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Factors Affecting Periphyton Abundance on Macrophytes in a Spring-Fed River in Florida

Permanent Link: http://ufdc.ufl.edu/UFE0021797/00001

Material Information

Title: Factors Affecting Periphyton Abundance on Macrophytes in a Spring-Fed River in Florida
Physical Description: 1 online resource (40 p.)
Language: english
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: do, florida, freshwater, grazers, karst, macrophytes, periphyton, spring
Fisheries and Aquatic Sciences -- Dissertations, Academic -- UF
Genre: Fisheries and Aquatic Sciences thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Past and present land use activities in Florida have resulted in broad-scale nutrient concentration increases in the groundwater system. Nutrient contaminated groundwater is not only a health concern, but also represents a potentially serious ecological problem. Because Florida?s extensive system of aquifers exist within a very permeable karst geology, there are myriad of pathways by which nutrient laden groundwater can enter and be mixed with surface water systems. Freshwater springs, for example, provide a direct conduit for contaminated groundwater discharge to surface water systems. It is in the surface waters where nutrients, such as nitrogen and phosphorus, have the greatest potential to negatively alter the ecology of aquatic ecosystems. Along the Ichetucknee River, several feeder springs have experienced vegetation losses over the past decade. The springs are not only enriched in nutrients, but also exhibit low dissolved oxygen concentrations, and low stream velocites. While eutrophication appears to be a plausible explanation for vegetation loss, this study investigated the possibility that nutrient contamination alone may not be responsible for vegetation loss. I hypothesized that low dissolved oxygen concentrations near spring vents and seeps preclude the existence of primary grazers and, as a consequence, macrophytes in these areas of low stream velocity accumulate more periphyton and grow more slowly than vegetation in more oxygenated, swiftly flowing portions of the river. An initial characterization of the abiotic environment and the macrophyte community of the Ichetucknee River indicated that the proposed pattern of interaction was evident throughout the system. Subsequently, a four-week translocation experiment was carried out where genets of the most abundant macrophyte, Sagittaria kurziana, were relocated to several river and spring locations to evaluate site specific differences in the rate of periphyton accumulation and potential effects on macrophyte growth. Results suggest that periphyton accumulation on S. kurziana is more rapid in feeder spring environments than in the main stem of the Ichetucknee River. The differences were likely due to low dissolved oxygen concentrations, low stream velocities and reduced grazer abundance in the feeder springs. There were, however, no detectable effects on macrophyte growth probably due to the short duration of the study.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Thesis: Thesis (M.S.)--University of Florida, 2008.
Local: Adviser: Frazer, Tom K.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0021797:00001

Permanent Link: http://ufdc.ufl.edu/UFE0021797/00001

Material Information

Title: Factors Affecting Periphyton Abundance on Macrophytes in a Spring-Fed River in Florida
Physical Description: 1 online resource (40 p.)
Language: english
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: do, florida, freshwater, grazers, karst, macrophytes, periphyton, spring
Fisheries and Aquatic Sciences -- Dissertations, Academic -- UF
Genre: Fisheries and Aquatic Sciences thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Past and present land use activities in Florida have resulted in broad-scale nutrient concentration increases in the groundwater system. Nutrient contaminated groundwater is not only a health concern, but also represents a potentially serious ecological problem. Because Florida?s extensive system of aquifers exist within a very permeable karst geology, there are myriad of pathways by which nutrient laden groundwater can enter and be mixed with surface water systems. Freshwater springs, for example, provide a direct conduit for contaminated groundwater discharge to surface water systems. It is in the surface waters where nutrients, such as nitrogen and phosphorus, have the greatest potential to negatively alter the ecology of aquatic ecosystems. Along the Ichetucknee River, several feeder springs have experienced vegetation losses over the past decade. The springs are not only enriched in nutrients, but also exhibit low dissolved oxygen concentrations, and low stream velocites. While eutrophication appears to be a plausible explanation for vegetation loss, this study investigated the possibility that nutrient contamination alone may not be responsible for vegetation loss. I hypothesized that low dissolved oxygen concentrations near spring vents and seeps preclude the existence of primary grazers and, as a consequence, macrophytes in these areas of low stream velocity accumulate more periphyton and grow more slowly than vegetation in more oxygenated, swiftly flowing portions of the river. An initial characterization of the abiotic environment and the macrophyte community of the Ichetucknee River indicated that the proposed pattern of interaction was evident throughout the system. Subsequently, a four-week translocation experiment was carried out where genets of the most abundant macrophyte, Sagittaria kurziana, were relocated to several river and spring locations to evaluate site specific differences in the rate of periphyton accumulation and potential effects on macrophyte growth. Results suggest that periphyton accumulation on S. kurziana is more rapid in feeder spring environments than in the main stem of the Ichetucknee River. The differences were likely due to low dissolved oxygen concentrations, low stream velocities and reduced grazer abundance in the feeder springs. There were, however, no detectable effects on macrophyte growth probably due to the short duration of the study.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Thesis: Thesis (M.S.)--University of Florida, 2008.
Local: Adviser: Frazer, Tom K.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0021797:00001


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FACTORS AFFECTING PERIPHYTON ABUNDANCE ON MACROPHYTES IN A
SPRING-FED RIVER IN FLORIDA
















By

VINCENT ANTHONY POLITANO


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS OF THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2008




























2008 Vincent Anthony Politano




























To my family









ACKNOWLEDGEMENTS

I thank my family and friends for their support and my advisors for their tutelage.









TABLE OF CONTENTS

page

A C K N O W L E D G E M E N T S .................................................................................. .....................4

L IST O F T A B L E S ..................................................................................................... . 6

LIST OF FIGURES .................................. .. ..... ..... ................. .7

ABSTRAC T .......................................................................................

CHAPTER

1 IN TR OD U CTION ......................................................... ................. .. ........ 10

2 M A TER IA L S A N D M ETH O D S ........................................ .............................................12

Q uantitative R iver and Spring Survey ........................................................................ ... ... 12
C hem ical and Physical Param eters...................................................................... .. .... 13
V egetation Sam pling .............................................................. ... ........ ........ ....13
Quantifying Periphyton Associated with SAV.............................................................. 14
T ran location E xperim ent............................................................................. .................... 15
S statistic al A n aly se s ................................ ........... .............................................................. 16

3 R E S U L T S ................................ ..........................................................19

Su rv ey R esu lts ................................................................19
T ranslocation E xperim ent............................................................................. ....................20

4 D ISC U S SIO N ............................................................................................ 33

L IST O F R E F E R E N C E S ............................................. ............................................................37

B IO G R A PH IC A L SK E T C H ................................................................................ ...................40









LIST OF TABLES


Table page

3-1. Summary of 2007 Survey Data Means + Standard Errors (n = # of samples) ............... 22









LIST OF FIGURES


Figure pe

2-1. Map of the Ichetucknee River course through the Ichetucknee Springs State Park. All
transect sampling was carried out in the upper portion of the river within the confines
of the park. Experimental work was conducted near Singing Spring, Devils Eye
(also known as Boiling Spring) and Mill Pond Spring.............................................17

2-2. Collapsed and expanded view of plant sampling apparatus.........................................18

3-1. Mean dissolved oxygen concentration with increasing distance downstream in the main
stem of the Ichetucknee River. Numbers along the x-axis correspond to river
transects with ascending values representing distance downstream..............................23

3-2. Mean dissolved oxygen concentration in the main stem of the Ichetucknee River and
three associated feeder springs (i.e. Singing Spring, Devil's Eye Spring, and Mill
P on d Spring). ........................................................... ................. 24

3-3. Mean stream velocity with increasing distance downstream in the main stem of the
Ichetucknee River. Numbers along the x-axis correspond to river transects with
ascending values representing distance downstream .............................. ...................25

3-4. Mean stream velocity in the main stem of the Ichetucknee River and three associated
feeder springs (i.e. Singing Spring, Devil's Eye Spring, and Mill Pond Spring). ............26

3-5. Mean periphyton abundance with increasing distance downstream in the main stem of
the Ichetucknee River. Numbers along the x-axis correspond to river transects with
ascending values representing distance downstream .............................. ...................27

3-6. Mean periphyton abundance in the main stem of the Ichetucknee River and three
associated feeder springs (i.e. Singing Spring, Devil's Eye Spring, and Mill Pond
S p rin g )................. .......... ................ ................................................2 8

3-7. Mean plant biomass with increasing distance downstream in the main stem of the
Ichetucknee River. Numbers along the x-axis correspond to river transects with
ascending values representing distance downstream .............................. ...................29

