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

MISSING IMAGE

Material Information

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

Subjects

Subjects / Keywords:
Environmental Engineering Sciences thesis, Ph. D   ( lcsh )
Dissertations, Academic -- Environmental Engineering Sciences -- UF   ( lcsh )
Genre:
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

Notes

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

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 003320037
sobekcm - AA00004681_00001
System ID:
AA00004681:00001

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