitaceae family differences in their growth structure render Hydrilla the superior competitor in most cases. Hydri/la forms a dense canopy at the water surface and reduces light penetration by 95% in the first 0.3 m of the water column (Haller and Sutton 19 75 ). Vallisneria communities

PAGE 36

19 produce less biomass, which is concentrated below the water surface so that light penetration is similar to that of open water. Hydri/la exhibits faster growth than Vallisneria. Haller and Sutton ( 197 5) determined that Vallisneria invests energy in the production of large quantities of nonphotosynthetic biomass that would appear to negate any advantage of its greater leaf area index as compared to Hydrilla. The difference in biomass production is also attributable to differences in reproductive strategy. Haller and Sutton (1975) determined that the production of millions of meristematic tissues per hectare by Hydrilla is a highly competitive strategy. McCreary (1991) characterized hydrilla and Vallisneria americana as exhibiting guerilla and phalanyx growth strategies, respectively. She proposed the use of V. americana in combination with an equally robust native canopy-forming phalanyx species in order to outcompete Hydrilla. In conclusion, use of a variety of species with a diverse array of reproductive and growth strategies appears to be the most likely way to avoid colonization of troublesome weedy exotics. Research being conducted by the Army Corps of Engineers Aquatic Plant Control Research Program has led to the development of a new revegetation method that they refer to as the "founder colony" approach (sensu Smart et al. 1998). The key to this approach is to treat submerged macrophytes introduced into the system much as one would treat fish i.e., close monitoring, habitat modification and restocking are provided, on a continuing basis, as necessary. Use of the founder colony approach has yielded successful results in reservoirs and natural lakes in several states including Texas, Oklahoma, Kansas, Alabama and New York (Smart et al. 1996, Smart et al. 1998). Establishment of diverse communities of native submerged aquatic plants in

PAGE 37

20 these systems resulted in improved water quality, enhanced fish habitat and prevention of invasion by weedy exotics. These results indicate the potential for the successful use of the founder colony approach in a wide variety of lake systems. Smart et al. (1996) suggested the use of preliminary investigations of selected environmental characteristics including sediment suitability to evaluate the viability of a location as submerged macrophyte habitat. Macrophyte Species Selection Establishment of diverse submersed macrophyte communities should be a fundamental goal oflake restoration projects. In order to accomplish this goal, species selected for lake restoration should include both annuals (pioneer species) and perennials and rand K-selected species In an ecological sense, lakes in which restoration methods have been recently used to improve water quality are disturbed environments. In addition, submersed aquatic plant communities are often absent from such systems for up to many years prior to restoration primarily due to insufficient light availability for sustained growth. Natural systems recover in a predictable ecological succession following a disturbance that destroys the plant community at a given site The first colonizers are r-selected pioneer species that exhibit rapid increases in biomass and produce large quantities of widely dispersed propagule material (Stearns 1977) These characteristics allow pioneer species to rapidly colonize available niches Pioneer species also modify the localized environment in a variety of ways These species promote stability and conditions favorable for subsequent establishment of perennials including increased sedimentation that creates more shallow areas suitable for macrophyte growth

PAGE 38

21 (Carpenter 1981) i ncreased water clarity due to decreased turbidity (Carpenter and Lodge 1986) decreased algal populations due to reduction in water column nutrients (Kufel and Ozimek 1994) and/or modifications in the aquatic food web (Schriver et al. 1995) Eventually the system enters a more advanced state of succession, and perennial species dominate the community composition. The life history of perennials includes a longer life span and increased accumulation of energy reserves which results in slower growth as compared to that of pioneer species. However the growth strategy of perennials makes these species more resistant to subsequent disturbance as compared to pioneer species (Grime 1979 Sheldon 1986). An additional advantage associated with the establishment of pioneer species is that these plants produce extensive seed banks that permit rapid recolonization following any future disturbance that might set the community back to an earlier successional stage (van der V a1k 1981 Sheldon 1986) The plasticity in response to environmental perturbation conferred to macrophyte communities by the combined life strategies of annual and perennial species in diverse communities is probably of pivotal I importance in the maintenance of some shallow eutrophic systems in the m~crophyte dominated stable state. Community diversity is a fundamental aspect of the founder colony approach. Smart et al. ( 1996) discussed the importance of selecting a variety of species both annuals and perennials r-selected and K-selected species as an important initial step in the use of this method Several criteria were used to select the macrophyte species investigated in this study. Initially selection was determined by the need to identify Florida native submersed macrophytes with a wide distribution and for which propagule material is

PAGE 39

22 readily available. In addition, a mix of annual and perennial species was selected in order to maximize the potential for establishment of viable, self-sustaining communities of SA V capable of out-competing exotic species in restored lakes. Finally, plants were selected based on their relative value as habitat for fish and other aquatic organisms resistance to herbivory and relative potential positive impact on the water quality of the lake. Description of Study Macrophytes Four species were selected using the aforementioned criteria -Najas guadelupensis (Spreng.) Magnus) Potamogeton illinoensis Merong, Vallisneria americana MichxJ and Chara sp. Annuals -Najas guadelupensis and Chara sp. both summer annuals are excellent pioneer species. N guadalupensis is often the primary colonizer in areas of disturbance (i.e. abandoned fish nests boat trails and in areas previously not colonized by submersed macrophytes (Lawson 1991 Hopson-Fernandes personal observation) N guadalupensis expansion is due to prolific seed production drought tolerance and ability to colonize by vegetative fragmentation and subsequent adventitious root formation. N guadalupensis exhibits a decumbent habit with very slender sparsely branched stems with numerous finely dissected (2 cm long and 1.2 mm wide) leaves (Westerdahl and Getsinger 1988) (Figure 2.1 ) In nature, N guada/upensis forms monospecific stands ( defined as those in which a single species contributes greater than 90% of the total biomass). There are 35 species of Chara occurring in the United States (Figure 2.2) The majority of the spec i es are dioecious. Reproduction also occurs via fragmentation.

PAGE 40

23 Chara sp typically occur at shallow depths but have been found at depths greater than 10 m. Some recent studies (e.g. Blindow 1991 Kufel and Ozimek 1994 Kufel and Kufel 2002) found that Chara may play an important role in improving water quality due to its storage capacity and ability to colonize shallow lakes previously dominated by phytoplankton. In a study conducted in Lake Okeechobee Steinman et al. (2002) observed high Chara biomass over a wide range of light levels. Charophytes were also the first submerged macrophytes to re-establish following a managed recession of the lake. Kufel and Kufel (2002) discuss additional positive effects of Chara growth in systems including relatively slower decomposition rates and lower contributions of sediment-derived nitrogen and phosphorus to the water column upon decomposition as compared to rooted vascular plants Perennials-P illinoensis a native perennial in the Potamogetonaceae is a common inhabitant of many Florida lakes. As compared to the other macrophytes included in this study P. illinoensis has slightly thicker stems and broad flat lanceolate leaves measuring 15 cm long by 6 cm wide (Westerdahl and Getsinger 1988) (Figure 2 3) The growth form of this plant involves the production of elongate stems which typically extend to the water surface The majority of the elodeid (sensu Hutchinson 1975) leaves are concentrated in the photic zone. P illinoensis exhibits low biomass density ( cf. Duarte and Kalff 1990) Members of the Potamogetonaceae propogate vegetatively via budding from underground rhizomes The formation of tubers structures in which the plant sequesters carbohydrate reserves is critical to the germination and early development of young plants (Hodgson 1966)

PAGE 41

24 V americana a perennial native in the Hydrocharitaceae, exhibits a growth form that is dissimilar to that of the other study plants (Figure 2.4) V americana grows as rosettes of elongate ribbon-like leaves measuring up to 2 m in length by ca. 3 cm in width (Westerdahl and Getsinger 1988) which arise from a stoloniferous rootstock. Each rosette usually gives rise to several stolons which in turn produce multiple rosettes. The root systems may allow V americana to exploit sediment nutrient reserves that are unavailable to other rooted macrophyte species (Titus and Stephens 1983). Titus and Stephens (1983) also observed that V americana is capable of altering its growth pattern in response to the presence of other plant species. Va/lisneria propagates by seeds and by the production of vegetative propagules Vallisneria concentrates biomass lower in the water column as compared to canopy-forming species and exhibits median biomass density (sensu Duarte and Kalff 1990) Submerged Macrophyte Biology According to the classification scheme for aquatic macrophytes developed by Arber (1920) and Sculthorpe (1967) submerged macrophytes are those aquatic plants which are rooted in the sediment. This is a heterogeneous group of plants composed of filamentous algae (e.g. Cladophora) certain macroalgae (e.g. Chara and Nitella) numerous mosses a few nonvascular macrophytes and approximately 20 families of vascular macrophytes (Wetzel 200 I). There is considerable evidence that aquatic angiosperms originated on land. Wetzel (200 I) discusses the fact that adaptation and specialization in aquatic macrophytes lags behind colonization of the aquatic habitat.

PAGE 42

25 He uses this phenomenon to explain the presence of nonfunctional vestigial structures such as cuticles and stomates in many submerged macrophyte groups. Life in the aquatic environment has, however, resulted in the development of salient morphological and physiological features in submerged macrophytes. Submerged macrophytes do not require a dominant erect axis; there is a reduction in the lignification of plant tissues and sclerenchyma and collenchyma are rarely present even in vascular tissues. There is no evidence of secondary growth or cambial development (Sculthorpe 1967, Wetzel 2001 ). In many species the vascular strands are condensed resulting in central lacunae. Submerged macrophytes also exhibit adaptations to low light availability similar to those displayed by terrestrial shade plants including a very thin cuticle, thin leaves (1-3 cell layers thick) and high numbers of chloroplasts in epidermal tissue. Leaves tend to be much more divided, resulting in much greater surface-to-volume ratios, than in terrestrial plants. Leaf morphology maximizes exposure to light and to dissolved gases and nutrients in the water column (Wetzel 2001). Many submerged macrophytes exhibit extreme heterophylly, often on the same stem or petiole. Submerged macrophytes can be divided into two groups based upon their growth form as determined by differences in apical organization: an abbreviated axis producing a rosette of radical leaves or an elongated flexuous stem with an abundance of leaves and rooted from the nodes (Sculthorpe 1967). The different growth forms are determined by differences in apical organization. Vegetative and clonal reproduction are the primary mechanisms for propagation and dispersal of submerged macrophytes. Although sexual reproduction

PAGE 43

26 has been retained vegetative reproduction plays a far more important role in the life history ofhydrophytes Submerged macrophytes propagate vegetatively via fragmentation horizontal expansion by rhizomes stolons runners and tubers and via the production of specialized organs such as turions (winter buds). Most species produce aerial insect or wind-pollinated flowers although there are some examples ofhydrophily (water-pollinated flowers) (e.g. the Najadales and many genera in the Hydrocharitaceae) (Sculthorpe 1967). Cox ( 1993) determined that hydrophily occurs in < 5% of aquatic species. Additional morphological and physiological adaptations are necessary to permit the flow of gases required to minimize the toxic effects of the byproducts of anaerobic fermentation in aquatic sediments and to sustain photosynthetic and respiratory metabolic processes (Wetzel 2001) Metabolically significant gases move throughout the plant body through large intercellular spaces and cortical gas spaces in roots and shoots. Internal lacunae make up a large portion of the total plant volume (often> 70%) (Wetzel 2001) A temporal difference in the production of oxygen during photosynthesis and subsequent release to the environment creates an internal positive pressure (Hartmann and Brown 1967 Sorrell 1991 ). This internal pressure plays a significant role in the internal mass flow of gases throughout the plant body. Sorrell and Dromgoole (1989) determined that large portions of the oxygen stored in the lacunae were used in respiratory metabolism without affecting the surrounding water. Moeslund et al (1981) concluded that, although oxygen to water exchange increases with increasing current oxygen concentrations in the surrounding water do not reflect the entire amount of oxygen produced during photosynthesis. This

PAGE 44

27 tendency to stockpile oxygen prompted Wetzel (2001) to suggest caution in the use of oxygen evolution experiments as a quantitative indicator of macrophyte photosynthesis. Much of the oxygen produced during photosynthesis is transported to the roots and diffuses into the microrhizosphere (Sand-Jensen et al 1982 Zhang et al. 1998) where it forms an oxidized layer immediately around the root and is utilized by microaerophyllic bacteria. There is increasing evidence that inorganic carbon availability may be the most significant factor limiting aquatic macrophyte growth in some systems The diffusion rate of gases in water is four orders of magnitude slower than in air. Submerged organs are also surrounded by a stagnant boundary layer that can be from several mm to cm thick (Wetzel 2001) that further impedes gas diffusion into the plant. In order to survive the challenges posed by carbon acquisition in the aquatic environment submerged macrophytes have evolved several adaptations that facilitate uptake conservation and recycling of carbon. Morphological modifications to stems leaves and petioles that facilitate absorption of dissolved gases include an extremely thin cuticle highly reduced mesophyll tissue concentration of photosynthetic pigments in the epidermis and thin tissues (1 to 3 cells thick) Once inside the plant body large intercellular lacunae facilitate internal diffusion of gases to all plant organs Most submerged species exhibit C3-Calvin-type photosynthesis with high rates of photorespiration ( Wetzel 2001 ) Additional carbon sources for hydrophytes include the CO2 produced during photorespiration and cellular respiration. Some softwater species also take up CO2 from sediments (Wetzel 2001). Kimber et al. (1999) concluded from isotope tests that the majority of the carbon fixed in

PAGE 45

28 Val/isneria was sediment-derived. Some aquatic angiosperms occupying carbon-poor systems photosynthesize via crassulacean acid metabolism (CAM) (e g. Val/isneria). These CAM plants assimilate CO2 at night and store it as malate for use in photosynthesis during the light hours. Submerged macrophytes have developed two basic strategies for carbon assimilation in the aquatic environment ( cf. reviews of Maberly and Spence 1983, Madsen and Sand-Jensen 1991 ). Some species depend primarily to exclusively on CO2 for their carbon source (Wetzel 1969, Van et al. 1976, Moeller 1978b, Kadono 1980) while others utilize bicarbonate (Raven 1970 Prins et al. 1980 Beer and Wetzel 1981, Lucas 1983) Obligate CO2 species are restricted to locales with sufficient levels of carbon dioxide to support their growth. Since bicarbonate often occurs in higher concentrations in natural waters as compared to carbon dioxide, uptake of bicarbonate would appear to be an advantageous adaptation (Wetzel 2001). This mechanism has been documented in many macroalgae, and in mosses and submerged angiosperms (Ruttner 1947, 1948, 1960, Bain and Proctor 1980). Raven and Lucas (1985) and Eighmy et al. (1991) discuss the energetic costs associated with the use of bicarbonate as the carbon source for photosynthesis Many submerged species exhibit low CO2 compensation points and relatively high productivity (Wetzel 2001). Submerged macrophytes occurring in lakes inhabit the littoral zone in the area extending from the shoreline to the depth at which light becomes limiting. Submerged macrophytes colonize all depths of the photic zone of lakes (Wetzel 2001). Vascular angiosperms can occur up to depths of approximately 10 m while nonvascular

PAGE 46

29 macrophytes (e.g. macroalgae) can be found growing up to the littoral-pelagic interface. McCreary (1991) provides a thorough review of the competitive causes for the zonation of macrophyte distribution characteristic of littoral areas. Environmental Factors Controlling Production Studies that have addressed the dynamics of submerged macrophyte communities suggest that macrophyte production is influenced by a variety of abiotic and biotic environmental factors. Among these factors are light availability (Van et al. 1976 Barko and Smart 1981 b Duarte and Kalff 1986, Chambers 1987a, Chambers and Kalff 1987 Canfield and Hoyer 1988b Hough and Fomwall 1988 Goldsborough and Kemp 1988 Chambers and Prepas 1990 Grimshaw et al. 2002) sediment composition and nutrients (Sculthorpe 1967, Barko and Smart 1983 Short 1987 Barko and Smart 1986 Barko et al. 1991 ) water transparency and depth (Spence 1967 Canfield et al 1985 Scheffer et al. 1992) nutrient availability (Spence 1967 Chambers and Kalff 1987b Canfield and Hoyer 1988b Hough and Fomwall 1988, Lauridsen et al. 1993) and temperature (Barko and Smart 1981b). Wind events were also found to have a significant effect on macrophyte production in the shallow lake studied by Lauridsen et al. (1993). Sculthorpe (1967) identified light intensity and quality the nature of the substrate and turbulence as the most s i gnificant environmental factors determining the distribution of communities, species and growth forms of submerged macrophytes. The effects of various biotic factors on macrophyte growth have been the topic of additional studies Sand-Jensen and Borum (1984) and Sand-Jensen (1990) observed a negative relationship between macrophyte growth and the degree of light

PAGE 47

30 attenuation by the epiphytes. In his 1971 study Allen described the antagonism (sensu Fitzgerald 1969) between macrophytes, epiphytes, and phytoplankton competing for available light and nutrients within aquatic systems In many systems grazing also plays an integral role in macrophyte community dynamics (Wetzel 1983, Cattaneo 1990 Lauridsen et al. 1993) Lodge (1991) reviewed the literature on the effects of herbivory on freshwater macrophytes. A variety of studies have reported species-specific responses of macrophytes to their environment (Spence 1964 Van et al. 1976 Chambers and Kalff 1987b Hough and Fomwall 1988 Chambers and Prepas 1990, Scheffer et al. 1992, Spencer et al. 2000 Cenzato and Ganf 2001 ). Scheffer et al. (1992) for example documented a differential response in two species of P. il/inoensis to changes in water depth in the study system Spencer et al. (2000) reported species-specific differences in the number of degree-days required for emergence of vegetative propagules of three submerged species. Changing environmental conditions often result in shifts in dominance among competing species within macrophyte communities The Role of Light in Submerged Macrophyte Growth Numerous studies have identified light availability as one of the most significant factors controlling macrophyte production in aquatic systems (Duarte and Kalff 1986 Canfield et al. 1985 Barko et al. 1986 Smith and Barko 1990) Various studies have investigated the impact of light attenuation on submerged macrophyte productivity (Carter and Rybicki 1990 Duarte 1991 ; Dunton 1994, Goodman et al. 1995 Masini et al 1995 Zimmerman et al. 1995 Livingston et al 1998) The classification scheme Gessner (1955) developed for submerged macrophytes based on

PAGE 48

31 their physiological adaptations to light availability indicates the extreme plasticity and adaptability of submerged macrophytes to the highly variable underwater light environment. The adaptation types include strictly shade adapted requiring low light intensities strictly light adapted and requiring high light intensities shade adapted but exhibiting optimum photosynthesis at intermediate light levels etc. Van et al. (1976) and Kenworthy and Fonseca (1996) reported species-specific differences in minimum light requirements. All submerged angiosperms are shade plants (Wetzel 2001). Spencer and Bowes (1990) determined that light saturation for photosynthesis ranges from 10-50% full sunlight. Van et al ( 1976) reported photosynthetic rates less than 5% of those achieved by terrestrial plants at atmospheric levels of CO2 for three species of submerged aquatic macrophytes. They attributed this to low activities of the carboxylation enzymes. Goldsborough and Kemp (1988) investigated the response and recovery of Potamogeton perfoliatus to experimentally induced shade during a 17-day treatment period followed by a 16-day "recovery period. During the treatment period plants responded by increasing photosynthetic pigments and producing elongate stems thinning lower leaves and canopy formation at the surface. Plants showed significant recovery 10 days after removal of light treatments. The results of their study indicated that the study species requires a minimum of 11 % full sunlight in order to survive and grow. Other investigations of photosynthetic capacity and compensation points indicated considerable variation among submerged macrophytes (Wetzel 2001) Light compensation points often occur at 1-3% full sunlight (Wilkinson 1963 Spence 1982, Bowes et al. 1977, Moeller 1980). Kimber et al. ( 199 5) reported that tuber production in Vallisneria americana ceased at light

PAGE 49

32 levels less than 5% of ambient sunlight. They discussed the implications of these results for vallisneria growth in relation to light attenuation by turbidity in their study system. Dennison (1987) discussed the use of photosynthesis vs irradiance curves together with diurnal light curves to predict growth responses to changes in light regime (Dennison and Alberte 1985) seasonal growth patterns and the maximum depth of colonization for Zostera marina. Carter et al. (1996) reported an I I-fold increase and a 38-fold increase in total biomass of V. americana americana in lighted cages in the Chesapeake Bay and the Potomac River. Plants exposed to increased light levels were more robust and fewer in number as compared to controls The Role of Sediments in Macrophyte Nutritional Ecology \ The function of roots in submersed macrophytes especially in angiosperms has been subject to debate (Wetzel 2001). After much research (reviewed in Gessner 1959 Wetzel 1964 Sculthorpe 1967 Hutchinson 1975) two theories were proposed: a) the function of roots was strictly to anchor the plant and b) the roots function in nutrient absorption from the substrate. Considerable recent research has now confirmed that the primary function of the root systems in aquatic macrophytes is to assimilate nutrients from the sediment (Barko and Smart 1986 Short 1987 Barko et al. 1991 Wetzel 2001 ) A positive absorptive capacity is present in the roots that facilitates uptake of sediment nutrients Most submerged species obtain the majority of their nutrient requirements from the interstitial water of the sediments where nutrients are present at much greater concentrations than in the water column. Shannon (1953) determined that absorptive capacity of the roots is enhanced by the presence of root hairs. Many species also exhibit symbiotic relationships with

PAGE 50

33 vesicular-arbuscular micorrhyzae (Sondergaard and Laegaard 1977 Tanner and Clayton 1985 Wetzel and van der Valk 1996). The mechanism for assimilation of sediment nutrients the solubilization and mobilization of soil nutrients by secreted organic acidsutilized by terrestrial plants is thought to be the same in submerged plants (Wetzel 2001). Researchers first became aware of the influence of sediment composition on the productivity and distribution of submerged macrophytes almost one century ago (Pond 1905 Pearsall 1920 Misra 1938) Subsequent studies conducted in a wide variety of aquatic systems have confirmed that sediment composition exerts a significant effect on submerged macrophyte growth (Moeller 1975, Anderson 1978 Sand-Jensen and Sondergaard 1979 Kiorboe 1980 Danell and Sjoberg 1982 Wheeler and Giller 1982 Barko and Smart 1983 Barko and Smart 1986 Barko et al. 1991, Livingston et al. 1998). Barko et al. (1991) reported that nitrogen phosphorus, iron manganese and micronutrients are taken up from the sediment. Calcium, magnesium sodium potassium, sulfate and chloride are assimilated from the water column. The majority of research into the plant available sediment nutrients has been conducted on phosphorus and nitrogen. Of this literature most has focussed on phosphorus (Barko et al. (1991). As a result of the large exchangeable pool of phosphorus in most lake sediments phosphorus is rarely the limiting factor in l hydrophyte growth (Wetzel 2001). Of the limited information available on the relative contributions of sediment and open water to the nitrogen economy of submerged aquatics several studies indicate that nitrogen can be assimilated from both the sediment and the open-water (Nichols and Keeney 1976 Short and McRoy

PAGE 51

34 1984). These isotope studies concluded that nitrogen uptake rates were positively correlated with concentration and that the study macrophytes preferred ammonium to nitrate for uptake. Nichols and Keeney (1976) reported that, since sediment ammonium concentrations are typically much greater than water column concentrations, sediment is probably the major source of nitrogen. There are relatively few documented cases of inorganic nutrient limitation in submerged aquatic macrophytes (Anderson and Kalff 1986, Barko et al. 1986). Barko and Smart (1983) concluded that sediment organic matter can greatly inhibit the growth of submerged macrophytes. Refractory organic matter appeared to have a longer-lasting inhibitory effect as compared to labile organic matter. Barko and Smart (1983) attributed this inhibition to the presence of high concentrations of soluble organic compounds in the interstitial water produced during anaerobic decomposition. In a later study involving the growth of Hydril/a and Myriophyllum on 40 different sediments collected from 17 North American lakes, Barko and Smart (1986) concluded that sediment density rather than organic matter content was most influential in regulating plant growth. They identified a significant relationship between macrophyte growth, nutrition and sediment density. Short (1987) reviewed the effects of sediment nutrients on seagrasses and concluded that seagrass production is strongly correlated with nutrient availability. He cites examples of how differences in the geochemistry of systems can result in either phosphorus or nitrogen limitation and concludes. He concludes that sediment geochemistry is the most significant factor controlling seagrass growth. Rybicki and Carter (1986) reported better growth of Va/lisneria americana on silty clay than on sand. Barko and Smart (1986) had similar results. They found that

PAGE 52

35 Hydrilla and Myriophyllum exhibited poor growth on highly organic sediments and on sands. The results of fertilization studies indicated that macrophyte growth limitation on these substrates was due to nutrient deficiencies. Amendment of sand substrates with fertilizer has been used in many studies to circumvent problems with nutrient limitation when using sand substrates ( c.f. Sutton 1985, 1993, 1996). Denny (1972b) reported species-specific responses to sediment composition and nutrient concentrations. Barko and Smart (1983) identified the difficulty in separating the effects of sediment nutrient availability from other sediment characteristics as one of the greatest challenges associated with investigations of the relationship between sediment composition and macrophyte growth. Culturing Submerged Macrophytes Early attempts to culture submerged macrophytes were complicated by the misconception that macrophyte nutrient requirements were water-derived ( c.f. Bourn 1932, Sculthorpe 1967) and that roots functioned simply as organs of attachment (c.f. Brown 1913, Den Hartog and Segal 1964). Further complicating the effort to culture submerged macrophytes was the use of culture media developed for macrophytic algae ( e.g. (Pringsheim and Pringsheim 1962, Forsberg 1965) and for hydroponic growth of terrestrial plants (Hoagland and Amon 1938). The realization of the importance of sediment nutrient acquisition in submerged aquatics by researchers such as Denny (1980) has resulted in significant advances in the culture of submerged macrophytes. Smart and Barko (1985), and Smart et al. (1996, 1998) provide a thorough discussion of culturing submerged aquatic plant species native to subtropical climes. Smart and Barko (1985) discuss the nutrient requirements of

PAGE 53

submerged aquatics relative to the uptake mechanism (i.e. sedimentversus water derived). 36 One of the challenges to conducting investigations of submerged macrophytes is the autocorrelation of environmental factors. Spence (1991) discussed the difficulty separating the effects of light and sediment composition on macrophyte growth poses for researchers. A plausible solution to this dilemma is the use of growth chambers located in ambient conditions. The use of growth chambers allows researchers to manipulate one variable and determine its effect in an otherwise controlled environment. Many studies investigating submerged macrophytes have been conducted in outdoor growth tanks (Sutton 1985, Short 1987, Sutton et al. 1992, Sutton and Portier 1995, Kimber et al. 1999, Spencer et al. 2000, Grimshaw et al. 2002). Grimshaw et al.(2002) used differing numbers of shade cloth layers to determine the response of several species of submerged aquatic macrophytes to differing light availability in the aquatic environment. Short (1987) used experimental mesocosms to investigate sediment nutrient effects on seagrass growth. Barko and Smart (1986) used large outdoor growth tanks to investigate sediment-related mechanisms of growth limitation in submerged macrophytes. Macrophyte growth studies in this experiment were conducted in large outdoor tanks (6.2 min length by 3-1 m in width by 0.9 m in height filled with pond water to a depth of 0.8 m). Pond water was the water source and was exchanged daily. Epiphytic Algae Aquatic epiphytes are defined as those organisms that attach to aquatic macrophytes (Wetzel 1983). The "epiphytic community" associated with aquatic

PAGE 54

37 macrophytes is composed of autotrophs and heterotrophs cohabitating in a matrix of detritus and mineral elements (Sand-Jensen et al. 1989). The autotrophic component includes epiphytic algae. This study focussed on the algal component of the epiphytic community associated with the submerged macrophytes occurring in the experimental tanks. From this point forward, the term epiphyte will be used to refer to the algal component only. Epiphytes are an integral component of the autotrophic community within many aquatic systems. Cattaneo and Kalff (1980) reported that epiphytes can play a significant role in the total primary production of macrophyte beds (up to 62%), a role which may have been underestimated in previous studies of other systems (Wetzel 1964, Adams et al. 1974). Burkholder and Wetzel (1989a) determined that, as much as 70-85% of the total carbon produced in littoral systems may be a direct by-product of epiphyte metabolism. Stable isotope analyses suggest the importance of attached algae as a source of carbon and nitrogen for higher trophic levels in some marine systems (Sullivan and Moncrieff 1990). Epiphyte growth is influenced by a variety of environmental factors. The epiphytic microenvironment-the metabolizing macrophyte-is an unstable one responding rapidly to variations in the host due to grazing pressure, age, changing nutrient status and light availability (Allanson 1973). Several studies (Cattaneo and Kalff 1979, Cattaneo and Kalff 1980, Rogers and Breen 1983, Borum 1987, Burkholder and Wetzel 1989a and Lalonde.and Downing 1991) have reported a correlation between macrophyte growth form and epiphyte colonization rates and maximum attainable biomass.

PAGE 55

38 The literature also suggests that epiphyte biomass is affected by a variety of additional environmental factors Wetzel (1964) reported a positive correlation between temperature and epiphyte biomass Several studies (Fox et al 1969 Phillips et al 1978 Cattaneo and Kalff 1980) have identified a positive relationship between epiphyte biomass and increasing water depth. This relationship may be due to decreased wave activity at greater water depths (Fox et al. 1969), decreased grazing pressure (Cattaneo 1990) or perhaps to a combination of both. Cattaneo (1990) concluded that increased grazing pressure contributed to a sudden decline in epiphyte biomass in Lake Memphremagog Canada Epiphyte communities are highly susceptible to loss due to scouring caused by heavy precipitation and strong wind events (Sand-Jensen 1983 Wetzel 1983 Kairesalo 1984 Sand-Jensen et al. 1989.) Tete et al. (1978) presented a thorough discussion of the influence of water flow rates on attached organisms in their 1978 review paper High epiphytic biomass has also been related to high light (Wetzel 1964 Pieczynska and Szczepanska 1966 Gons 1982) and nutrient availablity (Straskraba and Pieczynska 1970 Phillips et al. 1978 Cattaneo and Kalff 1980). In studies in different lacustrine systems, Shelden and Boylen (1975) Tai and Hodgkiss (1975) and Hooper-Reid and Robinson (1978) correlated decreased epiphyte biomass with nutrient deficiency. Cattaneo and Kalff (1980) reported a strong correlation between phosphorus and epiphyte production suggesting that phosphorus may be the growth-limiting nutrient for epiphytes Raschke (1993) observed that increased phosphorus loading in the Everglades National Park stimulated diatom growth. Davis et al. (1990) defined a significant relationship between light availability and phosphorus uptake by epiphytes.

PAGE 56

39 Within aquatic communities, competition between autotrophs for resources has a significant effect on the composition and dynamics of the epiphyte community In their 1971 and 1984 studies respectively Allen and Sand-Jensen and Borum reported the same phenomenon that Fitzgerald (1969) described as an antagonistic relationship between macrophytes epiphytes and phytoplankton Other researchers have investigated the effect of competition for light (Sand-Jensen and Borum 1984 Sand-Jensen 1990) and nutrients (Sondergaard and Sand-Jensen 1978) upon the composition and dynamics of the epiphyte community. Rapid nutrient and CO2 uptake rates make planktonic autotrophs more successful than their attached competitors for nutrients in the water column (Sondergaard and Sand-Jensen 1978). Competition for water column nutrients is typically greatest between pelagic and epiphytic autotrophs as rooted submerged macrophytes derive most of their nutrient requirements from the sediment (Sondergaard and Sand-Jensen 1978 Barko and Smart 1981a, Barko et al. 1991) Several studies (Wetzel et al. 1985 Rattray et al. 1991 Kimber et al. 1999) have suggested that submerged macrophytes may also utilize sediment-derived CO 2 under certain field conditions The Macrophyte-Epiphyte Complex Submerged aquatic macrophytes and associated epiphytic algal communities are keystone components of lacustrine ecosystems with significant macrophyte populations (Wetzel 1983 Wetzel 2001 Kalff2002). Several studies (Wetzel 1983 Moeller et al. 1988 Burkholder and Wetzel 1989a) have concluded that the high rates of productivity within the littoral zone of macrophyte-dominated lakes are due primarily to the presence of this primary producer complex. Aquatic macrophytes

PAGE 57

40 also provide critical habitat for a variety of organisms consumed by higher trophic levels including epiphytes invertebrates and bacteria (Soszka 1975 Cattaneo and Kalff 1980 Wiley et al. 1984 van der V elde 1987). The surfaces available for attachment of microorganis~s are considerable ; submerged vegetation provided a 5fold increase in colonizable surface area in the system investigated by Moeller et al. (1988) Howard-Williams and Allanson (1981) reported a 30-fold increase of surface area in P. illinoensis communities in their study system. Submerged macrophytes and associated epiphytes play a critical role in the nutrient dynamics of macrophyte-dominated systems (Cattaneo and Kalff 1980 Carpenter and Lodge 1986 Burkholder and Wetzel 1989b). Various studies (Carignan and Kalff 1980 Barko and Smart 1981 a, Canfield et al. 1983) have indicated the importance of aquatic macrophytes in improving water quality in nutrient-rich systems by a variety of mechanisms including sequestering nutrients (e.g. nitrogen and phosphorus) in tissues. [See section entitled Revegetation Projects in Lake Restoration for a discussion of the significance of macrophytes in the stable state equilibria in shallow lakes.] In his study in Lake Okeechobee Zimba determined that over 110 metric tons of phosphorus were bound in macrophyte tissue during the study period. Landers (1982) and Carpenter and Lodge (1986) discussed the importance of the role that nutrient release by senescing macrophytes plays in the cycling of nutrients within aquatic systems. Additional research has been done on the role of epiphytes in nutrient cycling. Several studies have documented the transfer of nutrients from living macrophyte tissue to the epiphyte community (Wetzel and Penhale 1979 Moeller et al. 1988).

PAGE 58

41 Other investigators (Riber et al. 1983, Carlton and Wetzel 1988 Moeller et al. 1988 Burkholder et al. 1990) observed direct nutrient uptake from the water column by the epiphyte community Zimba (1995) determined that approximately 84% of the total phosphorus removed form the water column by the macrophyte:epiphyte complex in Lake Okeechobee was bound in the epiphytes colonizing submerged macrophytes. Howard-Williams (1981) discussed the implications of subsequent sedimentation of senescent epiphytic biomass as a critical water-to-sediment vector in sediment-to water nutrient exchange. Despite the ecological importance of the macrophyte : epiphyte complex the dynamics of the relationship between epiphytes and macrophyte hosts are poorly understood (Allen 1971, Cattaneo and Kalff 1980 Wetzel 1983 Burkholder and Wetzel 1989b) Some researchers describe this relationship as a mutual symbiosis in which nutrient exchange is on going between epiphytes and host (Brezonik et al 1979). Other studies have concluded that the epiphyte:macrophyte relationship is best described as a type of parasitism" in which the epiphytes sap nutrients being pumped from the sediments by the macrophyte host (Harlin 1975 Moeller et al. 1988, Burkholder and Wetzel 1990 Burkholder et al. 1990). Sand-Jensen and Borum (1984) and Sand-Jensen (1990) describe the role that epiphytes can play in host light exclusion Rogers and Breen ( 1981) identified a necrotrophic relationship in which epiphytes played a critical role in the initial decomposition of leaf tissue in a P illinoensis species Other investigators have described the relationship as a neutral one in which the role of the macrophyte is primarily one of physical support (Cattaneo and Kalff 1978 Carignan and Kalff 1982). However the results of these

PAGE 59

42 latter studies indicated the presence of nutrient transfer. Investigations that have documented host-specific algal assemblages (Godward 1934 Prowse 1959 Blindow 1987) and differing epiphyte productivity levels as a function of host plant (Cattaneo and Kalff 1980) suggest that there is some degree of interaction between epiphytes and their hosts. In their study of phosphorus transfer between N guadalupensis flexilis and associated epiphytes Burkholder and Wetzel (1989b) concluded that there is a probable correlation between epiphytes and their microenvironment. Methods for Investigating Epiphytic Algae The relative lack of information on epiphytes and their relationship to their macrophyte hosts is due in large part to the degree of effort involved in the collection and preparation of these organisms for study (Hickman 1971, Main 1973). Several different processing methods are available for use by researchers investigating epiphyte community composition. The first method entails the use of artificial substrates Many studies have been conducted on algal colonization of artificial substrates (Allen 1971, Brown 1976 Siver 1977 Hooper-Reid and Robinson 1978 Cattaneo and Kalff 1979 Fontaine and Nigh 1983 Fairchild and Lowe 1984 Burkholder and Wetzel 1989b). Other research has indicated that this attempt to simplify the experimental design of epiphyte studies often yields communities that are not comparable to those occurring on natural substrates (Castenholz 1960 Sladeckova 1962 Tippet 1970 Brown 1976) Another approach involves examination of the plant surface using scanning electron microscopy (SEM) (Allanson 1973 Sieburth et al 1974 Burkholder and Wetzel 1989b ) There are several disadvantages associated with the use of SEM as the

PAGE 60

primary investigative tool. SEM is a relatively expensive technique. In addition, for many studies sample storage time required for transport to the laboratory would render epiphyte samples physiologically nonviable. A third possible technique for investigating epiphytes uses an acid digestion method to allow quantification of the total diatom component present on the natural substrate (Cattaneo and Kalff 1979). This method excludes nondiatomaceous components of the epiphytic flora. It also renders impossible comparison of the percent living versus dead component. 43 Many studies have identified mechanical removal of the attached algae from living macrophytes as the most effective way to address the community composition as well as the physiological state and activities of epiphytes (Sladeckova 1962, Gough and Woelkerling 1976, Cattaneo and Kalff 1980, Kairesalo 1980, Fairchild and Lowe 1984, Tanaka et al. 1984, Goldsborough and Robinson 1985, Moeller et al. 1988, Sand-Jensen et al. 1989, Goldsborough and Hickman 1991, Zimba and Hopson 1997). Mechanical removal was the method used in this study.

PAGE 61

44 Figure 2-1: Najas guadelupensis is a pioneer species in the Najadaceae.

PAGE 62

Clara spp. Musqrus ..... ,-.J.,, lrAS.C.W ...... "'llolofflll!'" .... ......_ I"' Figure 2-2: Chara spp. are macroalgae. \ 45 I I I I I I I I I I I I \ I I I I I \ I

PAGE 63

i"--tlot pt'O'lfidffl by. IF,U, C-ror AquMic Plmb Ulli-.cnily oC Flancla. OaiacsYille, 1993 46 Potam.,on llllnoensis Illinois pondweed Figure 2-3: Potamogeton illinoensis is a Florida native perennial with broad lanceolate leaves.