3-8. Mean plant biomass in the main stem of the Ichetucknee River and three associated
feeder springs (i.e. Singing Spring, Devil's Eye Spring, and Mill Pond Spring). ............30

3-9. Mean plant biomass in the main stem of the Ichetucknee River and three associated
feeder springs (i.e. Singing Spring, Devil's Eye Spring, and Mill Pond Spring)
following a four week translocation experiment. ................................... ............... 31

3-10. Mean periphyton abundance in the main stem of the Ichetucknee River and three
associated feeder springs (i.e. Singing Spring, Devil's Eye Spring, and Mill Pond
Spring) following a four week translocation experiment. ............................................32









Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

FACTORS AFFECTING PERIPHYTON ABUNDANCE ON MACROPHYTES IN A
SPRING-FED RIVER IN FLORIDA

By

Vincent Anthony Politano

May 2008

Chair: Thomas K. Frazer
Major: Fisheries and Aquatic Sciences

Past and present land use activities in Florida have resulted in broad-scale nutrient

concentration increases in the groundwater system. Nutrient contaminated groundwater is not

only a health concern, but also represents a potentially serious ecological problem. Because

Florida's extensive system of aquifers exist within a very permeable karst geology, there are

myriad of pathways by which nutrient laden groundwater can enter and be mixed with surface

water systems. Freshwater springs, for example, provide a direct conduit for contaminated

groundwater discharge to surface water systems. It is in the surface waters where nutrients, such

as nitrogen and phosphorus, have the greatest potential to negatively alter the ecology of aquatic

ecosystems. Along the Ichetucknee River, several feeder springs have experienced vegetation

losses over the past decade. The springs are not only enriched in nutrients, but also exhibit low

dissolved oxygen concentrations, and low stream velocites. While eutrophication appears to be a

plausible explanation for vegetation loss, this study investigated the possibility that nutrient

contamination alone may not be responsible for vegetation loss. I hypothesized that low

dissolved oxygen concentrations near spring vents and seeps preclude the existence of primary

grazers and, as a consequence, macrophytes in these areas of low stream velocity accumulate

more periphyton and grow more slowly than vegetation in more oxygenated, swiftly flowing









portions of the river. An initial characterization of the abiotic environment and the macrophyte

community of the Ichetucknee River indicated that the proposed pattern of interaction was

evident throughout the system. Subsequently, a four-week translocation experiment was carried

out where genets of the most abundant macrophyte, Sagittaria kurziana, were relocated to

several river and spring locations to evaluate site specific differences in the rate of periphyton

accumulation and potential effects on macrophyte growth. Results suggest that periphyton

accumulation on S. kurziana is more rapid in feeder spring environments than in the main stem

of the Ichetucknee River. The differences were likely due to low dissolved oxygen

concentrations, low stream velocities and reduced grazer abundance in the feeder springs. There

were, however, no detectable effects on macrophyte growth probably due to the short duration of

the study.









CHAPTER 1
INTRODUCTION

The structure and function of aquatic ecosystems is determined by many chemical,

physical and biological processes. Chemically driven processes that influence primary

production with consequences for higher-order organisms are typically classified as "bottom-up"

processes. In contrast, "top-down" processes are those in which higher-order organisms exert a

strong influence on the structure and function of the system. Although opposing in nature,

"bottom-up" and "top-down" processes co-occur (Heck et al. 2006). In some cases, however, the

balance between these opposing processes is disrupted with marked ecological consequences

(Turner et al. 1994).

Nutrient over-enrichment, for example, can lead to excessive primary production and

changes in habitat and community structure. In extreme cases, microalgae flourish and become

so abundant as to lethally shade benthic macrophytes and macroalgae (Duarte 1995).

Eutrophication is common in water bodies bordered by human development and ecologists are

becoming increasingly aware of the potential effects of anthropogenic nutrient enrichment

(Caccia and Boyer 2007).

Nutrient over-enrichment is of great concern in north central Florida where many aquatic

systems are affected by changing land use activities. The region's permeable karst geology

allows for pollutants to percolate into an extensive aquifer system. Nutrient pollutants in

Florida's groundwater, nitrogen and phosphorus in particular, are delivered to surface waters in

the region via more than 300 individual freshwater springs (Notestein et al. 2003). Many aquatic

ecosystems throughout north central Florida have experienced increases in nutrient pollution and

reports of vegetation loss attributable to algal overgrowth from prolonged anthropogenic nutrient

enrichment are increasingly common (e.g., Wright and McDonald 1986a, 1986b).









Nutrient enrichment, however, may not be the only factor contributing to vegetation loss in

spring-fed river systems. Low concentrations of dissolved oxygen and low stream velocities

may also play a role. For instance, aquifer water supplying spring-fed systems in Florida is often

hypoxic (Rosenau et al. 1977), presumably due to the microbial remineralization of organic

substrates. Additionally, when aquifer water enters the surface waters of a system it often does

so at a very low velocity (Kurz 2004). Low dissolved oxygen concentration could preclude the

existence of periphyton grazers and low stream velocity could facilitate the accumulation of

periphyton by reducing the sheer force near the boundary layer surrounding macrophyte blades.

Together, these factors may facilitate a pattern of vegetation loss whereby areas of low dissolved

oxygen concentration may have low populations of periphyton grazers and low stream velocities,

which allows periphyton to accumulate, in the absence of scouring, to levels capable of

negatively impacting the growth of rooted macrophytes.

The Ichetucknee River, located in north central Florida, is predominantly spring-fed and a

reduction in the abundance of rooted macrophytes in the system has been observed over the past

decade in conjunction with an increase in periphyton (Evans 2007). These findings are

consistent with a nutrient enrichment scenario and the Ichetucknee River does show elevated

levels of nitrate and phosphorus (Kurz 2004). I propose, however, that the pattern of vegetation

loss is dependent on dissolved oxygen concentrations and stream velocities which, in

combination, control the presence of periphyton grazers and the magnitude of the scouring force

of water. I hypothesize specifically that the growth potential of macrophytes in areas of low

dissolved oxygen concentrations and low stream velocities will be compromised due to shading

from periphytic algae that accumulates in the slow flowing water and proliferates in the absence

of grazers.









CHAPTER 2
MATERIALS AND METHODS

Study Site

The Ichetucknee River is a tributary of the Santa-Fe River which is part of the larger

Suwannee River basin in north central Florida. The river is fed, in large part, by water derived

from the Floridan Aquifer. A 1st magnitude headspring serves as the origin of flow, though

numerous feeder springs along the river's length also contribute to the river's flow. Exceptional

water clarity is a hallmark of the Ichetucknee system and the main stem of the river is densely

populated by submersed aquatic vegetation. The dominant macrophyte throughout the system is

Sagittaria kurziana (Kurz et al. 2003); however, the smaller feeder springs along the main stem

of the Ichetucknee River are often nearly devoid of macrophytes (Kurz et al. 2004).

The Ichetucknee is home to a variety of fish species including Micropterus, Heterandria

and Lepomis species in addition to a rich benthic invertebrate community represented by

numerous chironomids, crustaceans, and molluscs (McKinsey and Chapman 1998, Mattson et al.

1995). Dominant grazers of periphyton in the system include chironomids and a pleurocerid

snail, Elimiafloridensis, which grows to five centimeters in length and can live for nearly a

decade (Huryn et al. 1994). Recent research has shown that E. floridensis is more abundant in

the main stem of the Ichetucknee River than in the smaller spring runs (Dormsjo 2007), although

the presence of chironomids in the smaller spring runs has not been studied.

Quantitative River and Spring Survey

In January of 2007, a temporally focused effort provided estimates for several key

chemical and physical parameters as well as a quantitative characterization of submersed aquatic

vegetation and associated periphyton. All sampling was carried out at fourteen regularly-spaced

transects along 2 km of the main stem of the river as well as three transects along the runs of









three associated feeder springs, i.e. Singing Spring, Devils Eye Spring, Mill Pond Spring (Figure

2-1). Along each transect, three stations were sampled perpendicular to the direction of water

flow such that one station was sampled in mid-channel and the other two sampled halfway

between the bank of the river or spring run and the mid-channel station.

Chemical and Physical Parameters

Dissolved oxygen concentration (mgL-1), water temperature (C), and pH were measured in

situ at a depth of 0.5 m with a Yellow Springs Instrument Company model 650 hand-held meter.

Water depth (m) was measured at all stations with a collapsible fiberglass survey rod marked in

0.01 m increments. Stream velocities (ms-1) were measured at two-thirds of the water column

depth with a Marsh-McBirney model 2000 portable flow meter recording 5-second averages. Li-

Cor Instruments, Inc. quantum light sensors were employed to simultaneously collect surface and

downwelling light intensity (umole photons sm-2 of photosynthetically active radiation, PAR) at

three depths spanning the water column. Light attenuation (Kd) at each station was determined

from the equation: Kd = [ln (Io / Iz)] / z, where Io is the incident irradiance at the water surface

and Iz is the light intensity at depth z (m) (Kirk 1994).

Vegetation Sampling

Submersed aquatic vegetation was collected at each station using a 0.0625-m2 quadrat,

constructed of 4-inch diameter PVC with 900 elbow joints (Figure 2-2). During construction, the

frame of the device was sliced in half transversely to make a top u-shape and a bottom u-shape.

These two halves were then connected by six-foot panels of 425-micron NITEX mesh. Four

panels were used in total, but one panel remained attached to the frame on only one side of the

device in order to eventually close the three-sided u-shape into a square. During deployment, the

quadrat was collapsed, inserted into the SAV canopy by SCUBA divers and placed on the river

bed in its, three-sided form (with the fourth panel tucked back). The fourth panel was then









brought across between the u-shape tips to close the shape into a full square quadrat. The fourth

panel was connected to the opposite side of the u-shape by a zipper spanning the entire six-foot

length of the panel. With the panel connected, the entire top u-shape of the quadrat could be

separated from the bottom u-shape resting on the river bed and lifted, while simultaneously

zippering the fourth panel to its adjacent compliment. This sample maneuver resulted in the

enclosure of all SAV within the confines of the quadrat. In this position, the apparatus was then

folded over on itself to cover the top hole of the device and the above-ground SAV was cut at the

sediment/water interface. As the sampler was removed from the canopy and placed aboard the

research vessel, all gastropods associated with the substrate beneath the sampler were collected

as part of a complementary effort. Onboard the boat, the sampler was opened and all vegetation

was inspected for gastropods. All gastropods were identified, recorded and returned to the river.

Data concerning gastropod abundance and distribution are reported elsewhere (Dormsjo 2007).

SAV samples were removed from the device and stored in a zip-lock bag on ice during transport

to the laboratory for additional processing. At the laboratory, any incidental below-ground

biomass associated with the harvested plants was removed and discarded. The remaining plant

material was blotted dry with a paper towel. All leaf lengths were measured (to the nearest mm)

and the wet weight of the entire sample was determined (to the nearest mg). Plants were

subsequently dried at 600C for >48 hr to determine a dry weight.

Quantifying Periphyton Associated with SAV

Periphyton associated with SAV at each sample station was measured according to the

method originally outlined by Moss (1981) and subsequently modified by Canfield and Hoyer

(1988). First, a single blade of the dominant macrophyte at each sampling station was removed

from the river and placed in a 1-L Nalgene jar, pre-filled with 500 ml of deionized water.

Periphyton was then removed from the host macrophyte sample by vigorously shaking the 1-L









Nalgene jar containing the sample for 30 seconds. The resultant slurry was filtered through a 1-

mm screen into a Nalgene beaker. Fresh deionized water was added to the Nalgene jar and the

shaking / filtering process was repeated for a total of three times. The resultant slurry after three

shaking processes was homogenized and a sub-sample of known volume was filtered through a

Gelman type A/E 47 mm glass-fiber filter. The remaining volume of slurry was noted and the

filters were stored frozen prior to analysis of chlorophyll (APHA 1995).

Translocation Experiment

In addition to the river survey, a field experiment was performed in March 2007 to

quantify the rate of periphyton accumulation on macrophytes in the main river and feeder springs

and assess the potential influence of that periphyton accrual on macrophyte growth. This

experiment involved the relocation of individual, standardized genets of S. kurziana into cleared

plots within the river and three adjacent feeder springs, i.e. Singing Spring, Devil's Eye Spring,

and Mill Pond Spring. The use of translocated genets of S. kurziana was intended to reduce any

intrinsic variability between resident river and spring plants.

The genets of S. kurziana selected for the study were harvested near the confluence of

Devil's Eye Spring run and the main river. Chosen for their morphological uniformity, the 225

plants were severed from their stolon connections and individually placed in terra cotta pots with

sandy substrate and a sponge lid to secure the contents throughout the experiment. All potted

plants were placed into the main river channel in three groups of 75. Groups were placed just

upstream of the confluence of the main stem of the river and each of the three feeder springs, i.e.

Singing Spring, Devil's Eye Spring, and Mill Pond Spring. The substrate at each location was

cleared of SAV to ensure an adequate light environment for the study plants. The potted plants

were allowed one week of acclimation after which, all plants were rubbed clean of periphyton by

hand and cut to a standardized blade length of approximately 7.5 cm. Immediately after









standardization, 25 plants were harvested for initial measurements of plant biomass and

periphyton abundance. Half of the remaining 50 plants were moved to their respective feeder

springs and arrayed just downstream of the primary spring vent. The 25 remaining plants were

left in the river channel at the acclimation location and all plants were observed bi-weekly for 4

weeks. After 4 weeks, all experimental plants from the river and spring locations were harvested

and measures of plant biomass and periphyton abundance were made following the methods

previously described. Abiotic metrics were also sampled for a comparison of pre- and post-

experimental conditions.

Statistical Analyses

Standard ANOVA procedures were used to test for differences in chemical, physical and

biological characteristics between the main river transects and feeder spring transects (JMP IN v.

5.1 1989). Normality was assessed with the Shapiro-Wilk test and the assumption of equal

variance verified with a Brown-Forsythe test. All plant biomass and periphyton abundance data

were loglo+l transformed to improve normality and heteroscedasity.











































Figure 2-1. Map of the Ichetucknee River course through the Ichetucknee Springs State Park.
All transect sampling was carried out in the upper portion of the river within the
confines of the park. Experimental work was conducted near Singing Spring, Devils
Eye (also known as Boiling Spring) and Mill Pond Spring.






































Figure 2-2. Collapsed and expanded view of plant sampling apparatus.









CHAPTER 3
RESULTS

Survey Results

Mean dissolved oxygen concentration in the main stem of the river ranged between 3.2 and

7.4 mg L-1 and exhibited a general increase between feeder spring influences (Figure 3-1). Mean

dissolved oxygen concentrations did not differ between the feeder springs (Mean value + SE;

Singing Spring = 1.57 mgL-1 + 0.28; Devil's Eye Spring = 1.05 mgL-1 + 0.13; Mill Pond Spring

= 1.40 mgL-1 + 0.49) (ANOVA; df = 2, F = 0.56, P = 0.60). Relative to the three feeder springs,

the main river exhibited significantly higher dissolved oxygen concentrations (ANOVA; df= 1,

F = 86.31, P = <0.0001) (Figure 3-2).

Mean stream velocity in the main stem of river ranged between 0.04 and 0.30 ms-1 and

exhibited a general increase between feeder spring influences (Figure 3-3). Mean stream

velocity did not differ between the feeder springs (Mean value SE; Singing Spring = 0.04 ms-1

0.013; Devil's Eye Spring = 0.04 ms-1 0.0083; Mill Pond Spring = 0.05 ms-1 0.016)

(ANOVA; df = 2, F = 0.168, P = 0.85). Relative to the three feeder springs, the main river

exhibited significantly higher stream velocities (ANOVA; df= 1, F = 11.63, P = 0.003) (Figure

3-4).

Mean periphyton abundance on macrophytes within the main stem of river ranged

between 0.014 and 0.068 mg chl a g WW-1 and showed a trend of decreasing abundance between

feeder spring influences (Figure 3-5). Mean periphyton abundance on plants did not differ

between the three feeder springs (Mean value SE; Singing Spring = 0.30 mg chl a g WW1 +

0.13; Devil's Eye Spring = 0.42 mg chl a g WW-1 + 0.16; Mill Pond Spring = 0.19 mg chl a g

WW-1 + 0.02) (ANOVA; df = 2, F = 0.48, P = 0.64). Overall, the mean periphyton abundance in









spring environments was significantly higher than the mean periphyton abundance within the

main stem of the river (ANOVA; df = 2, F = 93.81, P < 0.0001) (Figure 3-6).

Estimates of plant biomass in the main stem of Ichetucknee River ranged between 1172

and 8676 g WW m-2 and exhibited a general increase with distance downstream (Figure 3-7).