PAGE 64

Vallisneria amaicona Tapeg,us ,.,_,,,.,,,.,_1,y: IF.U. c_.., -"'-u......,. e1,......._--.. 1,,. Figure 2-4: Vallisneria americana is a perennial with broad ribbonlike leaves. 47

PAGE 65

CHAPTER3 COMPARISON OF THE GROWTH OF FOUR SPECIES OF NATIVE SUBMERGED MACROPHYTES ON INORGANIC SEDIMENTS FROM A SHALLOW URBAN FLORIDA LAKE Introduction and Literature Review The role of submersed macrophyte roots as organs for physical attachment to the substrate versus absorption of sediment nutrients has been the subject of considerable historical debate (reviewed in Gessner 1959, Wetzel 1964 Sculthorpe 1967 Hutchinson 1975, Wetzel 2001 ). More recent research has confirmed that the primary function of the root systems is to assimilate nutrients from the sediment (Barko and Smart 1986 Short 1987, Barko and Smart 1991 Wetzel 2001). The roots take up nutrients primarily from the interstitial water of the sediments, where nutrients are present at much greater concentrations than in the water column. Shannon (1955) determined that the absorptive capacity of the roots is enhanced by the presence of root hairs. Many species also exhibit symbiotic relationships with vesicular-arbuscular micorrhyzae (Sondergaard and Laegaard 1977, Tanner and Clayton 1985 Wetzel and van der Valk 1996). The mechanism for assimilation of sediment nutrients is believed to be the same as that used by terrestrial plants the solubilization and mobilization of soil nutrients by secreted organic acids (Wetzel 2001 ). Although macroalgae typically obtain nutrients through foliar absorption from the water column rather than by rhizoidal structures (Wetzel 1983) uptake of phosphorus from sediment has been documented in some Charophytes (L i ttlefield and 48

PAGE 66

49 Forsberg 1965). Littlefield and Forsberg (1965) observed that Chara absorbed sediment phosphorus through the rhizoid from where it was translocated to other parts of the plant. Researchers have been aware of the influence of sediment physical composition on the productivity and distribution of submerged macrophytes since the early 1900 s (cf. Pond 1905 Pearsall 1920, Misra 1938). The results of numerous more recent studies conducted in a wide variety of aquatic systems have confirmed that sediment composition exerts a significant effect on submerged macrophyte growth (Moeller 1975 Anderson 1978, Sand-Jensen and Sondergaard 1979, Kiorboe 1980, Danell and Sjoberg 1982, Wheeler and Giller 1982, Barko and Smart 1983 Barko and Smart 1986, Barko et al. 1991, Livingston et al. 1998). Barko and Smart (1983) concluded that sediment organic matter can greatly inhibit the growth of submerged macrophytes. Their results further suggested that refractory organic matter appeared to have a longer-lasting inhibitory effect as compared to labile organic matter. They attributed this inhibition to the presence of high concentrat i ons of soluble organic compounds in the interstitial water produced during anaerobic decomposition. Rybicki and Carter (1986) reported better growth of Vallisneria americana on silty clay than on sand. Barko and Smart (1986) found similarly that Hydrilla and Myriophyllum exhibited poor growth on sands and on highly organic sediments. They identified the effect of long diffusion distances associated with low densities as the cause of the growth response to organic sediments. Other investigations have been focused on the effect of sediment chemica l composition on rooted submersed macrophyte growth Barko et al. (1991) reported

PAGE 67

50 that nitrogen, phosphorus, iron, manganese and micronutrients are taken up from the sediment whereas calcium, magnesium, sodium, potassium, sulfate and chloride are assimilated from the water column. The majority of research into sediment macro and micronutrients has been conducted on phosphorus and nitrogen. Of this literature, most has focused on phosphorus (Barko et al. 1991 ). As a result of the large exchangeable pool of phosphorus present in the sediments of most lakes, phosphorus is rarely the limiting factor in submersed macrophyte growth (Wetzel 2001) Literature available on the nitrogen economy of submerged aquatics is limited in comparison. Several isotope studies indicated that nitrogen can be assimilated from both the sediment and the open-water (Nichols and Keeney 1976, Short and McRoy 1984). The results of these studies suggested that nitrogen uptake rates were positively correlated with concentration and that ammonium was the preferred form of nitrogen for uptake Nichols and Keeney (1976) suggested that, since sediment ammonium concentrations are typically much greater than water column concentrations sediment is probably the major source of nitrogen for rooted submersed plants. Fertilization studies conducted in freshwater systems indicated that nitrogen limitation of submersed macrophyte growth may occur in some sediments (Anderson and Kalff 1986 Duarte and Kalff 1988, Moeller et al. 1988). There are relatively few documented cases of inorganic nutrient lim i tation in submerged aquatic macrophytes (Anderson and Kalff 1986 Barko e t al. 1986). Sho1t ( 1987) reviewed the effects of sediment nutrients on seagrasses and concluded that seagrass production is strongly correlated with nutrient a v ailability He cit e s ex ample s of how differences in the g eochemistry o f s ystem s can result in e i ther

PAGE 68

51 phosphorus or nitrogen limitation. He concluded that sediment geochemistry is the most significant factor controlling nutrient limitation of seagrass growth. The results of fertilization studies conducted by Barko and Smart ( 1986) indicated that macrophyte growth limitation on both sand and organic substrates was due to nutrient deficiencies. Many studies have used fertilizer amendments to circumvent problems with nutrient limitation when using sand substrates (c.f. Moeller 1983, Sutton 1985, 1993, Sutton and Latham 1996, this study). There is still considerable controversy, however, as to the relative importance of sediment chemical and physical composition in macrophyte nutrition (Sculthorpe 1967, Haslam 1978, Denny 1980, Barko and Smart 1986). Barko and Smart (1983) identified the difficulty in separating the effects of sediment nutrient availability from other sediment characteristics as one of the greatest challenges associated with investigations of the relationship between sediment composition and macrophyte growth. Additional studies have indicated that macrophyte growth is significantly impacted by the combined effects of sediment nutrient composition and physical characteristics. In a study involving the growth of Hydrilla and Myriophyl/um on 40 different sediments collected from 17 North American lakes, Barko and Smart (1986) identified a significant relationship between macrophyte growth, nutrition and sediment density. Their results suggested that sediment density is more influential than organic matter content in regulating plant growth. The results of several studies have suggested that differences in sediment composition may play a significant role in determining species composition within rooted submersed macrophyte communities. Denny (1972) reported species-specific

PAGE 69

52 responses to sediment composition and nutrient concentrations in a growth study that he conducted in concrete ponds. Denny explained these variations in growth response in terms of differences in anatomy and morphology that in turn affected sediment nutrient uptake among the study species. Barko and Smart (1980, 1981, 1986) observed similar species-specific variations in growth response to sediment fertility in several laboratory studies. Chambers (1987) observed a shift in community composition along a natural gradient in Lake Memphremagog such that the percentage of erect and canopy-forming species decreased and rosette and bottom dwelling species increased with decreasing sediment fertility. See Barko et al. (1991) for a comprehensive review of the ecological implications of variations in sediment composition on submersed macrophyte communities and littoral ecosystem processes. In their guide for establishing SAV, Smart and Barko (1996) suggested the importance of the use of preliminary investigations of sediment composition to evaluate the viability of a location as habitat for colonization by a diverse community of submerged macrophytes. A review of the literature indicated a paucity of information on the relationship between sediment composition and submersed macrophyte growth. Of the limited body of research on the macrophyte-sediment relationship, most studies have been focussed on nuisance exotic species such as Hydri/la and Myriophyl/um. Very little information has been published on the sediment requirements of desirable native submerged species. The objective of this study was to compare the growth of four species of Florida native submerged macrophytes with varied life histories in inorganic sediments from Lake Hollingsworth. The findings should contribute vital

PAGE 70

information on the growth habits of native submerged macrophytes and will be of value to lake managers for use in the development of a systematic approach to the establishment of diverse communities of desirable aquatic vegetation in restored Florida lakes. 53 The experimental procedure was designed to test several hypotheses based upon findings from the literature and previous experience. The first was that there would be spatial variation in the organic matter and nutrient content of the littoral sediments in Lake Hollingsworth. I also anticipated that N guade/upensis, P i//inoensis and Chara sp., the canopy-forming, erect species, would produce greater biomass in sediments with higher nutrient levels while net growth of V. americana, a rosette species, would be inversely related to sediment nutrient content. Based upon my personal experience growing stock cultures of the study plants I expected to observe differences in growth rate among the species such that N guade/upensis would be the fastest grower followed by P. il/inoensis, V. americana and lastly Chara sp. I further expected the growth rate of Chara sp to be positively related to increasing culture period length. I anticipated that N guada/upensis, V. americana and Chara sp. would produce the greatest biomass during the summer months while growth of P. i//inoensis, a species with a range distribution that stretches into more temperate regions, would be stimulated by the cooler temperatures of the winter months. Finally I hypothesized that sediments collected from the littoral zone of Lake Hollingsworth would have sufficient quantities of sediment nutrients to support the growth of N guadalupensis, P i//inoensis V. am erica na and Chara sp. when grown in the experimental growth tanks used in this study

PAGE 71

54 The study was limited to sediments with low organic matter content to avoid growth inhibition previously associated with high organic matter concentrations ( c.f. Barko and Smart 1983, 1986, 1991). Submerged macrophyte species were selected on the basis of several criteria. Initially, species selection was determined by the need to identify Florida native submersed macrophytes for which propagule material is widely available. In addition, a mix of annual and perennial species was selected in order to maximize the potential for establishing viable, self-sustaining communities of SA V capable of out-competing exotic species in restored lakes. Finally, macrophytes were selected based on their relative value as habitat for fish and other aquatic organisms, resistance to herbivory and relative potential positive impact on the water quality of the lake. Four species were identified using the aforementioned selection criteria -Najas guadelupensis (Spreng.) Magnus, Potamogeton illinoensis Merong. j Vallisneria americana Michaux) and Chara sp. (Refer to the Description of Study Macrophytes section in Chapter 2 for a detailed description of the study species.) N guadalupensis and Chara sp. were selected for inclusion in this study for several reasons. Both N guadalupensis and C hara are pioneer annual species that expand and rapidly cover the sediment with a carpet of vegetation hence filling a niche that would otherwise be ideal habitat for invasion by an exotic weedy species such as H y drilla In addition the increased surface area provided by the finely dissect e d "leaf' architecture characteristic of both of these native plants makes these macrophytes excellent habitat for fish-food organisms and refugia for juv enile fishes (E n g el 1985) V. ameri cana and P illinoensis ar e p e rennials

PAGE 72

55 Managed introduction of these four species should result in the establishment of diverse communities that can maintain restored lakes in a macrophyte-dominated stable state. The combination of growth strategies exhibited by these annuals and perennials should make the community relatively resistant to short-term environmental perturbations. Plasticity in the response of the community to changes in water depth and light regime is essential in shallow eutrophic lakes that experience frequent resuspension events and are susceptible to water level fluctuations caused by seasons of heavy rainfall or drought. A combination of growth strategies also improves the chances of the managed community to out-compete exotic species by eliminating available niche space. Materials and Methods Site Description Lake Hollingsworth is a 144 ha shallow (Zmean= 1.2 m) (City of Lakeland 1988-2000) urban lake located in central Florida (28 '30", 81 56'45") (Figure 31 ). The lake is a solution basin roughly circular in shape with a mean depth of 1.2 m (Lake Hollingsworth Diagnostic Feasibility Study 1994). Water inputs to the lake are in the form of rainfall, groundwater seepage, stormwater runoff and inputs from Lakes Morton and Homey. Groundwater recharge contributes up to 85% of the total water budget for the lake (SWFWMD 1994 Section II). Surface drainage flows southeast into Lake Bentley Paleolimnological study indicated that Lake Hollingsworth is naturally eutrophic (Brenner et al., 1995). This is probably due to the fact that the lake lies in the Bartow Embayment division of the Central Lakes District where the underlying bedrock consists of the phosphatic sands and clays of

PAGE 73

56 the Bone Valley region of Central Florida (Canfield and Hoyer 1992). In the early 1990's, the results of a Diagnostic Feasibility Study conducted on the lake indicated that Lake Hollingsworth was in an advanced state of aging with estimated sedimentation rates of approximately 30 cm in 20 years. The result of years of sedimentation was a layer of flocculent organic sediments measuring up to 4.6 m in thickness in some areas of the lake. The recommendation of the study was to restore Lake Hollingsworth using the method of whole lake hydraulic dredging. Dredging was commenced in 1999 and was halted before completion due to complications from drought conditions during the dredging period. Post-dredge monitoring efforts indicate a dramatic improvement in water quality in the lake. The lake is a highly valued resource, serving as the site for a variety of social, educational and recreational activities for the City of Lakeland and the surrounding community. The lake also supports sustenance, commercial and sport fisheries. Sediment Survey A survey study was conducted to screen the littoral sediments of Lake Hollingsworth in order to identify any possible locations at which sediment characteristics, such as flocculance or relatively high organic matter content, could inhibit submersed macrophyte growth. Lake Hollingsworth is a shallow, highly productive lake with the potential for highly variable organic sediment distribution. In their 1996 study of the variability of sediment distribution in shallow Florida lakes, Whitmore et al. (1996) indicated the importance of using systematic mapping to locate optimal coring sites. A grid was superimposed on the bathymetric map of the lake to identify sampling stations distributed to ensure equal area coverage of the

PAGE 74

57 littoral region (Hakanson 1981). The bathymetric map was drawn on April 13. The convention, when using the grid method, is that stations can either be located within the space between the lines or at the intersection oflines. In this study, stations were located within the spaces between the lines. The sampling grid identified twelve littoral stations occurring along the 2 ft (0.8 m) contour line. Four of the grid stations did not cover the 2 ft (0.8 m) contour line and were disregarded. Eighty centimeters was selected as the optimum planting depth based on several considerations. It has been previously determined that maximum depth of colonization for most submerged macrophyte species in shallow eutrophic lakes similar to Lake Hollingsworth is 1 m. I observed a significant decrease in the biomass of the study species at lake levels above 1 min Lake Okeechobee (Hopson 1995). Final lake stage in Lake Hollingsworth at completion of the restoration project was subject to fluctuation. In addition, increased turbidity in the system was expected to accompany the whole-lake dredging being conducted at the time of this study. The goal of this study was to provide practical information for use by managers in the lake. Therefore, I decided that planting at 0.8 m would allow for fluctuations in lake stage while ensuring that submerged macrophytes would have sufficient depth for growth while still having sufficient available light. The eight grid stations included in the survey were lettered from A to H, proceeding in a counterclockwise direction (Figure 3-1 ) Stations on the grid were 0.45 km apart on the average. Coordinates of station locations were determined using a Trimble CDS I GPS unit. Triplicate sediment samples were collected from each station using the sediment coring device described by Sutton (1982). Samples were stored in Ziplock

PAGE 75

58 bags and transported in a dark cooler. Samples were air-dried for at least 72 hours and then dried to constant weight in a forced-air drying oven at 60 C (Hakanson and Jansson 1983) Dried samples were homogenized and deflocculated in a hammer mill. Samples were then further homogenized using a clockwise layering method, weighed and separated into subsamples for nutrient, pH and organic matter analysis. The pH of the samples was determined by scooping 20 cm3 of the dried, homogenized sediments into plastic cups. Samples were hydrated by adding 40 mL of deionized water. Samples were then stirred thoroughly and allowed to settle for a minimum of 30 minutes. All samples were processed within 2 hours. A calibrated Orion Research model 601A/digital IONAL YZER was used to measure the sample pH. A standard was used as the last sample in each batch to verify the accuracy of the ionalyzer. Organic matter content was determined as weight loss on ignition (LOI) at 550 C in a muffle furnace (Hakanson and Jansson 1983). The results of this survey study were used to select four stations that appeared to provide the most suitable habitat for submersed macrophytes among the eight survey stations Sediment samples from the stations selected for the growth study (B, D, F and H) -were analyzed for the plant macro-and micronutrients P, K, Ca, Mg, Zn, Mn, Cu Al Na, Fe, er, NI-Li and NO3. All samples were extracted using Mehlich-1 extractant and analyzed by inductively coupled argon plasma (ICAP) spectroscopy (Southern Region Information and Exchange Group on Soil Testing and Plant Analyses 1983). Sediment Collection and Processing Three sediment cores from each of the four selected stations were collected and loaded into twelve 7.6 L polyethylen e nursery contain e rs. Containers were

PAGE 76

59 covered with plastic wrap to prevent drying of sediments during transport. Holes were punched in the plastic wrap to allow for oxygen transfer. Sediments were transported to the University of Florida Fort Lauderdale Research and Education Center (FLREC) (26 05'N and 80 14'W) and submerged within 24 hours of collection. The results of the analyses performed on samples collected during the preliminary survey were used to describe the sediment pH, organic matter content and concentration of selected macroand micronutrients. Experimental Environment and Procedures Plants were grown outdoors at the FLREC in concrete tanks (6.2 m L x 31 m W x 0.9 m H) on natural and artificial sediments. Pond water (Steward 1984) flows into the tanks at the surface of one end and out from a drainpipe at the other at a rate providing one volume exchange every 24 hr. Plants were exposed to natural daylight. Water temperature was measured using maximum/minimum thermometers placed 30 cm below the surface of the water. Readings were taken 5 days a week at approximately 3:00 P.M. each day. Total irradiance ( 400-1100 nm) (W m"2 ) was measured by a LICOR LI200SZ pyrometer. These data were sampled every 3.75 min and reported as 15-min averages by a data logger. Total irradiance was converted to photosynthetically active radiation (PAR) ( 400700 nm) assuming that PAR is approximately 45% of total irradiance (Baker and Froiun 1987). PAR in W m2 was converted to photosynthetic photon flux density (PPFD) units( mol photons s 1 m2 ) using a multiplier of 4.6 (see Table 3 in Thimijan and Heins 1983). The mean incident PPFD for the photic portion of an experimental period was found by averaging the nonzero fluxes. Accumulated PAR

PAGE 77

60 was found by multiplying the mean incident PPFD by the length of the photic period for the experiment. A total of 20 treatment groups ( 4 species x 4 sediment samples plus the control) were tested in each culture period. Three 7.6 L containers were planted for each treatment group, with four propagules per culture container, for a total n = 12 plants per treatment group and an overall total of 60 containers Plant propagules were obtained from stock cultures maintained at the FLREC. Propagules were harvested from similarly aged actively growing stock plants. Apical cuttings of N. guadalupensis 20 cm in length were planted to a depth of~ 3 nodes. Apical cuttings of P. illinoensis were planted to a depth of~ 2 nodes. Propagules of V. americana growing on rhizomes were planted to a depth such that the rhizome was submerged just beneath the sediment surface but the basal rosette was not covered. Apical cuttings of Chara sp. 20 cm in length were planted to a depth of~ 3 cm. Apical cuttings and rosettes were collected at the beginning of each culture period to give at least ten representative initial samples for each species. Each sample was dried at 60 to constant weight (Hakanson 1981 ). Mean g dry weight at the time of planting was calculated for each species. The total of 60 culture containers was divided equally into two groups of 30. Each group containing representatives of each treatment group and p l ant type, was placed into a separate tank. A random numbers table was used to arrange culture containers in four rows within each tank parallel to the flow of water (Figur e 3-2.) All species were submerged in 0.8 m of water The stud y was conduct e d o ver \ three culture periods from 30 April to 29 June 2001 (Spring Culture Period) 20 July to 2 1

PAGE 78

61 September 2001 (Summer Culture Period) and 19 December 01 to 22 February 02 (Winter Culture Period). Culture period length in each experiment (approximately 9 weeks) was adequate for the development of treatment-related differences in growth but minimized tissue deterioration associated with senescence. In a similar study conducted at the FLREC using sand media amended with controlled-release fertilizers, including Osmocote, to culture Hydrilla verticillata, a submersed macrophyte, Sutton and Latham (1996) documented statistical differences in growth after 8 weeks. (See Figure 1 1 of Sutton and Latham (1996) for a presentation of biomass data.) The control group consisted of plants grown in a medium of coarse builders' sand amended with 15-9-12 (N:P : K) Osmocote Southern Formula, a commercially available fertilizer. Osmocote is manufactured by Grace Sierra Horticulture Products Company, Milpitas, CA. This fertilizer is formulated to s l ow-release in soil over an 89 month period with increased rates of nutrient release at temperatures 21 C (Harbaugh and Wilfret 1981 ). Fertilizer was added at a rate of 40 g per pot for N. guadalupensis and P illinoensis and 15 g for V. americana and Chara (Dr. David Sutton UF FLREC personal communication). In the spring culture period the activity of the herbivorous moth Paraponyx diminutalis Snellen apparently caused a significant reduction in the above-sediment biomass of N. guadalupensis and P illino e nsis. The total loss in N. guadalup e nsis and P illinoensis above-sediment biomass due to herbivore damage was estimated to be approximately 50% (Figure 3-3). This estimate was made based upon field estimates of biomass loss in conjunction with trends in root:shoot ratios for N.

PAGE 79

62 guadalupensis observed in the swnmer and winter culture periods. The estimated loss fits within the range of loss reported in the literature. Estimated total biomass values for N guadalupensis and P. illinoensis were then obtained by adding the calculated loss to the actual total biomass values measured for each species. These estimated values were used in subsequent statistical analyses involving the growth of N guadalupensis and P illinoensis in the spring culture period. An emulsifiable concentrate of malathion (0,0-dimethyl dithiophosphate of diethyl mercaptosuccinate) was used to achieve a dosing concentration of 1.0 mg/L in order to control herbivore activity during the swnmer and winter culture periods. Tanks were dosed biweekly with a concentrate of Malathion (O, O-dimethyl dithiophosphate of diethyl mercaptosuccinate) to an initial concentration of 1.0 ppm in the summer and winter culture periods. Dosing was initiated when plant shoots reached the water surface in order to control the feeding activity of the herbivorous moth, Parapoynix diminutalis Snellen Plants were harvested and separated into above-sediment biomass (shoots) and below-sediment biomass (roots) at the end of each culture period. The length of each experiment (9 weeks) was adequate for the development of treatment relat e d differences in growth while minimizing tissue deterioration associated with senescence. Total number of plants harvested per pot was recorded for all species in the spring culture p e riod. (It was d e termined during this first harv est that the brittle nature of N guadalupensis and Chara stems made it very difficult to get a reproducible assessment of the number of plants of these two genera. Therefore the average numb e r of harvested plants per pot was quantified only for V a m e ri c ana and

PAGE 80

63 P illinoensis in the summer and winter culture periods.) Plant material was dried to constant weight (Hakanson 1981) at 60 C in a forced-air drying oven and dry weights were measured. Macrophyte growth was measured as the change in dry weight of plant biomass, after correction for epiphyte biomass ( explained below), since planting of propagule material. From this point forward, the term biomass will be used to refer to total plant biomass (shoots+ roots). Epiphyte biomass was removed from the macrophytes at the time of harvest. In the spring culture period, macrophyte material was washed gently with pond water in order to remove sediment, debris and epiphytic algae. In the summer and winter culture period, the mechanical removal technique described by Zimba and Hopson (1997) was used to separate epiphytic biomass from macrophyte biomass. (See Appendix A for a more detailed discussion of the method used.) A subsample of the resultant suspension containing the epiphytes was concentrated onto a glass fiber filter (0.7-m porosity) and chlorophyll a and phaeophytin a were determined in accordance with Standard Methods (SM 10200 H) (A.P.H.A. 1995). All epiphyte data collected were normalized to host plant dry weight. Chlorophyll a values corrected for phaeophytin a were used as a correction factor to determine total macrophyte yield. More rigorous efforts were also made in the summer and winter culture periods to use mechanical removal methods to maintain the tanks relatively free of both epiphytic and floating algae. Statistical Analysis of Results Sediment chemical composition, macrophyte biomass and ratios of root biomass to shoot biomass were analyzed using the general linear model (GLM)

PAGE 81

64 procedure of Statistical Analysis System (SAS) for personal computers (SAS Institute 1999-2001). Tukey s studentized range distribution test (HSD) procedure was used for means separation to investigate differences in the pH, organic matter and nutrient contents of the sediment and among and within species differences in macrophyte biomass and root:shoot ratios. Regression analysis (SAS Institute 1999-2001) was used to identify those sediment characteristics that had a significant effect on macrophyte growth. Sediment nutrients, pH and organic matter content and light and water temperature were used as the independent variables and macrophyte biomass was used as the dependent variable Stepwise multiple regression analysis was used to further evaluate the association between macrophyte biomass production and those environmental factors identified as significant. In an effort to improve the models sediment calcium magnesium potassium and sodium were excluded from analysis on the basis that numerous studies have shown that the water column is the primary source of these nutrients for submersed macrophytes. Data transformation was used to reduce vanance as necessary. Results Sediment Survey The results of the preliminary sediment survey study of Lake Hollingsworth littoral sediments r e vealed significant diffe rences in sediment organi c matter content and pH among the survey stations (Table 3-1). (See Figure 3-1 for a map of the survey study stations) Organic matter content(%) ranged from 0.38 % at station B to

PAGE 82

39.18% at station E. Station G sediments also had a high organic matter content (34.96%). The pH varied from a low of 5.4 at station B to a high of 8.0 at station F. 65 Four stations were selected that appeared to provide the most suitable habitat for submersed macrophytes among the eight survey stations (Figure 3-1 ). Study station selection criteria included low organic matter content, absence of flocculent sediment layer and protection from boat traffic. Comparison among the survey stations indicated differences in the relative amount of boat traffic in the different lake regions. Stations A and E were located in the path of two water ski courses in the lake. Consequently, these stations were eliminated due to heavy boat traffic that would be damaging to macrophyte communities. B, C, D, F and H were relatively protected from boat traffic. Stations B,D,F and H appeared to have the optimum combination of low organic matter, absence of flocculent layer and minimal perturbation. In my opinion, these locations had the best potential, dependent upon chemical composition, to be sites for the successful establishment of founder colonies of the study species. Chemical Composition of Study Sediments Differences in pH, percent organic matter and macroand micronutrient contents were apparent among the sediments (Table 3-2) The lake sediments were more alkaline than the control sediments with the exception of sediment from Station B which exhibited the lowest mean pH, 5.4 (Table 3-2 ) Organic matter contents of the natural sediments ranged from 0.42 to 1.08%, with Station D having the lowest percentage and Station F the highest percentage. Sediment from Station F also contained significantly higher calcium contents (5617 mgKg"1 ) than the other

PAGE 83

66 sediments. Magnesium, phosphorus, manganese and sodium levels were significantly greater at Station F and in the controls than in the other sediments. There were no significant differences in the content of these elements in the other sediments. Zinc was present at significantly highest levels in sediments from Station F and lowest in sediments from Station D. Control sediments dosed with 40 g of fertilizer (controls for N. guadalupensis and P. illinoensis) contained significantly greater levels of copper, potassium and chloride ion as compared with the other sediments. There were no significant differences in copper, potassium and chloride ion among the remaining sediments. No significant differences in manganese content were observed among the sediments. Aluminum content was lowest in sediments from Site D. Iron, ammonium and nitrate were detected in significantly greater amounts in the control sediments as compared with the lake sediments. A comparison of the relative iron contents observed in the control sediments to the amounts contributed by the Osmocote indicated the presence of iron in the sand used to create the control sediments. The iron content measured in the control sediments amended with 15 g of Osmocote were unexpectedly high relative to the those controls amended with 40 g of fertilizer. This may have resulted in levels of iron that were inhibitory to some species. Temperature and Irradiance during the Culture Periods As shown in Table 3-3, the highest average daily water temperature was recorded during the summer culture period (29.6 C) while the lowest average daily water temperature was recorded during the winter culture period (2 l .2C). The mean incident PAR were greatest during the spring culture period (806 mol s1 m2 ) and least during the winter culture period (624 mol s' m"2). Photoperiod was longest

PAGE 84

during the spring (13.8L:10.2D) and shortest during the winter culture period (1 lL:13D). Effects of Sediment on Macrophyte Production Spring culture period (30 April to 29 June 2001) 67 Analysis of variance of pooled total macrophyte biomass (n = 60) produced during the spring culture period using GLM procedures (SAS Institute 1999-2001) indicated highly significant differences due to plant type (Table 3-4). (Note that total biomass values for N. guadalupensis and P. illinoensis were corrected for losses due to herbivory. Refer to the Materials and Methods section for a description of the method used to estimate the corrected values.) There were no significant differences in total biomass due to sediment source or to the interaction between sediment source and plant type. Means separation using Tukey's HSD method indicated that there were no significant differences in biomass production among species in Site D, Site F and control sediments (a= 0 05). V americana produced significantly less biomass than the other species in Site B and Site H sediments. N. guadalupensis and Chara sp. produced greater biomass in the control sediments and most of the natural sediments than P. illinoensis and V americana (Table 3-5). V americ ana exhibited the slowest growth of all species in all but one sediment. Within species comparisons indicated that N. guadalupensis and Chara sp. produced produced greatest mean total biomass in control sediments (16.4 and 16 9 g DWT, respectively) ( F igur e 3 34) N. guadalupensis growth was slowest in Site H sediments (11.0 gown. C har a sp. accrued the least biomass in Site B sediments ( 4 1 g DWT). P illino e ns is produced greatest mean biomass in Sit e F sediments (9.9 g DWT) and least biomass in Site D

PAGE 85

68 sediments (6.0 g DWT). V. americana production was greatest (6.8 g DWT) on Site D sediments and lowest in Site B (2.3 g DWT). Analysis of variance using the GLM Procedure (SAS Institute 1999-2001) indicated that there were no statistically significant differences in macrophyte growth within species in response to sediment type (Figure 3-4a). Comparison of the mean number of individual plants produced by each species indicated that P illinoensis produced more plants than the other species in most of the sediments (Figure 3-Sa). As a general trend, all species produced the least number of individual plants on Site B sediments. Note that herbivory had a negative effect on the total number of plants counted and probably resulted in a significant underestimate of the total number of plants of N. guadalupensis and P illinoensis. Simple regression analysis used to investigate the relationship between macrophyte biomass production and sediment chemical composition suggested that sediment pH, OM and macroand micro-nutrients had relatively little effect on macrophyte growth in the spring culture period (Table 3-6). The only significant relationship was between aluminum and N. guadalupensis biomass. There were no other significant relationships. Root: shoot ratios produced by all species in response to all sediments were less than 1 (Figure 3-6a). Analysis of variance of macrophyte root:shoot rat i os using GLM procedures (SAS Institute 1999-2001) indicated highly significant differences in total root : shoot ratios due to plant type (P < .0001) (Table 3-7). There were no significant differences due to sediment source or to the interaction between sediment source and plant type. There were differences amon g and within the study species. V.

PAGE 86

69 americana allocated energy for the production of greater relative amounts of root biomass in all sediment types as compared with the other species. These differences were statistically significant in Site B Site D and Site H sediments N. guadalupensis ratios were significantly lower than that of the other species in Station D sediments. Within species comparisons suggested that N. guadalupensis and V. americana allocated relatively more resources to root production in Station B sediments as compared with the other sediments. In the case of N. guadalupensis the difference was statistically significant. P illinoensis and V. americana root:shoot ratios were lowest in response to the control sediments Summer culture period (20 July to 21 September 2001) Analysis of variance of pooled total macrophyte biomass (n = 60) produced during the summer culture period using GLM procedures (SAS Institute 1999-2001) indicated that sediment and plant type had a highly significant effect on macrophyte biomass production (P <.0001) (Table 3-8) The interaction between these two factors was not significant. Means separation using Tukey s HSD Procedure suggested that there were significant differences among and within macrophyte species in response to sediment type (a= 0 05) N. guadalupensis produced significantly higher biomass on all natural sediments as compared to the other species (Table 3-9). Chara sp exhibited the slowest relative growth in response to all sediments. This difference was statistically significant for growth in Site B and Site D sediments N. guadalupensis and P illinoensis exhibited more rapid growth in all sediments as compared to V. americana and Chara sp . There were no significant differences in growth among macrophytes in response to the control sediments. Within species comparisons

PAGE 87

70 suggested that all species exhibited the slowest growth in Site B sediments. This difference was statistically significant for V americana (18.6 g DWT) and Chara sp. (3.8 g DWT) (Figure 3-4b). V americana produced statistically greatest biomass in control, Site D and Site F sediments ( 44.4 41 and 28 g DWT). N guadalupensis and P illinoensis produced greatest biomass in control sediments, however, these differences were not found to be statistically significant (56.5 and 21 g DWT, respectively). Although Chara sp. growth was best in control sediments there were no statistical differences in the biomass produced in control, Site F Site Hand Site D sediments. V americana produced a greater number of individual plants per pot on all sediments as compared with P illinoensis (Figure 3-5b). V americana exhibited the greatest increase in total number of plants in response to Site D sediments while the greatest increase in number of P illinoensis plants was observed on control sediments. The results of simple regression analyses of macrophyte biomass and sediment chemical components indicated that there were species-specific differences in response to sediment pH OM macroand micro-nutrients and epiphyte biomass in this culture period (Table 3-6). Sediment phosphorus, copper manganese iron, ammonium, nitrate magnesium, potassium, sodium chloride and epiphyte biomass had highly significant (P < .0001) effects on total macrophyte biomass (n = 60) while aluminum had a significant effect on total biomass. Models with P illinoensis biomass and phosphorus copper manganese, iron ammonium nitrate, potassium sodium and chloride were all significant. Iron ammonium nitrate, and potassium

PAGE 88

71 were all found to have significant effects on V. americana biomass. Aluminum had a highly significant effect (P < .0001) on biomass while copper was only slightly significant. A significant negative relationship was observed between Chara sp. biomass and epiphyte biomass. None of the models with N. guadalupensis biomass gave significant results. The results of stepwise multiple regression analyses using a composite of the biomasses of all species (n=60) and the biomass of each individual species (n=l 5) as the response and the significant factors as the predictors also indicated species-related differences (Table 3-6). Total biomass was most significantly affected by copper (P < 0.0002) and ammonium (P < 0.0149). Biomass and ammonium were negatively related. Epiphyte biomass was the most significant predictor of Chara sp. biomass accumulation. Epiphyte biomass had a negative effect on Chara sp. biomass. Root: shoot ratios produced by all species in response to all sediment types were less than 1 (Figure 3-6b ). Analysis of variance of macrophyte root:shoot ratios using GLM procedures (SAS Institute 1999-2001) indicated differences in total pooled (n = 60) root:shoot ratios due to plant type (P <.0033) (Table 3-1 O). There were no significant differences due to sediment source or to the interaction between sediment source and plant type. There were differences among and within the study species (Figure 3-6b ). V. americana and P. illinoensis produced significantly greater root:shoot ratios on Site Band Site H sediments versus N. guadalup e nsis. There were no other species-specific responses to any of the other sediment types. Within species comparisons suggested that root:shoot ratios for N. guadalupensis were slightly greater on Site H and Site C sediments P illinoensis ratios were greatest on Site B

PAGE 89

72 Site H and control sediments while V americana produced the greatest mean ratio in response to Site B sediments. GLM analysis of epiphyte biomass (gig host DWT) indicated significant differences due to sediment source (P < 0.01) and highly significant host-specific differences (P <.0001) Epiphyte biomass on Chara sp. was greatest in Site B sediments. There were no other host-specific differences. Comparisons among species indicated that in control and Site D sediments, Chara sp and P illinoensis exhibited higher epiphyte biomass than V americana and N guadalupensis. There were no differences among the macrophytes in Site B, Site F or Site H sediments. Winter culture period (19 December 2001 to 22 February 2002) Analysis of variance of the composite macrophyte biomass (n = 60) produced during the winter culture period using GLM procedures (SAS Institute 1999-2001) suggested that plant type had a highly significant while sediment type had a significant effect on macrophyte biomass production (P <.0001 and P < 0.0004, respectively) (Table 3-11 ). The interaction between the two factors was slightly significant. Means separation using Tukey' s HSD Procedure suggested that there were significant differences among and within macrophyte species in response to sediment type (a.= 0.05) (Figure 3-4c). P illinoensis and N guadalupensis exhibited greater growth in all sediments as compared with V americana and Chara sp (Table 3-12). V americana biomass was lower than that produced by the other species in all sediments. P illinoensis biomass was significantly greater than that of the other species in Site B, Site D, Site H and control sediments. Within species comparisons indicated that N guadalupensis

PAGE 90

73 growth was significantly best in Sites F, C and H sediments. P. illinoensis accrued greatest biomass in control and Site H sediments, however, there were no significant differences in the biomass produced in any sediment type. Although V americana exhibited the greatest growth on Site H sediments (12.9 g DWT), differences in response to the different sediment types was minimal. Chara sp. accrued significantly greatest biomass on control sediments (21.3 g DWT) and lowest biomass in Site B (8.2 g DWT) and Site D sediments (7.3 g DWT) (Table 3-12). There were species-specific differences in macrophyte biomass production in response to sediment chemical composition. The results of simple regression analyses of macrophyte biomass using sediment pH, OM and macroand micro-nutrients as predictors indicated a highly significant relationship (p < .0001) between phosphorus, copper, manganese, ammonium, nitrate, magnesium, potassium, sodium and chloride and composite macrophyte biomass of all species (n = 60) (Table 3-6). Iron had a significant effect on composite biomass. Models with N guadalupensis biomass indicated highly significant relationships with organic matter, zinc and magnesium, significant relationships with phosphorus and manganese and slightly significant relationships with calcium and sodium. None of the models with V americana biomass gave significant results. Chara sp. biomass was highly related (p < .0001) to phosphorus, copper, manganese, iron ammonium, nitrate, magnesium potassium and sodium. P. il/inoensis produced a greater average number of individual plants per pot than V americana in all sediments (Figure 3-6c). P. illinoensis exhibited the greatest increase in mean number of plants per pot in control sediments. There were no

PAGE 91

74 obvious differences in the number of plants produced by V. americana in response to any of the sediments. Root: shoot ratios produced by all species in response to all sediment types were less than 1 (Figure 3-6c ). Graphical analyses indicated that P illinoensis and V. americana produced greatest root:shoot biomass on all sediments. Comparisons within species suggested that N guadalupensis ratios were greatest on Site D sediments. P. illinoensis produced greatest ratios in response to Site B and Site F sediments. V. americana produced considerably more root biomass in comparison to shoot biomass in Sit_e H sediments. Analysis of variance of macrophyte root:shoot ratios using GLM procedures (SAS Institute 1999-2001) indicated differences in total root:shoot ratios due to plant type( P < 0.0004) (Table 3-13). There were no significant differences due to sediment source or to the interaction between sediment source and plant type. Among species comparisons indicated that P. illinoensis and V. americana produced significantly greater ratios than N guadalupensis on Site B and Site F sediments. There were no significant differences among species on any of the other sediment types. Within species comparisons indicated that there were no statistical differences in macrophyte root:shoot response to sediment type. The results of GLM analysis of the data indicated that there were no significant host-specific differences in epiphytic biomass (gig host dry weight) during the winter culture period. There were no differences in epiphyte biomass due to sediment source or the interaction between sediment source and plant type.

PAGE 92

75 Identification of General Trends Graphical analysis of the data indicated differences in macrophyte biomass production among the three culture periods (Figure 3-4). Overall, greatest plant growth occurred during the summer culture period. Comparisons among species indicated that N guadalupensis produced the greatest biomass of all study species when grown in lake sediments in spring and in all sediments in summer P illinoensis exhibited the greatest growth among the species on four of the five sediment types during the winter growing period. Differences in biomass production within macrophyte species were also observed. The results suggest that N guadalupensis, V. americana and Chara sp. grew best during the summer culture period. P. illinoensis produced greatest biomass during and grew equally well in the summer and winter culture periods. With the exception of V. americana at station H, there was relatively little difference in the biomass production of V. americana and Chara sp during the spring and winter culture periods. Overall trends in macrophyte growth in response to different sediment types were also observed Generally, greatest macrophyte biomass accumulation during all culture periods occurred in control sediments. Site F and Site H were apparently the most suitable natural substrates for macrophyte growth. Station B sediments supported the least biomass production among the species over the three culture periods. Macrophyte biomass data collected during the summer and winter culture period were pooled and statistically analy z ed as a randomi z ed complete block design where culture periods were considered blocks. Data collected durin g the spring

PAGE 93

76 culture period were not included in this statistical analysis. (Refer to the Materials and Methods section for an explanation.) Analysis of the data using GLM procedures (SAS Institute 1999-2001) indicated highly significant differences in total pooled macrophyte biomass due to culture period sediment source plant type and the interaction between culture period and plant type (P < .0001 for all) (Table 3-14) A weak interaction was also noted for culture period and sediment source (P < 0.0142) No interaction was observed for sediment source and plant type or for all three effects together. There were significant differences in biomass among and between the study species (a.= 0.05) Means separation using Tukey' s HSD Method indicated that N. guadalupensis produced significantly greater biomass on F sediments as compared to the other species (Table 3-15). N. guadalupensis and P illinoensis biomass was significantly greater on Station B and Station H sediments as compared to that of V. americana and Chara sp. V. americana response on control sediments was significantly less than that of the other species. There were no significant differences in growth among the species when grown on Station D sediments Within species analysis of the variance in biomass indicated that Chara sp produced significantly greatest biomass in the control sediments Table 3-16). However it should be noted that there was only a slight difference between Chara sp. biomass produced in control and Site F Site Hand Site D sediments. P illinoensis produced greatest biomass in control and Site H sediments No significant differences were noted in the response of N. guadalupensis and V. americana biomass production to different sediments Further investigation of the effect of culture period on macrophyte biomass indicated that N. guadalupensis produced significantly greater biomass during the summer

PAGE 94

culture period followed by P. illinoensis and V. americana with statistically equal summer biomass. Chara sp produced the least summer biomass. P illinoensis produced the greatest biomass during the winter culture period while Chara sp and V. americana exhibited the least amount of growth. 77 A comparison of the mean number of individual plants produced per pot by each plant type indicated differences among species and within species during different culture periods (Figure 3-5). P. illinoensis produced greater numbers of plants in the winter than in the spring and summer culture periods. A considerably greater number of V. americana plants per pot was measured for the summer culture period than for the other culture periods. Comparison of the root:shoot biomass produced indicated values < 1 for all species during all culture periods (Figure 3-6). V. americana produced considerably greater root:shoot ratios in the spring as compared to the summer and winter culture periods when ratios were fairly similar. These findings may have been due to reduction of shoot material by herbivores. Ratios for P illinoensis were higher in the winter and spring than in the summer culture period. Similar root:shoot ratios were observed for N guadalupensis in the summer and winter culture periods. Slightly higher ratios in the spring culture period were probably skewed by an underestimate of shoot biomass due to herbivore damage. Statistical analysis of pooled root:shoot ratios (n = 120) observed during the summer and winter culture periods using GLM procedures (SAS Institute 1999-2001) suggested highly significant species-specific differences in root:shoot biomass (P <.0001) and a weak interaction between culture period and plant type (Table 3-17).