There was no significant difference in plant biomass between the three feeder springs. (Mean

value SE; Singing Spring = 1285 g WW m-2 281.85; Devils Eye Spring = 1670 g WW m-2

808.58; Mill Pond Spring = 1115 g WW m-2 381.26) (ANOVA; df = 2, F = 0.0098, P = 0.99).

Overall, the mean plant biomass along the main stem of the Ichetucknee River was significantly

higher than the mean plant biomass within the spring environments (ANOVA; df = 2, F = 24.07,

P < 0.0001) (Figure 3-8).

Translocation Experiment

Overall survivorship of translocated plants during the 4-week study period was 52% in the

main stem of the river and 96% in the feeder spring. Surviving plants in the river and feeder

springs exhibited no significant difference in growth as determined by a comparison of their

mean above ground biomasses (ANOVA; df = 1, F = 1.14, P = 0.34) (Figure 3-9). At time zero,

the mean leaf length of all plants was 7.54 cm ( 1.36). After the four week study period, the

mean leaf length of river plants was 9.40 cm ( 3.47) and that of the spring plants was 9.74 cm

(+ 3.01). Mean plant biomass and mean periphyton abundance did not differ between the three

feeder springs sites (Mean Plant Biomass (g WW + sd); Singing Spring = 2.54 + 1.48; Devil's

Eye Spring = 1.29 0.98; Mill Pond Spring = 1.40 + 0.68) (ANOVA; df = 2, F = 0.96, P = 0.48)

(Mean Periphyton Abundance (mg chl a g WW-1 sd); Singing Spring = 0.37 0.22; Devil's

Eye Spring = 1.10 1.14; Mill Pond Spring = 0.09 0.065) (ANOVA; df = 2, F = 0.13, P =

0.88). Overall, mean periphyton abundance tended to be greater on plants in the three feeder









springs than in the main river, although this difference was not statistically significant (ANOVA;

df = 2, F = 2.68, P = 0.18) (Figure 3-10).










Table 3-1. Summary of 2007 Survey Data Means + Standard Errors (n = # of samples)
Plant Periphyton Dissolved Stream Water
Biomass Abundance Oxygen Velocity Depth
Section (gWW m'2) (mg chl a g WW-1 ) (mgL-) (ms-1) (m)
River 4417 611 0.03 0.005 5.18 0.31 0.133 0.02 1.14 0.09
(n=14) (n=14) (n=14) (n=14) (n=14)

Spring 1357 + 283 0.30 0.07 1.34 0.19 0.05 0.007 0.83 0.20
(n=9) (n=9) (n=9) (n=3) (n=3)














'- 8
-J 8 -
E




5-
a




4
e 6-





3

S2-
0
I 1 -
0
a


41 6
singing Spring


8 10
Devils Eye Spring


141 16
Mill Pond Spring


Downstream I


Figure 3-1. Mean dissolved oxygen concentration with increasing distance downstream in the
main stem of the Ichetucknee River. Numbers along the x-axis correspond to river
transects with ascending values representing distance downstream.


* <


0 2


* Y i












I-.
t%5

.2


3

i
6 2

. 1i


River Spring


Figure 3-2. Mean dissolved oxygen concentration in the main stem of the Ichetucknee River and
three associated feeder springs (i.e. Singing Spring, Devil's Eye Spring, and Mill
Pond Spring).












0.500
-

E 0.400
SU
.2 0.300
E
0.200
4-

0.100

0.000


iii


8D 10
Devil's Eye Spring


14 16
Mill Pond Spring


Downstream I


Figure 3-3. Mean stream velocity with increasing distance downstream in the main stem of the
Ichetucknee River. Numbers along the x-axis correspond to river transects with
ascending values representing distance downstream.


0.600 1


41 6
Singing Spring


o 2











0.180 -


0.160 -

0.140 -

0.120 -

S0.100 -

S0.080 -
E
S0.060 -

0.040 -

0.020

0.000
River Spring


Figure 3-4. Mean stream velocity in the main stem of the Ichetucknee River and three associated
feeder springs (i.e. Singing Spring, Devil's Eye Spring, and Mill Pond Spring).










0.16

0.14
0-1
H
u 0.12
E





- 0.06
-

I -
S0.04
0


a 0.02
S0.06 -


L.


0-


444if


t.+i


0 2 4 1 6 8 1 10 12 14 1 16
Singing Spring Devil's Eye Spring Mill Pong Spring
Downstream

Figure 3-5. Mean periphyton abundance with increasing distance downstream in the main stem
of the Ichetucknee River. Numbers along the x-axis correspond to river transects
with ascending values representing distance downstream.












0.4 -


S0.35


S0.3 -

5
4 0.25
4"
0.2


0.15



t 0.2
0

r 0.05


River Spring


Figure 3-6. Mean periphyton abundance in the main stem of the Ichetucknee River and three
associated feeder springs (i.e. Singing Spring, Devil's Eye Spring, and Mill Pond
Spring).









16000 -


14000 -

12000 -

10000 -

8000

6000 -

4000 -

2000 -
0-


'4+


0 2 41 6 BI 10
Singing Spring Devil's Eye Spring


12 141 16
Mill Pond Spring


Downstream --
Figure 3-7. Mean plant biomass with increasing distance downstream in the main stem of the
Ichetucknee River. Numbers along the x-axis correspond to river transects with
ascending values representing distance downstream.


'ii


f











6000 -


5000


E 4000


" 3000
E
.9
E 2000


1000


0
River Spring


Figure 3-8. Mean plant biomass in the main stem of the Ichetucknee River and three associated
feeder springs (i.e. Singing Spring, Devil's Eye Spring, and Mill Pond Spring).












2.5 -


2-




1.5-

A
E


.a


0.5




0-


River


Spring


Figure 3-9. Mean plant biomass in the main stem of the Ichetucknee River and three associated
feeder springs (i.e. Singing Spring, Devil's Eye Spring, and Mill Pond Spring)
following a four week translocation experiment.












0.8 -


0.7
bt


S0.6 -
bat

0.5


S0.4
o

0.3


4 0.2


A. 0.1 -



River Spring


Figure 3-10. Mean periphyton abundance in the main stem of the Ichetucknee River and three
associated feeder springs (i.e. Singing Spring, Devil's Eye Spring, and Mill Pond
Spring) following a four week translocation experiment.









CHAPTER 4
DISCUSSION

The proposed pattern of interaction between dissolved oxygen, stream velocity, grazer

abundance, and periphyton abundance on host macrophytes was well supported by the

observations made during the survey of the Ichetucknee River and its feeder springs (see also

Dormsjo 2007). Dissolved oxygen concentrations were consistently low near spring sources

regardless of whether the spring source was the headspring of the river, any one of the three

feeder springs, or the many spring/river confluences along the main stem course. This finding is

consistent with data reported previously (Kurz et al. 2003 and 2004). Stream velocity, plant

biomass, and grazer abundance exhibited a similar pattern; lowest values for all the

aforementioned parameters occurred near spring sources (see also Dormsjo 2007). These

findings too are similar to those reported by Kurz et al. (2003 and 2004). As hypothesized,

periphyton abundance values were inversely related to dissolved oxygen, stream velocity, grazer

abundance, and plant biomass values. Where dissolved oxygen, stream velocity, grazer

abundance, and plant biomass values were low, periphyton abundance on host plants was high.

Literature on lotic systems suggests that the patterns reported here exhibit some generality.

For example, Sabater et al. (2000) found that benthic algal biomass in the Oria River, a Spanish

river with intense human activity in its watershed, was highest in locations where diel variations

in dissolved oxygen concentrations resulted in acute hypoxia. Episodes of hypoxia in areas of

high algal biomass in the Oria River have been linked to herbivorous fish kills (Sabater 2000)

suggesting that oxygen mediated grazing impacts are likely to be an important process in lotic

systems.

Additionally, stream velocity is often reported as a significant variable affecting both

periphyton and macrophyte abundance. Chambers et al. (1991) showed that sudden increases in









current velocity in two slow-flowing rivers in Canada resulted in decreased plant biomass

through uprooting. It's a logical assumption that periphyton abundance on macrophytes within

the same rivers would also decrease with increasing current velocity. For example, Giorgi et al.

(2005) observed that attached algal biomass decreased during times of flood in Pampean streams

suggesting that increasing current velocity exerts a significant scouring force on periphyton

communities. Similar conclusions have been reported by several additional research efforts (e.g.,

Birkett et al. 2007, Katano et al. 2005, Amon et al. 2007).

The results of the translocation experiment following the quantitative river survey were

likely confounded by the low survival rates of S. kurziana in the main stem of the river and the

short duration of the study. While 96% of the plants in the feeder springs survived, river plants

exhibited a relatively large loss (48%) resulting in few data for statistical comparison of

periphyton abundance on host plants between the main river and springs. Nevertheless, the rate

of periphyton accrual on plants in the feeder springs was marginally greater than on plants in the

main stem of the river. This finding is consistent with my hypothesis, but I was unable to detect

any statistically significant difference in plant growth that might be attributed to an increase in

periphyton load.

Some mortality of the translocated plants was expected during this experiment as short-

term mortality is common in such studies. For example, Zimmerman, et al. (1995) transplanted

Zostera marina, a functionally similar marine macrophyte, in San Francisco Bay, CA, and

reported high initial losses. Additionally, Hauxwell et al. (2003) transplanted Vallisneria

americana (a plant commonly found with S. kurziana) in Kings Bay, FL in 2001 and 2002 and

observed high initial mortality. In both cases, the investigators emphasized the importance of

transplant timing and experiment duration in relocation success (Zimmerman et al. 1995,









Hauxwell et al. 2003). Zimmerman et al. (1995) pointed out that although the eelgrass

transplants in San Francisco Bay, CA were partially successful, transplant survival could have

been improved by taking into account the role of carbon reserves when timing a transplant event

(Zimmerman et al. 1995). Hauxwell et al. (2003) suggested that similar transplant experiments

should run for 1-2 years to ensure natural growth responses from the transplants. The four-week

experimental period chosen for this study was necessary due to the high human use and

disturbance of the system during the summer months. Subsequent efforts to determine the

effects of periphyton accumulation on macrophyte growth in the Ichetucknee River will likely

require some intervention to lessen such impacts.

In addition to transplant duration and timing, it should be noted that experimental plants in

the main stem of the river were maintained at depths of approximately 1.5 m whereas plants in

the feeder springs were maintained at approximately 0.75 m. Although water clarity in the

Ichetucknee system is superb, it is possible that slight differences in water depth contributed to

plant loss in the main river as a consequence of increased light attenuation. The topography of

the Ichetucknee River dictated the depth at which the translocated plants would be placed and so

no depth standardization was possible. It is unclear whether differences in depth influenced the

experimental outcome, but light attenuation has a strong influence on the distribution and

abundance of aquatic macrophytes and many studies have shown a negative relationship between

increased light attenuation and the biomass of aquatic macrophytes (e.g., De Boer 2007, Loiselle

et al. 2007).

Despite the problems associated with plant transplant and translocation, the surviving

plants from this study did provided a natural substrate for a first order approximation of the rate

of periphyton accumulation. The periphyton loads on macrophytes in the Ichetucknee River









after only a four-week period were similar to standing crop values previously reported in the

river by Kurz et al. (2004). In 2004, mean periphyton abundance was 0.15 mg chl a gWW1 in

the main stem of the Ichetucknee River and 0.61 mg chl a gWW1 in the feeder springs. In 2007

(this study), mean periphyton abundance was 0.09 mg chl a gWW1 in the main stem of the

Ichetucknee River and 0.52 mg chl a gWW1 in the feeder springs. Interestingly, average rates of

stream velocity in the main stem of the Ichetucknee River during 2007 (0.133 ms-) were lower

than those in 2004 (0.160 ms-1) as a consequence of a regional drought that affected spring

discharge. Despite these slight differences, my stream velocity and periphyton abundance results

are consistent with previous work relating the two variables (Kurz et al. 2003 and 2004). Results

from this investigation reinforce the need for additional studies on flow rates and periphyton

accrual in this system and how these factors might interact with others such as changes in

nutrient loads, oxygen concentrations, light availability and grazing to affect the structure and

function of the ecological community.









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Loiselle SA, Cozar A, Dattilo A, Bracchini L, Galvez JA (2007) Light limitations to algal growth
in tropical ecosystems. Freshwater Biology 52(2): 305-312

Mattson RA, Epler JH, Hein MK (1995) Description of benthic communities in karst, spring-fed
streams of north central Florida. Journal of the Kansas Entomological Society 68(2): 18-
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McKinsey DM, Chapman LJ (1998) Dissolved oxygen and fish distribution in a Florida Spring.
Environmental Biology of Fishes 53: 211-223









Moss B (1981) The effect of fertilization and fish on community structure and biomass of
aquatic macrophyte and epiphytic algae populations: An ecosystem experiment. Journal
of Ecology 64: 313-342

Notestein SK, Frazer TK, Hoyer MV, Canfield DE (2003) Nutrient limitation of periphyton in a
spring-fed, coastal stream in Florida, USA. Journal of Aquatic Plant Management 41:57-
60

Odum HT (1957) Trophic structure and productivity of Silver Springs, Florida. Ecological
Monographs 27(1): 55-112

Rosenau JC, Faulkner GL, Hendry CW Jr., Hull RW (1977) Springs of Florida. Florida
Geological Survey Geological Bulletin No 31, revised. From
http://www.flmnh.ufl.edu/springs_of fl/aaj7320/content.html

Sabater S, Armengol J, Comas E, Sabater F, Urrizalqui I, Urrutia I (2000) Algal biomass in a
disturbed Atlantic river: water quality relationships and environmental implications.
Science of the Total Environment 263(1-3): 185-195

Turner ER, Rabalais NN (1994) Coastal eutrophication near the Mississippi River delta. Nature
368: 619-621.

Wright RM, McDonald AJ (1986a) Macrophyte growth in shallow streams. Field investigations.
Journal of Environmental Engineering 112: 952-966

Wright RM, McDonald AJ (1986b) Macrophyte growth in shallow streams. Biomass model.
Journal of Environmental Engineering 112: 967-981

Zimmerman RC, Reguzzoni JL, Alberte RS (1995) Eelgrass (Zostera marine L) transplants in
San-Francisco Bay role of light availability on metabolism, growth and survival.
Aquatic Botany 51(1-2): 67-86









BIOGRAPHICAL SKETCH

Vince Politano graduated summa cum laude from the University of Rhode Island with a

Bachelor of Science degree in marine biology. He completed his Master of Science degree at the

University of Florida in the Department of Fisheries and Aquatic Sciences.





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FACTORS AFFECTING PERIPHYTON AB UNDANCE ON MACROPHYTES IN A SPRING-FED RIVER IN FLORIDA By VINCENT ANTHONY POLITANO A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS OF THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2008 1

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2008 Vincent Anthony Politano 2

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To my family 3

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ACKNOWLEDGEMENTS I thank my family and friends for their support and my advisors for their tutelage. 4

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TABLE OF CONTENTS page ACKNOWLEDGEMENTS .............................................................................................................4LIST OF TABLES ...........................................................................................................................6LIST OF FIGURES .........................................................................................................................7ABSTRACT ...................................................................................................................... ...............8CHAPTER 1 INTRODUCTION ................................................................................................................ ..102 MATERIALS AND METHODS ...........................................................................................12Quantitative River and Spring Survey ....................................................................................12Chemical and Physical Parameters ..................................................................................13Vegetation Sampling .......................................................................................................13Quantifying Periphyton Associated with SAV ................................................................14Translocation Experiment ...................................................................................................... .15Statistical Analyses .......................................................................................................... .......163 RESULTS ..................................................................................................................... ..........19Survey Results ........................................................................................................................19Translocation Experiment ...................................................................................................... .204 DISCUSSION .................................................................................................................. .......33LIST OF REFERENCES ...............................................................................................................37BIOGRAPHICAL SKETCH .........................................................................................................40 5

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LIST OF TABLES Table page 3-1. Summary of 2007 Survey Data Means Standard Errors (n = # of samples) ....................22 6