PAGE 95

78 Further analysis indicated significant differences among plant types such that root:shoot biomass ratios for P illinoensis and V. americana were greater on Station B and Station F sediments as compared to N. guadalupensis (Table 3-18). There were no significant differences on any of the other sediments. V. americana root:shoot ratios were greater during the summer culture period as compared to the other species (P < 0.0032) while V. americana and P illinoensis root:shoot biomass was significantly greater than that of N. guadalupensis during the winter culture period (P < 0 0004). Within species comparisons indicated that P illinoensis produced significantly greater root biomass on Site B sediments and lowest root:shoot ratios on control sediments (Table 3-19) Sediment source did not appear to have a significant effect on the amount of below-sediment biomass produced by N. guadalupensis and V. americana during the summer and winter culture periods Results of analysis of pooled epiphyte data from the summer and winter culture periods (n=120) using the GLM procedure indicated that culture period had a highly significant effect (P < 0001) on epiphyte biomass (Table 3-20). Neither sediment source host macrophyte species or any interactions among the factors were significant. Means separation using Tukey s HSD Test indicated that the epiphytic biomass occurring on all four species was significantly greater in the winter than in the summer culture period (Table 3-21). Generally greater epiphyte biomass was associated with C hara sp and N. guadalupensis on all sediments however none of these differences were statistically significant (Table 3-22). Similarly there were no significant differences in the epiphyte biomass occurring within host species on any sediment type (Table 3-23). There was no apparent relationship between epiphyte

PAGE 96

biomass and sediment source during either the summer or the winter culture period (Table 3-24). Effects of Sediment, Temperature, Light and Epiphytes on Macropbyte Production 79 Simple regression models revealed differences in macrophyte growth response to sediment characteristics, light, water temperature and epiphyte biomass during the summer and winter culture periods. Results from the spring culture period were not included due to the unquantifiable effects ofherbivory on shoot biomass in the study species. The results suggested that sediment ammonium and nitrate had a highly significant effect on total pooled (summer and winter culture period) macrophyte biomass (n = 120) (p < .0001) (Table 3-25) Magnesium had a significant effect on total pooled (n = 120) and pooled N. guadalupensis biomass (n = 30). No other models with sediment nutrients and N. guadalupensis biomass were significant. Pooled P. illinoensis (n = 30) biomass was significantly related to phosphorus, copper, manganese, aluminum iron, ammonium, nitrate magnesium potassium sodium, and chloride. None of the models with pooled V. americana biomass (n = 30) and sediment nutrients were significant. Sediment phosphorus, copper, manganese, iron, ammonium, nitrate, magnesium potassium and sodium were all significantly related to pooled Chara sp. biomass (n = 30) Additional simple regression models using pooled summer and winter biomass also indicated that light, water temperature and epiphyte biomass had significant effects on the growth of the study species (Table 3-26). Mode l s relating pooled total biomass (n = 120) and biomass of N. guadalupensis and V. american a

PAGE 97

80 separately (n =30) suggested that total PAR (mol photons m2 per CP), mean instantaneous PAR (mol photons m2 s-1) and water temperature had a highly significant (p < .0001) effect on biomass production in all cases. None of the models with pooled Chara sp. biomass (n = 30) and pooled P. illinoensis biomass (n = 30) were significant. Stepwise multiple regression analyses conducted using pooled summer and winter macrophyte biomass as the dependent variable and the significant sediment nutrients and climatic factors identified using simple regression analyses as the independent variables indicated macrophyte growth in this study was affected by a ~ombination of factors. Total pooled biomass (n = 120) was most significantly affected by nitrate total PAR per culture period and ammonium (Table 3-27). The data indicated species-related differences in response to the independent variables. N guada/upensis and V americana biomass exhibited a strong positive relationship with water temperature. Water temperature explained almost 50% of the variation in N guadalupensis biomass and over 64% of the variation in V americana production. The results suggested that P illinoensis growth was positively correlated with sediment copper content and negatively correlated with sediment iron content. Collectively these two predictors explained over 44% of the variation in the biomass of this species. There was a significant positive relationship between Chara sp. growth and sediment phosphorus content. Discussion The results of the sediment survey conducted at the beginning of this study confirmed the hypothesis that that there would be spatial variation in the organic

PAGE 98

81 matter content of the littoral sediments in Lake Hollingsworth. Organic matter content in the sediment samples ranged from 0.38% to 39.18% (Table 3-1). Sediment pH values also ranged from 5.4 to 8.0. In their 1996 study of seven shallow productive Florida lakes including Lake Hollingsworth, Whitmore et al. identified the presence of highly variable sediment organic matter content. They attributed the lack of uniform organic buildup in their study lakes to frequent mixing, lack of thermal stratification and warm temperatures resulting in the breakdown of organic material. They identified three types of organic sediment distribution patterns: uniform distribution, distribution to deeper areas and distribution to peripheral areas and embayments where the type of distribution pattern greatly depends on lake bathymetry. The highly variable nature of organic sediment composition in their study lakes led these researchers to conclude that systematic sediment mapping surveys are necessary to characterize the sediments in shallow "wind-stressed" productive lakes such as Lake Hollingsworth The findings suggested the importance of beginning revegetation projects in Florida lakes with a preliminary investigation of sediment chemical composition The findings of the sediment survey conducted in this study made it possible to identify sites around the lake that were not only relatively protected from anthropogenic disturbance but that had organic matter contents that were not inhibitory to plant growth. Having this type of background information on a system should facilitate site selection for planting in revegetation projects. I believe that the study stations selected in this study should provide highly suitable habitat for the

PAGE 99

establishment of founder colonies (sensu Smart et al. 1996) of the study species in Lake Hollingsworth. 82 Analyses of sediment chemical composition corroborated the hypothesis that there would be spatial variation in the nutrient content of the littoral sediments in Lake Hollingsworth. The study sediments varied in pH, organic matter and nutrient content (Table 3-2). Natural sediments, with the exception of Site B sediments, were more alkaline than control sediments. Although organic matter contents were not available for the control sediments, low organic matter contents are typical for sand sediments. Therefore, even though the organic content of Site F sediments (1.08%) was significantly greater than that of the other natural sediments, the limited range of values made it difficult to identify any effects on macrophyte growth due to sediment organic content. Calcium content in Site F sediments was significantly greater than that of the other sediments (5617 mgK.t1). In my opinion, this value was high probably due to the presence of shell or pebble material in the analytical sample that was not thoroughly homogenized during processing. Control, Site F and Site H sediments all exhibited relatively high levels of phosphorus, zinc, copper, manganese and iron as compared with Site B and Site D sediments. Ammonium and nitrate were present in significantly greater amounts in the control sediments. Although there were significant differences in the content of some other nutrients in the sediments, i.e. potassium and magnesium, the literature indicates that these nutrients are primarily derived by submersed macrophytes from the water column (reviewed in Barko et al. 1991). Sutton (1990) observed similar chemical composition in sediments collected

PAGE 100

83 from Lake Okeechobee. Sediment nutrient analyses in his study were conducted using the same procedure as was used in this study. Light and temperature data gathered throughout the study indicated climatic variations among the culture periods. Highest average daily water temperature occurred during the summer culture period. Lowest water temperatures were observed during the winter. Despite low winter temperatures, average water temperatures were sufficient to meet the minimum requirement during each culture period for nutrient release by the Osmocote fertilizer used to amend the control sediments. Harbaugh and Wilfret (1981) determined that release rates of Osmocote are temperature-dependent and increase at temperatures above 21 C. Sutton and Latham (1996) measured minimum average water temperatures equal to or greater than 21 C during a growth study conducted at the FLREC using sand media amended with Osmocote. Based upon these water temperatures, they concluded that release rates remained high enough to maintain sufficient sediment concentrations of phosphorus, ammonium and nitrate during the winter culture period. Photoperiod was longest in spring and shortest in winter. Average PAR values showed a similar trend. These findings are probably best explained by the fact that partly cloudy days are the norm in South Florida Relatively lower average PAR values in summer compared to spring are probably due in part to afternoon thunderstorms that result in 100% cloud cover during parts of most summer afternoons. Biomass data collected in this study indicted that macrophyte growth and sediment nutrient content were positively related. Greatest biomass production occurred on control sediments probably due to the presence of significantly greater

PAGE 101

84 levels of ammonium and nitrate. Ammonium and nitrate were those sediment nutrients found to have the most significant impact on total macrophyte production in this study (Table 3-16). There are multiple examples in the literature in which nitrogen has been identified as one of if not the most probable factor controlling submersed macrophyte growth. For example, in their comparative growth study of Myriophyl/um spicatum and V americana americana, Titus and Adams (1979) reported that sediment nitrate content appeared to have a significant effect on the biomass production of Vallisneria. Studies conducted by Barko et al. (1988) and Barko et al. (1991) suggested that, although there is little evidence for limitation of SA V growth by sediment P, sediment nitrogen content may limit the growth of some submersed species. Squires and Lesack (2003) observed a positive relationship between macrophyte biomass and total sediment nitrogen in their study in several lakes in the Mackenzie Delta. The negative relationship observed in this stud y between ammonium and macrophyte biomass may indicate that ammonium was present in the control sediments at inhibitory levels for some or all of the study species. Another possible explanation is that sediment biochemistry in flooded soils affects the relationship between ammonium and macrophyte biomass production. Walstad (2003) observed cases in which ammonium levels were toxic to plant roots. She attributed this toxicity to bacterial metabolic processes that rapidly con v ert nitrates to toxic nitrites. Initially superior growth on higher density sand than on the finet extured lake sediments would appear to contradict the findings of several studies that h ave documented poor macrophyte growth on sand and hi ghl y or g anic sed i m e nts ( Sand-

PAGE 102

85 Jensen and Sondergaard 1979, Moeller 1983, Barko and Smart 1986). Barko and Smart (1986) concluded that sediment density or related factors regulate nutrient uptake by affecting nutrient diffusion distances. They concluded that nutrient uptake on low-density, high-porosity organic sediments was limited by long diffusion distances. They observed an increase in Hydrilla growth with increased sediment density. In the same study, they determined that Hydri/la and Myriophyllum grew best on fine-textured inorganic sediment. They observed that additions of fine-textured inorganic sediments to sediments previously determined to be unfavorable for SA V growth (i.e. organic and sandy sediments) resulted in improved macrophyte growth. Apparently, nutrient addition in the form of fertilizer was sufficient to meet the nutrient requirements of the study macrophytes. The control sediments had significantly higher levels of nutrients that encourage plant growth such as phosphorus and nitrogen as compared with the other sediments (Table 3-2). Sutton and Latham (1996) investigated soil porewater concentrations of sediment nutrients in sand media amended with Osmocote. They observed the following mean summer and winter phosphorus nitrate and ammonium values in the amended sediments after curing for 8 weeks: phosphorus-80 mg/L, 45 mg/L; nitrate -2125 mg/L, 1725 mg/L; ammonium-700 mg/L, 575 mg/L. These values are approximations of the data presented in Figure 1 of Sutton and Latham (1996). Growth on natural sediments also reflected the importance of sediment nutrient content. F and H were the best natural sediments for biomass production. These sediments contained relatively greater amounts of copper, zinc and phosphorus those nutrients found to be most significant to the growth of P illinoensis and Chara

PAGE 103

86 sp. in this study (Table 3-16). Barko and Smart (1986) concluded that the diminished macrophyte growth that they observed on organic sediments was due to multiple nutrient deficiency. In the same study, they observed that additions of phosphorus and a combination of phosphorus and iron to organic sediments had a significant positive effect on the growth of Hydrilla. Intuitively, we would expect that phosphorus would not be limiting in the phosphatic soils typical of the region, however, in his literature review of the effects of sediment nutrients on seagrasses, Short (1987) discussed the importance of the role of sediment geochemistry in plant nutrient-uptake from sediments. He cited the example of phosphorus limitation of plant growth in tropical environments and carbonate sediments due to binding of phosphorus in sediments. Biomass accumulation data collected in this study indicated that Station B sediments were the least suitable substrate for macrophyte growth. This trend was markedly more pronounced for the spring and summer culture periods while plants exhibited relatively improved growth on Station B sediments during the winter culture period. Initially, these results appear difficult to interpret given the fact that the chemical composition of Station B sediments was very similar to that of the other study sediments (Table 3-2). The major difference between the sediments was that Station B sediments were exposed due to drought conditions at the time of collection and subsequent subsample analysis. Perhaps the most plausible explanation is that oxidation of the sediments, in combination with low acidity (5.4), resulted in nutrient binding in the sediments making nutrients less available for plant uptake. Barko et al. (1988) reported a similar negative correlation between sediment oxidation and nutrient availability and plant growth. In contrast, Sutton (1990) observed improved

PAGE 104

87 growth of Hydrilla verticillata on dried sediments as compared with sediments maintained in the moist state prior to planting. The reasons for this discrepancy are not known. However, the observed increase in plant growth in Site B sediments in the winter culture period after sediments had been flooded appeared to confirm the explanation that soil nutrients were not as readily available for plant uptake in the oxidized sediments. The positive relationship between increasing sediment fertility and growth observed for all species contradicted my hypothesis that N guade/upensis, P. illinoensis and Chara sp., the canopy-forming, erect species, would produce greater biomass in sediments with higher nutrient levels while net growth of V. americana, a rosette species, would be inversely related to sediment nutrient content. The results obtained by pooling the biomass produced by the study plants during the summer and winter culture periods (n = 120) indicated that N guadalupensis and Chara sp grew best on control, Station F and Station H sediments. P illinoensis and V. americana produced greatest biomass on control and Station H sediments and control and Station D sediments, respectively. There is considerable documentation of the relationship between macrophyte life history and response to sediment fertility. Chambers (1987) observed a relationship between macrophyte growth form and sediment nutrient availability along a natural gradient in Lake Memphremagog. According to his findings, rosette and bottom-dwelling species grew better on less fertile soils while increasing fertility was associated with an increase in the growth of canopy-forming and erect species. In a competition study among seven aquatic macrophyte species, Wilson and Keddy (1986) observed that species with low competitive ability were

PAGE 105

typically found on nutrient-poor sites, while species with high competitive ability flourished on nutrient-rich sites. Perhaps the limited range of values investigated obscured the trends in this study that are documented in the literature. 88 Species-related responses to differences in sediment nutrient content are well documented in the literature. Denny (1972) observed a wide-range of responses in growth rate to sediment fertility among submersed macrophyte species. He concluded that these variations were due to anatomical and morphological differences among species investigated. Similar differences in species-specific responses to sediment fertility were observed in several studies by Barko and Smart (1980, 1981, 1986). Barko and Smart (1986) observed that Hydrilla was more sensitive to sediment nutrient composition as compared with Myriophyllum. Zimba et al. (1993) observed among species differences in the chemical composition of N guadalupensis, V. americana, P. illinoensis and Chara sp among the species. They concluded in the same study that plant tissue micronutrient concentrations, especially iron, copper and magnesium, were the most significant in the separation of N guadalupensis, V. americana, P. illinoensis and Chara sp. using discriminant analysis. Duarte and Kalff (1988) also reported species-specific differences in response to sediment nutrients in fertilization mesocosm studies. Barko et al. ( 1991) discussed the importance of species-specific macrophyte-sediment interactions in determining compositional changes in community composition over time. Evaluation of the root:shoot ratios supported the hypothesis that sediments collected from the littoral zone of Lake Hollingsworth would have sufficient quantities of sediment nutrients to support the growth of N guadalupensis, P

PAGE 106

89 illinoensis, V. americana and Chara sp. when grown in the experimental growth tanks used in this study. The root:shoot ratios of less than one observed for all species in response to all sediment types indicated that there was no sediment nutrient limitation of macrophyte growth in this study. High root:shoot ratios ( 1) are typically associated with submersed macrophytes growing in infertile environments (Aung 1974, Chapin 1980). Clarkson and Hanson (1980) identified this mechanism as a strategy for maximizing the volume of soil in contact with plant roots. Barko and Smart (1986) observed increasing root to shoot ratios with decreasing sediment fertility in Hydrilla and Myriophyllum. Denny (1972), Sand-Jensen and Sondergaard (1979) and Aioi (1980) observed a similar trend in other submersed species. Species-specific differences in root to shoot biomass production were consistent with the different life histories of the study species. As one might expect, the perennial species, P. illinoensis and V. americana, were characterized by significantly greater root:shoot ratios especially during the winter culture period as compared to the ruderal species, N guadalupensis. Resource allocation for the production of increased below-sediment biomass is a mechanism used by perennials to increase resistance to harsh environmental conditions i.e. those associated with winter conditions. The differences in macrophyte biomass accumulation observed among the culture periods confirmed the hypothesis that N guadalupensis V. americana and Chara sp. would produce the greatest biomass during the summer months while growth of P illinoensis, a species with a range distribution that stretches into more temperate regions, would be stimulated by the cooler temperatures of the winter

PAGE 107

90 months. Comparisons of the relative amounts of biomass produced by each species during each of the culture periods also indicated that, as hypothesized, N. guadalupensis was the fastest grower followed by P. illinoensis V americana and lastly, Chara sp. N. guadalupensis produced greatest biomass among the study species in the spring and summer culture periods (Figure 3-4 ). P illinoensis was the fastest growing species during the winter culture period. Within species comparisons indicated that N. guadalupensis and Chara sp. exhibited greatest summer growth. P. illinoensis grew equally well in the summer and winter culture periods. V americana growth was maximal in the summer culture period while spring and winter growth was similar. These results suggest that V americana competed more successfully with N. guadalupensis and P illinoensis during the summer culture period. Titus and Adams (1976) described V americana as a "summer specialist". I observed that Chara sp. was a slow starter when I was growing stock cultures of the study species. However, in time, Chara sp produced luxuriant growth and stable populations that, once established, have survived for several growing seasons. These observations would imply that, perhaps if culture periods had been longer, Chara sp. might have exhibited more competitive biomass production. Investigations of the effect of environmental factors on biomass accumulation in this study indicated that macrophyte growth in this study was significantly affected by a combination of climatic factors. Light had one of the most significant effects on pooled composite summer and winter biomass (n = 120) while water temperature explained almost 50% and 64.5% of the variation in N. guadalupensis and V americana biomass, respectively (Table 3-27). It should be noted that temperature

PAGE 108

91 effects in this study were probably more pronounced than they would be in a natural environment due to the small volume of water in the growth tank as compared to that of a lake. There are, however, numerous cases in the literature where a similar relationship between light and temperature and macrophyte production has been identified. In his literature review, Short (1987) cited the findings of multiple studies conducted over a wide range of geographical locations that suggested that the seasonal growth cycle of submersed macrophytes is determined by a combination of climatic factors including irradiance, photoperiod and temperature. Many studies have identified light as one of, if not the most, siwuficant factors affecting aquatic macrophyte growth (Canfield et al. 1985, Duarte and Kalff 1986, Barko et al. 1986, Smith and Barko 1990, Strand 1999). In their comparative study of Myriophyl/um spicatum and Val/isneria americana, Titus and Adams (1979) reported that, although both species exhibited similar carbon uptake rates and coexisted in the same Wisconsin lakes, low light availability resulted in morphological adaptations in M spicatum as a competitive mechanism. In a sediment fertilization study using sand rooting media amended with Osmocote and a second type of fertilizer, Sutton (1993) observed seasonal differences in Hydrilla growth. He attributed these differences in biomass produced during the fall and winter culture periods to the effects of water temperature on plant metabolic processes rather than on fertilizer nutrient release rates Dale (1986) observed that in the absence of a growth limiting sediment nutrient, species adaptations more commonly reflected the influences of light and temperature than the effects of sediment nutrient composition. He reported that, even in cases

PAGE 109

where there was sufficient water transparency, maximum depth of colonization was limited by water temperatures below the thermocline. 92 Macrophyte growth was al.so affected by epiphytic colonization. Generally greatest epiphyte biomass was observed on Chara sp. and N guada/upensis, the study species with a finely dissected leaf architecture. The most probable explanation for the fact that many of the graphical trends in the epiphyte data were not statistically different was due to the sampling protocol used. Since the epiphyte biomass data was to be used to calculate a correction factor for final macrophyte biomass the sampling protocol was designed to ensure that a representative estimate was made. Accordingly, epiphyte biomass samples were collected from a more mature, a mature and a young plant. This sampling regime resulted in high internal variation. This high variation may have masked relevant statistical trends. The sediment nutrient needs of the macrophytes also appeared to vary seasonally. Whereas no sediment nutrients were significant to N guada/upensis biomass accumulation in the spring and summer culture periods, zinc and phosphorus explained over 5 8% of the variation in macrophyte biomass in the winter culture period (Table 3-6) Chara sp. followed a similar pattern such that sediment nutrients only appeared to play a significant role in the winter culture period where sediment phosphorus explained almost 66% of the variation in biomass. Nutrient composition was also a more significant factor in V americana growth in the summer as compared to the other culture periods while sediment nutrients played a more significant role in P. illinoensis growth in the summer and winter culture periods. Copper was the most significant sediment nutrient for P. il/inoensis growth explaining 41 and 36% of the

PAGE 110

variation in biomass during the summer and winter culture periods, respectively (Table 3-6). 93 Field results indicated that there was a significant difference in the susceptibility of the study species to grazing by the larvae of Parapoynix diminutalis Snellen, an aquatic moth. Herbivore damage eliminated > 50% of above-sediment N. guadalupensis and P. illinoensis biomass while V. americana and Chara sp. appeared relatively unaffected. Painter and McCabe (1988) reported that herbivory by insect larvae can result in reductions of macrophyte root or shoot biomass ranging up to 100%. In his comprehensive literature review on herbivory on freshwater macrophytes, Lodge (1991) observed that grazing preference was negatively correlated with the phenolic content in plant tissues The yield of N. guadalupensis and P. illinoensis in all sediments during the spring culture period was probably underestimated due to the conservative approach taken to estimate the reduct ion in above-sediment biomass due to herbivory. (See the Materials and Methods section for a description of the method used to estimate ) Conclusions The results of this study provide init i al evidence that the sediments occurring at stations B, D, F and H in Lake Hollingsworth had sufficient quantities of sediment nutrients to support the growth of N. guadalupensis guadelupensis, Potamogeton illinoensis, Vallisn e r i a americana and Chara sp Field-testing of these results is necessary in order to determine the effect of such factors as sediment quantity on the applicability of these findings to the natural environment. The results of this investigation furth e r indicate that, although all species should grow year round late

PAGE 111

94 spring appears to be the optimum time in which to introduce propagules of N guada/upensis, P illinoensis, V americana and Chara sp. into restored systems. Submersed macrophyte growth in this study appeared to be significantly affected by a combination of factors including water temperature and sediment macroand micronutrients. Macrophyte growth response to climatic and sediment factors was species-related. However, additional investigation over a greater range of sediment organic matter contents nutrient levels and physical characteristics is necessary in order to further elucidate the growth requirements of submersed aquatic macrophytes

PAGE 112

Table 3-1: Organic matter content and pH of sediments (n=3) from the preliminary survey. Values presented are means followed by standard error. Analysis of variance using GLM procedures followed by Tukey's HSD procedure was used to identify differences among stations. Means within a column followed by the same letter are not "fi 1 d"ffi th 5 1 1 d. Tuk HSD P d s1gru 1cant IY 1 erent at e o eve accor mg to ey s roce ure. Station Organic Matter (%) pH I A 0.68 0.07 b 5.8 0.1 e I B 0.42 0.09 b 5.4.1 f C 0.45 0.05 b 6.3 0.1 cd D 0.38 0.05 b 6.5 0.1 C I E 39.18 1.7 a 6.1 0.1 de I F 1.08 0.10 b 8.0 0.0 a I G 34.96 .9 a 6.3 0.1 cd H 0.59 0.02 b 7b 95

PAGE 113

Table 3-2: Organic matter, pH and selected macroand micronutrient composition of sediments from the four study stations and control sediments. Each value is the mean of three 1 00g sub-samples of sediment from each sediment source followed bv the standard error. Analysis of variance using GLM procedures followed by Tukey's HSD procedure was used to identify differences among stations. Means within a column followed by the same letter are not significantly different at the 5% level according to Tukey's HSD Procedure. Sediment Source PH OM p NH4 N03 (%) (mg Kg-1 ) (mg Kg-1 ) (mg Kg-1 ) Station B 5.37 + 0.09 e 0.42 + 0.09 b 6.5 + 0.12 b 7.00 0.44 b 18.46 2.32 b Station D 6.53 + 0.13 be 0 39 + 0.05 b 3.73 + 0.35'b 6.19 0.20 b 16.24 0.64 b Station F 8.03 + 0.03 a 1.08 0.10 a 79.43 28.67ab 5 72 0.50 b 15.21 1.85 b Station H 7.00 + 0 b 0.59 + 0.02 b ll.9+1.12b 5.46 0.60 b 13.44 2.07 b Control 15g 6.00 + 0 ed NA 105.9 + ab 145.00 47.23 ab 558.92 186.26 ab Control40g 5.77 + 0.23 de NA 246.33 + 50.04 a 393.02 + 150.14 a 1600.71 648.15 a Sediment Source Fe Cu Mn Zn K (mg Kg-1 ) (mg Kg-1 ) (mg Kg-1 ) (mg Kg-1 ) (mg Kg-1 ) Station B 10.82 1.13 b 0.07 0.003 b 0.23 0.02 b 0.76 0.10 e 7 55 0.61 b Station D 5.74 0.79 b 0.04 0.003 b 0.20 0.04 b 0.40 0.02 e 3.63 0.27 b Station F 10.92 2.49 b 0.21 0.01 b 1.62 0.10 ab 7.77 0.19 a 10.47 0.75 b Station H 5.69 + 0.40 b 0.19 0.003 b 0.24 0.02 b 1.45 + 0.05 be 5.03 + 0.13 b Control 15g 58.53 8.08 a 0.90 + 0.28 b 2.57 + 1.38 ab 1.70 + 0.47 be 350.33 197.94 ab Control40g 72.5 10.01 a 2.64 0.68 .a 4.23 + 1.05 a 3.08 + 0.86 b 626.67 + 144.73 a Sediment Source M2 Ca Na Al er (mg Kg-1 ) (mg Kg-1 ) (mg Kg-1 ) (mg Kg-1 ) (mg Kg-1 ) Station B 15.5 0.70 b 73.93 2.20 b 11.0 0.56 b 36.03 + 3.51 ab 7.03 0.81 ab Station D 5.63 0.35 b 73.63 3.53 b 5.9 + 0.12 b 16.6 1.81 b 2.83 0.23 b Station F 52.3 3.36 ab 5616.67 + 259.63 a 14.5 + 0.31 ab 44.5 + 13.17 a 3.30 + 0.40 b Station H 10.93 + 0.49 b 126.1 24.49 b 7.13 + 0.22 b 31.63 + 0.63 ab 3.97 + 0.38 b Control 15g 46.97 + 24.18 ab 154.67 15.59 b 18.67 + 6.59 ab 18.1 +0.79ab 6.80 1.92 ab Control40g 77.63 19.23 a 206 + 30.14 b 29.6 + 6.01 a 21.67 + 2.22 ab 18.23 0.75 a \0 O'I

PAGE 114

Table 3-3: Temperature and irradiance during the three culture periods. Temperature values are average daily temperatures followed heses are the lowest and highest measured temoeratures for each culture oeriod _._ -----------------------Culture Period (CP) Water Temperature Total PAR3 Mean Instantaneous Mean Period (OC) (mol photons m2 PAR3 Photoperiod (days) oer CP) (mol ohotons s1m2 ) (hours) Spring 26.6 0.3b 2.44 X lQYD 806b 13.8L:10.2D 61 4/30 to 6/29/01 b (20-33.5t 1.83 X 109c (2-2306) 47c 5/14 tO 6/29/01 C 27.3 0.3c 783c (20-33.5/ (2-2302) Summer 29.6 0.2 2 24 x l0Y 742 13.lL:10.9D 64 7/20/ to 9/21/01 (20-34) (2-2153) Winter 21.2 0.3 1.63 X lQY 624 11.0L:13.0D 66 12/19/01 to 2/22/02 (11-30) (2-1863) 3Photosynthetically active radiation. b These values apply to Najas, Vallisneria and Chara. The discrepancy in PAR values and length of culture periods among the study species was caused by the lack of availability of viable propagule material at the initial time of planting. This resulted in a two-week delay in planting time for Potamogeton as compared with the other species. c These values apply to Potamogeton. Table 3-4: Spring Culture Period-30 April to 29 June 2001. Results of analysis of variance using GLM Procedure (SAS Institute 1999-2001) to investigate the effect of sediment source plant type and the interaction between these two factors on macrophyte h Source DF Type III SS Mean Square F-value Pr>F Sediment source (S) 4 122.3145657 30.5786414 1.70 0.1708 Plant type (PT) 3 577 .13334529 192.3778176 10.68 <.0001 S*PT 12 221.6270488 18.4689207 1.03 0.4467 \0 -.)

PAGE 115

98 Table 3-5. Spring Culture Period 30 April to 29 June 2001. Dry weight of study macrophytes cultured on sediments collected from the four study stations in Lake Hollingsworth and on artificial sediments. Values for each species are the mean biomass for three pots. The standard error follows the mean. Shoot biomass represents all above sediment biomass including some rhizome and adventitious root material. Root biomass represents all below-sediment biomass and includes some rhizome material. Means for a given sediment source followed by the same lowercase letters are not significantly different (a= 0.05). Sediment Plant Type Dry Weight source (g) Shoot Root Shoot+Root Mean Root:Shoot Station B Najas 9.6 1.2 2.7 0.7 12.3 1.8 a 0.28 0.04 Potamogeton 8.0.0 1.4 0.3 9.4 2.3 ab 0.18 0.01 Vallisneria 1.6 0.4 0.7 0.2 2.3 0.5 b 0.44 0.07 Chara 4.1 0.5 NA 4.1 0.5 ab NA Station D Najas 13.2 3.2 1.1 0.5 14.3 3.7 a 0.08 0.01 Potamogeton 5.0 0.5 1.0 0.7 6.0.1 a 0.20 0.02 Vallisneria 5.1 .4 1.7 0.6 6.8 3.0 a 0.37 0.04 Chara 9.7_.0 NA 9.7 .0a NA Station F Najas 11.3 1.9 1.1 0.3 12.4 2.2 a 0.10 0.02 Potamogeton 8.5 1.5 1.4 0.3 9.9.5a 0.16 0.05 Vallisneria 4.3 0.4 1.5 1.0 5.8 1.4 a 0.35 0.20 Chara 12.4 4.5 NA 12.4 4.5 a NA Station H Najas 9.7 .6 1.3 0.1 11.0 0.8 a 0.13 0.003 Potamogeton 6.9 0.03 1.4 0.1 8.3 0.1 ab 0.20 0.02 Vallisneria 3.3 0.4 1.2 0.1 4.5 .6 b 0.36 0.03 Chara 12.2 NA 12.2 a NA Control Najas 14.2 4.2 2.2 0.6 16.4 4.7 a 0.15 0.01 408 Potamogeton 7.4 0.8 0.8 0.1 8.2 0.8 a 0.11 0.02 Control Vallisneria 3.8 1.6 0.7 0.1 4.5 1.6 a 0.18 0.12 15 Chara 16.9 4.5 NA 16.9 4.5a NA a Control 40 sediments were composed of washed builder s sand amended with 40 g of 15-9-12 Osmocote Plus. b Control 15 sediments were composed of washed builder's sand amended with 15 g of 15-9-12 Osmocote Plus.

PAGE 116

Table 3 -6: Stepwise multiple regression analysis results using macrophyte bi o mass for each species during each culture period as the dependent variable and sediment macroand micronutrient concentrations (mgKf1 ) and epiphyte biomass as the independent Culture Period Dependent Independent variables found Significant independent Cumulative R1 F value Prob.> F variables to be significant in simple variables regression analyses (a= o.o5t Spring Composite NS0 biomass of all species Najas biomass NS0 -------Potamogeton Al 0.1214 Al 29.10 5.33c 0.0380(1 biomass Val/isneria NSb -----biomass Chara bi o mass NS0 -------Summer Composite P, Cu, Mn, Al, Fe, NH4, 68.058 5 Cu 22.14 16.2 0 0.0 00 2 biomass of all NO3, epiphyte biomass -0.3892 NH4 30.03 6.31 0.0149 species Najas biomass NS0 ------Potamogeton P, Cu, Mn, Fe, N~, NO3, 9.3042 Cu 41.15 9.09 0.0100 biomass Vallisneria Cu, Al, Fe, ~. NO3 -0.7420 Al 47.55 11.79 0.0044 biomass Chara biomass Epiphyte biomass -1.3205 Epiphyte biomass 41.44 8.06c 0.0130 \0 \0

PAGE 117

Table 3-6: Continued Culture Period Dependent Independent variables Significant independent Cumulative R.i F value Prob.> F variables found to be significant in variables simple regression analyses (a= 0.05)a Winter Composite P, Cu, Mn, Fe, NH4 NO3 68.0585 Cu 22.14 16.20 0.0002 biomass of all -0.3892 N~ 30.03 6.31 0.0149 species Najas biomass P Zn, Mn 2.5794 Zn 47.80 10.99 0.0062 0.0457 P 58.11 2.71 0.1280 Potamogeton P, Cu, Fe, N~, NO3 6.9493 Cu 35.75 7.23 0.0186 biomass Vallisneria NSb ------biomass Chara biomass P, Cu, Mn, Fe,~. NO3 0.0749 P 65.53 24.71 0.0003 a These independent variables were identified as significant in simple regression models with macrophyte biomass. Although other nutrients may have been significant factors, only those sediment nutrients known from the literature to be derived from the sediment were included in these multiple regression analyses. Values for sediment nutrients were mean values measured in subsamples of each sediment type taken during the sediment survey study. bNo independent variables were identified in initial investigations using simple regression models. ct-value dP>ltl ..... 0 0

PAGE 118

Table 3-7: Spring Culture Period-30 April to 29 June 2001. Results of analysis of variance using GLM Procedure (SAS Institute 1999-2001) to investigate the effect of sediment source, plant type and the interaction between tthese two factors on macrophyte root:shoot ratios. Source DF Type III SS Mean Square F-value Pr>F Sediment source (S) 4 0.07920971 0.01980243 1.79 0.1574 Plant type (PT) 2 0.41140822 0.20570411 18.62 <.0001 S*PT 8 0 06583398 0.00822925 0.74 0.6522 Table 3-8: Summer Culture Period-20 July to 21 September 2001. Results of analysis of variance using GLM Procedure (SAS Institute 1999-2001) to investigate the effect of sediment source, plant type and the interaction between these two factors on hvte b' Source DF Type III SS Mean Square F-value Pr>F Sedimentsource(S) 4 3377.848571 844.462143 9.33 <.0001 Plant type (PT) 3 7062.072762 2354.024254 26.02 <.0001 S*PT 12 980.133679 81.677807 0.90 0.5525 -0 -

PAGE 119

102 Table 3-9. Summer Culture Period-20 July to 21 September 2001. Dry weight of study macrophytes cultured on sediments collected from the four study stations in Lake Hollingsworth and on artificial sediments. Values presented for each species are the mean biomass for three pots. The standard error follows the mean Shoot biomass represents all above-sediment biomass including some rhizome and adventitious root material. Root biomass represents all below-sediment biomass and includes some rhizome material. Means for a given sediment source followed by the same lowercase letters are not significantly different ( a = 0.05). Sediment Plant Type Dry Weight Source (g) Shoot Root Shoot+Root Mean Root:Shoot Station B Najas 32.9 4.0 2.9 0.3 35.8 3.7 a 0.09 0.02 Potamogeton 17.1 1.2 3.5 0.3 20.6 0.9 ab 0.21 0.03 Vallisneria 15.0 1.9 3.6 .2 18.6 2.1 b 0.25 0.02 Chara 3.8 1.6 NA 3.8 1.6 C NA Station D Najas 47.0 9.5 5.1 0.7 52.1 9.0 a 0.12 0.04 Potamogeton 27.5 4 1 3.5 0.3 31.0 4.3 ab 0.13 0.01 Val/isneria 35.4 6.6 5.6 I.I 41.0 6 6 ab 0.17 0.04 Chara 17.4 4.5 NA 17.4 4.5 b NA Station F Najas 48.9 3.4 4.0 0.4 52.9 3.3 a 0.08 0.01 Potamogeton 25.4 4.5 3.4 0.7 28.8 4.3 b 0.14 0 .01 Vallisneria 23 9 1.9 4.1 0.4 28.0 1.9 b 0.17 0.02 Chara 20.0 2.3 NA 20.0 2.3 b NA Station H Najas 34 8 4.2 6.1 1.4 40.9 2.8 a 0.19 0.07 Potamogeton 28.8 4.1 3.3 0.2 32 1 4.2 ab 0.12 0.02 Vallisneria 19.5 3.8 4.7 0 8 24.2 .6 b 0.24 0.01 Chara 19.0 2.0 NA 19.0 2.0 b NA Control Najas 49.8 7.7 6.7 0.3 56.5 7.9 a 0.14 0.02 40a Potamogeton 46.0 13.7 5.2 1.4 51.2 15.0 a 0.12 0.01 Control Vallisneria 37.4 5 3 7.0 1.9 44.4 3.5 a 0.21 0.09 }5 Chara 21.0 4.0 NA 21.0.0a NA a Control 40 sediments were composed of washed builder s sand amended with 40 g of 15-9-12 Osmocote Plus. b Control 15 sediments were composed of washed builder s sand amended with 15 g of 15-9-12 Osmocote Plus.