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LIST OF FIGURES Figure page 2-1. Map of the Ichetucknee River course thr ough the Ichetucknee Springs State Park. All transect sampling was carried out in the uppe r portion of the river within the confines of the park. Experimental work was conducted near Singing Spring, Devils Eye (also known as Boiling Spring) and Mill Pond Spring. .....................................................172-2. Collapsed and expanded view of plant sampling apparatus. .................................................183-1. Mean dissolved oxygen concentration with increasing distance downstream in the main stem of the Ichetucknee River. Numb ers along the x-axis correspond to river transects with ascending values representing distance downstream. .................................233-2. Mean dissolved oxygen concentration in th e main stem of the Ichetucknee River and three associated feeder springs (i.e. Singing Spring, Devils Eye Spring, and Mill Pond Spring). .....................................................................................................................243-3. Mean stream velocity with increasing di stance downstream in the main stem of the Ichetucknee River. Numbers along the xaxis correspond to ri ver transects with ascending values representing distance downstream. ........................................................253-4. Mean stream velocity in the main stem of the Ichetucknee Rive r and three associated feeder springs (i.e. Singing Spring, De vils Eye Spring, and Mill Pond Spring). .............263-5. Mean periphyton abundance with increasing distance downstream in the main stem of the Ichetucknee River. Numbers along the xaxis correspond to river transects with ascending values representing distance downstream. ........................................................273-6. Mean periphyton abundance in the main stem of the Ichetucknee River and three associated feeder springs (i.e. Singin g Spring, Devils Eye Spring, and Mill Pond Spring)................................................................................................................................283-7. Mean plant biomass with increasing dist ance downstream in the main stem of the Ichetucknee River. Numbers along the xaxis correspond to ri ver transects with ascending values representing distance downstream. ........................................................293-8. Mean plant biomass in the main stem of the Ichetucknee River and three associated feeder springs (i.e. Singing Spring, De vils Eye Spring, and Mill Pond Spring). .............303-9. Mean plant biomass in the main stem of the Ichetucknee River and three associated feeder springs (i.e. Singing Spring, De vils Eye Spring, and Mill Pond Spring) following a four week tran slocation experiment. ..............................................................313-10. Mean periphyton abundance in the main stem of the Ichetucknee River and three associated feeder springs (i.e. Singin g Spring, Devils Eye Spring, and Mill Pond Spring) following a four week translocation experiment. .................................................32 7

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Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science FACTORS AFFECTING PERIPHYTON AB UNDANCE ON MACROPHYTES IN A SPRING-FED RIVER IN FLORIDA By Vincent Anthony Politano May 2008 Chair: Thomas K. Frazer Major: Fisheries a nd Aquatic Sciences Past and present land use activities in Flor ida have resulted in broad-scale nutrient concentration increases in the groundwater syst em. Nutrient contaminated groundwater is not only a health concern, but also represents a potentially serious ecolo gical problem. Because Floridas extensive system of aquifers exist within a very permeable karst geology, there are myriad of pathways by which nutrient laden groun dwater can enter and be mixed with surface water systems. Freshwater springs, for exampl e, provide a direct conduit for contaminated groundwater discharge to surface water systems. It is in the surface waters where nutrients, such as nitrogen and phosphorus, have th e greatest poten tial to negatively alter the ecology of aquatic ecosystems. Along the Ichetucknee River, severa l feeder springs have experienced vegetation losses over the past decade. The springs are not only enriched in nutrients but also exhibit low dissolved oxygen concentrations, and low stream ve locites. While eutrophication appears to be a plausible explanation for vegetati on loss, this study investigated the possibility that nutrient contamination alone may not be responsible for vegetation loss. I hypothesized that low dissolved oxygen concentrations near spring vents and seeps precl ude the existence of primary grazers and, as a consequence, macrophytes in th ese areas of low stream velocity accumulate more periphyton and grow more slowly than vegetation in more oxygenated, swiftly flowing 8

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9 portions of the river. An initial characteriza tion of the abiotic environment and the macrophyte community of the Ichetucknee River indicated that the propose d pattern of interaction was evident throughout the system. Subsequently, a f our-week translocation experiment was carried out where genets of the most abundant macrophyte, Sagittaria kurziana were relocated to several river and spring locations to evaluate si te specific differences in the rate of periphyton accumulation and potential effects on macrophyte growth. Results suggest that periphyton accumulation on S. kurziana is more rapid in feeder spring en vironments than in the main stem of the Ichetucknee River. The differences were likely due to low dissolved oxygen concentrations, low stream veloci ties and reduced grazer abundance in the feeder springs. There were, however, no detectable effects on macrophyte growth probably due to the short duration of the study.

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CHAPTER 1 INTRODUCTION The structure and function of aquatic eco systems is determined by many chemical, physical and biological processes. Chemically driven processes that influence primary production with consequences for higher-order organisms are typical ly classified as bottom-up processes. In contrast, top-down processes ar e those in which higher-order organisms exert a strong influence on the structure and functi on of the system. Although opposing in nature, bottom-up and top-down processes co-occur (H eck et al. 2006). In some cases, however, the balance between these opposing processes is disrupted with marked eco logical consequences (Turner et al. 1994). Nutrient over-enrichment, for example, can lead to excessive primary production and changes in habitat and community structure. In extreme cases, microalgae flourish and become so abundant as to lethally shade benthi c macrophytes and macroalgae (Duarte 1995). Eutrophication is common in water bodies borde red by human development and ecologists are becoming increasingly aware of the potential e ffects of anthropogenic nutrient enrichment (Caccia and Boyer 2007). Nutrient over-enrichment is of great concern in north centr al Florida where many aquatic systems are affected by changing land use activ ities. The regions permeable karst geology allows for pollutants to percolate into an exte nsive aquifer system. Nutrient pollutants in Floridas groundwater, nitrogen an d phosphorus in particular, are de livered to surface waters in the region via more than 300 individual freshwater springs (Notestein et al. 2003). Many aquatic ecosystems throughout north central Florida have experienced incr eases in nutrient pollution and reports of vegetation loss attri butable to algal overgrowth from prolonged anthropogenic nutrient enrichment are increasingly common (e.g., Wright and McDonald 1986a, 1986b). 10

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Nutrient enrichment, however, may not be the only factor contributing to vegetation loss in spring-fed river systems. Low concentrations of dissolved oxygen and low stream velocities may also play a role. For instance, aquifer wate r supplying spring-fed systems in Florida is often hypoxic (Rosenau et al. 1977), presumably due to the microbial remineralization of organic substrates. Additionally, when aquifer water enters the surface waters of a system it often does so at a very low velocity (Kurz 2004). Low di ssolved oxygen concentration could preclude the existence of periphyton grazers and low stream velocity could facilitate the accumulation of periphyton by reducing the sheer force near the boundary layer surrounding macrophyte blades. Together, these factors may facilitate a pattern of vegetation loss whereby areas of low dissolved oxygen concentration may have low populations of periphyton grazers and low stream velocities, which allows periphyton to accumulate, in the absence of scouring, to levels capable of negatively impacting the growth of rooted macrophytes. The Ichetucknee River, located in north central Florida, is predomin antly spring-fed and a reduction in the abundance of root ed macrophytes in the system has been observed over the past decade in conjunction with an increase in periphyton (Evans 2007). These findings are consistent with a nutrient enrichment scenario and the Ichetucknee River does show elevated levels of nitrate and phosphorus (Kurz 2004). I pr opose, however, that the pattern of vegetation loss is dependent on dissolved oxygen concentrations and stream velocities which, in combination, control the presence of periphyton grazers and the magnitude of the scouring force of water. I hypothesize specifica lly that the growth potential of macrophytes in areas of low dissolved oxygen concentrations and low stream velocities will be compromised due to shading from periphytic algae that accumulates in the slow flowing water and proliferates in the absence of grazers. 11

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CHAPTER 2 MATERIALS AND METHODS Study Site The Ichetucknee River is a tri butary of the Santa-Fe River which is part of the larger Suwannee River basin in north central Florida. The river is fed, in large part, by water derived from the Floridan Aquifer. A 1st magnitude headspring serves as the origin of flow, though numerous feeder springs along the rivers length also contribute to the rivers flow. Exceptional water clarity is a hallmark of the Ichetucknee syst em and the main stem of the river is densely populated by submersed aquatic vegetation. Th e dominant macrophyte throughout the system is Sagittaria kurziana (Kurz et al. 2003); however, the smalle r feeder springs along the main stem of the Ichetucknee River are often nearly devoid of m acrophytes (Kurz et al. 2004). The Ichetucknee is home to a vari ety of fish species including Micropterus Heterandria and Lepomis species in addition to a rich benthi c invertebrate community represented by numerous chironomids, crustaceans, and mollu scs (McKinsey and Chapman 1998, Mattson et al. 1995). Dominant grazers of periphyton in the system include chironomids and a pleurocerid snail, Elimia floridensis which grows to five centimeters in length and can live for nearly a decade (Huryn et al. 1994). Recent research has shown that E. floridensis is more abundant in the main stem of the Ichetucknee River than in the smaller spring runs (Dormsjo 2007), although the presence of chironomids in the smaller spring runs has not been studied. Quantitative River and Spring Survey In January of 2007, a temporally focused e ffort provided estimates for several key chemical and physical parameters as well as a qu antitative characterizatio n of submersed aquatic vegetation and associated periphyton. All sampli ng was carried out at fourteen regularly-spaced transects along 2 km of the main stem of the river as well as three transects along the runs of 12