PAGE 120

Table 3-10: Summer Culture Period -20 July to 21 September 2001. Results of analysis of variance using GLM Procedure (SAS Institute 1999-2001) to investigate the effect of sediment source, plant type and the interaction of these two factors on macrophyte root:shoot ratios. Source DF Type III SS Mean Square F-value Pr>F Sediment source (S) 4 0.020748 0.005187 1.26 0.3084 Plant type (PT) 2 0.057243 0.028622 6.94 0.0033 S*PT 8 0.036890 0.004611 1.12 0.3797 Table 3-11: Winter Culture Period-19 December 2001 to 22 February 2002. Results of analysis of variance using GLM Procedure (SAS Institute 1999-2001) to investigate the effect of sediment source plant type and the interaction between these two factors on J Source DF Tvoe III SS Mean Square F-value Pr>F Sediment source (S) 4 1457.814725 3 64.453681 6.57 0.0004 Plant type (PT) 3 6163.120948 2054.373649 37.04 <.0001 S*PT 12 1398.410282 116.534190 2.10 0.0402 0 v.>

PAGE 121

104 Table 3-12. Winter Culture Period -19 December 2001 to 22 February 2002. Dry weight of study niacrophytes cultured on sediments collected from the four study stations in Lake Hollingsworth and on artificial sediments. Values presented for each species are the mean biomass for three pots The standard error follows the mean. Shoot biomass represents all above-sediment biomass including some rhizome and adventitious root material. Root biomass represents all below-sediment biomass and includes some rhizome material. Means for a given sediment source followed by the same lowercase letters are not significantly different ( a = 0.05). Sediment Plant Type Dry Source Weight (g) Shoot Root Shoot+Root Mean Root:Shoot Station B Najas 12.6 1.8 1.2 0.2 13.8 1.9 b 0.10 0.005 Potamogeton 21.3 1.4 6.1 0.8 27.4 2.0 a 0.29 0.03 Vallisneria 6.0 0.9 1.3 0.2 7.3 I.Ob 0.22 0.04 Chara 8.2 0.8 NA 8.2 0.8 b NA Station D Najas 9.8 3.1 1.1 0.1 10.9 3.2 b 0.11 0.05 Potamogeton 25.7 0.3 5.4 0.2 31.1 .4a 0.21 0.004 Val/isneria 6.1 1.3 1.3 0.3 7.4 1.6 b 0.21 0.02 Chara 7.3 1.2 NA 7.3 1.2 b NA Station F Najas 33.4 8.8 2.6 0.7 36.0 9.5 a 0.08 0.009 Potamogeton 21.2 4.1 6.1 1.7 27.3 5.7 a 0.29 0.03 Vallisneria 7.3 1.3 1.1 0.6 8.4 1.9 a 0.15 0.05 Chara 13.2 .7 NA 13.2 4.7 a NA Station H Najas 23.8 7.0 1.6 0.1 25.4 6.9 ab 0.07 0.03 Potamogeton 32.3 4.8 5.4 0.4 37.7 4.4 a 0.17 0.05 Vallisneria 9.7 1.1 3.2 1.2 12.9 1.4 b 0.33 0.14 Chara 10.5 1.9 NA 10.5 1.9 NA Control 408 Najas 29.7 1.8 2.6 0.8 32.3 2.5 ab 0.09 0.02 Potamogeton 41.9 10.4 6.3 1.1 48.2 11.6 a 0.15 0.01 Control 15b Vallisneria 5.8 1.8 0.9 0.03 6.7 1.9 C 0.16 0 06 Chara 21.3 1.5 NA 21.3 1.5 ab NA a Control 40 sediments were composed of washed builder s sand amended with 40 g of 15-9-12 Osmocote Plus. b Control 15 sediments were composed of washed builder's sand amended with 15 g of 15-9-12 Osmocote Plus.

PAGE 122

Table 3-13: Winter Culture Period -19 December 200 I to 22 February 2002. Results of analysis of variance using GLM Procedure (SAS Institute 1999-2001) to investigate the effect of sediment source plant type and the interaction between these two factors on .l.1.1.U'-'.1.Vt.J.l.lJ \.'-' .1.VV\.e.JIJ..IVVI. .1.L,1,\..1.VtJe Source DF Type III SS Mean Sauare F-value Pr>F -Sediment Source 4 0.021118 0.005279 0.73 0.5772 (SS) Plant type (PT) 2 0.148970 0 074485 10.33 0.0004 SS*PT 8 0.091293 0.011412 1.58 0.1731 Table 3-14: Results of analysis of variance using GLM Procedure (SAS Institute 1999-2001) of pooled total macrophyte biomass of all species combined produced during the summer and winter culture periods (n = 120) to investigate the effect of culture period, diment source. olant tvoe and the interaction between the fi -J Source DF Type III SS Mean Square F-value Pr>F Culture period (CP) I 4368.353429 4368.353429 59.97 <.0001 Sediment source (S) 4 3935.090475 983.772619 13.50 <.0001 Plant type (PT) 3 9420.311571 3140.103857 43.11 <.0001 C:P*S 4 971.075191 242.768798 3.33 0.0142 CP*PT 3 3762.750644 1254.250215 17.22 <.0001 S*PT 12 1483 .280431 123.606703 1.70 0.0835 CP*S*PT 12 877 638647 73.136554 1.00 0.4535 -0 Vl

PAGE 123

106 T a ble 3-15: Differences among the study species in the pooled mean biomass produced during the summer and winter culture periods (n=24) determined using Tukey's HSD Test. Sediment Source Macrophyte Mean Biomass (g DWT) Tukey Grouping Stati o n B N f!Uadelupensis 24. 80 A P illinoensis 24.04 A V. americana 12 93 AB Chara sp. 6.42 B Station D N f!Uade/upensis 31.47 A P illinoensis 31.05 A I V. americana 24.23 A Charasp. 12.37 A I Station F N guade/upensis 44.43 A P. illinoensis 27.25 B V. americana 18.18 B Charasp. 16.58 B Stati o n H P illinoensis 34.92 A N f!Uade/upensis 34.71 A V. americana 18.57 B Chara sp. 14.75 B I Control 40a P. illinoensis 49.7 A N f!Uade/upensis 44.4 AB Control 15 V. americana 25.5 AB Charasp. 21.1 B a Control 40 sediments were composed of washed builder's sand amended with 40 g of 15-9-12 Osmocote Plus b Control 15 sediments were composed of washed builder's sand amended with 15 g of 15-9 12 Osmocote Plus.

PAGE 124

107 Table 3-16: Differences within the study species in the pooled mean biomass produced during the summer and winter culture periods (n=30) determined using Tukey's HSD Test. Macrophyte Sediment source Mean Biomass (g DWT) Tukey Grouping N guadelupensis Station F 44.43 A Control 40a 44.40 A Station H 34 .71 A Station D 31.47 A I Station B 24.80 A I I P illinoensis Control 40a 49.70 A Station H 34.91 AB Station D 31.05 B Station F 27.25 B Station B 24.06 B V. americana Control 15 25.52 A Station D 24.23 A Station H 18.57 A I Station F 18.18 A I Station B 12.93 A I Charasp. Control 15 21.14 A Station F 16.58 AB Station H 14.75 AB I Station D 12.37 AB I Station B 6.42 B a Control 40 sediments were composed of washed builder s sand amended with 40 g of 15-9-12 Osmocote Plus. b Control 15 sediments were composed of washed builder s sand amended with IS g of 15-9-12 Osmocote Plus.

PAGE 125

108 Table 3-17: Results of analysis of variance using GLM Procedure (SAS Institute 19992001) of pooled macrophyte root:shoot rati o s from the summer and winter culture periods (n = 90) to investigate the effect of culture period, sediment source, plant type and the interac t ion between the factors. Source DF Type III SS Mean Square F-value Pr>F Culture period (CP) 1 0.0095 8 9 0.009589 1.70 0.1973 Sediment source (S) 4 0.032 6 64 0.008166 1.45 0.2297 Plant type CPn 2 0.165277 0.082638 14.65 <.0001 CP*S 4 0.008985 0.002246 0.40 0.8091 CP*PT 2 0.044910 0.022455 3.98 0.0239 S*PT 8 0.091688 0.011461 2.03 0.0579 CP*S*PT 8 0. 036163 0.004520 0.80 0.6037 Table 3-18: Differences in the pooled mean root:shoot ratios (n=l8) among the study d t d Tuk HSD T species e emune usmg ey s est. Sediment Source Macrophyte Mean Root:Shoot Ratio Tukey Grouping Station B P. illinoensis 0. 2491 A V. americana 0 .2338 A I N. J.rUadelupensis 0.0956 B I I Station D V. americana 0.1947 A P. illinoensis 0 1704 A N. guadelupensis 0.1307 A Station F P. illinoensis 0.2094 A I V. americana 0.1527 AB I I N. guadelupensis 0 .0809 B I Station H V. americana 0.2912 A P. illinoensis 0.1499 A I N. J.r1,1adelupensis 0.1454 A l I Control 158 V. americana 0.2006 A Control 40 P. illinoensis 0.1404 A I N. J.r1,1adelupensis 0.1134 A 8 Control 15 sediments were composed of washed builder's sand amended with 15 g of 15-9-12 Osmocote Plus. b Control 40 sediments were composed of washed builder's sand amended with 40 g of 15-9-12 Osmocote Plus

PAGE 126

109 Table 3-19: Differences within macrophyte species in the pooled mean root:shoot ratios produced during the summer and winter culture periods (n=30) determined using Tu.key's HSD Test. Macrophyte Sediment source Mean Root:Shoot Ratio Tukey Grouping N. f?uade/upensis Station H 0.1454 A Station D 0.1307 A I Control 40a 0.1134 A Station B 0.0956 A Station F 0.0809 A I I P. illinoensis Station B 0.2491 A Station F 0.2094 AB Station D 0.1704 AB Station H 0.1499 AB Control 40a 0 1404 B I I V americana Station H 0 2912 A I Station B 0.2338 A I Control 15 0.2006 A Station D 0.1947 A Station F 0.1527 A a Control 40 sediments were composed of washed builder s sand amended with 40 g of 15-9-12 Osmocote Plus. b Control 15 sediments were composed of washed builder's sand amended with 15 g of 15-9-12 Osmocote Plus. Table 3-20 : Results of analysis of variance using GLM Procedure (SAS Institute 19992001) of pooled epiphyte biomass from the summer and winter culture periods (n = 120) to investigate the effect of culture period, sediment source plant type and the interaction between the factors Source DF Type III SS Mean Square F-value Pr>F Culture period (CP) 1 8948 2605 8948.2605 36.78 <.0001 Sedimentsource(S) 4 1096.6994 274.1748 1.13 0.3501 Plant type (PT) 3 655.1598 218.3866 0.90 0.4464 CP*S 4 1402.4206 350.6052 1.44 0.2286 CP*PT 3 239.8873 79.9624 0.33 0.8046 S*PT 12 4006.0660 333.8388 1.37 0.1979 CP*S*PT 12 4760.6347 396 7196 1.63 0.1008

PAGE 127

110 Table 3-21: Differences in pooled mean epiphyte biomass occurring in the summer and winter culture periods (n=30). Means separation was performed using Tukey's HSD Test. Macrophyte Culture period Epiphyte biomass Tukey Group Pr>F (mg/g host DWT) Chara sp Winter 23.540 A 0.0067 Summer 5.822 B N guadelupensis Winter 25.175 A <.0001 Summer 2.485 B P illinoensis Winter 19.654 A 0.0320 Summer 3.427 B V americana Winter 15.983 A 0.0236 Summer 1.280 B l

PAGE 128

Table 3-22: Differences in pooled mean epiphyte biomass occurring on each host macrophyte species in each sediment type (n=l 8) in the summer and winter culture d M t d Tuk HSD T t peno. eans were separa e USlll ey s es. 111 Sediment Macrophyte Epiphyte Biomass (mg/g DWT) Tukey Grouping Source Station B Chara sp. 17.84 A I P. illinoensis 12.43 A l N. guadelupensis 11.13 A I V. americana 3.86 A Station D Chara sp. 22.18 A I N. guadelupensis 14.90 A V. americana 8.98 A P. illinoensis 4.59 A I Station F Chara sp. 10.08 A N. guadelupensis 8.88 A V. americana 7.40 A P. illinoensis 7.00 A Station H P illinoensis 28.06 A N. guadelupensis 11.07 A I Chara sp. 8.15 A I V. americana 4.77 A I Control 408 N. guadelupensis 23.31 A P. i/linoensis 5.62 A I Control 15 V. americana 21.12 A I Chara sp. 17.15 A a Control 40 sediments were composed of washed builder's sand amended with 40 g of 15-9-12 Osmocote Plus. b Control 15 sediments were composed of washed builder's sand amended with 15 g of 15-9-12 Osmocote Plus.

PAGE 129

112 Table 3-23: Differences in mean pooled epiphyte biomass (n=30) occurring on each host macrophyte species in the swnmer and winter culture periods at the study stations. Means t d Tuk HSD T t were separa e usmg ey s es. Macrophyte Station Epiphyte Biomass Tukey Group Pr>F (mg/ghost DWT) Chara sp. Station D 22 1 8 A 0 6925 Station B 17.84 A Control 158 17.15 A Station F 10.08 A Station H 8.15 A N. guadelupensis Control 40b 23.31 A 0.6615 Station D 14.90 A Station B 11.13 A Station H 11.07 A Station F 8.88 A P. illinoensis Station H 28.06 A 0.2824 Station B 12.43 A Station F 7.00 A I Control 40b 5.62 A Station D 4.59 A V. americana Control 158 21.12 A 0 4478 Station D 8.98 A Station H 4.77 A Station F 4.44 A : Station B 3.86 A 8 Control 15 sediments were composed of washed builder's sand amended with 15 g of 15-9-12 Osmocote Plus. b Control 40 sediments were composed of washed builder s sand amended with 40 g of 15-9-12 Osmocote Plus

PAGE 130

Table 3-24: Differences in mean epiphyte biomass (n=60) occurring at each station during the summer and winter culture periods. Means seoaration was done usimz: Tukev's HSD T --. -~ ----., ---Culture period Sediment source Epiphyte Biomass Tu.key Group P r>F (mg.lg host DWT) Summer Station B 5 39 A 0 1715 Control 158 and Control 40 3.17 A Station F 2.85 A Station H 2.76 A Station D 2.12 A Winter Control 158 and Control 40 30.43 A 0.3166 Station H 23.61 A Station D 23.21 A Station B 16.21 A Station F 11.85 A a Control 15 sediments were composed of washed builder's sand amended with 15 g of 15-9-12 Osmocote Plus. b Control 40 sediments were composed of washed builder's sand amended with 40 g of 15-9-12 Osmocote Plus Table 3-25: Results of the use of simple regression analysis to evaluate the relative significance of each sediment characterist i c on the pooled mean biomass of all species combined (total) (n = 120) and each individual species (n = 30) during the summer and win ter culture periods. Those characteristics that were found to have a significant effect are indica ted with X. Highly s i gnificant _,_ ----J--------------.,-Plant pH OM p Zn Cu Mn Al Fe NH4 NO3 Ca Mg K Na C l Composite X+ X+ X Najas X Pot X X X X X X X X X X X Val Chara X X X X X X X X X _. _. w

PAGE 131

Table 3-26: Results of the use of simple regression analysis to evaluate the relative significance of light and water temperature on the pooled mean biomass of all species (n = 120) and each individual species (n = 30) during the summer and winter culture periods. Those characteristics that were found to have a significant effect are indicated with X. Highly significant characteristics (P <.0001) are denoted bv X Plant Epiphyte Biomass Total PAR Mean Instantaneous Water Temperature (mg/ghost DWT) PAR (umol photons m2 CP"1 ) (umol photons s1 m"2 ) (OC) Composite biomass of X X+ X+ X+ all species Najas X X+ X+ X+ Potamof!eton Vallisneria X+ X+ X+ Chara --.,:..

PAGE 132

Table 3-27: Stepwise multiple regression analysis results using pooled macrophyte biomass produced during the summer and wi nter culture periods (n = 120) for composite biomass of all species and n = 30 for each individual species). Macrophyte biomass w as used as the dependent variable and sediment macroand micronutrient concentrations, light, water temperature and epiphyte biomass ( mg/g .._.._,.,_,.., ......, -.,,-..... I_._, -.-.-.... ._.._ __ ...,_._ .. __ ..a ____ ... _.., \'-............ ,. Dependent Independent variables found Significant independent Cumulative R F value Prob.> F variables to be significant in simple variables regression analyses (a.= 0.05)8 Composite NH4, NO3, total PAR\ 0.3540 NO3 18.36 25.63 <.000 1 biomass of all PAR c, water temperature, 2.00lE-8 total PAR 32.83 24.35 <.0001 species epiphyte biomass -1.3880 35.48 4.60 0.0340 Najas biomass PAR, total PAR, water 2.8953 Water temperature 48.69 23.73 < 000 1 temperature, epiphyte biomass Potamogeton P, Cu, Mn, Al, Fe NH4 39.0962 Cu 38.04 17 19 0.0003 biomass NO3 -1.2241 Fe 44.44 3.11 0 0891 Vallisneria PAR, total PAR, water 2.7015 Water temperature 64.52 50.91 <.0001 biomass temperature Chara biomass P Cu, Mn, Fe, N~, NO3, 0.0597 P 31.17 12.23 0.0016 a These independent variables were identified as significant in simple regression models with macrophyte biomass. Although other nutrients may have been significant factors, only those sediment nutrients known from the literature to be derived from the sed iment were included in these multiple regression analyses. These independent variables were previously identified as significant in simple regression models with macrophyte biomass. Values for sediment nutrients were mean values measured in subsamples of each sediment type taken during the sediment survey study. b total PAR per culture period (mol photons m 2 per CP) c mean instantaneous PAR during each culture period (mol photons s1 m2 ) -Vl

PAGE 133

E Belmar St 0.2 Lk Hollingsws:o~rt:h~D~r=:===::::::=::::::-:;;:.==~~ -__ ~. 0 H 0.2 A 0.4 0.6 B 0 8 miles Figure 3-1: Map of Lake Hollingsworth showing the location of the preliminary sediment survey stations. Stations B D, F and H were selected as the study stations for further investigation. ...... ...... O'I

PAGE 134

Sediment Suitability Study 6 sediment types: B, D, F, H, Control 40 and Control 15 4 plant types* triplicate samples per sediment type= 12 pots 60 pots divided equally between 2 tanks H20 IN c=) 3 culture periods 00000000 0000000 00000000 0000000 H20 OUT I > Figure 3-2: A diagrammatic sketch of the distribution of7. 6-L nursery containers in the experimental tanks Containers were arranged at random Pots were divided to ensure representative distribution of combinations of macrophyte species and sediments between the tanks. ---..J

PAGE 135

--~ 8."" 20 .. C, '-------;;;;;;;;-------c 15 -,..._ t t 10 t-B--:I J: -Ill>;; e 5 1 ~.. tNil t' 1 o I ~"'I ro;, Q B D F H Co40 Sediment source m Estimated lo ss &I Actual a 20 g_~ i I 15 ~=-----1mr,m,-mm I ~.. I "'"" .__ .. 10 --::, ... -111>;; e 5 ~.. t-101.w Q B D F H Co4 0 Srdimrnt sourer 13'1 Esti m ated loss C5I A c tual b Figure 3-3: Biomass produced by Najas and Potamogeton during the spring culture period. Bars represent the mean value determined for three culture containers per plant type. The lower portion of each bar rep r esents t he measured values The upper portion of each bar represents the calculated biomass lost to herbi v ory ...... ...... 00

PAGE 136

i 10I==============j i ',:I 60 r=----------=J 8. 8. 40 .. ~ 50 l-------=i 3 t 30 a m Naj as a Potamogeton 11:1 Vall i sneria .. 8. 70 i o,:i 6 0 ab ._ ~ 50 8. 8. 40 ~ -lll1~1lf:b1~1I I I _ _Jffi_1 I 3 t 3 0 -I-IIJ.--::---lllllt.11Peo-i1ts1L -:I ft ~.::: 20 .; e Io .im~'-111:::m, 0 a Chara -:I .::: 2 0 ~l l lllil ~ lllll~-Jll!Rllil8111 .. e 1 0 0 Q B D F H Co40 Col5 Q B D F H Co4 0 Col5 Sediment source a .. 8. 10,--------i o,:i 60 .. c:, 8. c 5 0 ---8. 40 r----.-----7b-----.1if-~i--= ::' = 3 0 f.T~~il~~,19----il--__J -;.,.::: 20 'i e IO ~fa".----::f...-~11~~~.-llll--~ 0 Q B D F H Co40 Col5 Sediment source Sediment source D Najas l!I Potamogeton a Vallisneria m Chara C D Najas Ill Potamogeton 11:1 Vallisneri a m Chara b Figure 3-4: A comparison of the mean biomass produced by each plant species when grown in sediments from stations B D F and Hand controls for each of the three culture periods. Control sediments designated as Co40 and Col 5, were amended with 40 g and 15 g of Osmocote fertilizer respectively. Biomass values represent the mean value determined for three culture containers per plant type Bars are the standard error. Means for a given species with the same lowercase letters above them are not significantly different. a) Spring culture period 4 / 30 /01 to 6 / 29/01 Biomass for Najas and Potamogeton are estimated values corrected for loss to herbivory. b) Summer culture period 7/20/01 to 9/21/01. c) Winter culture period 12 / 19 /01 to 2/22 / 02. ..... ..... \0

PAGE 137

i 120 .. "Cl &, -~ 100 m Najas &. ... .. Q, = 80 60 l!I Potamogeton a Vallisner i a !.,, 120 I &. ~ 100 ------:;:::-----A....----___J1 H!~aJIJmiJam ii !IS Potamogeton a Vallisne ria ... -0 -; 40 ..... 11 : 20 E c. 0 = z 8 D F H Co40 Col5 Sediment source i 120 .. "Cl &, -~ 100 &. 80 .... "!.; 60 ... -0 -; 40 ..... J .. 20 a &. 0 = z C Chara B D a J '" 20 E &, 0 = z F H C o 4 0 Col5 Sediment s ource 8 D F H Co40 Col5 Sediment source ga Potamogeton a Vallisneria C Figure 3-5: A comparison of the average number of individual plants produced by each species when grown in the six sediments. Control sediments designated as Co40 and Col 5, were amended with 40 g and 15 g of Osmocote fertilizer respectively. Values are means of three culture containers per macrophyte species per sediment type. Bars are the standard error. Means for a given species with the same lowercase letters above them are not significantly different. a) Spring culture period 4/30/01 to 6/29/01. Average Najas and Potamogeton values may be underestimated due to stem loss resulting from herbivore activity b) Summer culture period 7/20/01 to 9/21/01. c) Winter culture period 12/19/01 to 2/22/02. b -N 0

PAGE 138

1 0 6 a .. a 2!. '8 0.5 a --a f., 8. 0 4 ., j 0 3 a ~-; ... 0.2 8 2!. .c !i 0.1 J 0 B D ... a 8. 0 6 .. a 2!. a 'g 0 5 ,._, c a a a Najas I a a a Iii Potamogeton a f 0 3 ::: a a T~ i; Vallisneria -o B 0 2 -Q .. ] 2!. 0.1 .. C 0 & F H Co40 Col5 B D F H Sediment source Sediment source 8. 0 6 .. 2!. 0 5 a co '8 ---co4 al 2!. .r. .: f 03 I .l:. a ii': .a a m Najas 1:1 Potamogeton B Vallisneria ~"O B 0 2 .. j 2!. 0 1 j 0 B D F H Co40 Col5 Sediment source ii D Najas 1:11 Potamogeton a 1:11 Vallis neria Co40 Co15 Figure 3-6: Ratio of root:shoot biomass for the four study species in the spring summer and winter culture periods. Ratios represent the mean value determined for three culture containers per plant type Control sediments designated as Co40 and Cols were amended with 40 g and 15 g of Osmocote fertilizer, respectively. Bars are the standard error Means for a given species with the same lowercase letters above them are not significantly different. a) Spring culture period 4/30/01 to 6/29/01 Biomass for Najas and Potamogeton are estimated values corrected for loss to herbivory. b) Summer culture period 7/20/01 to 9/21/01. c) Winter culture period 12/19/01 to 2/22/02 -N -

PAGE 139

i 20 E ._.. ,i 15 ~ -r r io "C "C .... 5 >. -g,.c: 0 ;e. B i 100 E ._.. -........ 80 .c: .c: tlil~ .i i 60 "C "C 40 fi 20 -!, .c: 0 ;e. B D F H Co40 Col5 Sediment so u rce a a a D F H Co40 Col5 Sediment source a Najas 151 Potamogeton Iii Vallisn er ia rn C hara a a Najas l!I Potamog e ton e Vallisn e r i a o Chara b Figure 3 7 : Epiphyte biomass occurring on the study plants. Values indicated are the mean of the biomass determined at the time of harvest for three individual representative plants of each host species Control sediments designated as Co40 and Co15 were amended with 40 g and 15 g of Osmocote fertilizer respectively. Bars are the standard error. Means with the same lowercase letters above them are not significantly different. a) Summer culture period (7/20 9/21 / 01). b) Winter culture period (12/19 /01 2 / 22 / 02). ...-N N

PAGE 140

CHAPTER4 LIGHT REQUIREMENTS FOR FOUR SPECIES OF NATIVE SUBMERSED MACROPHYTES: IMPLICATIONS FOR THE RESTORATION OF SHALLOW EUTROPHIC LAKES 1. ASSESSMENT OF THE LIGHT REQUIREMENTS OF MATURE PLANTS Introduction Numerous studies have identified light availability as one of the most significant factors controlling macrophyte production in aquatic systems (Duarte and Kalff 1986, Canfield et al. 1985, Barko et al. 1986, Smith and Barko 1990, Strand 1999). Additional studies have investigated the impact of light attenuation on submerged macrophyte productivity and growth (Carter and Rybicki 1990, Duarte 1991, Dunton 1994, Goodman et al. 1995, Masini et al. 1995, Zimmerman et al. 1995, Livingston et al. 1998 Grimshaw et al. 2002). Dennison (1987) discussed the use of photosynthesis vs. irradiance curves together with diurnal light curves to predict growth responses to changes in light regime (Dennison and Alberte 1985), seasonal growth patterns and the maximum depth of colonization for Zostera marina. All submerged angiosperms are shade plants (Wetzel 2001). Spencer and Bowes (1990) determined that light saturation for photosynthesis ranges from 10-50% full sunlight. The classification scheme Gessner (1955) developed for submerged macrophytes based on their physiological adaptations to light availability reflects the extreme plasticity and adaptability of submerged macrophytes to the highly variable underwater light environment. The adaptation types identified include strictly shade adapted requiring low light intensities strictly light adapted requiring high light 123

PAGE 141

124 intensities, shade adapted but exhibiting optimum photosynthesis at intermediate light levels, etc. Some aquatic macrophytes are capable of adapting to lower light environments via changes at the ecvllular and the whole-plant level (Wetzel 2001). Cellular adaptations include changes in pigment and enzyme concentrations and composition (Dennison and Alberte 1982, Barko and Filbin 1983). Morphological responses to increasing shade include changes in length and biomass proportions (i.e ofleaves and stems) (cf. Barko et al. 1982). Goldsborough and Kemp (1988) investigated the response and recovery of Potamogeton perfoliatus to experimentally induced shade during a 17-day treatment period followed by a 16-day "recovery" period. During the treatment period, plants responded by increasing photosynthetic pigments and producing elongate stems, thinning lower leaves and canopy formation at the surface. Plants showed significant recovery 10 days after removal of light treatments. The findings of more recent research have indicated that there is considerable variation in photosynthetic capacity and compensation points among submerged macrophyte species (Van et al. 1976 Kenworthy and Fonseca 1996 Wetzel 2001). Light compensation points often occur at 1-3% full sunlight (Wilkinson 1963 Spence 1982, Bowes et al. 1977 Moeller 1980). Kimber et al. (1995) reported that tuber production in Vallisneria americana ceased at light levels less than 5% of ambient sunlight. They discussed the implications of these results for V americana growth in relation to light attenuation by turbidity in their study system The purpose of this study was to investigate the amount of photosynthetically active radiation (PAR) at which there was no net growth of Najas guadelupensis

PAGE 142

125 Potamogeton illinoensis, Vallisneria americana and Chara sp. The underwater light environment of shallow productive systems is highly variable due to changes in light regime resulting primarily from resuspension events and fluctuations in phytoplankton standing crop. A review of the literature indicates that data available on the light requirements of submersed macrophytes is sparse and highly variable (Kimber et al. 1995). Most of the studies that have been conducted have investigated the light requirements of weedy exotic species. The four species selected for investigation in thfs study, Najas guadalupensis, Potamogeton illinoensis, Vallisneria americana and Chara sp., are native species commonly occurring in Florida lakes. N guadalupensis and Chara sp. are annuals; .P. illinoensis and V americana are perennials. Of the limited information available, at the time of this study, essentially no quantitative data was available for Najas guadalupensis, Potamogeton illinoensis and Chara. Although numerous studies have indicated that Vallisneria americana may have a low light affinity (cf. Titus and Adams 1979, Davis and Brinson 1980, Kimber et al. 1995, Grimshaw et al. 2002), the high suseptibility of the light capability to the effects of other environmental factors can often result in high light requirements for this species ( cf. Barko et al. 1982, Carter and Rybicki 1990, Doyle and Smart 2001 ).Further study is required in order to elucidate some of these apparent contradictions. In an attempt to address the significant differences in the light microenvironments of mature shoots and actively growing emergent propagule plant material, this study was divided into two parts such that three of the six experiments were designed to investigate the light requirements of mature plants while the experiments conducted in the second phase addressed propagule light requirements.

PAGE 143

126 The experiments in this first part were designed to test several hypotheses. The first hypothesis was that N guadelupensis and Chara sp. would exhibit the highest light requirements for net growth due to self-shading due to the habit and growth strategies of these species. I anticipated that V. americana would exhibit the lowest light requirement for net growth among the study species, approximately 4% incident irradiance. Based upon the literature, I expected the PPFD for no net growth of P illinoensis and N. guadelupensis to be approximately 11 % and 15% incident irradiance, respectively. I anticipated PPFD for no net growth of Chara sp. to range between 4 and 20% incident irradiance. I further expected to observe photoinhibition in those species that are either canopy-formers or have an erect habit, N guadelupensis, P. illinoensis and Chara sp., at light levels > 26.2% incident irradiance Additional information on the growth response of macrophyte species to decreased light availability should be of value to lake managers whose goal it is to determine which species to plant and maximum planting depths in revegetation projects. Materials and Methods Experimental Environment and Procedures Najas guadelupensis and Chara sp. are fast-growing pioneer plants with a finely dissected leaf architecture. Potamogeton illinoensis and Vallisneria americana are perennials with flat, lanceolate and elongate, ribbon-like leaves, respectively. (See Chapter 3 for a more detailed description of the study plants). Propagules (apical cuttings of N. guadalupensis P. illinoensis and Chara sp. and suckers of V.

PAGE 144

127 americana) were harvested from stock cultures of approximately the same age and in a state of active growth maintained at the FLREC from plants originally collected in Lake Okeechobee, Florida (Dr. David L. Sutton, UF FLREC, personal communication). Sixty 7.6-L black plastic nursery pots 22.5 cm in top diameter and 20 cm deep were loaded to 11 cm from the top with air-dried coarse builders' sand. Osmocote Plus Southern Formula 15-9-12 (N:P:K), a commercially available fertilizer, was added as a layer to each container and mixed into the sand at a rate of 40 g per pot for N. guadalupensis and P. illinoensis, and 15 g for V. americana and Chara sp (Dr. David Sutton, UF FLREC, personal communication). This fertilizer is formulated to slow-release in soil over an 8-9 month period with increased rates of nutrient release at temperatures 21 C (Harbaugh and Wilfret 1981 ). Each container was then filled with sand to within 2.5 cm of the top Containers were submerged in concrete tanks measuring 6.2 min length by 3-1 min width by 0.9 min height filled with pond water to a depth of 0.8 m. Twenty-centimeter apical cuttings of N. guadalupensis, Chara sp and P. illinoensis and single rosettes of V. americana were then planted at a frequency of four propagules per pot. N. guada/upensis and Chara sp. were planted to a depth of~ 3 nodes. P illinoensis was planted to a depth of at least 2 nodes. Individual sucker plants of V. americana were cut from the rhizome, roots were gently washed to remove organic sediments and each rosette was planted deep enough to submerge the rhizome beneath the sediment surface. Care was taken to avoid covering the basal rosette. Two (Experiment 1) and three containers (Experiment 2 and 3) were planted per treatment group for each macrophyte species. Pond water from a groundwater fed pond (as described by Steward 1984) located on-

PAGE 145

128 site at the UF FLREC flowed into the tanks at the surface of one end and out from bottom drains at the other end at a rate that allowed for an exchange of water every 24 hr. After planting, the experimental propagules were allowed to grow to maturity in full sunlight for at least a 4-week acclimation period. The light variable was introduced after the macrophytes reached maturity. Maturity was defined as growth that was "topped out" (e.g. shoots had reached the water surface). Pots were arranged to allow at least 1 foot of space between containers in order to prevent competitive shading. Containers were placed in rows parallel to the flow of water in the tanks ( see Figure 4-1 ). Growing all plants in the same water prevented skewing of the data due to variability in the nutrient composition of the water column. A wooden frame 19 .22 m2 in area was placed over and positioned on the tank walls. Cross beams were used to create five rectangles each 3 7 m2 in area. Shade cloth was used in differing numbers of layers to adjust experimental shade levels to 1 %, 2.6%, 5 .8% 26 2% and 100% incident PAR at the surface below the treatment groups. The control group was not shaded and was exposed to full sunlight. The experiment was conducted over three culture periods : August 22 to September 16 2001 February 25 to April 13, 2002 and July 16 to August 31, 2002. Each of the three experiments was a random design with four light treatments with two replicates per species per treatment in Experiment 1 and three replicates per plant species per treatment in Experiments 2 and 3. Data are presented on a per container basis. Culture period length in each experiment was adequate for the development of treatment related differences but minimi z ed tissue deterioration associated with senescence.

PAGE 146

129 Water temperature was measured using maximum/minimum thermometers placed 30 cm below the surface of the water. Readings were taken 5 days a week at approximately 3:00 P.M. each day. Water temperature was calculated as the mean of the maximum and minimum values from the thermometers for a recording period. Two recently certified 2-pi quantum sensors attached to a LI-COR datalogger were used to measure instantaneous photosynthetic photon flux density. Multiple simultaneous measurements taken above and one centimeter below the shade cloth in each treatment group throughout the day from 0700 to 1700h on three separate days during the culture period were used to calculate the percent transmittance for each treatment. Sheets of Weed Block were used between the treatment groups in Experiments 2 and 3 to prevent light transfer among the groups while still permitting water flow through the tank A long-term incident PPFD mean was calculated using short-term incident means of total irradiance (400-1100 nm) (W m -2 ) measured by a LICOR LI200SZ pyrometer located on-site and maintained by the University of Florida Florida Automated Weather Network (FAWN) Short-term incident means were based on data collected every 3.75 minutes and averaged and reported every 15 minutes. Total irradiance was converted to photosynthetically active radiation to (PAR) ( 400-700 nm) assuming that PAR is approximately 45% of total irradiance (Baker and Froiun 1987). PAR in Wm-2 was converted to photosynthetic photon flux density (PPFD) units( mol photons s -t m-2 ) using a multiplier of 4 6 (see Table 3 in Thimijan and Heins 1983 ). The long term mean incident PPFD for the photic portion of an experimental period was found by averaging the nonzero fluxes. Accumulated PAR was found by multiplying the

PAGE 147

130 mean incident PPFD by the length of the photic period for the experiment. The long term incident PPFD mean was multiplied by the mean percent transmittance discussed above to obtain mean estimates of the incident PPFD at the air-water interface in each treatment. Pot level incident PPFD in each treatment was estimated using Equation 4.1. Iz = I0 (% light attenuation by shade cloth) e-kz where: Iz = incident irradiance above each treatment group, I0 =irradiance at depth, z, k = light extinction coefficient, z = depth, in this case, 60 cm. Equation 4.1 The light extinction coefficient was calculated from simultaneous measurements of incident irradiance and irradiance at a given depth (depth varied from to 32 to 47 cm). The light extinction coefficient was calculated using Equation 4.2 Equation 4.2 Light measurements were taken on several sampling dates throughout the course of the entire study: 27 April 2002, 2 and 3 August 2003 and 7 October 2003 in order to ensure representative sampling of seasonal variation in the value of the coefficient. Actual measurements of the pot-level irradiance were taken on several sample dates in order to field-test the accuracy of the calculated values. Irradiance values reported in this study were not corrected for reflectance At the end of each study period, plants were harvested and separated into aboveand below-sediment biomass. The above-sediment portions of three individual

PAGE 148

131 representative plants of each species were separated and placed into individual Ziplock bags. The bags were placed into a dark cooler and processed within six hours of collection. The mechanical separation technique described by Zimba and Hopson (1997) was used to separate epiphytic biomass from macrophyte biomass. A subsample of the resultant suspension was concentrated onto a glass fiber filter (0.7 m porosity) and chlorophyll a and phaeophytin a were determined in accordance with Standard Methods (SM 10200 H) (A.P .H.A. 1995). All epiphyte data collected were normalized to host plant dry weight. Chlorophyll a values corrected for phaeophytin a were used as a correction factor to determ ine total macrophyte yield Total aboveand below-sediment biomass was then dried to constant weight (Hakanson 1981) at 60C in a forced-air drying oven and dry weights were measured. Macrophyte success was defined in terms of total (above and below-sediment) biomass accumulation. Growth in each container was determined as the difference in the g DWT from the start to the end of each experiment. The initial g DWT was estimated from the weights of at least ten representative plants collected and processed at the time that the light variable was introduced. The absence of Weed Block curtains between the treatment groups in Experiment 1 allowed transfer of light through the treatment groups. Field observations of the diurnal change in the angle of the sun were used in conjunction with the percent shade measured for each treatment group to estimate the total amount of light received in each treatment group during the study period. These estimates were based on the assumptions that

PAGE 149

132 1) light was passing through the treatments in an east to west direction from 6 to 11 AM, in a west to east direction from 1 to 7 PM and that light contamination between treatments was negligible between the hours of 11 AM to 1 PM, 2) light contamination between the groups was only significant at the pot and mid-water levels A Weed Block curtain was installed between each treatment group to prevent light transfer between treatments in subsequent experiments. Weed Block was chosen in order to allow water flow through the treatment groups. This modified design was used for Mature Plant Light Requirements Experiments 2 and 3. Data Analysis All macrophyte biomass data were statistically analyzed using GLM procedures (SAS Institute Inc. 1999-2001). Significant means (p 0.05) were separated using Tukey s HSD Test. Best-fit curves based on Michaelis.:.Menten kinetics were used to investigate the the relationship between photosynthetic photon flux density and macrophyte biomass. The photosynthetic photon flux density for no net growth of each of the submersed macrophyte species was calculated as the x intercept. Data were transformed to reduce the variance as necessary (Ricker 1973). Data points greater than two standard deviations away from the mean were considered outliers and were excluded from further analysis. Results Temperature and Irradiance Average daily water temperature during the study period was relatively constant with highest temperatures occurring during Experiment 1 (29.8 C) while lowest temperatures were measured during Experiment 2 (23.2 C) (see Table 4-1).