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three associated feeder springs i.e. Singing Spring, Devils Ey e Spring, Mill Pond Spring (Figure 2-1). Along each transect, three stations were sampled perpendicular to the direction of water flow such that one station was sampled in mid-channel and the other two sampled halfway between the bank of the river or spri ng run and the mid-channel station. Chemical and Physical Parameters Dissolved oxygen concentration (mgL-1), water temperature (oC), and pH were measured in situ at a depth of 0.5 m with a Yellow Springs In strument Company model 650 hand-held meter. Water depth (m) was measured at all stations with a collapsible fiberglass survey rod marked in 0.01 m increments. Stream velocities (ms-1) were measured at two-thirds of the water column depth with a Marsh-McBirney model 2000 portable flow meter recording 5-second averages. LiCor Instruments, Inc. quantum light sensors were employed to simultaneously collect surface and downwelling light intensity (umole photons s-1m-2 of photosynthetically ac tive radiation, PAR) at three depths spanning the wate r column. Light attenuation (Kd) at each station was determined from the equation: Kd = [ln (Io / Iz)] / z, where Io is the incident irradi ance at the water surface and Iz is the light intensity at depth z (m) (Kirk 1994). Vegetation Sampling Submersed aquatic vegetation was collect ed at each station using a 0.0625-m2 quadrat, constructed of 4-inch diameter PVC with 90o elbow joints (Figure 2-2) During construction, the frame of the device was sliced in half transversely to make a top u-shape and a bottom u-shape. These two halves were then connected by sixfoot panels of 425-micron NITEX mesh. Four panels were used in total, but one panel remained attached to the frame on only one side of the device in order to eventually close the three-side d u-shape into a square. During deployment, the quadrat was collapsed, inserted into the SAV canopy by SCUBA divers and placed on the river bed in its, three-sided form (with the fourth pa nel tucked back). The fourth panel was then 13

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brought across between the u-shape ti ps to close the shape into a fu ll square quadrat. The fourth panel was connected to the opposite side of the u-shape by a zipper spanni ng the entire six-foot length of the panel. With the panel connected, the entire top u-shape of the quadrat could be separated from the bottom u-shape resting on th e river bed and lifted, while simultaneously zippering the fourth panel to its adjacent compliment. This sample maneuver resulted in the enclosure of all SAV within the confines of the quadrat. In this position, the apparatus was then folded over on itself to cover th e top hole of the device and the above-ground SAV was cut at the sediment/water interface. As the sampler wa s removed from the canopy and placed aboard the research vessel, all gastropods associated with the substrate beneath the sampler were collected as part of a complementary effort. Onboard th e boat, the sampler was opened and all vegetation was inspected for gastropods. All gastropods were id entified, recorded and re turned to the river. Data concerning gastropod abundance and distribu tion are reported elsewhere (Dormsjo 2007). SAV samples were removed from the device and st ored in a zip-lock ba g on ice during transport to the laboratory for additional processing. At the laboratory, any incidental below-ground biomass associated with the harvested plants was removed and discarded. The remaining plant material was blotted dry with a paper towel. A ll leaf lengths were meas ured (to the nearest mm) and the wet weight of the entire sample was de termined (to the nearest mg). Plants were subsequently dried at 600C for >48 hr to determine a dry weight. Quantifying Periphyton Associated with SAV Periphyton associated with SAV at each samp le station was measured according to the method originally outlined by Moss (1981) and s ubsequently modified by Canfield and Hoyer (1988). First, a single blade of the dominant m acrophyte at each sampling station was removed from the river and placed in a 1-L Nalgene jar, pre-filled with 500 ml of deionized water. Periphyton was then removed from the host macr ophyte sample by vigorously shaking the 1-L 14

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Nalgene jar containing the sample for 30 seconds. The resultant slurry was filtered through a 1mm screen into a Nalgene beaker. Fresh deionized water was added to the Nalgene jar and the shaking / filtering process was repeated for a total of three times. The resultant slurry after three shaking processes was homogenized and a sub-sample of known volume was filtered through a Gelman type A/E 47 mm glass-fiber filter. The remaining volume of slurry was noted and the filters were stored frozen prior to analysis of chlorophyll (APHA 1995). Translocation Experiment In addition to the river survey, a field experiment was performed in March 2007 to quantify the rate of periphyton accumulation on macr ophytes in the main river and feeder springs and assess the potential influence of that periphyton accrual on m acrophyte growth. This experiment involved the relocation of individual, standard ized genets of S. kurziana into cleared plots within the river and three adjacent feeder springs, i.e. Singing Spring, Devils Eye Spring, and Mill Pond Spring. The use of translocated genets of S. kurziana was intended to reduce any intrinsic variability between re sident river a nd spring plants. The genets of S. kurziana selected for the study were ha rvested near the confluence of Devils Eye Spring run and the main river. Chosen for their morphological uniformity, the 225 plants were severed from their st olon connections and individually pl aced in terra cotta pots with sandy substrate and a sponge lid to secure the contents throughout the experiment. All potted plants were placed into the main river channel in three groups of 75. Groups were placed just upstream of the confluence of the ma in stem of the river and each of the three feeder springs, i.e. Singing Spring, Devils Eye Spring, and Mill Pond Spring. The subs trate at each location was cleared of SAV to ensure an adequate light e nvironment for the study plants. The potted plants were allowed one week of acclimation after which, all plants were rubbed clean of periphyton by hand and cut to a standardized blade length of approximately 7.5 cm. Immediately after 15

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standardization, 25 plants were harvested for initial measurements of plant biomass and periphyton abundance. Half of the remaining 50 plants were moved to their respective feeder springs and arrayed just downstream of the prim ary spring vent. The 25 remaining plants were left in the river channel at th e acclimation location and all plants were observed bi-weekly for 4 weeks. After 4 weeks, all experimental plants from the river and spring locations were harvested and measures of plant biomass and periphyt on abundance were made following the methods previously described. Abiotic metrics were al so sampled for a comparison of preand postexperimental conditions. Statistical Analyses Standard ANOVA procedures were used to te st for differences in chemical, physical and biological characteristics between the main river transects and feed er spring transects (JMP IN v. 5.1 1989). Normality was assessed with the Shap iro-Wilk test and the assumption of equal variance verified with a Brown-Forsythe test. All plant biomass and periphyton abundance data were log10+1 transformed to improve normality and heteroscedasity. 16

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Figure 2-1. Map of the Ichetuc knee River course through the Iche tucknee Springs State Park. All transect sampling was carried out in the upper portion of the river within the confines of the park. Experimental wo rk was conducted near Singing Spring, Devils Eye (also known as Boiling Spring) and Mill Pond Spring. 17

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18 Figure 2-2. Collapsed and expanded vi ew of plant sampling apparatus.

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CHAPTER 3 RESULTS Survey Results Mean dissolved oxygen concentration in the main stem of the river ra nged between 3.2 and 7.4 mg L-1 and exhibited a general increase between feed er spring influences (Figure 3-1). Mean dissolved oxygen concentrations did not differ between the feeder springs (Mean value + SE; Singing Spring = 1.57 mgL-1 0.28; Devils Eye Spring = 1.05 mgL-1 0.13; Mill Pond Spring = 1.40 mgL-1 0.49) (ANOVA; df = 2, F = 0.56, P = 0.60). Relative to the three feeder springs, the main river exhibited signi ficantly higher dissolved oxygen concentrations (ANOVA; df = 1, F = 86.31, P = <0.0001) (Figure 3-2). Mean stream velocity in the main st em of river ranged between 0.04 and 0.30 ms-1 and exhibited a general increase betw een feeder spring influences (Figure 3-3). Mean stream velocity did not differ between the feeder springs (Mean value SE; Singing Spring = 0.04 ms-1 0.013; Devils Eye Spring = 0.04 ms-1 0.0083; Mill Pond Spring = 0.05 ms-1 0.016) (ANOVA; df = 2, F = 0.168, P = 0.85). Relative to the three feeder springs, the main river exhibited significantly higher stream veloci ties (ANOVA; df = 1, F = 11.63, P = 0.003) (Figure 3-4). Mean periphyton abundance on macrophytes within the main stem of river ranged between 0.014 and 0.068 mg chl a g WW-1 and showed a trend of decreasing abundance between feeder spring influences (Fi gure 3-5). Mean periphyton a bundance on plants did not differ between the three feeder springs (Mean va lue SE; Singing Spring = 0.30 mg chl a g WW-1 0.13; Devils Eye Spring = 0.42 mg chl a g WW-1 0.16; Mill Pond Spring = 0.19 mg chl a g WW-1 0.02) (ANOVA; df = 2, F = 0.48, P = 0.64). Overall, the mean periphyton abundance in 19