PAGE 150

133 The mean photic instantaneous photosynthetic photon flux density (PPFD) was greatest during Experiment 2 (831 mol s-1 m-2 ) and least during Experiment 1 (696 mol s-1 m-2). Photoperiod was shortest during Experiment 2 (12.4 hr) (Table 4-1). Partly cloudy days are the norm in South Florida. Relatively lower average PAR values in summer as compared to spring are probably due in part to afternoon thunderstorms that result in 100% cloud cover during parts of most summer afternoons. Effects of Light Availability on Macrophyte Production Experiment 1 (8/22/01 to 9/16/01) Mean incident PPFD measured at the air-water interface of the treatment groups ranged from 696 mol s-1 m-2 or 100% of incident PAR with no shade in the control group to 5.1 mol s-1 m-2 or 0 7 % incident PAR in the 99% shade group. Mean incident PPFD at the pot level (z = 60 cm) was approximately 30% of the incident PAR available at the air-water interface ranging from 174 mol s-1 rn-2 in the control group to 1.5 mol s-1 rn-2 in the 99% shade group (Table 4-2). Comparison of the final dry weights to the mean dry weight measured for the samples collected at the time of introduction of the light exclusion device to establish an initial biomass indicated a problem with the values estimated for Chara sp . Accordingly, net growth values determined for Chara sp were not included in subsequent analyses There were significant treatment effects among and within the macrophyte species N guadalupensis produced significantly more biomass than the other species in the 73.8% shade group (Table 4-3). V americana and P illinoensis growth was

PAGE 151

134 statistically greater than that of N. guadalupensis in the 99% shade group. There were no differences among the species in the other treatment groups. Comparisons within species indicated that N. guadalupensis produced significantly lower biomass at shade levels~ 94.2%. P. illinoensis growth was greatest with 73 .8% shade and least in the 99% shade treatment. There were no significant treatment effects on V. americana biomass production in this experiment. Comparison of the estimated irradiance at which there was no net growth indicated species-specific differences in the amount of PAR required for macrophyte growth. Macrophyte biomass production increased with increasing light availability up to 26.2% incident PAR. There was a slight decrease in the growth of N. guadalupensis and P illinoensis at light levels > 26.2% incident PAR Growth rat es of V. americana appeared to saturate and level out at light levels 26.2% incident PAR (Figure 4-4). The apparent photosynthetic photon flux density for no net N. guadalupensis growth was estimated to be 34.8 mol s1 m2 at a depth of 1 cm below the water surface or 5% incident PAR (Fig. 4-2). The apparent photosynthetic photon flux density for no net P. illinoensis growth was estimated to be 27. 8 mol s1 m 2 at a depth of 1 cm below the water surface or 4% incident PAR (Figure 4-3). The estimated photosynthetic photon flux density for no net V. americana growth was estimated to be 13.9 mol s 1 m2 at a depth of 1 cm below the water surface or 2% incident PAR (Figure 4-4) Experiment 2: 2/25/01 to 4/13 /01 PAR measured at the air-water interface of the treatment groups ranged from 831 mol s 1 m 2 or 100% of incident PAR with no shade in the control group to 6 .0

PAGE 152

I 135 mol s1 m2 or 0. 73 % incident PAR in the 99% shade group (Table 4-4). PAR available at the pot level (z = 60 cm) was approximately 30% of the PAR available at the air-water interface ranging from 243 mol s1 m2 in the control group to 1.7 mol s1 m2 in the 99% shade group (Table 4-4). Comparison of the final dry weights to the mean dry weight measured for the samples collected at the time of introduction of the light exclusion device to establish an initial biomass indicated a problem with the values estimated for V. americana. Accordingly, net growth values determined for V. americana were not included in subsequent analyses. Analysfa of variance using GLM procedures (SAS Institute 1999-2001) indicated that treatment and plant species had a highly significant effect on macrophyte yield in this experiment (P < .0001). There were significant treatment effects among and within the macrophyte species. Chara sp. produced significantly more biomass than the other species in the 5 8, 2.6 and 0.7% shade groups {Table 4-5). N. guadalupensis exhibited the lowest relative growth in the 26.2, 2.6 and 0. 7% light groups. There were no differences among the species in the control group. Comparisons within species indicated that N. guadalupensis produced significantly lower biomass at light levels 100%. P. illinoensis growth decreased significantly at light levels 5.8% full sun and below. Chara sp. biomass production declined significantly when available light at the water surface was 26.2% full sun and below. Comparison of the estimated irradiance at which there was no net growth indicated species-specific differences in the amount of PAR required for macrophyte

PAGE 153

136 growth. Biomass production of N. guadalupensis and V. americana increased linearly with increasing light availability (Figures 4-5 and 4-7, respectively). P. illinoensis net growth appeared to depend on light in accordance with the Michaelis-Menten relation (Figure 4-6) with growth leveling out at irradiances > 26.2% incident PAR. The apparent photosynthetic photon flux density for no net N. guadalupensis growth was estimated to be 416 mol s-1 m-2 at a depth of 1 cm below the water surface or 50.3% incident PAR (Figure 4-5). The estimated PPFD for no net growth of both P. illinoensis and Chara sp was 191 mol s-1 m-2 at a depth of 1 cm below the water surface or 23% incident PAR (Figures 4-6 and 4-7). Analysis of the root to shoot ratios for the study species using GLM Procedures (SAS Institute 1999-2001) indicated significant differences within and among plant types in response to decreasing light availability. The ratio of root biomass to shoot biomass was significantly greater in P. illinoensis and V. americana in all treatment groups (a=0.05). The trend to produce more root biomass in response to decreasing light availability was significantly greater in P. il/inoensis and V. americana (Table 4-6). Experiment 3: 7/16/02 to 8/31/02 PAR measured at the air-water interface of the treatment groups ranged from 821 mol s -1 m -2 or 100% of incident PAR with no shade in the control group to 6 mol s-1 m-2 or 0.7 % incident PAR in the 99% shade group (Table 4-2) PAR available at the pot level (z = 60 cm) was approximately 30% of the PAR available at the air-water interface ranging from 240 mol s -1 m -2 in the control group to 1.8 mol s -1 m-2 in the 99% shade group (Table 4-7).

PAGE 154

Analysis of variance using GLM procedures (SAS Institute 1999-2001) indicated that treatment and plant species had a highly significant effect on macrophyte yield in this experiment (P < .0001, P < 0.0007 respectively). A significant interaction between these two factors was also observed (P <.0001). 137 There were significant treatment effects among and within the macrophyte species. N. guadalupensis and P. illinoensis produced significantly more biomass than the other species in the control and 26.2% light treatment groups. {Table 4-8). V. americana and Chara sp. exhibited the lowest greatest growth in the 1 % light group while N. guadalupensis produced the least biomass in this treatment. There were no differences among the species in the 5 8 and 2.6% groups. Comparisons within species indicated that N. guadalupensis produced significantly lower biomass at light levels~ 5.8% {Table 4-8). P. illinoensis growth decreased significantly at light levels below 26.2% and again at levels 5.8% full sun and less. Chara sp. biomass production declined significantly when available light at the water surface was 5.8% full sun and below. There was a slightly significant decline in V. americana growth at light levels below 26.2% and a significant decline at light levels below 2.6% full sun. The results from treatment C for V. americana did not fit the trend observed in the other four treatment groups and were excluded from statistical analysis. Comparison of the estimated irradiance at which there was no net growth indicated species-specific differences in the amount of PAR required for macrophyte growth. N. guadalupensis biomass production increased with increasing light availability (Figure 4-8). Growth rates of P. illinoensis V. americana and Chara sp. appeared to saturate and level out at light levels 26.2% incident PAR (Figures 4-9

PAGE 155

138 to 4.11 ). The apparent PPFD for no net N. guadalupensis growth was estimated to be 57.5 mol s1 m2 at the water surface or 7% incident PAR (Figure 4-8). The estimated PPFD for no net P. illinoensis growth was 82.1 mol s1 m2 at the water surface or 10% incident PAR (Figure 4-9). The apparent PPFD for no net V. americana growth was estimated to be 49.3 mol s1 m2 at the water surface or 6% incident PAR (Figure 4-10). The estimated PPFD for no net Chara sp. growth was 98.5 mol s1 m2 at the water surface or 12% incident PAR (Figure 4-11). There were also significant differences in the root:shoot ratios within and between macrophyte species. Statistical analyses of the data using GLM Procedures (SAS Institute 1999-2001) indicated species-specific responses in root to shoot ratios due to treatment group {Table 4-9). P. il/inoensis and V. americana root biomass increased with decreasing light availability. Comparisons between plant types indicated that P. illinoensis and V. americana produced greater root to shoot biomass at stations A, B and C as compared with the other species. P. illinoensis root to shoot ratios were greater than those of the other macrophytes in treatments D and E. Effects of Light Availability on Macrophyte Chlorophyll a The data indicate that there were differences in the amount of chlorophyll a produced by the study plants among and within the study species. Analysis of variance using GLM procedures (SAS Institute 1999-2001) indicated that plant species had a highly significant effect on macrophyte chlorophyll a (mg/g macrophyte dry weight) in all three experiments. Significant differences due to shade level were observed in Experiments 1 and 2.

PAGE 156

139 Among-species comparisons of the effect of decreasing light availability on the amount of macrophyte chlorophyll a measured per g macrophyte DWT indicated that V. americana frequently produced significantly greater chlorophyll a than the other study species. This trend was observed in all three experiments (Figure 4-12). Differences in macrophyte chlorophyll a were also observed among the three experiments. N. guadalupensis and V. americana exhibited considerably greater chlorophyll a contents in Experiment 1 as compared with the other experiments. P. illinoensis chlorophyll a content was also greater during Experiment 1 while greatest values for Chara sp. were measured during Experiment 3. Discussion Light is recognized as one of, if not the most, important factors affecting the growth of submersed aquatic macrophytes. This relationship is particularly well defined in highly turbid, eutrophic lakes ( van Dijk et al. 1992, Lauridsen et al.1994, Strand 1999). Light availability drives a variety of population dynamics within natural plant communities including species composition, distribution and maximum depth of colonization. However, despite the fact that the importance of light to SA V growth is so well-accepted, there remains considerable uncertainty as to the specific light requirements of submersed macrophytes. Studies conducted to date vary widely and few have distinguished between the requirements for plant survival and reproduction (Kimber et al. 1995). Dennison et al. (1993) observed that, at present, there is no consensus concerning the light environment required for the growth and survival of V. americana in shallow water bodies. A review of the literature indicates that minimum light requirements vary from species to species and are affected by the

PAGE 157

140 length of the growing season (Table 4-10). In his investigation of 8 species of seagrasses, Dennison (1987) observed light compensation points that varied from 9 to 26 mol m-2 s-1 Goldsborough and Kemp (1988) concluded from their treatment and "recovery'' studies that 11 % ambient irradiance was required for the survival of Potamogeton perfoliatus. Sand-Jensen and Madsen (1991) observed among-species differences in their comparative study of the light requirements of charophytes, bryophytes and angiosperms. Van et al. (1976) used photosynthetic rate measurement studies to calculate the light compensation points of two native and two exotic species of submersed macrophytes: Hydrilla verticillata Ceratophyllum demersum, Myriophyllum spicatum and Cabomba caroliniana. They concluded that H. verticillata had the lowest LCP -15 mol m-2 s-1 followed by C. demersum and M spicatum -both 35 mol m-2 s-1 C. caroliniana exhibited the greatest light requirement with an estimated LCP of 55 mol m-2 s-1 They also observed that Hydrilla had the lowest light requirement to achieve half-maximal photosynthetic rate. They inferred that the superior photosynthetic efficiency conferred by these adaptations probably explains the competitive advantage that H verticil/ata has over many submersed macrophyte species. Carter et al. (1996) reported an 11-fold increase and a 38-fold increase in total biomass of Vallisneria americana in lighted cages in the Chesapeake Bay and the Potomac River. Plants exposed to higher ligh t levels were more robust and fewer in number as compared to controls. In their 1998 study, Blanch et al. concluded that recruitment of above-sediment biomass in Vallisneria may be completely restricted when irradiance is less than 35 mole m-2 s-1 Canfield et al. ( 1985) estimated LCP' s for hydrilla equivalent to less than 1 % full sun at the

PAGE 158

141 maximwn depth of colonization in several study lakes. (See Table 2 in Canfield et al. 1985) Spence and Chrystal (1970) reported LCP's less than 1 E m2 s1 in their study of the light requirements of submersed macrophytes. The results indicated that decreasing light had a significant effect on macrophyte growth in this study. The plants responded to decreasing light availability by reducing total, above and below-ground dry weight There was a concommitant decrease in the nwnber of V. americana and P. illinoensis plants per pot with increasing shade. (No data are available for N. guadalupensis and Chara sp. -see Materials and Methods.) In a laboratory study of the effects of turbidity on V. americana Doyle and Smart (2001) observed similar decreases in total AFDM and plant nwnber per pot. Grimshaw et al. (2002) also reported a decrease in the AFDM of V. americana with decreasing light. In this study, N. guadalupensis, P. illinoensis and Chara sp. exhibited elongation of stems, thinning of lower leaves and increased canopy formation in response to increasing shade. Goldsborough and Kemp (1988) observed similar shade responses in P. peifoliatus. The amount of light required for the net growth of the submersed aquatic macrophytes in this study varied among species ranging from 13.9 to 415.5 mol m2 s 1 or 2 to 50% incident irradiance (Table 4-11) There was no apparent relationship between light requirements of and N. guadalupensis and Chara sp. and their growth habit, however, higher N. guadalupensis light requirements may have been due to self-shading by the extensive canopy formation charateristic of this species Vallisneria americana exhibited the lowest minimwn light requirement for net growth of all of the study species During Experiment 1, V. americana produced new

PAGE 159

142 vegetative growth at less than 2% of surface incident light or 13.9 mol photons m2 s {Table 4-11). Many studies have suggested that V. americana is well-adapted to low light environments (cf. Titus and Adams 1979, Davis and Brinson 1980, Kimber et al. 1995, Grimshaw et al. 2002). Titus and Adams (1979) described V. americana as a shade-adapted summer specialist. Davis and Brinson (1980) concluded that V. americana is a turbidity-tolerant native species. Kimber et al. (1995) observed tuber production at light levels as low as 5% surface light. Grimshaw et al. (2002) determined that no net growth of V. americana occurred at 4.09% surface irradiance or 29 mol photons m2 s1 (measured 27 cm above the sediment surface). Macrophyte light requirements also varied on a seasonal basis {Table 4-11 ). Light contamination in Experiment 1 precluded the use of the results from Experiment 1 in a quantitative seasonal comparison accordingly, only the results from Experiments 2 and 3 were used. N. guadalupensis, P. illinoensis and Chara sp. exhibited a considerably greater minimum light requirement for growth in the winter / spring than in the summer. Other environmental factors such as greater tota l PPFD in summer as compared to winter / spring (1822 versus 178 1 Mol photons m2 ) and differences in photoperiod, solar angle and water temperature probably contributed to this phenomenon No data was available to make a seasonal comparison of the light requirements for V. americana. Despite the characteristics V. americana possesses that make it a very attractive candidate for use in restoration projects, caution should be used when considering planting monocultures of this species. There is considerable implication in the literature that environmental factors other than light have a highly significan t

PAGE 160

143 effect on V. americana growth, hence possibly explaining the seemingly contradictory findings that V. americana often exhibits high light requirements ( cf. Barko et al. 1982, Carter and Rybicki 1990, Doyle and Smart 2001). In addition, due in part to the concentration of biomass close to the sediment, Vallisneria is often out competed by canopy-forming plants such as Hydrilla (Haller and Sutton 1975). There was no apparent effect of decreased light availability on macrophyte chlorophyll a concentration. The sample size (n = 3) used in this study was not large enough to ensure representative sampling of shoot materials of differing ages. The high internal variation obscured any observable trends in macrophyte chlorophyll a production in response to increasing shade in this study. Goldsborough and Kemp (1988) observed significant increases in chlorophyll a content in response to decreasing light within 3 days of introduction of the light variable. Possible explanations for this contradiction include differences in the length of the experiment 17 days in their experiment versus 25, 48 and 46 days respectively in Experiments 1, 2 and 3 of this study. V. americana exhibited significantly greater chlorophyll a content per g macrophyte dry weight than the other study species. Decreasing PAR resulted in significant increases in root to shoot ratios within species in both of the experiments in which root:shoot ratios were calculated. P. illinoensis and V. americana exhibited significantly greater root:shoot ratios as compared with N. guadalupensis in all experiments. The typical life strategy of perennial species involves investment in organs such as roots that can allow the plant to survive periods of harsh environmental stress. Haller and Sutton (1975) discuss the implications of significantly greater energy allocation to below ground biomass by V.

PAGE 161

144 americana on its relative competitiveness with Hydrilla. Doyle and Smart (2001) measured higher above:below-ground AFDM at higher shade levels. Grimshaw et al. (2002) did not observe a significant effect of light on above to below-ground ratios. The explanation for these discrepancies in the effect of shading on the above:below ground biomass of V. americana is unknown at present. Conclusions There was a decrease in total biomass produced by N. guadalupensis guadelupensis, Potamogeton illinoensis, Vallisneria americana and Chara sp. in response to decreasing PAR. There was a decrease in above to below-ground biomass ratios for all species as available light decreased. The perennial species, P. illinoensis and V. americana, produced significantly greater below-ground biomass as compared to the annual, N. guadalupensis. V. americana appeared to be the most well-adapted study species for survival in low light environments. The combination of low light compensation point, high concentration of chlorophyll a and extensive root structure possibly confer an advantage to V. americana in shallow turbid systems. However, additional study is required in order to clarify some of the contradictory findings regarding the light requirements of V. americana before managers should rely on monocultures of V. americana. In summary, establishment of viable SA V communities composed of a combination of several species exhibiting diverse life strategies is the most advisable goal for revegetation projects especially in shallow eutrophic systems. The findings of this study suggest that the optimum time to plant N. guadalupensis, P. illinoensis and

PAGE 162

145 V. americana is during the summer when the light requirements for these species is minimal. The data suggest that minimum PPFD levels approximately 12% ambient light would be required to allow for the summertime growth of diverse macrophyte communities consisting of mature plants of all of the study species. The results of this study indicated that summer appeared to be the optimum planting time for the study species. Additional research is needed in order to quantify the amount of light required by submersed macrophytes in all stages of their life cycles. A better understanding of the role of light in inter-specific competition is also required.

PAGE 163

146 Table 4-1: Temperature and irradiance during the three culture periods. Temperature values are average daily temperatures followed by the standard deviation. Values shown in arentheses are the lowest and hi est measured tern ratures for each culture riod. Culture Period Water Temperature Mean Instantaneous PAR8 Photoperiod ol m2 s1 Experiment 1 29.8 1.3 696 (12.8L:11.2D) 8/22-9/16/01 27 to 32 (2 2130) Experiment2 23.2.4 831 (12.4L:11.6D) 2/25-4/13/02 18 to 31 (2 2343) Experiment 3 29.5 0.5 821 (13.4L:10.6D) 7/16 8/31/02 (27.5 to 32.0 (2 2327) 8Photosynthetically active radiation. Values shown are means of the daily average PAR measured over the course of each respective culture period.

PAGE 164

Table 4-2: Experiment 1: Estimated average instantaneous, daily and total photosynthetic photon flux density (PPFD) received over the period 22 August to 16 September 2001 (25 days) assuming 12.8-hour daylength Values shown have been corrected for light contamination between treatment groups. See materials and methods section for a desc ri p tion of the procedure u sed to estimate the correction factor. ---------------------------------Treatment Light level Total PPFD Daily PPF D Instan t ane ous PP F D (% light) For CP8 mol*d1m2 umol*m-2* s1 Mol*m2 Surface Pot0 Surface Pot0 Surface Pot0 Surface A 100 0 25.0 801.8 200.8 32.l 8 0 696 0 B 26.2 11.5 210.4 92.71 8.4 3.7 182 6 C 5.8 2.9 46 3 23 2 1.9 0.9 40. 2 I) 2.6 0 9 20.78 7 0 0.8 0.3 1 8.0 E 0.7 0.3 5 9 2.7 0.2 0.1 5.1 8Culture period. bPot level estimates are not corrected for self-shading by the above-sediment portions of the indiv i dual m a crophytes. Quantification of these values is beyond the scope of this research The degree of self-shading should vary with species differences in leaf architecture and growth stra tegy. Pot0 174.3 80 0 20. 1 6.1 2. 4 --.l

PAGE 165

Table 4-3: Results of analysis of net growth (g dry weight per pot per culture period) of above-ground macrophyte biomass produced in Experiment 1 using GLM procedures (SAS Institute 1999-2001) Values are the averages calculated for two culture containers per macrophyte species per treatment group followed by the standard error. Averages within a column followed by the same letter are not ficantlv different at the 5% level according to Tukev s HSD Method J = Macrophyte Species Treatment8 Najas Potamogeton Vallisneria Chara A 22.3 12.1 ab 7.0 1.7 ab 7.0.0a -3.8 0.5 B 38.5 6.9 a 13.5 1.8 a 4.7.7a 1.0 4.3 C -1.6 3.0 b 1.6 2.3 be 0.3 0.03 a -8.4 1.3 D -13.0 3.6 b -1.4 0.3 be -0.7 1 a -2.4 0.9 E -15.0 1.7 b -1.9 0.4 C 0.8 I.Sa -7.3 0 2 8Treatments are the same as indicated in Table 4.2. Table 4-4: Experiment 2: Estimated average instantaneous, daily and total PPFD received over the period 25 February to 13 Aoril 2002 48 days). Assumes 12.4-hour daylength. Light level Total PPFD Daily PPFD Instantaneous PPFD (llight) ForCP mol*m -2*d-1 l -2 -1 umo m s Treatment Mol*m-2 Surface Pot8 Surface Pot8 Surface Pot8 Surface Pot8 A 100.0 29.2 1780.6 520.3 37.l 10.8 831.0 242.8 B 26 2 7.7 467.2 136.6 9.7 2.9 218.1 63.7 C 5.8 1.7 102.7 30.1 2.1 0.6 47.9 14.0 D 2.6 0.8 46.1 13.5 1.0 0.3 21.5 6.3 E 0.7 0.2 13.0 3.7 0.3 0.1 6.1 1.7 8Pot level estimates are not corrected for self-shading by the above-sediment portions of the individual macrophytes. Quantification of these values is beyond the scope of this research. The degree of self-shading should vary with species differences in leaf architecture and growth strategy. ...... 00

PAGE 166

Table 4-5: Results of analysis of net growth (g dry weight per pot per culture) of total macrophyte biomass (above plus below ground biomass) in Experiment 2 using OLM procedures (SAS Institute 1999-2000) Values are the means calculated for three culture containers per macrophyte species per treatment group followed by the standard error. Means within a column followed by the same letter are not significantly different at the 5% level according to Tukev's HSD Method J Macrophyte Species Treatment8 N guadalupensis P illinoensis V. americana Chara sp. A 60.6 16.5 a 28.4 13. 5 a -13.8 0.9 NA 78.5 15.3 a B -35.5 2.6 b 3.5 2.3 a -16.4 1.5 NA 3.7 10.9 b C -54 0 1.0 b -47.0 1.5 b .9.9NA -6.9 .8 b D -50.2 3.2 b -43.5 1.7 b -4 5 0.3 NA -15.1 4 8 b E -54.3 0.6 b -44.7 0 6 b -1.8 0.1 NA -20.9 0.1 b 8Treatments are the same as indicated in Table 4.4. Table 4-6: Root:shoot ratios for Experiment 2. Values are the means calculated for three culture containers per macrophyte species per treatment group followed by the standard deviation. All data were log(y+ 1) transformed prior to analysis by OLM procedures (SAS Institute 1999-2001). The nontransformed values are presented here. Means within a column followed by the same letter are not ficantlv different at the 5% level according to Tuk, J Macrophyte Species Treatment8 N j?uadalupensis P illinoensis V. americana A 0.03 0.01 b 0.12 0.01 C 0.17 0.05 C B 0.04 0.00 b 0.11 0.01 e 0.28 0.16 be C 0.17 0.01 ab 0.90 0.18 b 0.51 .41 be 0 0.27 0.19 a 1.61 0.59 ab 0.76+0.18 ab E 0.48 .24 a 2.93 1.87 a 1.90 + 0.62 a 8Treatments are the same as indicated in Table 4.4. ..... l,C)

PAGE 167

Table 4-7: Experiment 3: Estimated average instantaneous, daily and total PPFD received over the culture period (CP) 1 6 July ---. -------' ---.,,/ ----------------------..1 ----~---Treatment Light level Total PPFD Daily PPFD Instantaneous PPFD (% light) forCP mol*d-1*m-:z umo l s-1m-:z* mol*m-2 Surface Pot8 Surface Pot8 Surface Pot8 Surface A 100.0 29.2 1821.8 532.3 39.61 11.6 821.0 B 26.2 7.7 478.1 140.0 10.39 3.0 215.4 C 5.8 1.7 105.1 30.7 2 29 0.7 47.4 D 2.6 0 8 47.2 13.8 1.03 0.3 21.3 E 0.7 0.2 13.3 3.9 0.3 0 1 6.0 11Pot level estimates are not corrected for self-shading by the above-sediment portions of the individual macrophytes. Quantification of these values is beyond the scope of this research. The degree of self-shading should vary with species differences in leaf architecture and growth strategy. Pot8 239 9 63 0 13. 8 6.2 1.8 Table 4-8: Results of analysis of net growth (g dry weight per pot per culture)oftotal macrophyte biomass (above plus below ground biomass) in Experiment 3 using GLM procedures (SAS Institute 1999-2000) Values are the means calculated for three culture containers per macrophyte species per treatment group followed by the standard error. Means within a column followed by the same letter are not sil!Ilificantlv different at the 5% level accordimz to Tuk --------------~ ----------------Macrophyte Species Treatment8 Najas Potamogeton V allisneria Chara A 173.1 69.2 a 88.7 10.2 a 10.8 3.9 a 23.3 9.3 a B 71.2 14.20 ab 6.7. 9.2 b 7.7 2.6 ab 12.9 12.5 a C -18.5 19.4 b -19 0 0.5 C 10.3 7.0NA -26.7 0.3b D -17.0 17.0 b -31.7 1.3 C -1.2 0.5 b -26.1 1.6 b E -58 0 12.2 b -34.8 1.4 C 8Treatments are the same as indicated in Table 4.7. -4.0 1.1 b -27.3 0.4 b -Vl 0

PAGE 168

151 Table 4-9: Root:shoot ratios for Experiment 3. Values are the means calculated for three culture containers per macrophyte species per treatment group followed by the standard dc::viation. Means within a column followed by the same letter are not significantly d'ffi t t th 5 1 1 d' t Tuk HSD M th d 1 eren a e o eve accor mg o ey s e 0. Macrophyte Species Treatment Group Najas Potamogeton V allisneria A 0 04 0.01 a 0.05 0.01 C 0.16 0.03 C B 0.03 0.00 a 0.07 0.02 be 0.13 0.04 be C 0 .05 0.02 a 0.19 0.06 be 0.11 0.03 be D 0.04 0.01 a 0.52 0.17 ab 0.20 0.04 ab E 0.07 0.04 a 0.72 0.23 a 0.27 0.03 a

PAGE 169

Table 4-10: Selected field observations and experimental conclusions concerning the light requirements of several species of bmersed macroph J Observed an inter-specific variation in LCP's among four species of SA V ranging VAN ET AL. 1976 from 55 umole photons m2 s1 to 15 mole photons m2 s1 Estimated that an average midday irradiance of at least 250 mole photons m2 s1 AGAMI and AGAMI 1980 would be necessary for seed production Estimated that the light level that determined the lower depth limit of plant CHAMBERS and KALFF 1985 colonization could be as much as 21 % of surface light Estimated that Potamogeton perfoliatus required> 11 % of ambient irradiance for GOLDSBOROUGH and KEMP 1988 survival Observed that an average of 100 umol*m.ls1 was necessary at the sediment-water CARTER and RYBICKI 1990 interface for submersed macrophvtes to survive in the tidal Potomac River Estimated that 7% of surface light or 505 mol m1 per year was needed for rooted SAND-JENSEN and MADSEN 1991 aquatic plants to grow. Concluded that the light requirements for submersed plant growth vary widely and KIMBER ET AL. 1995 few of these [studies] have distinguished between requirements for plant survival and plant reproduction. Determined that the PPFD for no net growth of Vallisneria americana, measured GRIMSHAW ET AL. 2002 approximately a quarter meter from the sediment surface was 29 mole photons m2 s1 or 4.09% surface irradiance. Estimated that the minimum PPFD for no net growth of N. guadelupensis was 34.8 THIS STUDY mole photons m2 s1 or 5% ambient light, for P. illinoensis was 27.8 mole photons m2 s1 or 4% ambient light, for V. americana was 13.9 mole photons m2 s 1 or 2% ambient light and for Chara sp. was 377.7 mole photons m2 s1 or 12% ambient light. -Vl N

PAGE 170

Table 4-11: A comQarison of the seasonal variation in light levels at which there is zero net growth of the study SQecies. Najas Potamogeton Vallisneria Chara LCP PPFD LCP PPFD LCP PPFD LCP (%) (mol photons (%) (mol photons (%) (mol :Photons (%) m-2 s-12 m 2 s-12 m-s-12 Experiment 1 5 0 34.8 4.0 27.8 2.0 13.9 NA 8/22 to 9/16/01 Experiment 2 50.0 415.5 23 0 191.1 NA NA 23.0 2/25 to 4/13/02 Experiment 3 7.0 57.5 10.0 82.1 6.0 49 3 12.0 7 /16 to 8/31/02 PPFD (mol f ho tons m-s-12 NA 191.1 377.7 ..... VI vJ

PAGE 171

Mature Light Requirement Experiments 1, 2 and 3 and Propagule Plant Light Requirement Experiment 1 Hp IN .. I ) .. 5 Treatment Groups Triplicate samples of 4 plant types= 12 pots per group Pots randomly arranged 3 culture periods 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 O 0 0 0 0 0 0 0 0 0 0 0 0 0 o0o 0 0 0 0 0 o0o 0 0 0 0 0 0 0 0 A B C D E H p our c:=.> Figure 4-1: Experimental set-up for mature plant light requirement E xperimen t s 1, 2 and 3 and propagule plant light requirement Experiment 1 Containers were arranged randoml y withi n e ach t r eatment gr oup. Note : In mature plan t light requirement Experimen t 1, only two con t ainers per species were used in each treatment group (n = 2). -VI

PAGE 172

..... 60 t:,J) -40 I = ..... ~= '"C '"C 0 20 I 5% t:,J) --..... ..... 0 0 e t:,J) ~'! 20 40 60 80 1 ..... -20 z Percent Incident PAR Figure 4-2: Experiment 1: Graphical interpretation of the net growth ( g dry weight per pot per culture period) of Najas guadelupensis in response to the percent incident PAR at the water surface. A best -fit curve, based upon Michaelis-Menten kinetics, was used to estimate the x-intercept, indicated by the downward facing arrow. The x-intercept which represents that percent incident PAR at which there was no net growth. ..... V1 V1

PAGE 173

20 ..c -15 = te 10 Q -.._, C. 5 ..c Q C. e 0 C.
PAGE 174

.... 15 ..= Oil -= 1 0 .... ge~ 12% Oil -0 5 '-" c: ..= Q,. ~/ i Q,. 0 Q,. 0 8--5 (I) 20 40 60 8 0 1 ())0 z Percent Inciden t PAR Figure 4-4: Experiment 1: Graphical interp r etation of the net growth ( g dry weight per pot per culture period) of Val/isneria americana in response to t h e percent incident PAR at the water surface. A best-fit curve, based upon Michaelis Menten kinetics, w as use d t o esti mate the xi nterce p t, i ndicated by t h e downward facing arrow. The x intercept represents that percent inc i dent P AR at which t h e r e was no net growth. -VI -...J

PAGE 175

100 ..c: bf) -; 50 ta~ I 50% bf) -= 0 '---' c ..c: (D 40 60 80 i & -50 = -100 z Percent Incident PAR F igure 4-5 : Experiment 2 : Graphical interpretat i on of the net growth ( g dry weight per pot per culture period) of Najas guadelupen s is in response to the percent incident PAR at the water surface. A best-fit curve was used to estimate the x intercept indicated by the downward facing arrow The x-intercept represents that percent incident PAR at which there was no net growth. Outlying data points were excluded from analysis and are indicated in the figu r e as open circles 1$0 .... Vt 00

PAGE 176

...,_ 60 ..c: 40 ; ; ...,_ I 23% ~= 20 = '-" c: 0 ..c: =i i -20 = -40 ...,_ =-60 z Percent incident PAR Figure 4-6: Experiment 2: Graphical interpretation of the net growth ( g dry weight per pot per culture period) of Potamogeton illinoensis in response to the percent incident PAR at the water surface. A best-fit curve based on Michaelis Menten kinetics was used to estimate the x-intercept indicated by the downward facing arrow. The x-intercept represents that percent incident PAR at which there was no net growth Outlying data points were excluded from analysis and are indicated in the figure as open circles. ..... v-, \0

PAGE 177

...._ 120 -= 100 -; 80 ...._ 60 el) -Q 40 !. ---= ...._ 20 i Q Q C. 0 el) -20 FY 20 40 60 80 1$0 ...._ C. -40 z Percent incident PAR Figure 4-7: Experiment 2: Graphical interpretation of the net growth ( g dry weight per pot per culture period) of Chara sp. in response to the percent incident PAR at the water surface. A best-fit curve was used to estimate the x-intercept, indicated by the downward facing arrow The x-intercept represents that percent incident PAR at which there was no net growth. -' 0

PAGE 178

.... 300 0 ---~ !. 200 .,._ e.ll~ 100 I "-" = 7% i -!. 0 0 -.,._ ~& r 20 40 60 80 1(1)0 8_ -100 z Percent incident PAR Figure 4-8: Experiment 3: Graphical interpretation of the net growth ( g dry weight per pot per culture period) of Najas guadelupensis in response to the percent incident PAR at the water surface. A best-fit curve based on Michaelis-Menten kinetics, was used to estimate the x-intercept indicated by the downward facing arrow. The x-intercept represents that percent incident PAR at which there was no net growth. Outlying data points were excluded from analysis and are indicated in the figure as open circles. -O'I ......

PAGE 179

...,._ 120 ..= l:)J) 100 i ; 80 ...,._ 60 l:)J) -0 40 c ..= c.. 20 i c.. 0 c.. 0 -l:)J) -20 $~ 20 40 60 80 1(1)0 ...,._ c.. -40 z Percent incident PAR Figure 4-9: Experiment 3: Graphical interpretation of the net growth ( g dry weight per pot per culture period) of Potamogeton illinoensis in response to the percent incident PAR at the water surface. A best-fit curve, based on Michaelis Menten kinetics, was used to estimate the x-intercept, indicated by the downward facing arrow. The x-intercept represents that percent incident PAR at which there was no net growth. ..... O'I N

PAGE 180

..c bJ) -; ~] bJ) -'.._I~ ..c Q. i 0 & 8. z 0 c !. 25 20 15 10 5 0 -5 -10 0 0 i L.U '+U OU ~U 1 '110 Percent incident PAR Figure 4-10: Experiment 3: Graphical interpretation of the net growth ( g dry weight per pot per culture period) of Vallisneria americana in response to the percent incident PAR at the water surface. A best-fit curve, based on Michaelis Menten kinetics was used to estimate the x-intercept, indicated by the downward facing arrow. The x-intercept represents that percent incident PAR at which there was no net growth. Outlying data points were excluded from analysis and are indicated in the figure as open circles. -' w

PAGE 181

...... i i 0 -...... z = ...... ,.... a~ 0 --...... !. 8. 40 30 20 10 0 -10 -20 -30 -40 1H / '}() LU) hf) Xf) l IDQ Percent incident PAR Figure 4-11 : Experiment 3 : Graphical interpretation of the net growth ( g dry weight per pot per culture period) of. Chara sp. in response to the percent incident PAR at the water surface A best-fit curve based on Michaelis-Menten kinetics was used to estimate the x-intercept indicated by the downward facing arrow. The x-intercept represents that percent incident PAR at which there was no net growth. Outlying data points were excluded from analysis and are indicated in the figure as open circles ...... i

PAGE 182

,_ 30 'a. 25 L-----------,---, m Najas e .!,II f 2 0 a Potamogeton '5 ;:, 1 5 b Iii! Vallisneria >. Oil I O l:J Char a t 1 5 .i.:=.--a.--Ulli,8!,......,.dHlll;: l:i '-' 0 -UIS!ib...,...llll!i!Sa.,.JW:iBl~l&II: i 100 26 24 5 77 2 59 : 30,--------------n ~: I I .: 15 >. Oil 10 +------r--------1 -a. ol) e !. ... 0 I Plli'Bn ll'5Bn PRB-, IJl'iEm QIR'R-I i I I I I 100 26 24 5 77 2 59 Percent incident PAR a Percent incident PAR : 30.,....----------~ H~:I I .: 15 Oil 10 1--------"--" -------~ -;t.-~ 1 i 't 5 :c;c \i 5: ~ -, ,i. ... '-' 0 i 100 26 24 5 77 2 59 Percent incident PAR D Najas la Potamogeton El Vallisneria OChara C m Najas Ill Potamogeton Iii! Vallisneria C Chara b Figure 4-12: Mature plant light requirement experiments: Among species comparisons of macrophyte chlorophyll a measured for each of the study plants during a) Experiment 1 (8/22-9/16/01), b) Experiment 2 (2/25-4/13/02) and c) Experiment 3 (7/16-8/31/02). Bars represent the means of three samples (n=3) per macrophyte species ; Error bars represent the standard error. Means with the same letter are not significantly different. .... VI

PAGE 183

166 CHAPTERS LIGHT REQUIREMENTS FOR FOUR SPECIES OF NATNE SUBMERSED MACROPHYTES: IMPLICATIONS FOR THE RESTORATION OF SHALLOW EUTROPHIC LAKES 2. ASSESSMENT OF THE LIGHT REQUIREMENTS OF VEGETATNE PROPAGULES Introduction Numerous studies have identified light availability as one of the most significant factors controlling macrophyte production in aquatic systems (Duarte and Kalff 1986, Canfield et al. 1985, Barko et al. 1986, Smith and Barko 1990, Strand 1999). Additional studies have investigated the impact of light attenuation on submerged macrophyte productivity and growth (Carter and Rybicki 1990, Duarte 1991, Dunton 1994, Goodman et al. 1995, Masini et al. 1995, Zimmerman et al. 1995, Livingston et al. 1998, Grimshaw et al. 2002). Dennison (1987) discussed the use of photosynthesis vs. irradiance curves together with diurnal light curves to predict growth responses to changes in light regime (Dennison and Alberte 1985), seasonal growth patterns and the maximum depth of colonization for Zostera marina. All submerged angiosperms are shade plants (Wetzel 2001). Spencer and Bowes (1990) determined that light saturation for photosynthesis ranges from 10-50% full sunlight. The classification scheme Gessner (1955) developed for submerged macrophytes based on their physiological adaptations to light availability reflects the extreme plasticity and adaptability of submerged macrophytes to the highly variable underwater light environment. The adaptation types identified include strictly shade adapted requiring low light intensities, strictly light adapted requiring high light

PAGE 184

167 intensities, shade adapted but exhibiting optimum photosynthesis at intermediate light levels, etc. Some aquatic macrophytes are capable of adapting to lower light environments via changes at the ecvllular and the whole-plant level (Wetzel 2001). Cellular adaptations include changes in pigment and enzyme concentrations and composition (Dennison and Alberte 1982, Barko and Filbin 1983). Morphological responses to increasing shade include changes in length and biomass proportions (i.e. ofleaves and stems) (cf. Barko et al. 1982). Goldsborough and Kemp (1988) investigated the response and recovery of Potamogeton perfoliatus to experimentally induced shade during a 17-day treatment period followed by a 16-day "recovery" period. During the treatment period plants responded by increasing photosynthetic pigments and producing elongate stems, thinning lower leaves and canopy formation at the surface. Plants showed significant recovery 10 days after removal of light treatments. The findings of more recent research have indicated that there is considerable variation in photosynthetic capacity and compensation points among submerged macrophyte species (Van et al. 1976, Kenworthy and Fonseca 1996, Wetzel 2001). Light compensation points often occur at 1-3% full sunlight (Wilkinson 1963 Spence 1982, Bowes et al. 1977, Moeller 1980). Kimber et al. ( 1995) reported that tuber production in Va/lisneria americana ceased at light levels less than 5% of ambient sunlight. They discussed the implications of these results for V americana growth in relation to light attenuation by turbidity in their stud}'. system. The purpose of this study was to investigate the amount of photosynthetically active radiation (PAR) required for the survival and growth of vegetative propagules

PAGE 185

168 of Najas guadelupensis, Potamogeton illinoensis, Vallisneria americana and Chara sp. The underwater light environment of shallow productive systems is highly variable due to changes in light regime resulting primarily from resuspension events and fluctuations in phytoplankton standing crop. A review of the literature indicates a need for further investigation of the light requirements for plant reproduction. Information currently available submersed macrophytes is sparse and highly variable. Most of the studies that have been conducted have investigated the light requirements of weedy exotic species. The experiments in this phase of the study were designed to investigated the growth response of vegetative propagules of the four study species to decreasing light availability. The experiments in this study were designed to test several hypotheses. First, I hypothesized that plants grown from propagules would have higher light requirements than mature plants of the same species. I anticipated that V. americana would exhibit the greatest capability for growth in low levels of light. I further expected that plants grown from propagules would not become photoinhibited during the course of each culture period. Additional information on the growth response of vegetative propagules to decreased light availability should be of value to lake managers interested in the selection of species for use in revegetation projects and in the calculation of maximum planting depths.

PAGE 186

Materials and Methods Experimental Environment and Procedures 169 Propagules (apical stem cuttings of N guadalupensis, P. illinoensis and Chara sp and suckers of V americana) were harvested from stock cultures of approximately the same age and in a state of active growth maintained at the FLREC from plants originally collected in Lake Okeechobee, Florida (Dr. David L. Sutton, UF FLREC, personal communication). In Experiment 1, sixty 7.6-L black plastic nursery pots 22.5 cm in top diameter and 20 cm deep were loaded to 11 cm from the top with airdried coarse builders' sand. Osmocote Southern Formula 15-9-12 (N:P:K), a commercially available fertilizer, was added as a layer to each container and mixed into the sand at a rate of 40 g per pot for N guadalupensis and P illinoensis, and 15 g for V americana and Chara (Dr. David Sutton, UF FLREC, personal communication). This fertilizer is formulated to slow-release in soil over an 8-9 month period with increased rates of nutrient release at temperatures 21 C (Harbaugh and Wilfret 1981). In Experiments 2 and 3, 135 4-L black plastic nursery containers 16.5 cm in top diameter by 16.5 cm deep were loaded to 8 cm from the top with air-dried coarse builders' sand. A layer of Osmocote Southern Formula 15-9-12 (N :P:K) was added to each pot at a rate of 30 g for P. illinoensis and 11.3 g for V americana and Chara sp (Dr. David Sutton, UF FLREC, personal communication). Each container in all three Experiments was then filled with sand to within 2.5 cm of the top. Containers were submerged in concrete tanks measuring 6.2 min length by 3-1 min width by 0.9 min height filled with pond water to a depth of0.8 m. Twenty-: centimeter apical cuttings of N guadalupensis Chara sp. and P illinoensis and single

PAGE 187

170 rosettes of V americana were then planted at a frequency of four propagules per pot. N guada/upensis and Chara sp. were planted to a depth of~ 3 nodes. P i//inoensis was planted to a depth of at least 2 nodes. Individual sucker plants of V americana were cut from the rhizome roots were gently washed to remove organic sediments and each rosette was planted deep enough to submerge the rhizome beneath the sediment surface Care was taken to avoid covering the basal rosette. Pond water from a groundwater fed pond located on-site at the UF FLREC flowed into the tanks at the surface of one end and out from bottom drains at the other end at a rate that allowed for an exchange of water every 24 hr. Containers were placed in rows parallel to the flow of water in the tanks (Figure 4-1 ) Growing all plants in the same water prevented skewing of the data due to variability in the nutrient composition of the water column. A wooden frame 19.22 m2 in area was placed over and positioned on the tank walls Cross beams were used to create five rectangles each 3.7 m2 in area in Experiment 1 and fifteen rectangles each 0.87 m2 in area in Experiments 2 and 3 Shade cloth was used in differing numbers of layers to adjust experimental light levels to 0.96% 3.57% 7 29%, and 27% full sun in Experiment 1, 0.6% 1.8% 5.1 % and 6.5% full sun in Experiment 2 and 2.8%, 8.3% 11.4% and 26.2% full sun in Experiment 3 at the air-water interface below the treatment groups. The control group in all experiments was not shaded and was exposed to full sunlight. Sheets of Weed Block were used between the treatment groups in all experiments to prevent light transfer among the groups while still permitting water flow through the tank. In

PAGE 188

171 Experiments 2 and 3, shade cloth was attached to the peripheral beams of the frame and draped over the outer walls of the tank. The experiment was repeated over three culture periods: 27 April to 14 July 2002, 21 April to 7 June 2003 and 28 June to 2 August 2003. Experiment 1 was a random design with four light treatments with three replicates per plant species per treatment. Experiments 2 and 3 were complete randomized block designs such that each row of treatment groups was considered a block and n = 9 pots per plant species per light level. Data are presented on a per container basis. Culture period length in each experiment was adequate for the development of treatment-related differences but minimized tissue deterioration associated with senescence. Water temperature was measured using maximum/minimum thermometers placed 30 cm below the surface of the water. Readings were taken 5 days a week at approximately 3:00 P .M. each day. Water temperature was calculated as the mean of the maximum and minimum values from the thermometers for a recording period. Two recently certified 2-pi quantum sensors attached to a LI-COR datalogger were used to measure instantaneous photosynthetic photon flux density. Multiple simultaneous measurements taken above and one centimeter below the shade cloth in each treatment group throughout the day from 0700 to 1700h on three separate days during the culture period were used to calculate the percent transmittance for each treatment. Sheets _of Weed Block were used between the treatment groups in Experiments 2 and 3 to prevent light transfer among the groups while still permitting water flow through the tank.

PAGE 189

172 A long-term incident PPFD mean was calculated using short-term incident means of total irradiance ( 400-1100 nm) (W m"2 ) measured by a LICOR LI200SZ pyrometer located on-site and maintained by the University of Florida Florida Automated Weather Network (FAWN). Short-term incident means were based on data collected every 3 .75 minutes and averaged and reported every 15 minutes. Total irradiance was converted to photosynthetically active radiation to (PAR) ( 400-700 nm) assuming that PAR is approximately 45% of total irradiance (Baker and Froiun 1987). PAR in Wm 2 was converted to photosynthetic photon flux density (PPFD) units( mol photons s 1 m"2 ) using a multiplier of 4.6 (see Table 3 in Thimijan and Heins 1983). The long term mean incident PPFD for the photic portion of an experimental period was found by averaging the nonzero fluxes. Accumulated PAR was found by multiplying the mean incident PPFD by the length of the photic period for the experiment. The long term incident PPFD mean was multiplied by the mean percent transmittance discussed above to obtain mean estimates of the incident PPFD at the air-water interface in each treatment Pot level incident PPFD in each treatment was estimated using Equation 5.1. Iz = I0 (%light attenuation by shade cloth) ekz where: I2 = incident irradiance above each treatment group I0 =irradiance at depth z k = light extinction coefficient Equation 5 1 z = depth in this case 60 cm for Experiments 1 and 2 and 4 7 cm for Experiment 3.

PAGE 190

173 The light extinction coefficient was calculated from simultaneous measurements of incident irradiance and irradiance at a given depth (depth varied from to 32 to 47 cm). The light extinction coefficient was calculated using Equation 5.2. Equation 5 .2 Light measurements were taken on several sampling dates throughout the course of the entire study: 27 April 2002, 2 and 3 August 2003 and 7 October 2003 in order to ensure representative sampling of seasonal variation in the value of the coefficient. Actual measurements of the pot-level irradiance were taken on several sample dates in order to field-test the accuracy of the calculated values. Irradiance values reported in this study were not corrected for reflectance. Procedures for sample collection and processing during and following harvest were the same as those described in the Materials and Methods section of Chapter 3. Macrophyte success was defined in terms of growth. Growth in each container was determined as the difference in the gram dry weight from the start to the end of each experiment. The initial gram dry weight was estimated from the weights of at least ten representative plants collected and processed at the time that the light variable was introduced. Data Analysis All macrophyte biomass data were statistically analyzed using OLM procedures (SAS Institute, Inc. 1999-2001 ). Significant means (P 0.05) were separated using Tukey's HSD Test. Regression analysis was used to investigate the

PAGE 191

174 relationship between photosynthetic photon flux density and macrophyte biomass. Data were transformed to reduce the variance as necessary (Ricker 1973). Data points greater than two standard deviations away from the mean were considered outliers and were excluded from further analysis. The photosynthetic photon flux density for no net growth of each of the submersed macrophyte species was calculated using Equation 5 .1. Equation 5 .1 is a modification by Grimshaw et al. (2002) of Equation 16.30 developed by Zar ( 1996). v: Yi-a Al=--b where : Xi is the estimated photosynthetic photon flux density mean Y i is set to zero a is the Y intercept and b is the slope of the regression line. Results Temperature and Irradiance Equation 5 .1 Water temperature during the study period was relatively constant with highest measured mean temperatures occurring during Experiment 2 (26 2 C) while lowest average temperatures were measured during Experiment 1 (24.8C) (Table 5-1). Mean photosynthetic photon flux density (PPFD) was greatest during Experiment 2 (824 mol s -1m-2 ) and least during Experiment 1 (777 mol m-2 s-1). Relatively lower average PAR values in summer as compared to spring are probably due in part to afternoon thunderstorms that result in 100% cloud cover during parts of most

PAGE 192

swnmer afternoons. Photoperiod ranged from 13.5 hours in Experiment 2 to 13.8 hours in Experiments 1 and 3 (Table 5-1 ). Effects of Light Availability on Propagule Macrophyte Production Experiment 1 (4/27/02 to 7/14/02) 175 PAR measured at the air-water interface of the treatment groups ranged from 777 mol m2 s1 or 100% incident PAR with no shade in the control group to 5.67 mol m2 s1or 0.73 % incident PAR in the 99% shade group. PAR available at the pot level (z = 60 cm) was approximately 30% of the PAR available at the air-water interface ranging from 227 mol m2 s1 in the control group to 1.7 mol m2 s1 in the 99% shade group (Table 5-2). Analysis of variance using GLM procedures (SAS Institute 1999-2001) indicated that treatment, plant species and the interaction between treatment and plant species had a highly significant effect on macrophyte yield in this experiment (P < .0001). There were significant treatment effects among and within the macrophyte species. N guadalupensis produced significantly greater yield than the other species in the control group and in the 0 7% light group. Chara sp exhibited statistically less growth in the control than the other species. There were no significant differences in growth among the species at 5.8% incident light. Comparisons within species indicated that all species produced significantly lower biomass at shade levels~ 74% (Table 5-3). There was a second significant decrease in V americana biomass at shade levels~ 94%.

PAGE 193

176 Comparison of the light compensation point (LCP) estimated using regression models indicated species-specific differences in the amount of PAR required for macrophyte growth. The results suggested that macrophyte biomass production decreased linearly with decreasing light availability. There was a strong regression relationship (R2 = 90.1 %) between PAR and N guadalupensis yield (Figures 5-1 and 5-2). Using the equations from Figures 5-1 and 5-2, the apparent photosynthetic photon flux density for no net N guadalupensis growth was estimated to be 59.8 mol m2 s1 (7.7 % incident PAR) and 17.5 mol m2 s1 (2.3% incident PAR) at the air-water and sediment-water interface respectively. PAR explained over 94% of the variance in P. illinoensis yield (Figure 5-.3). Using the equations from Figures 5-3 and 5-4, the apparent photosynthetic photon flux density for no net P illinoensis growth was estimated to be 63.4 mol m2 s1 (8.3% incident PAR) and 18.6 mol m2 s"1 (2.4% incident PAR) at the air-water and sediment-water interface, respectively. PAR explained nearly 70% of the variance in V. americana biomass (Figure 5-5). Using the equations from Figures 5-5 and 5-6 the apparent photosynthetic photon flux density for no net V. americana growth was estimated to be 64.1 mol m2 s1 (8.3% incident PAR) and 18.7 mol m2 s1 (2.4% incident PAR) at the air-water and sediment-water interface, respectively. There was a strong relationship (R2= 81.12%) between Chara sp. biomass production and PAR (Figure 57). Using the equations from Figures 5.7 and 5.8 the apparent photosynthetic photon flux density for no net Chara sp. growth was 159.9 mol m2 s1 (20.6% incident PAR) and 46.7 mol m2 s1 (6% incident PAR) at the air-water and sediment-water interface respectively

PAGE 194

177 Experiment 2: 4/21/03 to 6/7/03 PAR measured at the air-water interface of the treatment groups ranged from 824 mol m2 s1 or 100% incident PAR with no shade in the control group to 5.1 mol m2 s1or 0.6 % incident PAR in the 99% shade group. PAR available at the pot level (z = 60 cm) was approximately 30% of the PAR available at the air-water interface ranging from 240.8 mol m2 s1 in the control group to 1.5 mol m2 s1 in the 99% shade group (Table 5-6). Analysis of variance using GLM procedures (SAS Institute 1999-2001) indicated that light, plant type and the interaction between these two factors had a highly significant effect on macrophyte yield in this experiment (P < .0001). There were significant treatment effects among and within the macrophyte species. Chara sp. produced significantly greater yield than the other species in the control group. V americana produced statistically greatest biomass as compared to the other study species in all the light treatment groups. Comparisons within species indicated a significant decrease in the growth of all species at light levels 6.5% incident PAR (Table 57). Comparison of the light compensation point (LCP) estimated using regression models indicated species-specific differences in the amount of PAR required for macrophyte growth. The results suggested that macrophyte biomass production decreased linearly with decreasing light availability. There was a very strong regression relationship (R2 = 93.9%) between PAR and V americana yield (Figure 5-9). Using the equations from Figures 5-9 and 5-10, the apparent photosynthetic photon flux density for no net V americana growth was estimated to

PAGE 195

178 be 150.5 mol m-2 s-1 (18.3% incident PAR) and 43 9 mol m-2 s-1 (5.3% incident PAR) at the air-water and sediment-water interfaces, respectively. PAR explained over 90% of the variance in P. illinoensis yield (Figure 5-11). Using the equation from Figures 5-11 and 5-12, the apparent photosynthetic photon flux density for no net P. i/linoensis growth was estimated to be 182.5 mol m-2 s-1 (22.2% incident PAR) and 53.3 mol m-2 s-1 (6.5% incident PAR) at the air-water and sediment-water interfaces, respectively. Chara sp. biomass and PAR were strongly related (R2 = 78.77%) (Figure 5-13). Using the equation from Figures 5-13 and 5-14, the apparent photosynthetic photon flux density for no net Chara sp. growth was estimated to be 94.4 mol m-2 s -1 (11.5% incident PAR) and 27.5 mol m-2 s-1 (3.3% incident PAR) at the air-water and sediment-water interfaces, respectively. Experiment 3: 6/28 to 8/2/03 PAR measured at the air-water interface of the treatment groups ranged from 821 mol m-2 s-1 or 100% of incident PAR with no shade in the control group to 22.9 mol m-2 s-1or 2.8 % incident PAR in the 97% shade group. PAR available at the sediment-water interface (z = 60 cm) was approximately 40% of the PAR available at the air-water interface ranging from 328.4 mol m -2 s-1 in the control group to 9.2 mol m-2 s-1 in the 97% shade group (Table 5-8). Analysis of variance using G LM procedures (SAS Institute 1999-2001) indicated that light, plant type and the interaction between these two factors had a highly significant effect on macrophyte yield in this experiment (P < .0001). There were significant treatment effects among and within the macrophyte species. Chara sp. exhibited greater growth than the other species in all treatment

PAGE 196

179 groups except the 2.8% light group in which V. americana biomass was greatest. Comparisons within species indicated that all species produced greatest biomass in the control group. Chara sp. and V. americana growth decreased at light levels :s; 26.2% and again at light levels :s; 2.8%. There were no statistical differences in P. il/inoensis growth at light levels :s; 26.2% (Table 5-9). Comparison of the light compensation point (LCP) estimated using regression models indicated species-specific differences in the amount of PAR required for macrophyte growth. The results suggested that macrophyte biomass production decreased linearly with decreasing light availability. There was a strong regression relationship (R2 = 77.83%) between PAR and V. americana yield (Figure 5-15). Using the equations from Figures 5-15 and 5-16 the apparent photosynthetic photon flux density for no net V. americana growth was estimated to be 134.9 mol m2 s"1 (16.4% incident PAR) and 53 8 mol m2 s1 (6.6% incident PAR) at the air-water and sediment-water interfaces, respectively PAR explained over 75% of the variance in P. il/inoensis yield (Figure 5-17). Using the equations from Figures 5 17 and 5-18, the apparent photosynthetic photon flux density for no net P il/inoensis growth was estimated to be 350.2 mol m2 s1 (42.7% incident PAR) and 140.1 mol m2 s1 (17.1 % incident PAR) at the air-water and sediment-water interfaces, respectively Chara sp. biomass and PAR were strongly related (R2= 80.36%) (Figure 5-19). Using the equations from Figures 5-19 and 5-20, the apparent photosynthetic photon flux density for no net Chara sp. growth was estimated to be 25 mol m2 s1 (3% incident PAR) and 10 mol m2 s1 (1.2% incident PAR) at the air-water and sediment-water interfaces, respectively.

PAGE 197

180 Field observations at the time of harvest indicated the presence of the herbivorous moth, Parapoynx diminuta/is Snellen, in all treatment groups other than the controls in Experiment 3. Although Malathion was added to each of the control groups in order to control herbivory, concentrations in the light treatment groups were apparently insufficient to eliminate this herbivore. Accordingly, we believe that herbivory had a significant negative effect on P. illinoensis production in all replicates of treatments B through E that led to a subsequent overestimate of the PPFD at which there was no net growth. Parapoynx diminuta/is does not appear to feed on V. americana and Chara sp. (Hopson-Fernandes, personal observation). Effects of Light Availability on Macrophyte Chlorophyll a in Propagules Analysis of variance using GLM procedures (SAS Institute 1999-2001) indicated that treatment and plant species had a highly significant effect on macrophyte chlorophyll a (mg/g macrophyte DWT) in Experiment 1. The interaction between these two factors was slightly significant (P<0.0139). Macrophyte chlorophyll a content was not measured in Experiments 2 and 3. The data indicate that there were differences in the amount of chlorophyll a produced among and within the study species. Among-species comparisons of.the effect of decreasing light availability on the amount of macrophyte chlorophyll a measured per g macrophyte DWT indicated that V. americana produced significantly greater chlorophyll a than the other study species in all of the experimental light environments (Figure 5-21). Within species comparisons suggested that there was no relationship between Chara sp. chlorophyll a content and decreasing light availability. N guadalupensis produced statistically greatest chlorophyll a in the

PAGE 198

181 26.2% light group. N. guadalupensis chlorophyll a content decreased significantly in the 5.8% light group and again in the 0.7% light group. P illinoensis chlorophyll a content was greatest in the 26.2% and decreased significantly in the 2.6% light group. V. americana produced the greatest amounts of chlorophyll a in the 26.2% light group while a significant decline in chlorophyll a was observed in the 0. 7% group Discussion Light is recognized as one of, if not the most, important factors affecting the growth of submersed aquatic macrophytes. This relationship is particularly well defined in highly turbid, eutrophic lakes (van Dijk et al. 1992, Lauridsen et al.1994, Strand 1999). Light availability drives a variety of population dynamics within natural plant communities including species composition, distribution and maximum depth of colonization However, despite the fact that the general significance of light to SA V growth is so well-accepted, there remains considerable uncertainty as to the specific light requirements of submersed macrophytes Studies conducted to date vary widely and few have distinguished between the requirements for plant survival and reproduction (Kimber et al. 1995). Dennison et al. (1993) observed that, at present, there is no consensus concerning the light environment required for the growth and survival of V. americana in shallow water bodies. A review of the literature indicates that minimum light requirements vary from species to species and are affected by the length of the growing season (Table 5-10) In his investigation of 8 species of seagrasses, Dennison (1987) observed light compensation points that varied from 9 to 26 mol m-2 s -1 Goldsborough and Kemp (1988) concluded from their treatment and "recovery" studies that 11 % ambient irradiance was required for the survival of

PAGE 199

182 Potamogeton perfo/iatus. Sand-Jensen and Madsen (1991) observed among-species differences in their comparative study of the light requirements of charophytes, bryophytes and angiosperms. Van et al. ( 197 6) used photosynthetic rate measurement studies to calculate the light compensation points of two native and two exotic species of submersed macrophytes: Hydrilla verticil/ata, Ceratophy/lum demersum, Myriophy/lum spicatum and Cabomba caro/iniana. They concluded that H verticillata had the lowest LCP -15 mol s1 m 2 followed by C. demersum and M spicatum-both 35 mol s' m2 C. caro/iniana exhibited the greatest light requirement with an estimated LCP of 55 mol s1 m2 They also observed that Hydrilla had the lowest light requirement to achieve half-maximal photosynthetic rate. They inferred that the superior photosynthetic efficiency conferred by these adaptations probably explains Hydrilla's competitive advantage over many submersed macrophyte species. Canfield et al. (1985) estimated LCP's for hydrilla equivalent to less than 1 % full sun at the maximum depth of colonization in several study lakes. (See Table 2 in Canfield et al. 1985). Spence and Chrystal (1970) reported LCP's less than 1 E m2 s1 in their study of the light requirements of submersed macrophytes. The findings of this research suggest that light had a statistically significant effect on macrophyte growth. Light explained over 90% of the variance in N guadalupensis yield in Experiment 1, from 75 to 95% of the variation in P. il/inoensis biomass, from 70 to 94% of the variance in V. americana yield and greater than 78% of the variation in Chara sp. biomass production in all three experiments. The plants responded to decreasing light availability by reducing total, above and below-ground

PAGE 200

183 dry weight. In a laboratory study of the effects of turbidity on vallisneria, Doyle and Smart (2001) observed similar decreases in total AFDM in response to decreasing light availability. Grimshaw et al. (2002) also reported a decrease in the AFDM of V. americana with decreasing light. N guadalupensis, P. illinoensis and Chara sp. exhibited elongated stems relatively lesser numbers of lower leaves and increased canopy formation in response to increasing shade. Goldsborough and Kemp (1988) observed similar shade responses in P. perfoliatus. The results indicated that changes in chlorophyll a content in relation to light availability varied according to plant species. V. americana exhibited significantly greater chlorophyll a content per g macrophyte DWT than the other study species in all treatment groups Comparisons within macrophyte species indicated that there was no apparent effect of decreased light availability on Chara sp. chlorophyll a concentration. However greatest chlorophyll a concentrations were measured in the 26 2% light group for all of the other species. This result was possibly due to the absence of sufficient energy at lower light levels to produce increased chlorophyll. Goldsborough and Kemp (1988) observed significant increases in chlorophyll a content in response to decreasing light within 3 days of introduction of the light variable. Chlorophyll concentrations returned to normal levels following removal of the light variable. The sample size (n = 3) used in this study was not large enough to ensure representativ e s ampling o f s hoot materials o f differing ages. The high internal variation obscured any observable trends in macrophyte chlorophyll a production in response to increasing shade in this study

PAGE 201

184 The results also suggested relationship between length of growing period and total PPFD for the culture period and light requirements. N guadalupensis, P. illinoensis and V. americana exhibited lowest light requirements during the spring/summer culture period (Experiment 1) (Table 5-11 ). The length of this experiment was approximately twice that of the other two experiments. The plants also received considerably greater total PPFD in Experiment 1, 3011 mol photons m 2 than in the other two experiments, 1922 and 1427 mol photons m2 It seems intuitive that immature plants might have greater light requirements when first established in order to ensure sufficient light levels at the sediment-water interface .. The amount of light required for the growth of propagules of the submersed aquatic macrophytes in this study also varied seasonally (Table 5-11 ). N guadalupensis, P. illinoensis and V. americana exhibited lowest minimum light requirements in the late spring to early summer (59.8, 63.4 and 64.l mol photons m, respectively). Chara sp. exhibited lowest light requirements in summer and highest light requirements in the spring/summer. These results would tend to suggest that other factors besides light may have a more significant on Chara sp. growth Conclusions There was a decrease in total biomass produced by Najas guadelupensis Potamogeton illinoensis Val/isneria americana and Chara sp. in response to decreasing PAR. Macrophyte chlorophyll a content appeared to be unaffected by decreasing PAR. There was a decrease in above to below-ground biomass ratios for all species as available light decreased. The perennial species, P. illinoensis and V.

PAGE 202

185 americana, produced significantly greater below-ground biomass as compared to the annual, N guada/upensis. Vallisneria appeared to be the most well-adapted study species for survival in low light environments. The combination of low light compensation point, high concentration of chlorophyll a and extensive root structure possibly confer an advantage to vallisneria in shallow turbid systems. However, additional study is required in order to clarify some of the contradictory findings regarding the light requirements of V allisneria before managers should rely on monocultures of V allisneria. In summary a combination of several or all of the study species should be considered in order to ensure the maximum possibility for the successful establishment of a healthy sustaining communities of desirable native submerged plants in shallow eutrophic lakes. Establishment of propagules of N guadalupensis, P. illinoensis and Chara sp. during the late spring/early summer will require PPFD levels greater than 8% ambient light. The results suggested that summer is the optimum time to plant Chara sp . Additional research is needed in order to quantify the amount of light required by submersed macrophytes in all stages of their life cycles. A better understanding of the role of light in inter-specific competition is also required.

PAGE 203

186 Table 5 -1: Temperature and irradiance during the three culture periods Temperature values are average daily temperatures followed by the standard deviation. Values shown in parentheses are the lowest and the highest measured temperatures for each culture "d peno. Culture Period Water Temperature Mean Instantaneous Photoperiod (C) PPFD8 (hr) (u.mol s-1 m-2 ) Experiment 1 24.8 2.2 777 (13.8L:10 .2D) 4/27 -7 /14/02 (23.4 26.8) (0-2240) Experiment 2 26.2 1.7 824 (13.5L : 10.5D) 4/21 6/7 /03 (22.6 to 30.4) (0 2283) Experiment 3 28.2 0.9 821 (13.8L:10.2D) 6/28 8 /2/03 (22.3 to 33.4) (0-2337) 8Photosynthetic photon flux density (PAR). Values shown are means of the daily average PAR measured over the course of each respective culture period.

PAGE 204

Table 5-2: Experiment 1: Estimated average instantaneous, daily and total photosynthetic photon flux density (PPFD) received over me penoo L., Apn1 m 1 '+ Ju1y l 'o oays J assummg 1-' .o-nour oay1en gm. Treatment Light level Total PPFD DailyPPFD Instantaneous PPFD (% light) For CP8 mol*m2d1 umol* s1 m2 Mol*m-2 Surface Potb Surface Potb Surface Potb Surface Potb A 100.0 29.2 3010.9 879.8 38.6 11.3 777.0 227.0 B 26.2 7.7 790.5 231.0 10.1 3.0 204.0 C 5.8 1.7 173.7 50.8 2.2 0.7 44.8 D 2.6 0.8 78.0 22.8 1.0 0.3 20.1 E 0.7 0.2 22.0 6.4 0.3 0.1 5.7 8Culture period. bPot level estimates are not corrected for self-shading by the above-sediment portions of the individual macrophytes. Quantification of these values is beyond the scope of this research. The degree of self-shading should vary with species differences in leaf architecture and growth strategy. 59.6 13.10 5.9 1.7 Table 5-3: Results of within species analysis of net yield of total macrophyte biomass (above plus below ground biomass) in Experiment 1 using GLM procedures (SAS Institute 1999-2001) Values are the means calculated for three culture containers per macrophyte species per treatment group followed by the standard error. Means within a column followed by the same letter are not "ficantlv different at the 5% level according to Tukev's HSD Method -Macrophyte Species Treatment8 Naias Potamogeton Vallisneria Chara A 105.8 16.6a 52.4 6.2 a 4.9 3.5 a 3.0 1.0 a :a 1.8 0.2 b 5.9.lb 1.1 0.2 b -0.2.2 b C -0.2 0.0 b -0.6.0 b -0.2 0.2 C -0.5 0.1 b 0 -0.3 0 b (No survival) -0.6 0 b (No survival) -0.3 0.0 C -0.6 0.0b E -0.3 0 b -0.6 0 b (No survival) -0.6 0.0 C -0.6 0 b (No survival) 8Treatments are the same as indicated in Table 5.2. -00 .....:i

PAGE 205

188 Table 5-4: Within species comparisons of root:shoot ratios for Experiment 1. Values are the means calculated for three culture containers per macrophyte species per treatment group followed by the standard error. All data were analyzed using GLM procedures (SAS Institute 1999-2001). Means within a column followed by the same letter are not .fi tl d.ffi t t th 5 I 1 d. t Tuk HSD M th d s1gm 1can 1y 1 eren a e o eve accor mg o ey s e 0. Macrophyte Species Treatmerit8 Naias Potamogeton V allisneria A 0.03 0.00a 0.09 0.00a 0.12 0.04 b B 0.03 0.01 a 0.08 0.00 a 0.28 0.04 b C 0.31 0.24 a 0.09 0.09 a 2.38 0.01 ab D 0.00 a 0.00a 2.40 0.49a E 0.05 0.02 a 0.00a 0.28 0.00 b Table 5-5: Comparisons among species of root:shoot ratios for Experiment 1. Values are the means calculated for three culture containers per macrophyte species per treatment group followed by the standard error. All data were analyzed using GLM procedures (SAS Institute 1999-2001). Means within a column followed by the same letter are not .fi 1 d.ffi th 5 1 1 d. Tuk HSD M th d s1gm 1cant lY 1 erent at e o eve accor mg to ey s e 0. Treatment Macrophyte Root to Shoot Ratio Tukey Group A V. americana 0.12 0.04 A P. illinoensis 0.09 0.00 A N guadalupensis 0.03 .00 A B V. americana 0.28 0.04 A P. illinoensis 0.08 0.00 B N guadalupensis 0.03 0.01 B C V. americana 2.38 0.01 A N guadalupensis 0.31 0 .24 B P. illinoensis 0.09 .09 B D V. americana 2.40 0.49 A P. illinoensis 0 B Najas 0 B E V. americana 0.28 0.00 A N guadalupensis 0.05 0.02 B P. illinoensis 0 B

PAGE 206

Table 5-6: Experiment 2: Estimated average instantaneous, daily and total photosynthetic photon flux density (PPFD) received over LJ ., Treatment Light level Total PPFD Daily PPFD Instantaneous PPFD (% light) ForCP8 mol*m-2*d-1 umol* s-1 m-2 Mol*m-2 Surface Potb Surface Pot Surface Pot0 Surface Potb A 100.0 29 2 1922.2 561.7 40.l 11.7 824.0 240.8 B 6.5 1.9 125.3 36.6 2.6 0.8 53.7 15.7 C 5.1 1.5 98.8 28.9 2.1 0.6 42.4 12.4 D 1.8 0.5 34.4 10.1 0.7 0.2 14.8 4.3 E 0.6 0.2 11.9 3.5 0.3 0.1 5.1 1.5 8Culture period. bPot level estimates are not corrected for self-shading by the above-sediment portions of the individual macrophytes. Quantification of these values is beyond the scope of this research. The degree of self-shading should vary with species differences in leaf architecture and growth strategy. Table 5-7: Results of withinspecies analysis of net growth of total macrophyte biomass (above plus below ground biomass) in Experiment 2 using GLM procedures (SAS Institute 1999-2001) Values are the means calculated for three culture containers per macrophyte species per treatment group followed by the standard error. Means within a column followed by the same letter are not ficantlv different at the 5% level according to Tukev' s HSD Method Macrophyte Species ireatment8 P. illinoensis V. americana Chara sp. A 4.83 + 0.96 a 2.53 0.36 a 13.11 .31 a B -0.87 0.20 b -0.21 0.09 b -0.70 0.10 b C -1.02 + 0.05 b -0.28 0.13 b -1.03 0 .05 b D -1.08 0 b (No survival) -0.49 0.02 b -1.13 0 b (No survival) E -1.08 0 b (No survival) -0.50 0.04 b -1. 13 0 b (No survival) 8Treatments are the same as indicated in Table 5-4. ..... 00 \0

PAGE 207

Table 5-8: Experiment 3: Estimated average instantaneous, daily and total photosynthetic photon flux density (PPFD) received over L Treatment Light level Total PPFD Daily PPFD Instantaneous PPFD (% light) For CP8 mol*m-2*d-1 umol*m-2s-1 Mol*m-2 Surface Pot0 Surface Pot Surface Pot0 Surface Pot0 A 100.0 40.0 1427.6 571.0 40.8 16.3 821 328.4 B 26.2 10.5 374.6 149.8 10.7 4.3 215.4 86.2 C 11.4 4.6 163.0 65.2 4.7 1.9 93.8 37.5 D 8.3 3.3 118.3 47.3 3.4 1.4 68.1 27.2 E 2.8 1.1 39.8 15.9 I.I 0.5 22.9 9.2 8Culture period. bPot level estimates are not corrected for self-shading by the above-sediment portions of the individual macrophytes. Quantification of these values is beyond the scope of this research. The degree of self-shading should vary with species differences in leaf architecture and growth strategy. Table 5-9: Results of analysis of net growth of total macrophyte biomass (above plus below ground biomass) in Experiment 3 using GLM procedures (SAS Institute 1999-2001) Values are the means calculated for three culture containers per macrophyte species per treatment group followed by the standard error. Means within a column followed by the same letter are not significantly different at he 5% level according to Tu.key's HSD Method Macrophyte Species Treatment8 Potamogeton V allisneria Chara A 1.04 0.26 a 1.44 0.16 a 5.75 0.92 a B -0.38 0.10 b 0.27 0.06 b 2.58 0.66 b C -0.43 0.03 b -0.13 0.15 be 0.87 0.30 be D -0.58 0.02 b -0.08 0.15 be 0.56 0.21 be E -0.64 0 b (No survival) -0.38 0.05 C -0.45 .06 C 8Treatments are the same as indicated in Table 5-6. ......

PAGE 208

Table 5-10: Selected field observations and experimental conclusions concerning the light requirements of several species of Observed an inter-specific variation in LCP's among four species of SA V ranging VAN ET AL. 1976 from 55 mole photons m-2 s-1 to 15 mole photons m-2 s-1 Estimated that an average midday irradiance of at least 250 mole photons m-2 s-1 AGAMI and AGAMI 1980 would be necessary for seed production Estimated that the light level that determined the lower depth limit of plant CHAMBERS and KALFF 1985 colonization could be as much as 21 % of surface light Estimated that Potamogeton perfoliatus required > 11 % of ambient irradiance for GOLDSBOROUGH and KEMP 1988 survival Observed that an average of 100 umol*m-zs- was necessary at the sediment-water CARTER and RYBICKI 1990 interface for submersed macrophytes to survive in the tidal Potomac River Estimated that 7% of surface light or 505 mol*m-z per year was needed for rooted SAND-JENSEN and MADSEN 1991 aquatic plants to grow. Concluded that the light requirements for submersed plant growth vary widely and KIMBER ET AL. 1995 few of these [studies] have distinguished between requirements for plant survival and plant reproduction. Determined that the PPFD for no net growth of Val/isneria americana measured GRIMSHAW ET AL. 2002 approximately a quarter meter from the sediment surface, was 29 mole photons m-2 s-1 or 4.09% surface irradiance. Calculated that the minimum PPFD at the sediment-water interface for no net THIS STUDY growth ofpropagules of N guada/upensis was 60 mole photons m-2 s-1 or 7.7% incident irradiance, for P. illinoensis was 63 mole photons m-2 s-1 or 8.2% incident irradiance, for V. americana was 64.1 mole photons m-2 s-1 or 8.3% incident irradiance and for Chara sp. was 25 mole photons m-2 s-1 or 3% incident irradiance .. .... \0 ....

PAGE 209

Table 5-11: A comparison of the seasonal variation in light levels at which there was zero net growth of the study species The percentages and PPFD values listed in the first row for each experiment are values measured at the air-water interface while values listed in the second row occurred at the sediment-water interface. Najas Potamogeton LCP PPFD LCP (%) (mol photons (%) -1 -22 s m Propagule 7.7 59.8 8.2 Experiment 1 2.3 17.9 2.4 4/27 to 7/14/02 Propagule ----22.2 Experiment 2 6.5 4/21 to 6/7 /03 Propagule ----42.78 Experiment 3 17.l 8 6/28 to 8/2/03 PPFD (mol photons il m-22 63.4 18.6 182.5 53.3 350.2 140.1 V allisneria LCP (%) 8.3 2.4 18. 3 5.3 16.4 6.6 PPFD (mol photons -1 -22 s m 64.1 18.7 150.5 43.9 134.9 53.8 8Values not considered representative due to herbivory and/or competitive shading by other study species. Chara LCP (%) 20.6 6 0 11.5 3.3 3.0 1.2 PPFD (mol photons -1 -22 s m 159.9 46.7 94.4 27.5 25.0 10.0 I.O N

PAGE 210

.... 150 Q0 -r-... y = l.1103x-8.554 100 0 R2 = 0.9011 -"CS ,-._ = 50 '-" -. = ~~"CS .... = 0 0 0 -(I) 20 40 60 80 100 110 .... -50 z Percent incident PAR Figure 5-1: Propagule light requirements Experiment 1: Linear regression of PAR at the air-water interface versus the net growth (g dry weight per container per 78 days) of Najas guadalupensis. Outlying data points were excluded from analysis and are indicated in the figure as open circles. ...... \0 vJ

PAGE 211

.= 1 50 QC -t---y == 3.8056 x 8 .5672 1 00 R2 == 0 9009 0 "'C ,.-_ = 50 ..._, -= .= f "'C = 0 0 0 -(D 5 10 15 2 0 2 5 3 -50 z Mid-water percent incident PAR Figure 5-2: P r o pagule light requ irements Ex p eriment 1: Linear regression of mid-water PAR, measured at the sediment-wa ter inte r face, ve r sus the net gr owth (g dry weight per co ntainer per 7 8 days) of Najas guade/upens i s Outlying dat a points were exclud ed fro m an a lysis an d are i ndic ate d in the figure as ope n circles. ..... ':f.

PAGE 212

80 l:)J)~ -"'CS 00 60 Q~ "'CS 40 l:)J) ..._.. .. ,S = 20 ; Q ...... .. = 0 l:)J) Q ...... CJ .. Z -20 y = 0.559x 4.5634 R2 = 0.9488 20 40 60 80 100 110 Percent incident PAR Figure 5-3 : Propagule light requirements Experiment I: Linear regression of PAR at the air-water interface versus the net growth (g dry weight per container per 78 days) of P. illinoensis Since there was no survival in the two lowest light treatment groups, the I% light group was excluded from the model. ..... \0 VI

PAGE 213

..,._ ..-.. 80 rl:l bi)~ y = l .9164 x -4 5789 '"O 60 00 ~t""R2 = 0 9487 -'"O 40 bi) ~20 ..,._ = ; = ..,._ = 0 = ..,._ CJ -(I) 10 20 30 Z 8,. -20 Mid-water percent incident PAR Figure 5-4: Propag u le l i ght re qu irements Experi m ent 1: Linear regression of mid -water PAR measured at the sediment-water interface vers u s the net gr o wth (g dry weight per c o ntainer per 78 days) of P. illinoensis. Since there was no survival in the two l o west light treatm en t groups the 1 % light gr oup was exclude d fr o m the model. \0 O"I

PAGE 214

20 -"C ao 15 c~ ,:, 10 ~Q.,_ __,. ,.c= ..... = -0 J. = ~o ..... J. 5 0 Z -5 Q.,_ y = 0.0902x0.7439 R2 = 0.6985 20 40 60 80 100 110 Percent incident PAR Figure 5-5: Propagule light requirements Experiment 1: Linear regression of PAR at the air-water interface versus the net growth (g dry weight per container per 78 days) of V. americana. -\0 -i

PAGE 215

";' 20 bl)~ y = 0.3093x0.745 4 ....C "'C ; 00 15 ~t--R2 = 0.6985 ,.. ,.. "'C 10 bl) ,._,,.. ,.= 5 ... = ; 0 ... 0 ,.. = bl) 0 ... CJ ,.. 5 ()) 10 20 30 z Mid-water percent incident PAR F i gure 5 6 : Prop ag u le light requ irements Exp e ri m ent 1: Linear r egression of mid -water PAR, measured at the sediment-water interface, v ers u s the net gr o wth (g dry weig h t per c o ntainer per 78 days) of V. americana. -" 00

PAGE 216

..... ...-... 6 rl.l : I ...C ,:s y = 0.0364 x -0 .7491 00 R2= 0.8 112 ,:s 3 ='-" 2 ..... = ; 1 0 ..... = ~o 0 ..... CJ Z -1 Qf'. =2Q 4g 9Q gg lQQ 120 Percent incident PAR Figure 57 : Propa gule light re qu irements Experiment I: Linear regression of PAR at the air-water interface versus the net growth (g dry weight per c o ntainer per 7 8 d ays) of Chara sp .....

PAGE 217

... 6 bf) = 5 -"'C 00 4 t---c 3 "'C c.. bf) 2 ,._,~ = 1 ..... = 0 0 ... = bf) 0 1 e,j ... -z -2 y = 0.1247x0.7496 R2 = 0.8111 Mid-water percent incident PAR Figure 5-8: Propagule light requirements Experiment 1: Linear regression of mid-water PAR, measured at the sediment-water interface, versus the net growth (g dry weight per container per 78 days) of Chara sp. N 0 0

PAGE 218

...... 6 0J) ..... '"C 4 I y = 0.0271x-0.4948 0 i:: 00 R2 = 0.9385 -'"C 0J) C. 2 ..._.,. ........... i:: = 0 ...... = 0 0J) 0 (D--20 4 0 60 8 0 1 0 0 110 ...... Cj -Z -2 C. Percent incident PAR Figure 5-9. Pro p agule ligh t requirements Experiment 2: Linear regression of PAR at the air-water interface versus the net growth (g dry weight per c o ntaine r per 4 8 d ays) of V. americana. O utlyi n g data points were e xcluded from analysis and are indicated in the N figure as o p en circles. 8

PAGE 219

....,._..-.. 6 ..c rl:l bl)~ 0 -"CS y == 0.0928x 0.4945 Q0 4 R2 == 0.9385 "CS bl) Q,_ 2 .._.,i.. ..c : ....... I 0 = 0 ....... ... = 0 bl) 0 5 10 1 5 20 25 3 0 3 ....... CJ ... Z -2 Q,_ Mid-water percent incident PAR Figure 5 1 0 J>rop ag ule lig h t re q uirements Experiment 2: Linear regression of mid-water PAR, measured at the sediment-water i nterfa c e, ve rsus the n e t gr o wth (g dry w e ight per co ntainer per 4 8 d ays) of V americana. Outlying data points were excluded from analysis and are indicated in the figure as open circles. N s

PAGE 220

... 8 .= r:l:l -~ : 6 I y = o.0597x 1.3221 R2 = 0.9248 t 4 "'C C. ~ .= : 2 ... -= f: = Q I o 0 : 2 r 20 40 60 so 100 110 z C. Percent incident PAR Figure 5-11. Propagule light requirements Experiment 2 : Linear regression of PAR at the air-water interface versus the net growth (g dry weight per container per 48 days) of P. illinoensis. Outlying data points were excluded from analys i s and are indica ted i n the figure as open circles. Since there was no survival in the two lowest light treatment groups the 1 % light group was excluded from the model. N 0 \.H

PAGE 221

...... 8 fl.l y == 0 20 4 1 x 1.32 1 4 -"C 6 00 R2 == 0.9248 "C 4 ..._.. 2 ...... -= 0 ...... 0 = ~= ...... C'.J 5 10 15 20 25 3 0 3 -z Mid-water percent incident PAR Figure 5-12. P rop agule light r e quirements Experiment 2: Linear regression of mi dwater PAR, measured at the sediment water interfa c e, v e r sus the n e t growth (g dry weight per container per 48 d ays) of P. illinoensis. Outly i ng d ata points were excluded from an a l y si s an d ar e i nd icate d in the figure as ope n ci rcles N 0

PAGE 222

ii 251 y == 0.1376x1.5762 -~ 20 R2 == 0.7877 00 c. 15 "C Q.. 10 ...... 5 = = ...... i. = 0 t:)1)0 ...... CJ -(D 20 40 60 80 100 110 Z -5 Q.. Percent incident PAR Figure 5-13. Propagule light requirements Experiment 2: Linear regression of PAR at the air-water interface versus the net growth (g dry weight per container per 48 days) of Chara sp. Outlying data points were excluded from analysis and are indicated in the figure as open circles. Since there was no survival in the two lowest light treatment groups, the 1 % ligh t group was excluded from the model. N 0 Vl

PAGE 223

,,._ ,-._ 25 -~ ,-o 20 Q0 15 "CS C. 10 : .... -= 0 .... = ~o .... y 5 0 z -5 y = 0.4708x-1.5746 R2 = 0.7877 5 10 15 20 25 3 3 Mid-water percent incident PAR Figure 5.14. Propagule light requirements Experiment 2: Linear regression of mid-water PAR measured at the sediment-water interface versus the net growth (g dry weight per container per 48 days) of Chara sp Outlying data points were excluded from analysis and are indicated in the figure as open circles. Since there was no survival in the two lowest light treatment groups the 1 % light group was excluded from the model. N 0

PAGE 224

.....,_,,--. 2 .= r,j bJ) y = 0.0 176x-0.2891 -'"CS 1.5 "' R2 = 0.7783 ,. ,. 1 '"CS bJ) C. 0 5 ,...._, ,. .= : ....... 0 0 ....... 0 5 $I t+ 20 40 60 80 100 120 ....... CJ ~ ,. 1 z ~ -C. Percent incident PAR F i gure 5-15 : Pr opa gu l e l ight r eq u irements Ex p erime n t 3: Linear regression of PAR at the air wate r interface vers u s the net growth (g dry weight per c o ntainer per 4 8 days) of V. americana. N 0 -.....1

PAGE 225

2 -= bl) y = 0.0442x -0 2896 "CS 1.5 R2 = 0.7784 Ir) ~ff') 1 -"CS bl) =0.5 ~--= .. 0 0 -0.5 (DI a. 10 20 30 4 0 5 -z 1 =Mid-water percent PAR Figure 5 16: Propagule light requirements Experiment 3 : Linear regression of mid-water PAR, measured at the sediment-water interface, ver s u s t h e net gr o wth (g dry weight per container per 35 days) of V. americana. N 0 00

PAGE 226

-.,,i,.-... 2 .5 blJ 2 ..... "'CS y = 0.0172x0.7335 In 1.5 R2 = 0.7531 "'CS blJ C. 1 ...._., 0.5 -.,,i ..... = 0 0 -.,,i = llO blJ 8 -0.5 (b_ 40 60 80 100 -.,,i 1 z C. Percent incident PAR Figure 5-17 : Pr o p~gule light requirements Experiment 3: Linear regressio n of PAR at the air water interface versus the net growth (g dry weight per c o ntainer per 35 d ays) of P il/inoensis. Outlying data points were excluded from analysis and are indicate d in the figure as open circles. N 0 \0

PAGE 227

,.-_ l':'-J ...= = -'"CS In ff"l ~ '"CS C. ~'-"~ ...= = -= 0 = ~o z C. 2.5 2 1.5 1 0.5 0 -0.5 -1 y = 0.043x -0. 734 R~ = 0.753 Mid-water percent incident PAR Figure 5-18: Propagule light requirements Experiment 3: Linear regression of mid-water PAR, measured at the sediment-water interface, versus the net growth (g dry weight per container per 35 days) of P. illinoensis. Outlying data points were excluded from analysis and are indicated in the figure as open circles N -0

PAGE 228

...... ,..= 1 2 bl) In 10 I 0 Ji-. y = 0.0535 x -0 162 4 8 t~ R2 = 0.8036 Ji-. 6 bl) = -= 4 I 0 ,..= ...... = 0 2 0 CJ Ji-. Ji-. bl) 0 ...... -2 0 20 40 60 80 1 0 0 1 20 z Percent incident PAR Figure 5 1 9 : Pr opag ul e light re qu irements Exp eri m e n t 3: Line a r regressi o n of PAR at the air w ater interface vers u s the net growth (g dry weight per cont ainer per 35 days) of Chara sp. O utlying data points were exclu ded from analysis and are indicated in t h e figure as open circles. N -

PAGE 229

.---. 12 = I 0 -~ ,e 10 y = 0.134 1x 0.1639 lf) 8 c~ R2 = 0.8037 "CS Q. 6 ..._.... 4 I 0 ..... = -. = 2 = ..... = 0 ~= ..... CJ -2 z Q. Mid-water percent PAR Figure 5-2 0 : Propagule light r equi rements Experiment 3: Lin ear r e gression of mid -water PAR, measured at the sediment-wa ter interface, ve rsus the net growth (g dry weigh t per container per 35 days) of C h ara sp. Outlying data points were excluded from anal ysis and a re ind i c ated in the figure as ope n circles. N -N

PAGE 230

-4 -4 ~,,-.. ..... C. 0 01) -.. ]~ 01) -a = e -~ <'.J = = 15 10 5 0 a a A B C D Percent incident PAR E IDID Najas II Potamogeton m Vallisneria II Chara Figure 5-21: Among species comparisons of macrophyte chlorophyll a produced during propagule plant light requirement Experiment 1 (4/27 to 7/14/02) Bars represent the means of three samples (n=3) per macrophyte species. Error bars represent the standard error. Means with the same letter are not significantly different at the 5% level according to Tukey's HSD Method. N ..... w

PAGE 231

CHAPTER6 SUMMARY AND CONCLUSIONS 214 Submerged vascular macrophytes are an important ecological component of aquatic systems. These primary producers provide habitat for invertebrates, epiphytes, fish and a variety of other organisms. The distribution and growth of submersed macrphytes are influenced by a variety of environmental factors including sediment and light. The results of Objective 1 of this study indicated that the sediments occurring at stations B, D, F and H in Lake Hollingsworth were suitable substrates for the growth of Najas guadalupensis, Potamogeton illinoensis, Vallisneria americana and Chara sp. when grown in experimental growth tanks. These results, in combination with the observation that root to shoot ratios were always less than 1 for all plant types, indicate that the sediment nutrient concentrations investigated in this study were adequate to support the growth of all four species. Field-testing of these results is necessary in order to determine the effect of such factors as sediment quantity on the applicability of these findings to the natural environment. Late spring appeared to be the optimum time in which to introduce propagules of Najas guadalupensis, Potamogeton illinoensis, Vallisneria americana and Chara sp. into systems to be restored. N. guadalupensis, V. americana and Chara sp. all exhibited the most luxurious growth during the summer months. P. illinoensis also produced vigorous summertime growth Accordingly, planting in late spring should provide sufficient

PAGE 232

215 time for the plants to acclimate to their new environment and in order to be able to maximize their growth potential during the summer. This period of strong growth should allow the plants to firmly establish. Plant growth appeared to be influenced by a combination of factors including light, water temperature and sediment nutrients. The results of Objective 2 indicated that there was a decrease in total biomass produced by Najas guadalupensis, Potamogeton illinoensis, Vallisneria americana and Chara sp. in response to decreasing PAR. Above to below-ground biomass ratios for all species also decreased as the light decreased. The perennial species, P. il/inoensis and V. americana, produced significantly greater below-ground biomass as compared to the annual, N. guadalupensis. Comparison of the growth response of mature and propagule representatives of the same species indicted that propagules of N. guadalupensis, P. illinoensis and V. americana had higher light requirements for net growth as compared with mature plants of the same species This observation is probably best explained by the large quantity of energy required to power all of the metabolic activities involved in the initial extension of shoot material up through the water column. This trend was reversed for Chara sp. The reason for this discrepancy is presently unknown. Temporal varaiation in macrophyte light requirements was also observed. Generally, macrophytes exhibited higher light requirements for net growth during the late winter to early spring culture period. Establishment of the study species during the growing season will require PAR levels that will provide sufficient energy for the growth of each of the individual species. The findings of this research indicated that the light required for no net loss of mature plants ranged from 2 to 50% incident irradiance while propagule light requirements ranged from 3 to 22.5%. This

PAGE 233

216 variation in light requirements among the species and between mature and propagule plants suggests that greater quantities of light would be required to establish a diverse habitat than would be required to grow any individual species. V. americana, appeared to be the most well-adapted study species for survival in low light environments. Light requirements for mature plants ranged from 2 to 6% incident light and 8.3 to 18.3 % for propagule plants. The combination of low light capability, high concentration of chlorophyll a and extensive root structure possibly confer an advantage to V. americana in shallow turbid systems. The results ohhis study indicate the need for further investigation of the effects of sediment and light on native submerged macrophytes. The limited range of sediment organic matter contents and nutrient levels investigated probably obscured macrophyte growth responses to some sediment factors in this study High variances observed in the data collected in both Objectives also probably confounded the identification of statistically significant differences in many cases. Many questions remain unanswered for lake managers seeking guidelines for the use in selecting and establishing desirable native plants in restored systems. In order to provide these answers, additional investigation of the relationship between plant nutrition and sediment physical and chemical composition is needed Further study is also needed in order to quantify the amount of light required by submersed macrophytes in all stages of their life cycles. A better understanding of the role of light in inter-specific competition is also needed.

PAGE 234

APPENDIX METHODS Grid Method 2 1 7 Lake Hollingswmth is a shallow, highly productive lake with the potential for highly variable organic sediment distribution. In their 1996 study of the variability of sediment distribution in shallow Florida lakes, Whitmore et al. (1996) indicate the importance of using systematic mapping to locate optimal coring sites. In order to ensure representative assessment of littoral sediments, a sampling scheme was developed by superimposing a grid on the bathymetric map of Lake Hollingsworth drawn on April 13, 1992 (Figure A.1) Use of the grid method facilitated identification of sampling stations distributed evenly throughout the lake littoral zone to ensure equal area coverage of the littoral region (Hakanson 1981). The convention, when using the grid method, is that stations can either be located within the space between the lines or at the intersection of lines. In this study, stations were located within the spaces between the lines. The -sampling grid has twelve littoral stations of which eight were sampled. Four of the grid stations did not include the 0.8 m contour line and were disregarded Grid stations included in the survey were lettered from A to H pr-0ceeding in a counterclockwise direction. Stations on the grid were an average of 0.45 kilometers apart. Navigation to sa ~!iJ!6 s tations was achieved using a Trimble CDS 1 GPS unit.

PAGE 235

Station F [ Lake Hollngsworth In Poll Comilr ] 218 A N ----.... ,. ..... .......... .... ._._ ... ..,.. __ ,::.ii=.= ....... ::.,~=:. u!!!!!!!!liiiiiiiiiiil!! !!!!!!!!!!!!!uiiiiiiiiiiiiiiul!!!!!!!!!!!!!!!!!!iuiiiiiiiiiiiiiiiiiiiiau .. Figure Al. Sampling grid for identifying sediment survey study station locations. Spaces within lines mark sampling sites and were established by superimposing a grid on the bathymetric map of Lake Hollingsworth drawn on April 13 1992. Sediment Nutrient Analyses Sediment nutrient analyses were performed using the Mehlich-1 Extraction Procedure (Southern Region Information and Exchange Group on Soil Testing and Plant Analyses 1983) by the Analytical Research Laboratory of the Soil and Water Scienc e Department University of F lorida, Gainesville As described in the UF/IFAS Extension Soi l Testing Laboratory (ESTL) Analytical Procedures and Training

PAGE 236

219 Manual written by Rao S. Mylavarapu and Elizabeth D. Kennelley, 4-cm3 of dry soil (approximately 5 g mineral soil) are scooped into an extracting bottle. Twenty mL of Mehlich-1 Extracting Solution is added to the bottle. The extracting solution consists of a combination of0.0125M H2SO4 and 0.05M HCI. Samples are shaken on a reciprocal shaker for 5 min. Samples are then filtered and sediment nutrient concentrations are measured using inductively coupled argon plasma (ICAP) spectroscopy. Instrument readings, reported in mgL-1 are then converted to mgKg-1 DWT using the following equation: mg* IL mLsoln l000g = mg L 1 OO0mL gsoil 1kg kg Epiphyte Biomass Determination Method The mechanical removal method described by Zimba and Hopson (1997) was used to separate the epiphytic algae from the individual macrophytes. Three randomly selected individual macrophytes were placed in separate 1-L plastic bottles containing 100 mL of distilled water. Each bottle was then agitated by hand at approximately 180 revolutions per minute. A subsample of the resultant epiphyte suspension was filtered through 1 mm screening to remove macrophyte fragments. The epiphyte slurry was subsampled to facilitate the investigation of two parameters. A subsample of the suspension was concentrated onto glass fiber filters (0.7m porosity). Epiphyte chlorophyll samples were processed and chlorophyll a and phaeophytin a and chlorophyll a, b and c were determined in accordance with Standard Methods (SM 10200 H) (A.P.H.A. 1995) guidelines and equations. Epiphyte chlorophyll concentrations were normalized to dry weight of host plant.

PAGE 237

220 Mean epiphyte biomass per gram dry weight calculated for each macrophyte species was used to estimate the total epiphytic component of the final biomass (g dry weight) measured for each macrophyte sample. Chlorophyll a corrected for phaeophytin a and relative percentages of chlorophyll a, b and c were used to investigate epiphyte response to the treatment groups. Chlorophyll data was also used to determine if the epiphytic community exhibited any host specificity. In addition, macrophyte biomass was corrected by subtracting epiphyte weight from the final dry weight measured for each macrophyte species in response to each treatment group. Macrophyte Chlorophyll Method Triplicate samples of macrophyte tissue approximately 5 cm in length were collected for each macrophyte species for each treatment group Apical tips were collected for N. guadalupensis, P. illinoensis and Chara sp .. Leaf tips were collected for V. americana. Epiphyte biomass was removed using the mechanical removal method described by (Zimba and Hopson 1997) (see above). Wet weight (g) was measured Macrophyte samples were then stored in the dark in the freezer at -20C for no more than 90 days until processed and analyzed for chlorophyll a and phaeophytin a. The chlorophyll was extracted by freezing the leaf segments with approximately 2 mL of liquid nitrogen, pulverizing them with a mortar and pestle, and extracting them in 90% acetone for 24 hours in the freezer at -20C. When necessary, pigments were diluted 1:5 with 90% acetone. The optical densities of the extracts were measured using a Beckman DU520 General Purpose UV NIS Spectrophotometer. Macrophyte chlorophyll was determined using the equations outlined in Standard Methods (SM 10200 H ) (A.P.H A. 1995).

PAGE 238

LITERATURE CITED Adams, M. S., J. Titus,and M. McCracken. 1974. Depth distribution of photosynthetic activity in a Myriophyllum spicatum community in Lake Wingra. Limnol. Oceanogr. 19:377-390. Aioi; K. 1980. Seasonal change in the standing crop of eelgrass, Zostera marina L., in Odawa Bay, Central Japan. Aquatic Botany 8: 343-354. Allanson, B. R. 1973. The fine structure of the periphyton of Chara sp. and Potamogeton natans from Wytham Pond, Oxford, and its significance to the macrophyte-periphyton metabolic model ofR.G. Wetzel and H. L. Allen. Freshwater Biol. 3:535-542. Allen, H. 1971. Primary productivity, chemo-organotrophy and nutritional interactions of epiphytic algae and bacteria on macrophytes in the littoral of a lake. Ecol. Monogr. 41:97-127. American Public Health Association (APHA). 1995. Standard methods for the examination of water and wastewater. 19th Edition. American Public Health Association, Washington D.C. 1268pp. Anderson, F. 0. 1978. Effects of nutrient level on the decomposition of Phragmites communis. Trin. Arch. Hydrobiol. 84:42-54. Anderson, M. R. and J. Kalff. 1986. Nutrient limitation of Myriophyllum spicatum growth in situ. Freshwater Biol. 16:735-743. Anderson, M. R. and J. Kalff. 1988. Submerged aquatic macrophyte biomass in r4elation to sediment characteristics in tern temperate lakes. Freshwater Biol. 19:115-121. Annadotter, H., G. Cronberg, R. Aagren, B. Lundstedt, P.A. Nilsson and Sv. Strobeck. 1999. Multiple techniques for lake restoration. Hydrobiologia 395/396 (Dev. Hydrobiol. 136):77-85. Anon. 1996. Control algae and excess vegetation in lakes. Land and Water 40:38-40. Arber, A. 1920. Water plants: a study of aquatic angiosperms. University Press, Cambridge. 221

PAGE 239

Ashley, K. I. and K. J. Hall. 1990. Factors influencing oxygen transfer in hypolimnetic aeration systems. Verh. Int. Verein. Limnol. 24:179-183. 222 Aung, L. H. 1974. Root-shoot relationships Pp. 29-61. In: E.W. Carson (Ed.) The Plant Root and its Environment. University Press of Virginia, Charlottesville, Virginia, USA. Bain, J T. and M. C F. Proctor. 1980 The requirement of aquatic bryophytes for free CO2 as an organic carbon source: Some experimental evidence. New Phytol. 86:393-400. Baker, K. S. and R. Frouin. 1987 Relation between photosynthetically available radiation and total insolation at the ocean surface under clear skies. Limnol. Oceanogr. 32: 1370-1377. Balls, H., B. Moss and K. Irvine. 1980. The loss of submerged plants with eutrophication. I Experimental design, water chemistry, aquatic plant and phytoplankton biomass in experiments carried out in ponds in the Norfolk Broadland. Freshwat. Biol. 22:71-87. Barbieri, A. and M Simona. 2001. Trophic evolution of Lake Lugano related to external load reduction: Changes in phosphorus and nitrogen as well as oxygen balance and biological parameters. Lakes and Reservoirs: Resaerch and Management 6 : 37 47. Barko, J W 1982. Influence of potassium source (sediment vs. open water) and sediment composition on the growth and nutrition of a submersed freshwater macrophyte (Hydrilla verticillata (L.f. Royle)). Aquat. Bot. 12 : 157-172 Barko, J.W. M.S. Adams and N.L. Clesceri. 1986 Environmental factors and their consideration in the management of submersed aquatic vegetation: A review. J. Aquat. Plant Manage 24: 1 10. Barko, J.W. D. Gunnison and S R. Carpenter. 1991. Sediment interactions with submersed macrophyte growth and community dynamics. Aquat. Bot. 41 :41-65. Barko, J W., D G Hardin and M.S. Matthews 1982. Growth and morphology of submersed freshwater macrophytes in relation to light and temperature. Can. J Bot. 60: 877 887 Barko J. W and R.M. Smart. 1980. Mobilization of sediment phosphorus by submersed fr e shwater macrophytes Freshwater Biol. 10 : 229-238. Barko, J.W. and R.M. Smart. 1981a. Sediment-based nutrition of submersed macrophytes Aquat. Bot. 10 : 339 352.

PAGE 240

223 Barko, J. W. and R. M. Smart. 1981b. Comparative influences oflight and temperature on the growth and metabolism of selected submersed freshwater macrophytes. Ecol. Monogr. 51:219-235. Barko, J. W. and R. M. Smart. 1983. Effects of organic matter additions to the growth of aquatic plants. Journal of Ecology 71: 161-17 5. Barko, J. W. and R. M. Smart. 1986. Sediment-related mechanisms of growth limitation in submersed macrophytes. Ecology 67:1328-1340. Barko, J. W., R. M. Smart, D. G. McFarland and R. L. Chen. 1988. Interrelationships between the growth of Hydrilla verticillata (L.f.) Royle and sediment nutrient availability. Aquat. Bot. 32:205-216. Barko, J. W. and W. F. James. 1998. Effects of submerged aquatic macrophytes on nutrient dynamics, sedimentation and resuspension. In E. Jeppesen, M. Sondergaard, M. Sondergaard and K. Christoffersen, eds. The Structuring Role of Submerged Macrophytes in Lakes. New York: Springer-Verlag, 197214. Barko, J. W., D. Gunnison and S. R. Carpenter. 1991. Sediment interactions with submersed macrophyte growth and community dynamics. Aquat. Bot. 41 :4165. Bengtsson, L. S., S. Fleischer, G. Lindmark and W. Ripl. 1975. Lake Trumrnen restoration project. I. Water and sediment chemistry. Verb. Int. Verein. Limnol. 19:1080. Beer, S. and R. G. Wetzel. 1981. Photosynthetic carbon metabolism in the submerged aquatic angiosperm Scirpus subterminalis. Plant Sci. Lett. 21:199-207. Blanch, S. J., G. G. Ganf and K. F. Walker. 1998. Growth and recruitment in Vallisneria americana as related to average irradiance in the water column. Aquat. Bot. 61:181-205. Blindow, I. 1991. The composition and density of epiphyton on several species of submerged macrophytes the neutral substrate hypothesis tested. Aquat. Bot. 29:157-168. Borum, J. 1987. Dynamics of epiphyton on eelgrass (Zostera marina L.) leaves: relative roles of algal growth, herbivory and substratum turnover. Limnol. Oceanogr. 32:986-992. Bowes, G., A. S. Holaday and W. T. Haller. 1979. Seasonal variation in the biomass, tuber density and photosynthetic metabolism ofhydrilla in three Florida lakes. J. Aquat. Plant Manage. 17:61-65.

PAGE 241

224 Bowes, G. T. K. Van, L.A. Garrard and W. T. Haller. 1977. Adaptation to low light levels by Hydrilla verticillata. J. Aquat. Plant Manage. 15:36-40. Brenner, M. and M. W. Binford. 1988 Relationships between concentrations of sedimentary variables and trophic state in Florida lakes. Can. J. Fish. Aquat. Sci. 45:294-300. Brenner, M., T. J. Whitmore, J. H. Curtis and C. L. Schelske. 1995. Historical ecology of a hypereutrophic Florida lake. Lake and Reserv. Manage. 11 :255271. Brown, H. D. 1976. A comparison of the attached algal communities of a natural and an artificial substrate. J. Phycol. 12:301-306. Brown, W. H. 1913. The relation of the substratum to the growth of Elodea. Phillipine J. Sci. 8:1-20. Bourn, W. S. 1932. Ecological and physiological studies on certain aquatic angiosperms. Contr. Boyce Thompson Inst. 4 : 425-496. Brezonik, P. L., E. C Blancher II, V. B Meyers, C.L. Hilty, M. K. Leslie, C.R. Kratzer, G.D. Marbury, B. R. Synder, T. L. Crisman and J. J. Messer. 1979. Factors affecting primary production in Lake Okeechobee, Florida. Engineering Report to the Florida Sugar Cane League. Report No. 07-79-01. University of Florida, Gainesville. Burkholder, J.M. and R. G. Wetzel. 1989a. Epiphytic microalgae on natural substrata in a hardwater lake: seasonal dynamics of community structure, biomass and ATP content. Arch Hydrobiol./Supple. 83, 1:1-56 Burkholder, J M and R. G Wetzel. 1989b Microbial colonization on natural and artificial macrophytes in a phosphorus-limited, hardwater lake J. Phycol. 25:5565. Burkholder, J.M., R. G. Wetzel and K. L. Klomparens. 1990 .. Direct comparison of phosphate uptake by adnate and loosely attached microalgae within an intact biofilm matrix. Appl. Environ, Microbio.56:2882-2890. Canfield, D. E. and M. V Hoyer. 1988a The eutrophication of Lake Okeechobee. Lake and Res. Manage. 1:21-31. Canfield, D. E. and M. V. Hoyer. 1988b. Influence of nutrient enrichment and light availability on the abundance of aquatic macrophytes in Florida streams. Can. J. Fish. Aquat. Sci. 45 : 1467-1472

PAGE 242

225 Canfield, D. E. Jr. and M. V. Hoyer. 1992. Aquatic macrophytes and their relation to the limnology of Florida lakes. Final report submitted to the Bureau of Aquatic Plant Management, Florida Department of Natural Resources, Tallahassee, Florida. 608pp. Canfield, D. E., Jr., K. A. Langeland, M. J. Maceina, W. T. Haller and J. V. Shireman. 1983. Trophic state classification of lakes with aquatic macrophytes. Can. J. Fish. Aquat. Sci. 40:1713-1718. Canfield, D. E., Jr., K. A. Langeland, S. B. Linda and W. T. Haller. 1985. Relations between water transparency and maximum depth of macrophyte co ionization in lakes. J. Aquat. Plant Manage 23:25-28. Canfield, D.E., Jr, J V. Shireman, D.E. Colle, Haller, W.T., Watkins, C.E. TI and Maceina, M.J. 1984 Prediction of chlorophyll a concentrations in Florida lakes: importance of aquatic macrophytes. Can. J. Fish. Aquat. Sci. 41:497501. Carignan, R. and J. Kalff. 1980. Phosphorus sources for aquatic weeds: water or sediments? Science 207:987-988. Carignan, R. and J. Kalff. 1982. Phosphorus release by submerged macrophytes: significance to epiphyton and phytoplankton. Limnol. Oceanogr. 27:419-427 Carlton, R. G and R. G. Wetzel. 1988. Phosphorus flux from lake sediments: Effect of epipelic algal oxygen production. Limnol. Oceanogr. 33:562-570. Carpenter, S.R. 1981 Submersed vegetation: An internal factor in lake ecosystem succession The Am. Naturalist 118:372-383. Carpenter, S R and D M. Lodge. 1986. Effects of submersed macrophytes on ecosystem processes. Aquat. Bot. 26:341-370 Carter, D R., S. Carter and J. L. Allen. 1994. Submerged macrophyte control using plastic blankets. Water Science and Technology 29:119-126. Carter, V. and N B. Rybicki. 1985. The effects of grazers and light penetration on the survival of Vallisneria americana Michx in the tidal Potomac River, Maryland. Aquatic Botany, 23 : 197-213 Carter, V. and N.B. Rybicki 1990 Light attenuation and submersed macrophyte distribution in the tidal Potamac River and Estuary. Estuaries 13 : 441-442. Carter V., N .B. Rybicki and M Turtora 1996 Effects of increased photon irradiance on the growth o f Vallisneria americana in the tidal Potomac River Aquat. Bot. 54:337-345.

PAGE 243

226 Castenholz, R. W. 1960. Seasonal changes in the attached algae of freshwater and saline lakes in the Lower Grand Coulee, Washington. Limnol. Oceangr. 5:1-28. Cattaneo, A. 1990. The effect of fetch on periphyton spatial variation. Hydrobiologia 206:1-10. Cattaneo, A. and J. Kalff. 1978. Seasonal changes in the epiphyte community of natural and macrophytes in Lake Memphremagog (Que. & Vt.). Hydrobiologia 60:135-144. Cattaneo, A. and J. Kalff. 1979. Primary production of algae growing on natural and artificial aquatic plants: A study of interactions between epiphytes and their substrate. Limnol. Oceanogr. 24:1031-1037. Cattaneo, A. and J. Kalff. 1980. The relative contribution of aquatic macrophytes and their epiphytes to the production of macrophyte beds. Limnol. Oceanogr. 25:280-289. Cenzato, D. and G. Ganf. 2001. A comparison of growth responses of two species of Potamogeton with contrasting canopy architecture. Aquat. Bot. 70:53-66. Chambers, P. A. and J. Kalff 1987a. Light and nutrients in the control of aquatic plant community structure. I. In situ observations. J. Ecol. 75:611-619. Chambers, P.A. and J. Kalff. 1987b. Light and nutrients in the control of aquatic plant community structure. II. In situ observations. J. Ecol. 75:621-628. Chambers, P.A. and E. E. Prepas. 1990. Competition and coexistence in submerged plant communities: The effects of species interactions versus abiotic factors. Freshwater Biol. 23:541-550. Chapin, F. S., ill. 1980. The mineral nutrition of wild plants. Annual Review of Ecological Systems 11: 223-260. City of Lakeland. 1988-2000. Long-term limnological data for Lake Hollingsworth. In Polk County Water Atlas developed by Polk County, the Florida Center for Community Design and Research, School of Architecture and Community Design, University of South Florida in association with the City of Lakeand, City ofWinterhaven, Polk County Property Appraiser, Lakes and Education/ Action Drive and the Southwest Florida Water Management District. Clarkson, D. T. and J.B. Hanson. 1980. The mineral nutrition of higher plants. Annual Review of Plant Physiology. 31 :239-298.

PAGE 244

227 Cooke, G.D., E. B. Welch, S. A. Peterson and P.R. Newroth. 1993. Restoration and Management of Lakes and Reservoirs, 2nd Ed. Lewis Publishers, Boca Raton 548p. Cooper-Reid, N. M. and G. G. C. Robinson. 1978. Seasonal dynamics of epiphytic algal growth in a marsh pond: competition, metabolism, and nutrient availability. Can. J. Bot. 56:2441-2448. Cox, P.A. 1993. Water-pollination in plants. Sci. Amer. 269:68-74. Crosson, H. 1992. Aquatic weevil may bring watermilfoil under control. Lake Line. 12:7-10. Dale, H. M. 1986. Temperature and light: The determining factors in maximum depth distribution of aquatic macrophytes in Ontario, Canada. Hydrobiologica 133:7377. Danell, K. and K Sjoberg 1982. Successional patterns of plants, invertebrates and ducks in a man-made lake Journal of Applied Ecology 19:395-409. Davis, G. J. and M. M. Brinson. 1980. Responses of submersed vascular plant communities to environmental change. U.S. Fish and Wildl. Serv., U.S.D.I., Washington, D.C. 69 pp. Davis, L. S., J.P. Hoffinan and P. W. Cook. 19990. Production and nutrient accumulation by periphyton in a wastewater treatment facility. J. Phycol. 26:617-623. Den Hartog, C. and S. Segal. 1964. A new classification of the water plant communities. Acta Botanica Neerl. 13:367-393. Dennison, W. C. 1987. Effects of light on seagrass photosynthesis and depth distribution. Aquat. Bot.: 2715-26 Dennison, W. C. and R. S. Alberte. 1985. Role of daily light period in the depth distribution of Zostera marina (eelgrass). Marine Ecology Progress Series, 25:51-61. Dennison, W. C., R. J. Orth, K. A. Moore, J.C. Stevenson, V. Carter, S Kollar, P. W. Bergstrom and R.A. Batiuk. 1993. Assessing water quality with submersed aquatic vegetation. Bioscience. 43:86-94. Denny, P. 1972a. Sites of nutrient absorption in aquatic macrophytes. J. Ecol. 60:819829. Denny, P. 1972b. Zonation of aquatic macrophytes around Habukara Island, Lake Bunyoni, S.W. Uganda. Hydrobiologia 12:249-257.

PAGE 245

Denny, P. 1973. Lakes of south-western Uganda II. Vegetation studies on Lake Bunyonyi. Freshwater Biology 3:123-135. 228 Denny, P. 1980. Solute movement in submerged angiosperms. Biol. Rev. 50:65-92. Diehl, S. 1988. Foraging efficiency of three freshwater fishes: effects of structural complexity and light. Oikos 1988:209-214. Donnabaum, K., M. Schagerl and M.T. Dokulil. 1999. Integrated management to restore macrophyte domination. Hydrobiologia 395/396:87-97. Doyle, R. D. and R. M. Smart. 2001. Impacts of water column turbidity on the survival and growth of Vallisneria americana winterbuds and seedlings. J. Lake Reserve. Manage 17:17-28. Drenner, R. W. and K. D. Hambright. 1999. Biomanipulation offish assemblages as a lake restoration technique. Archiv. fuer Hydrobiologie 146:129-165. Duarte, C. M. 1991. Seagrass depth limits. Aquat. Bot. 40;363-377. Duarte, C. M and J. Kalff. 1986. Littoral slope as a predictor of the maximum biomass of submerged macrophyte communities. Limnol. Oceanogr. 31: 10721080. Duarte, C. M. and J Kalff. 1988. Influence oflake morphometry on the response of submerged macrophytes to sediment fertilization Duarte, C. M and J. Kalff. 1990. Biomass density and the relationship between submerged macrophyte biomass and plant growth form. Hydrobiologia. 196:1723. Dunton, K. H 1994. Seasonal growth and biomass of the tropical seagrass Halodule wrightii in relation to continuous measurements of underwater irradiance. Mar. Biol. 120: 479-489. Eighmy, T. T., L. S. Jahnke and W.R. Fagerberg. 1991. Studies of Elodea nuttallii grown under photorespiratory conditions. II. Evidence for bicarbonate active transport Plant Cell Environ. 14 : 157-165. Engel, S 1985. Aquatic community interactions of submerged macrophytes Wisconsin Department of Natural Resources Technical Bulletin 156 Madison. Engel, S. 1987. The restructuring oflittoral zones. Lake and Res. Manage. 3:235-242 Fairchild, G. W. and R. L. Lowe. 1984. Artificial substrates which release nutrients: Effects on periphyton and invertebrate succession. Hydrobiologia 114: 29-37.

PAGE 246

229 Finlayson, C.M., T.P. Farell and D.J. Griffiths. 1980. Studies of the hydrobiology of a tropical lake in north-western Queensland. ill. Growth, chemical composition and potential for harvesting of the aquatic vegetation. Aust. J. Mar. Freshw. Res. 31 :589-96. Fitzgerald, G. P. 1969. Some factors in the competition or antagonism among bacteria, algae and aquatic weeds. J. Phycol. 5:351-359. Fontaine, T, D. and D. G. Nigh. 1983. Characteristics of epiphyte communities on natural and artificial submersed lotic plants: Substrate effects. Arch. Hydrobiol. 96:293-301. Forsberg, C. 1965. Nutritional studies of Chara in axenic cultures. Physiol. Plant. 275-290. Fox, J. L., T. A. Olaug and T.A. Oldson. 1969. The ecology ofperiphyton in western Lake Superior. 1. Taxonomy and distribution. Bull. Water Res. Cent. Univ. Minn.14:1-97. Geddes, M. C. 1984. Limnology of Lake Alexandria, River Murray, South Australia, and the effects of nutrients and light on the phytoplankton. Aust. J. Mar. Freshw. Res. 35:399-415. Gessner, F. 1955. Hydrobotanik. Die Physiologischen Grundlagen der Pflanzenverbreitung im Wasser. I. Energiehaushalt. VEB Deutscher Verlag der Wissenschaften, Berlin. 701pp. Gessner, F. 1959. Hydrobotanik. Die Physiologischen Grundlagen der Pflanzenverbreitung im Wasser. IT. Stoffhaushalt. VEB Deutscher Verlag der Wissenschaften, Berlin. 701pp. Gliwicz, Z.M. 1990. Why do cladocerans fail to control algal blooms? Hydrobiologia 200/201 :83-97. Godward, M. 1934. An investigation of the causal distribution of algal epiphytes. Beih. Bot. Zbl. 52(A):506-539. Goldsborough, W.J. and W.M. Kemp. 1988. Light Responses of a Submersed Macrophyte: Implications for Survival in Turbid Waters. Ecology 69: 1775-1786. Goldsborough, L. G. and M. Hickman. 1991. Acomparison ofperiphytic algal biomass and community structure on Scirpus va/idus and on a morphologically similar artificial substratum. J. Phycol. 27:196-206.

PAGE 247

Goldsborough, L. G. and G. G. C. Robinson. 1985. Seasonal succession of diatom epiphyton on dense mats of Lemna minor. Can. J.B. 23322339. 230 Gons, H. J. 1982. Structural and functional characteristics of epiphyton and epipelon in realtion to their distribution in Lake Vechten. Hydrobiologia 95:79-114. Goodman, J.L., K. A. Moore, W. C. Dennison. 1995. Photosynthetic responses of eelgrass (Zostera marina L.). to light and sediment sulfide in a shallow barrier lagoon. Aquat. Bot. 50:37-47. Gough, S. B. and W. J. Woelkerling. 1976. On the removal and quantification of algal aufwuchs from macrophyte hosts. Hydrobiologia 48:203-207. Grime, J.P. 1979. Plant strategies and vegetation processes. John Wiley and Sons. Grimshaw, H.J., K. Havens, B. Sharfstein, A. Steiman, D. Anson, T. East, R. P. Maki, A. Rodusky and K-R. Jin. 2002. The effects of shading on morphometric and meristic characteristics of Wild Celery, Vallisneria americana MICHX., transplants from Lake Okeechobee, Florida. Arch. Hydrobiol. 155:65-81. Haag, K. H. and D. H. Habeck. 1991. Enhanced biological control of water hyacinth following limited herbicide application. J. Aquat. Plant Manage. 29:24-28. Hakanson, L. 1981. A manual of lake morphometry. Springer-Verlag, New York, 78pp. Hakanson, L. and M. Jansson. 1983. Principles oflake sedimentology. Springer Verlag, New York, 316pp. Haller, W. T. and D. L. Sutton. 1975. Community structure and competition between Hydrilla and Vallisneria. Hyacinth Contr. J. 13:48-50. Harbaugh, B. K. and G. J. Wilfret. 1981. Factors to consider when using Osmocote for poinsettia production in Florida. Bradenton AREC Res. Rep. GC1981, University of Florida, Gainesville, 4pp. Harlin, M. M 1975. Epiphyte-host relations in seagrass communities. Aquat. Bot. 1:125-131. Hartmann, R. L. and D. L. Brown. 1967. Changes in internal atmosphere of submersed vascular hydrophytes in relation to photosynthesis. Ecology 48:252-258. Haslam, S. M. 1978. River plants. Cambridge University Press, Cambridge. Hoagland, D.R. and D. I. Amon. 1938. The water culture method for growing plants without soil. Calif. Agric. Exp Stn. Circ. 347, 32pp.

PAGE 248

231 Hickman, M. 1971 The standing crop and primary productivity of the epiphyton attached to Equisetum jluviatile L. in Priddy Pool, North Somerset. Br. Phycol. J. 6:51-59. Hodgson, R. H. 1966. Growth and carbohydrate status of sago pondweed. Weeds 14:263-268 Hooper-Reid, N. M. and G. G. C Robinson. 1978. Seasonal dynamics of epiphytic algal growth in a marsh pond: competition, metabolism and nutrient availability. Can. J. Bot. 56: 2441-2448 Hopson, M. S. 1995. Temporal variation in biomass of the dominant submersed macrophytes and associated algal epiphytes in Lake Okeechobee, Florida. Master's Thesis, University of Florida, Gainesville, 150pp. Hosper, S. H. 1989. Biomanipulation, new perspective for restoring shallow, eutrophic lakes in The Netherlands Hydrobiol. Bull. 23:5-11. Hosper, H 1994. An ecosystem-based approach for the restoration of shallow lakes in the Netherlands. Lake Reserv. Manage 9:82. Hosper, S H. 1999. Stable states, buffers and switches : an ecosystem approach to the restoration and management of shallow lakes in the Netherlands. Water Sci. Technol. 37 : 151-164. Hough, R. A. and M. D. Fomwall. 1988. Interactions of inorganic carbon and light availability as controlling factors in aquatic macrophyte distribution and productivity. Limnology and Oceanography 33:1202-1208. Howard-Williams, C. 1981 Studies on the ability of a Potamogeton pectinatus community to remove dissolved nitrogen and phosphorus compounds from lake water. J. Appl. Ecol. 18:619-637. Howard-Williams, C and R.B. Allanson. 1981. An integrated study on littoral and pelagic primary production in a South African coastal lake Arch. Hydrobiologia, 92:507-534 Hulon, M.W. 1994. Restoring Lake Jackson, Osceola County, Florida. Lake Reserv. Manage 9 : 83. Hutchinson, G E. 1975. A treatise on limnology. ill. Limnological botany. John Wiley and Sons New York, 660pp Jeppesen, E ., J.P Jensen, M. Sondergaard, T Lauridsen, L J Pedersen and L. Jensen 1997 Top-down control in freshwater lakes: The role of nutrient state, submerged macrophytes and water depth. Hydrobiologia 342/343 : 151-164.

PAGE 249

232 Jeppesen, E., P. Kristensen, J.P. Jensen, M. Sondergaard, E. Mortensen and T. Lauridsen. 1991. Recovery resilience following a reduction in external phosphorus loading of shallow, eutrophic Danish lakes: Duration, regulating factors and methods for overcoming resilience. Mem. 1st. Ital. ldrobiol. 48:127148. Jeppesen, E. M., M. Sondergaard, B. Kronvang, J.P. Jensen, L. M. Svendsen and T. L. Lauridsen. 1999. Lake and catchment management in Denmark. Hydrobiologia 395/396:419-432. Jeppesen, E., M. Sondergaard, E. Mortensen, P. Kristensen, B. Riemann, H.J. Jensen, J.P. Muller, 0. Sortkjaer, J.P. Jensen, K. Christoffersen, S. Bosselmann and E. Dall. 1990. Fish manipulation as a lake restoration tool in shallow, eutrophic temperate lakes 1: cross-analysis of three Danish case studies. Hydrobiologia 200/201 :205-218. Jordan, W.R. III., M.E. Gilpin and J.D. Ober, eds. 1987. Restoration ecology: A synthetic approach to ecological research. Cambridge University Press, New York. Kadono, Y. 1980. Photosynthetic carbon sources in some Potamogeton species. Bot. Mag. Tokyo 93:185-193. Kairesalo, T. S. 1980. Comparison of in-situ photosynthic activity of epiphytic, epipelic and planktonic algal communities in an oligotrophic lake, Southern Finland. J. Phycol. 16:57-62. Kairesalo, T. S. 1984. The seasonal succession of epiphytic communities within an Equisetumfluviatile L. stand in Lake Paajarvi, southern Finland. Int. Rev. Gesam. Hydrobiol. 69:475-505. Kairesalo, T., S. Laine, E. Luokkanen, T. Malinen and J. Keto. 1999. Direct and indirect mechanisms behind successful biomanipulation. Hydrobiologia 395/396:99-106 Kalff, J. 2002. Limnology. New Jersey:Prentice Hall, 592pp. Kelly, M., M. J. Spence and G. Medley. 1994. The restoration of Banana lake: Diversion and dredging. Lake and Reservoir Management 9:86. Kenworthy, W. J. and M. S. Fonseca. 1996. Light requirements ofseagrasses. Estuaries 19:740-750. Killgore, K. J., R. P Morgan and N. B. Rybicki. 1989. Distribution and abundance of fishes associated with submersed aquatic plants in the Potomac River. North American Journal of Fisheries Management 9: 101-111.

PAGE 250

233 Kimber, A., W. G. Crumpton, T. B. Parkin and M.H. Spalding. 1999. Sediment as a carbon source for the submersed macrophyte Vallisneria. Plant Cell and Environment 22:1595-1600. Kimber, A., J. L. Owens and W. G. Crumpton. 1995. Light availability and growth of wildcelery (Vallisneria americana) in upper Mississippi River backwaters. Regulated Rivers: Research and Management 11:167-174. Kiorboe, T. 1980. Distribution and production of submerged macrophytes in Tipper Grund (Ringkobing Fjord, Denmark) and the impact of waterfowl grazing. J. Ecol. 17: 675-687. Kufel, L. and I. Kufel. 2002. Chara beds acting as nutrient sinks in shallow lakes a review. Aquatic Botany. 72:249-260. Kufel, L. and T. Ozimek. 1994. Can Chara control phosphorus cycling in Lake Luknajno (Poland)? Hydrobiologia. 275:277-283. Lake Hollingsworth Diagnostic Feasibility Study: A Report prepared by the City of Lakeland Lakes Program, Southwest Florida Water Manangement District and the Polk County Natural Resources Division with partial funding by the United Staes Environmental Protection Agency, Volume I, November 1994. LaLonde, S. and J. A. Downing. 1991. Epiphyton biomass as related to lake trophic status, depth and macrophyte architecture. Can. J. Fish. Aquat. Sci. 48:22852291. Lampert, W. 1994. Laboratory studies on zooplankton-cyanobacteria interactions. N.Z. J. Mar. Freshwat. Res. 21:483-490. Landers, D.H. 1982. Effects of naturally senescing aquatic macrophytes on nutrient chemistry and chlorophyll a of surrounding waters. Limnol. Oceanogr. 27:428439. Lauridsen, T.L., E. Jeppersen and F.O. Andersen. 1993. Colonization of submerged macrophytes in shallow fish manipulation Lake Vaeng: Impact of sediment composition and water fowl grazing. Aquat. Bot. 46:1-15. Lauridsen, T.L., E. Jeppesen and M. Sondergaard. 1994. Colonization and succession of submerged macrophytes in shallow Lake Vaeng following fish manipulation. Hydrobiologia 275/276:233-242. Lawson, P. 1991. Southern naiad a neglected native. Aquatics 13:4-6.

PAGE 251

234 Limon, M.J., O.T. Lind, D.S. Vodopich, R. Doyle and B.G. Trotter. 1989. Longand short-term variation in the physical and chemical limnology of a large, shallow, turbid tropical lake (Lake Chapala, Mexico). Arch. Hydrobiol./Suppl. 83:57-81. Lindenschmidt, K. E. and P. F. Hamblin. 1997. Hypolimnetic aeration in Lake Tegel, Berlin. Water Research 31: 1619-1628. Littlefield, L. and C. Forsberg. 1965. Absorption and translocation ofphosphorus-32 by Chara g/obularis Thuill. Physiol. Plant. 18:291-296. Livingston, R.J., S.E. McGlynn and X. Niu. 1998. Factors controlling seagrass growth in a gulf coastal system: Water and sediment quality and light. Aquatic Botany, 60:135-159. Lodge, D.M. 1991. Herbivory on freshwater macrophytes. Aquat. Bot. 41:195-224. Lucas, W .J. 1983. Photosynthetic assimilation of exogenous HCO3 by aquatic plants. Annu. Rev. Plant Physiol. 34:71-104. Maberly, S.C. and D.H.N. Spence. 1983. Photosynthetic inorganic carbon use by freshwater plants. J. Ecol. 71 :705-724. Maceina, M.J. and D.M Soballe. 1990. Wind-related limnological variation in Lake Okeechobee, Florida. Lake Reservoir and Management, 6:93-100. Madsen, T.V. and H. Brix. 1997 Growth, photosynthesis and acclimation by two submerged macrophytes in relation to temperature. Oecologia 110:320-327. Madsen, T.V. and K. Sand-Jensen. 1991. Photosynthetic carbon assimilation in aquatic macrophytes. Aquat. Bot. 41 :5-40. Main, S. P. 1973. The distribution of epiphytic diatoms in Yaquina Estuary, Oregon. Ph.D. Dissertation, Oregon State Univ., Corvallis, 11 lpp. Masini, R. J. J. L. Cray, CJ. Simpson, A. J. McComb 1995. Effects oflight and temperature on the photosynthesis of temperate meadow-forming seagrasses in Western Australia. Aquat. Bot. 49:239-254. May, R.M. 1977. Thresholds and breakpoints in ecosystems with a multiplicity of stable states. Nature 269:471-477. May, R.M 1981 Models for two interacting populations. In: R.M. May ( ed), Theoretical Ecology Blackwell, Oxford: 78-105. McCreary, N. J. 1991. Competition as mechanism of submersed macrophyte community structure. Aquat. Bot. 41: 177-193.

PAGE 252

235 McQueen, D. J 1998. Freshwater food web biomanipulation: A powerful tool for water quality improvement, but maintenance is required. Lakes and Reservoirs: Research and Management 3:83-94 Mitchell, C.P 1980. Control of water weeds by grass carp in two small lakes. N. Z. J. Mar. Freshwater Res. 14:381-390. Misra, R.D. 1938.Edaphic factors in the distribution of aquatic plants in the English lakes. J. Ecol. 26:41-51. Mitchell, S F. 1989 Primary production in a shallow eutrophic lake dominated alternately by phytoplankton and by submerged macrophytes. Aquat. Bot. 33:101-110. Moeller, R.E 1975. Hydrophyte biomass and community structure in a small, oligotrophic New Hampshire lake. Verh. Intemat. Verein. Limnol. 19:10051012. Moeller, R.E. 1978a. Seasonal changes in biomass, tissue chemistry and net production of the evergreen hydrophyte, Lobelia dortmanna. Can. J. Bot. 56:1425-1433. Moeller, R.E. 1978b. Carbon uptake by the submerged hydrophyte Utricularia purpurea. Aquat. Bot. 5:209-216 Moeller, R.E. 1980. The temperature-determined growing season of a submerged hydrophyte: Tissue chemistry and biomass turnover of Utricularia purpurea. Freshwat. Biol. 10:391-400 Moeller, R.E. 1983. Nutrient-enrichment of rhizosphere sediments: an experimental appraoch to the ecology of submersed macrovegetation Pp. 145-149. In : Proceedings of the International Symposium on Aquatic Macrophytes. Nijmegen, The Netherlands. Freshwater Biological Association, Dorset, England. Moeller, R.E., J.M. Burkholder and R.G Wetzel. 1988. Significance of sedimentary phosphorus to a rooted submersed macrophyte (Najas flexilis (Willd.) Rostk. and Schmidt) and its algal epiphytes. Aquat. Bot. 32 : 261-281. Moeslund, B., M.G. Kelly and N Thyssen. 1981. Storage of carbon and transport of oxygen in river macrophytes: Mass-balance, and the measurement of primary productivity in rivers Arch. Hydrobiol. 93 : 45-51. Moss, B. 1990 Engineering and biological approaches to the restoration from eutrophication of shallow lakes in which aquatic plant communities are important components. Hydrobiologia 200/201 :367-377.

PAGE 253

Moss, B 1999. Ecological challenges for lake manangement. Hyclrobiologia. 395/396: 3-11. 236 Mylavarapu, R.S. and E. D. Kennelley. 2002. UF/IF AS Extension Soil Testing Laboratory (ESTL) Analytical procedures and training manual. Soil and Water Science Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences Series 312, Circular 1248, Univ. of Florida, Gainesville, Florida Neville, C.M. 1985 Physiological response of juvenile rainbow trout, Salmo gairdneri, to acid and aluminumprediction of field responses from laboratory data. Can. J Fish. Aquatic Sci. 42:2004-2019. Nichols, S.A. 1991. The interaction between biology and the management of aquatic macrophytes. Aquatic Botany 41 :225-252. Nichols, D.S. and D.R. Keeney. 1976. Nitrogen nutrition of Myriophyllum spicatum uptake and translocation of 15N by shoots and roots. Freshwater Biol. 6: 145154 Painter D.S and K .J McCabe. 1988. Investigation into the disappearance of Eurasian watermilfoil from the Kawartha lakes. J. Aquat. Plant Manage. 26:3-12. Patel, G. 1995 Rapid dewatering and reuse of dredged organic sediment in an urban environment. Lake and Reserv. Manage. 11 : 181. Pearsall, W. H 1920. The aquatic vegetation of the English lakes J. Ecol. 8 : 163-199. Pearsall, W H 1922 A suggestion as to factors influencing the distribution of free floating vegetation. J Ecol. 9:241 -253. Perrow, M. R., M. L. Meijer, P Dawidowicz and H. Coops. 1997 Biomanipulation in shallow lakes: State of the art. Hydrobiologia 342-343:355-365. Phillips, G., A. Bramwell, J. Pitt, J. Stansfield and M. Perrow. 1999. Practical application of25 years' research into the management of shallow lakes. Hydrobiologia 395/396:61-76. Phillips, G. L., D Eminson and B Moss 1978. A mechanism to account for macrophyte decline in progressively eutrophicated freshwaters Aquat. Bot. 4:103-126. Pieczynska, E and W Szczepanska. 1966. Primary production in the littoral of several Masurian lakes Int. Ver. Theor. Angew. Limnol. Verh 16 : 372 379

PAGE 254

Pieterse, A.H. 1981. Hydrilla verticillata--a review. Abstracts on Tropical Agriculture, 7:9-34. 237 Pond, R.H. 1905. Contributions to the biology of the Great Lakes." The biological relation of aquatic plants to the substratum. University of Ann Arbor, Michigan. 43pp. Pringsheim, E.G. and 0. Pringsheim. 1962. Axenic culture of Utricularia. Am. J. Bot. 49:898-901. Prins, H.B. A., J. F. H. Snel, R. J Helder and P. E. Zanstra. 1980. Photosynthetic HCO3 utilization and OHexcretion in aquatic angiosperms. Light-induced pH changes at the leaf surface. Plant Physiol. 66:818-822. Prowse, G. A. 1959. Relationships between algal species and their macrophyte hosts. Nature 186:1204-1205. Ramamoorthy, S. 1988. Effect of pH on specification and toxicity of aluminum to rainbow trout (Sa/mo gairdneri). Can. J. Fish. Aquatic Sci. 45:634-642. Raven, J.A. 1970. Exogenous inorganic carbon sources in plant photosynthesis. Biol. Rev. 45:167-221. Raven, J. A. and W. J. Lucas. 1985. Energy costs of carbon acquisiti~n In W. J. Lucas and J. A. Berry (eds.) Inorganic Carbon Uptake by Aquatic Photosynthetic Organisms. Amer. Soc. Plant Physiol., Beltsville, Maryland, pp 305-325. Riber, H. H., J.P. Sorrensen and A. Kowalscewski. 1983. Erxchange of phosphorus between water, macrophytes and epiphytic periphyton in the littoral of Mikolajskie Lake, Poland. pp. 235-243. In R. G. Wetzel (ed.) Periphyton of Freshwater Ecosystems. Boston: Dr. W. Junk Publishers. Ricker, W.E. 1973. Linear regressions in fishery research. J. Fish. Res. Bd. Canada 30:409-434 Robertson, D. M., G. L. Goddard, D.R. Helsel and K. L. MacKinnon. 2000. Rehabilitation of Delavan lake, Wisconsin. Lake and Reservoir Management 16 : 155-176. Rogers, K. H. and C. M. Breen. 1981. Effects of epiphyton on Potamogeton crispus L. leaves. Microb. Ecol. 7:351-363. Rogers, K. H. and C. M Breen. 1983. An investigation ofmacrophyte, epiphyte, and grazer interactions. pp. 217-226. In R. G Wetzel (ed.) Periphyton of freshwater ecosystems.Boston: Dr. W. Junk.

PAGE 255

238 Roijackers, R. M.M. and P. J. T. Verstraelen 1988. Ecological investigations in three shallow lakes of different trophic levels in The Netherlands. Verh. Internal. Verein. Limnol. 23:489-495. Romie, K. 1994. Lake Hollingsworth Eutrophication Modeling. /n: Lake Hollingsworth Diagnostic Feasibility Study: A Report prepared by the City of Lakeland Lakes Program, Southwest Florida Water Manangement District and the Polk County Natural Resources Division with partial funding by the United Staes Environmental Protection Agency, Volume I, pp. II-1 to II-37. Raschke, R. L. 1993. Diatom (Bacillariophyta) community response to phosphorus in the Everglades National Park, USA.Phycologia 32:48-58. Rattray, M. R., C. Howard-Williams and J.M. A. Brown. 1991. Sediment and water as sources of nitrogen and phosphorus for submerged rooted aquatic macrophytes. Aquat. Bot. 40:225-237. Ruttner, F. 1947 Zur Frage der Karbonatassimilation der Wasserpflanzen. I. Die Beiden Haupttypen der Kohlenstoffaufnahme. Ost. Bot. Z. 94:265-294. Ruttner, F. 1948 Zur Frage der Karbonatassimilation der Wasserpflanzen. II. Das Verhalten von Elodea canadensis und Fontinalis antipyretica in Losungen von Natrium-bzw. Kaliumbikarbonat. Ost. Bot. Z. 95:208-238. Ruttner, F. 1960: uber die Kohlenstoffaufnahme bei Algen aus der Rhodophyceengattung Batrachospermum Schweiz Z. Hydrol. 22:280-291. Rybicki, N.B. and V. Carter. 1986. Effect of sediment depth and sediment type on the survival of Vallisneria americana Michx grown from tubers Aquat. Bot. 24: 233-240. Rydin, E., B. Huser and E. B. Welch. 2000 Amount of phosphorus inactivated by alum treatments in Washington lakes. Limnol. Oceanogr. 45:226-230. Rydin, E. and E. B. Welch 1998 Aluminum dose required to inactivate phosphate in lake sediments. Water Research 32: 2969-2976. Salonen, V. P. and E. Varjo. 2000. Gypsum treatment as a restoration method for sediments of eutrophied lakes experiments from southern Finland. Environ. Geol. 39:353-359pp. Sand-Jensen, K. 1983. Physical and chemical parameters regulating growth of periphytic communities. pp. 63-71. In R. G Wetzel (ed.) Periphyton of freshwater ecosystems. Developments in hydrobiology 17. Boston: Dr. W Junk.

PAGE 256

Sand-Jensen, K. 1990. Epiphyte shading: Its role in resulting depth distribution of submerged aquatic macrophytes. Fol. Geobot. 25:315-320. 239 Sand-Jensen, K., D. Borg and E. Jeppesen. 1989. Biomass and oxygen dynamics of the epiphyte community in a Danish lowland stream. Freshwater Biol. 22:431-433. Sand-Jensen, K. and J. Borum. 1984. Epiphyte shading and its effect on photosynthesis and diel metabolism Lobelia dortmanna L. during the spring bloom in a Danish lake. Aquat. Bot. 20:109-119. Sand-Jensen, K. and J. Borum. 1991. Interactions among phytoplankton, periphyton and macrophytes in temperate freshwaters and estuaries. Aquat. Bot. 41:137-175. Sand-Jensen, K. and T. V. Madsen. 1991. Minimum light requirements of submerged freshwater macrophytes in laboratory growth experiments. J. Ecol. 79:749-764. Sand-Jensen, K., C. Prahl and H. Stokholm. 1982. Oxygen release from roots of submerged aquatic macrophytes. Oikos 38:349-354. Sand-Jensen, K. and M. Sondergaard. 1979. Distribution and quantitative development of aquatic macrophytes in relation to sediment characteristics in oligotrophic Lake Kalgaard, Denmark. Freshwater Biol. 9: 1-11. Shannon, E.L. 1953. The production ofroot hairs by aquatic plants. Am. Midland Nat. 50:474-479. Scheffer, M. 1990. Multiplicity of stable states. Hydrobiologia 200/201: 475-486. Scheffer, M., M.R. de Redelijkheid and F Nopert. 1992. Distribution and dynamics of submerged vegetation in a chain of shallow eutrophic lakes. Aquat. Bot. 42:199-216. Scheffer, M., S.H. Hosper, M.L. Meijer, B. Moss and E. Jeppesen. 1993. Alternative equilibria in shallow lakes. Trends Ecol. Evol. 8:275-279. Schriver, P, J. Bogestrand, E. Jeppesen and M. Sondergaard. 1995. Impact of submerged macrophytes on fish-zooplankton-phytoplankton interactions: Large scale enclosure experiments in a shallow eutrophic lake Freshwater Biology 33:255-270. Sculthorpe, C.D. 1967. The Biology of Aquatic Vascular Plants. London: Edward Arnold, London, 610p.

PAGE 257

240 Shapiro, J. 1990. Biomanipulation-Tool for water management. Hydrobiologia 200201:13-27. Shelden, R. B. and C. W. Boylen. 1975. Factors affecting the contribution by epiphytic algae to the primary productivity of an oligotrophic freshwater lake. Applied Microbiol. 30:657-667. Sheldon, S.P. 1986. The effects of short-term disturbance on a freshwater macrophyte community. J. Freshwater Ecol. 3:309-317. Shireman, J.V., M.V. Hoyer, M.J. Maceina and D.E. Canfield. 1985. The water quality and fishing of Lake Baldwin, Florida: Four years after macrophyte removal by grass carp. Lake Reserv. Manage. 1:201-206. Short, F. T. 1987. Effects of sediment nutrients on seagrasses: Literature review and mesocosm experiment. Aquat. Bot. 27:41-57. Short, R.M. and McRoy, C.P. 1984. Nitrogen uptake by leaves and roots of the seagrass Zostera marina L. Bot. Mar. 27:547-555. Siber, P.A. 1977. Comparison of attached diatom communities on natural and artificial substrates. J. Phycol. 18:402-406. Sieburth, J.M., R. D. Brooks, R. V. Gessner, C. D. Thomas and J.L. Tootle. 1974. Microbial colonization of marine plant surfaces as observed by scanning electron microscopy, 418-432.p. In R.R. Colwell and R Y. Morita (small eds) Effects of the Environment on Microbial Activies. Baltimore: Univ. Park Press. Sladeckova, A 1962. Limnological investigation methods for the periphyton ("Aufwuchs") community. Bot. Rev. 28:286-352. Smart, R.M. and J.W. Barko. 1985. Laboratory culture of submersed freshwater macrophytes on natural sediments. Aquat. Bot. 21:251-263. Smart, R.M. and J.W. Barko. 1989. Competitive interactions of submersed aquatic macrophytes in relation to water chemistry and other environmental conditions. Proceedings of the 23rd Annual Meeting on the Aquatic Plant Control Research Program, MP A-89-1, USAE-WES, Vicksburg, MS, pp.159-164. Smart, R.M., J.W. Barko and D.G. Macfarland. 1994. "Competition between Hydrilla verticillata and Vallisneria americana under different environmental conditions," Technical Report A-94-1, U.S. Army Waterways Experiment Station, Vicksburg, MS. Smart, R. M. and G. 0. Dick. 1999. Propogation and Establishment of Aquatic Plants: A Handbook for Ecosystem Restoration Projects. U.S. Army Corp of Engineers Technical Report A-99-4, 26p.

PAGE 258

Smart, R.M., G.0. Dick and R.D. Doyle. 1998. Techniques for establishing native aquatic plants. J. Aquat. Plant Manage. 36:44-49. 241 Smart, R. M. and R. D. Doyle. 1995. "Ecological theory and management of submersed aquatic plant communities," Information Exchange Bulletin A-953, Aquatic plant Control Research Program, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS. Smart, R. M., R. D. Doyle, J. D. Madsen and G. 0. Dick. 1996. Establishing native submersed aquatic plant communities for fish habitat. American Fisheries Society Symposium. 16:347-356. Smeltzer, E. 1990. A successful alwn/aluminate treatment of Lake Morey, Vermont. Lake Reserv. Manage. 6:9-19. Smith, B. 1995. The use of sonar as an innovative tool to restore aquatic ecosystems. Lake Reserv. Manage. 11: 122. Smith, C. S. and J. W. Barko. 1990. Ecology of eurasian watermilfoil. J. Aquat. Plant Manage. 28:55-63. Sondergaard, M. and K. Sand-Jensen. 1978. Total autotrophic production in oligotrophic Lake Kalgaard~ Denmark. Verh. Intemat. Verein. Limnol. 20:667673. Sondergaard, M., E. Jeppesen and J.P. Jensen. 2000a. Hypolimnetic nitrate treatment to reduce internal phosphorus loading in a stratified lake. Lake Reserv. Manage. 16:195-204. Sondergaard, M., E. Jeppesen, J.P. Jensen and T. Lauridsen. 2000b. Lake restoration in Denmark. Lakes Reserv.: Res. Manage. 5:151-159. Sondergaard, M. and S. Laegaad. 1977. Vascular-arbuscular mycorrhiza in some aquatic vascular plants. Nature. 268:232-233 Sondergaard, M. and B. Moss. 1998. Impact of submerged macrophytes on phytoplankton in shallow freshwater lakes. In E. Jeppesen, M. Sondergaard and K. Christoffersen (eds.) The Structuring Role of Submerged Macrophytes in Lakes. New York: Springer-Verlag, 115-132 pp. Sorrell, B. K. 1991. Transient pressure gradients in the lacunar system of the submerged macrophyte Egeria densa Planch. Aquat. Bot. 39:99-108. Sorrell, B. K. and F. I. Dromgoole. 1989. Oxygen diffusion and dark respiration in aquatic macrophytes. Plant Cell Environ. 12:293-299.

PAGE 259

Soszka, G. J. 1975. Ecological relations between invertebrates and submerged macrophytes in the lake littoral. Ekologia Poloska 23:393-415. Southern Region Information and Exchange Group on Soil Testing and Plant Analyses (SRIEG 18). 1983. Reference soil test methods for the Southern region of the United States. Southern Cooperative Series Bull. 289. Univ. of Georgia, Athens, Ga. 242 Spence, D.H.N. 1967. Factors controlling the distribution of freshwater macrophytes with particular reference to the lochs of Scotland. J. Ecol. 55: 147-170. Spence, D.H.N. 1982. The zonation of plants in freshwater lakes. Adv. Ecol. Res. 12:37-125. Spence, D.H.N. and J. Chrystal. 1970. Photosynthesis and zonation of freshwater macrophytes. II. Adaptability of species of deep and shallow water. New Phytol. 69:217-227. Spencer, W. and G. Bowes 1990. Ecophysiology of the world's most troublesome aquatic weeds. In A.H. Pieterse and K.J. Murphy, eds. Aquatic weeds: The ecology and management of nuisance aquatic vegetation. Oxford Univ. Press, Oxford, pp. 39-73. Spencer, D.F., G.G. Ksander, J.D. Madsen and C.S. Owens. 2000. Emergence of vegetative propagules of Potamogeton nodosus, Potamogeton pectinatus, Vallisneria americana and Hydril/a verticillata based on accumulated degree days. Aquat. Bot. 67:237-249 Squires, M. and Lesack, L.F. W. 2003. The relation between sediment nutrient content and macrophyte biomass and community structure along a water transparency gradient among lakes of the Mackenzie Delta. Can. J. Fish. Aquat. Sci. 60:333343. Straskraba, M and E. Pieczynska 1970. Field experiments on shading effects by emergents on littoral phytoplankton and periphyton production. Rozpravy Cekosl. Akad. Ved. Rada Matern Prir. Ved. 80:7-32 Statistical Analysis System. 1999-2001. SAS Institute Inc Release 8.2. Cary, N.C. Stearns, S. C. 1977. The evolution oflife history traits: A critique of the theory and review of the data. An.nu. Rev. Ecol. Syst. 8:145-171. Steinman, A. D., K.E. Havens, A. J. Rodusky, B. Sharfstein, R. T. James and M. C Harwell. 2002. The influence of environmental variables and a managed water recession on the growth of charophytes in a large, subtropical lake. Aquatic Botany. 72:297-313.

PAGE 260

Steward, K. K. 1984 Growth ofhydrilla (Hydrilla verticillata) in hydrosoils of different composition. Weed Sci. 32:371-375. Strand, J. A. 1999. Submerged macrophytes in shallow eutrophic lakes: regulating factors and ecosystem effects. Ph.D. thesis, Dept. Ecol. and Limnol., Lund University, Sweden. 243 SWFMD. 1994. Section II: Lake Hollingsworth Eutrophication Modeling. In: Lake Hollingsworth Diagnostic Feasibility Study: A Report prepared by the City of Lakeland Lakes Program, Southwest Florida Water Manangement District and the Polle County Natural Resources Division with partial funding by the United Staes Environmental Protection Agency, Volume I, November 1994. Sullivan, M J. and C. A Moncrieff. 1990. Edaphic algae are an important component of saltmarsh food-webs: evidence from multiple stable isotope analyses. Mar. Ecol. Prog. Ser. 62:149-159. Sutton, D.L. 1982. A core sampler for collecting hydrilla propagules. J. Aquat. Plant Manage. 20:57-59. Sutton, D L. 1985. Density of tubers and turions ofhydrilla in South Florida. J. Aquat. Plant Manage. 23 :64-67. Sutton, D. L. 1990 Comparison of two methods for evaluating growth ofhydrilla in sediments collected from Lake Okeechobee. J. Aquat. Plant Manage. 28:80-83. Sutton, D. L. 1993. Injection of nutrients into sand rooting media for culture of dioecious hydrilla. J. Aquat. Plant Manage. 31 :64-69 Sutton, D. L. and W G H. Latham. 1996. Analysis of interstitial water during culture of Hydrilla verticillata with controlled release fertilizers. Aquatic Botany 54: 1-9. Sutton, D. L. and K. M Portier. 1995. Growth of dioecious hydrilla in sediments from six Florida lakes. J Aquat. Plant Manage. 33 : 3-7. Sutton, D. L., T K. Van and K. M Portier. 1992 Growth of dioecious and monoecious hydrilla from single tubers. J Aquat. Plant Manage 30:15-20 Tai, Y C and I. J. Hodgkiss 1975 Studies on plover Cove Reservoir, Hong Kong ill. Seasonal changes in naturally occuring periphytic communities. Freshwater Biol. 5 : 85 103 Tanaka, N., K. Ohwada, M Sugiyama, A. Asakawa, M Iikura and S. Kitamura. 1984 Seasonal occurences of epiphytic microalgae on the natural seaweeds and artificial seagrasses in Ago Bay. Bull. J. Soc. Sci. Fish 50: 1665-1669.

PAGE 261

244 Tanner, C. C. and J. S. Clayton. 1985. Effects ofvesicular-arbuscular mycorrhizas on growth and nutrition of a submerged aquatic plant. Aquat. Bot. 22:377-386. Tett, P., C. Gallegos, M. G Kelly, G. M. Hornberger and B. J. Cosby. 1978. Relationships among substrate, flow and benthic microalgal pigment density in the Mechums River, Virginia. Limnol. Oceanogr. 23:785-797. Thimijan, R. W. and R. D. Heins 1983. Photometric, radiometric and quantum light units of measure: A review of procedures for interconversion. HortScience 18:818-822. Timms, R. M and B. Moss. 1984. Prevention of growth of potentially dense phytoplankton populations by zooplankton grazing, in the presence of zooplanktivorous fish, in a shallow wetland ecosystem. Limnology and Oceanography 29:472-486 Tippett, R. 1970. Artificial surfaces as a method of studying populations of benthic mico-algae in freshwater. Br. Phycol. J. 5:187-199. Titus, J E. and M. S. Adams 1979. Coexistence and the comparative light relations of the submersed macrophytes Myriophyllum spicatum L. and Vallisneria americana MICHX. Oecologia 40:273-286. Titus, J.E. and M. D. Stephens. 1983. Neighbor influences and seasonal growth patterns for Vallisneria americana in a mesotrophic lake. Oecologia. 56:23-29 Van, T. K., W. T. Haller, G. Bowes and L.A. Garrard. 1976. Effects oflight quality on growth and chlorophyll composition in Hydril/a verticillata. J.Aquat. Plant Manage. 15:29-31. Van der Molen, D. T and R. Portielje. 1999. Multi-lake studies in The Netherlands : trends in eutrophication. Hydrobiologia 408/409: 359-365 van der Valk, A.G 1981. Succession in wetlands: A Glesonian approach. Ecology 62:688-696. Van der Velde G. 1987. Aquatic macrophytes, their function for animals Act. Bot. Neerl. 36:323-366. Van Dijk, G., A.W. Breukelaar and R. Gijlstra 1992. Impact oflight climate history on seasonal dynamics of a field population of Potamogeton pectinatus L. during a three-year period (1986-1988). Aquat. Bot. 43:17-41. van Nes, E H 2002. Dominance of charophytes in eutrophic shallow lakes when should we expect it to be an alternative stable state? Aquatic Botany 72:275 296

PAGE 262

245 Walstad, D. 2003. Ecology of the planted aquarium (2nd Ed). Echinodorus Publishing, Chapel Hill, N. C. 194pp. Westerdahl, H.E. and K.D. Getsinger. 1988. Aquatic Plant Identification and Herbicide Use Guide. Prepared for Department of the Anny, waterways Experiment Station, Anny Corps of Engineers Technical Report A-88-9. Wetzel, R. G. 1964. A comparative study of the primary productivity of higher aquatic plants, periphyton, and phytoplankton in a large, shallow lake. Int. Ver. Ges. Hydrobiol. 49: 1-64 Wetzel, R. G. 1969. Factors influencing photosynthesis and excretion of dissolved organic matter by aquatic macrophytes in hard-water lakes. Verb. Intemat. Verein. Limnol. 17:72-85. Wetzel, R. G. 1983. Limnology. 2nd Ed. Saunders College Publishing, Chicago, 767pp. Wetzel, R. G. 1999a. Plants and water in and adjacent to lakes. In A. J. Beard and R. L. Wilby, eds. Eco-hydrology: Plants and Water in Terrestrial and Aquatic Environments. Routledge, London, pp. 269-299. Wetzel, R. G. 1999b. Biodiversity and shifting energetic stability within freshwater ecosystems. Arch. Hydrobiol. Spec. Issues Advanc. Limnol. 54:19-32. Wetzel, R. G. 2001. Limnology: Lake and River Ecosystems 3rd Ed.: Academic Press, New York 1006pp. Wetzel, R. G., E. S. Brammer, K. Lindstrom and C, Forsberg. 1985. Photosynthesis of submersed macrophytes in acidified lakes. II. Carbon limitations and utilizations ofbenthic CO2 sources. Aquat. Bot. 22:107-120. Wetzel, R. G. and P.A. Penhale. 1979. Transport of carbon and excretion of dissolved organic carbon by leaves and roots/rhizomes in seagrasses and their epiphytes. Aquat. Bot. 6:149-158. Wetzel, R.G. and A.G van der Valk. 1996. Vesiculararbuscular mycorrhizae in prairie pothole wetland vegetation in Iowa and North Dakota. Can. J. Bot. 74:883-890. Wheeler, B.D. and K.E. Giller 1982. Status of aquatic macrophytes in an undrained area of fen in the Norfolk Broadlands, England. Aquat. Bot., 12:277-296. Whitmore, T. J., M. Brenner and C .L. Schelske. 1996. Highly variable sediment distribution in shallow, wind-stressed lakes: A case for sediment-mapping surveys in paleolimnological studies. Journal of Paleolimnology 15:207-221.

PAGE 263

Wilkinson, R.E. 1963. Effects of light intensity and temperature on the growth of waterstargrass, coontail, and duckweed. Weeds 11 :287-290. 246 Wilson, S.D. and P.A. Keddy. 1986. Species competitive ability and position along a natural stress/disturbance gradient. Ecology, 67:1236-1242. Wiley, J M., R. W. Gorden, S. W. Waite and T. Powless. 1984. The relationship between aquatic macrophytes and fish production in Illinois ponds: A simple approach. N. Am. J. Fish. Manage. 4:111-119. Winfield, I J. 1986. The influence of simulated aquatic macrophytes on the zooplankton consumption rate of juvenile roach, Rutilus rutilus, rudd, Scardinius eurythrophthalmus, and perch, Perea fluviatilis Journal of Fish Biology, 29:37-48 Yeo, R. R. and J .R. Thurston. 1984. The effect of dwarf spikerush (Eleocharis coloradensis) on several submersed aquatic weeds. J. Aquat. Plant Manage 22:52-56. Zar, J.H. 1996 Biostatistical Analysis, 3rd Ed. Upper Saddle River, Prentice-Hall, Inc., New York, 662 pp. Zhang, X., F. Zheng and D. Mao. 1998. Effect of iron plaque outside roots on nutrient uptake by rice (Oryza sativa L.). Zinc uptake by Fe deficient rice. Plant Soil 202:33-39. Zimba, P. V 1995. Epiphytic algal biomass of the littoral zone, Lake Okeechobee, Florida (USA). Ergeb. Limnol./Adv. Limnol. 45 : 233 240 Zimba, P. V. M. S. Hopson and D. E. Colle. 1993.Elemental composition of five submersed aquatic plants collected from Lake Okeechobee Florida Journal of Aquatic Plant Management 31: 13 7-140 Zimba, P. V ., M. S. Hopson, J.P. Smith, D. E. Colle and J. V. Shireman. 1995. Chemical composition and distribution of submersed aquatic vegetation in Lake Okeechobee, Florida (1989-1991) Arch. Hydrobiol., Spec. lss. Advanc Limnol. 45 : 241-246. Zimba, P.V. and M.S. Hopson. 1997. Quantification of epiphyte removal effic i ency from submersed aquatic plants. Aquat. Bot. 5 8 : 173-179 Zimmerman, R. C., J. L. Reguz z oni and R. S Alberte 1995 E elgrass (Zostera marina L.) transplants in San Francisco Bay: Role oflight availability on metabolism, growth and survival. Aquat. Bot. 51: 67 86

PAGE 264

BIOGRAPHICAL SKETCH Margaret S. Hopson-Fernandes was born in Jacksonville, Florida on March 6, 1967. Margaret grew up in Atlantic Beach, Florida. She graduated third in a class of 485 students from Duncan U. Fletcher High School in 1985. Margaret began her university studies at Jacksonville University in Jacksonville, Florida where she majored in biology and minored in chemistry. She received her Bachelor of Arts degree in 1989, graduating magna cum laude. Margaret entered the University of Florida for the first time as a postbaccalaureate student in 1989. She was admitted to Graduate School at the University of Florida in the Department of Botany in January of 1990. Margaret worked as a graduate teaching assistant for the Department of Botany throughout her tenure as a Masters student. Margaret received her Master of Science degree in 1995. After completing her thesis, Margaret moved to Brasilia, Brazil, where she taught various grades and subjects at the American School of Brasilia. She married fellow ecologist and Gator, Carlos Fernandes, in January of 1997. Their first child, Eddie was born in June of 1998 The Fernandes family returned to Gainesville in January of 1990 when Margaret began her doctoral program in the Department of Environmental Engineering Sciences. Margaret was awarded a Graduate Assistance in Areas of National Need (GAANN) Fellowship in August of 1990. Margaret's daughter, Maria, was born on September 25 2001, the day after Margaret returned from harvesting the second replication of Experiment 1. During her tenure as a doctoral student, Margaret was a teaching 247

PAGE 265

248 assistant for several courses offered by the Department of Environmental Engineering Sciences. Margaret received a Supplemental Retention Award from the University of Florida, Office of Graduate Minority Programs in January of 2005. Margaret was awarded her degree of Doctorate of Philosophy in April 2005 Margaret is a member of Omicron Delta Kappa and Phi Kappa Phi.

PAGE 266

I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality as a dissertation for the degree of Doctor of Philosophy. Engineering Sciences I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Edward J. Phlips, C
PAGE 267

This dissertation was submitted to the Graduate faculty of the College of Engineering and to the Graduate School and was accepted as partial fulfillment of the requirements for the degree of Doctor of philosophy. May2005 Pramod P Khargonekar Dean, College of Engineering Kenneth J. Gerhardt Interim Dean, Graduate School

PAGE 268

' LO 1780 20 __ ,f/190 UNIVERSITY OF FLORIDA I I I II IIIIII Ill Ill lllll lllll II IIIIII IIII IIII Ill 11111111111 1111111 3 1262 08554 2578


xml version 1.0 encoding UTF-8
REPORT xmlns http:www.fcla.edudlsmddaitss xmlns:xsi http:www.w3.org2001XMLSchema-instance xsi:schemaLocation http:www.fcla.edudlsmddaitssdaitssReport.xsd
INGEST IEID EC927O9IP_HL4653 INGEST_TIME 2011-11-02T14:59:53Z PACKAGE AA00004681_00001
AGREEMENT_INFO ACCOUNT UF PROJECT UFDC
FILES