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spring environments was significantly higher th an the mean periphyton abundance within the main stem of the river (ANOVA; df = 2, F = 93.81, P < 0.0001) (Figure 3-6). Estimates of plant biomass in the main st em of Ichetucknee River ranged between 1172 and 8676 g WW m-2 and exhibited a general increase with distance downstream (Figure 3-7). There was no significant difference in plant bi omass between the three feeder springs. (Mean value SE; Singing Spring = 1285 g WW m-2 281.85; Devils Eye Spring = 1670 g WW m-2 808.58; Mill Pond Spring = 1115 g WW m-2 381.26) (ANOVA; df = 2, F = 0.0098, P = 0.99). Overall, the mean plant biomass along the main stem of the Ichetucknee River was significantly higher than the mean plant biomass within the spring environments (ANOVA; df = 2, F = 24.07, P < 0.0001) (Figure 3-8). Translocation Experiment Overall survivorship of transl ocated plants during the 4-we ek study period was 52% in the main stem of the river and 96% in the feeder sp ring. Surviving plants in the river and feeder springs exhibited no significant difference in gr owth as determined by a comparison of their mean above ground biomasses (ANOVA; df = 1, F = 1.14, P = 0.34) (Figure 3-9). At time zero, the mean leaf length of all plants was 7.54 cm ( 1.36). After the four week study period, the mean leaf length of river plants was 9.40 cm ( 3.47) and that of the spring plants was 9.74 cm ( 3.01). Mean plant biomass and mean peri phyton abundance did not differ between the three feeder springs sites (Mean Plant Biomass (g WW sd); Singing Spri ng = 2.54 1.48; Devils Eye Spring = 1.29 0.98; Mill Pond Sp ring = 1.40 0.68) (ANOVA; df = 2, F = 0.96, P = 0.48) (Mean Periphyton Abundance (mg chl a g WW-1 sd); Singing Spring = 0.37 0.22; Devils Eye Spring = 1.10 1.14; Mill Pond Sp ring = 0.09 0.065) (ANOVA; df = 2, F = 0.13, P = 0.88). Overall, mean periphyton abundance tended to be greater on plants in the three feeder 20

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springs than in the main river, although this difference was not statisti cally significant (ANOVA; df = 2, F = 2.68, P = 0.18) (Figure 3-10). 21

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Table 3-1. Summary of 2007 Survey Data Means Standard Errors (n = # of samples) Plant Biomass Periphyton Abundance Dissolved Oxygen Stream Velocity Water Depth Section (gWW m-2 ) (mg chl a g WW-1) (mgL-1) (ms-1) (m) River 4417 611 0.03 0.005 5.18 0.31 0.133 0.02 1.14 0.09 (n=14) (n=14) (n=14) (n=14) (n=14) Spring 1357 283 0.30 0.07 1.34 0.19 0.05 0.007 0.83 0.20 (n=9) (n=9) (n=9) (n=3) (n=3) 22

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Figure 3-1. Mean dissolved oxygen concentration with increasing distance downstream in the main stem of the Ichetucknee River. Nu mbers along the x-axis correspond to river transects with ascending values representing distance downstream. 23

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Figure 3-2. Mean dissolved oxygen concentration in the main stem of the Ichetucknee River and three associated feeder springs (i.e. Singing Spring, Devils Eye Spring, and Mill Pond Spring). 24

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Figure 3-3. Mean stream velocity with increasing distance downstr eam in the main stem of the Ichetucknee River. Numbers along the xaxis correspond to ri ver transects with ascending values representing distance downstream. 25

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Figure 3-4. Mean stream velocity in the main stem of the Ichetucknee River and three associated feeder springs (i.e. Singing Spring, De vils Eye Spring, and Mill Pond Spring). 26

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Figure 3-5. Mean periphyton abunda nce with increasing distance downstream in the main stem of the Ichetucknee River. Numbers along the x-axis correspond to river transects with ascending values representing distance downstream. 27

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Figure 3-6. Mean periphyton abundance in the main stem of the Ichetu cknee River and three associated feeder springs (i.e. Singin g Spring, Devils Eye Spring, and Mill Pond Spring). 28

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Figure 3-7. Mean plant biomass w ith increasing distance downstream in the main stem of the Ichetucknee River. Numbers along the xaxis correspond to ri ver transects with ascending values representing distance downstream. 29

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Figure 3-8. Mean plant biomass in the main stem of the Ichetucknee River and three associated feeder springs (i.e. Singing Spring, De vils Eye Spring, and Mill Pond Spring). 30

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Figure 3-9. Mean plant biomass in the main stem of the Ichetucknee River and three associated feeder springs (i.e. Singing Spring, De vils Eye Spring, and Mill Pond Spring) following a four week tr anslocation experiment. 31

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32 Figure 3-10. Mean periphyton abund ance in the main stem of th e Ichetucknee River and three associated feeder springs (i.e. Singin g Spring, Devils Eye Spring, and Mill Pond Spring) following a four week translocation experiment.

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CHAPTER 4 DISCUSSION The proposed pattern of interaction between dissolved oxygen, stream velocity, grazer abundance, and periphyton abundance on hos t macrophytes was well supported by the observations made during the survey of the Ichetucknee River and its feeder springs (see also Dormsjo 2007). Dissolved oxygen concentrations were consistently low near spring sources regardless of whether the spring source was the h eadspring of the river, any one of the three feeder springs, or the many spring/river confluen ces along the main stem course. This finding is consistent with data reported previously (K urz et al. 2003 and 2004). Stream velocity, plant biomass, and grazer abundance exhibited a si milar pattern; lowest values for all the aforementioned parameters occurred near sp ring sources (see also Dormsjo 2007). These findings too are similar to those reported by Kurz et al. (2003 and 2004). As hypothesized, periphyton abundance values were inversely related to dissolved oxygen, stream velocity, grazer abundance, and plant biomass values. Where dissolved oxygen, stream velocity, grazer abundance, and plant biomass values were low, periphyton abundance on host plants was high. Literature on lotic systems suggests that the pa tterns reported here exhibit some generality. For example, Sabater et al. (2000) found that benthic algal biomass in the Oria River, a Spanish river with intense human activity in its watershed, was highest in locations where diel variations in dissolved oxygen concentrati ons resulted in acute hypoxia. Episodes of hypoxia in areas of high algal biomass in the Oria River have been linked to herbivorous fish kills (Sabater 2000) suggesting that oxygen mediated grazing impacts are likely to be an importa nt process in lotic systems. Additionally, stream velocity is often reported as a signifi cant variable affecting both periphyton and macrophyte abundance. Chambers et al. (1991) showed that sudden increases in 33

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current velocity in two slow-flowing rivers in Canada resulted in decreased plant biomass through uprooting. Its a logica l assumption that periphyton a bundance on macrophytes within the same rivers would also decrease with increasi ng current velocity. For example, Giorgi et al. (2005) observed that attached al gal biomass decreased during times of flood in Pampean streams suggesting that increasing current velocity ex erts a significant scour ing force on periphyton communities. Similar conclusions have been repo rted by several additional research efforts (e.g., Birkett et al. 2007, Katano et al. 2005, Arnon et al. 2007). The results of the translocation experiment following the quantitative river survey were likely confounded by the lo w survival rates of S. kurziana in the main stem of the river and the short duration of the stud y. While 96% of the plants in the f eeder springs survived, river plants exhibited a relatively large loss (48%) resultin g in few data for statistical comparison of periphyton abundance on host plants between the main river and springs. Nevertheless, the rate of periphyton accrual on plants in the feeder springs was marginally greater than on plants in the main stem of the river. This finding is consiste nt with my hypothesis, but I was unable to detect any statistically significant differe nce in plant growth that might be attributed to an increase in periphyton load. Some mortality of the translocated plants was expected during this experiment as shortterm mortality is common in such studies. Fo r example, Zimmerman, et al. (1995) transplanted Zostera marina, a functionally similar marine macrophyte, in San Francisco Bay, CA, and reported high initial losses. Additiona lly, Hauxwell et al. (2003) transplanted Vallisneria americana (a plant commonly found with S. kurziana) in Kings Bay, FL in 2001 and 2002 and observed high initial mortality. In both cases, the investigator s emphasized the importance of transplant timing and experiment duration in relocation success (Zimmerman et al. 1995, 34

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Hauxwell et al. 2003). Zimmerman et al. ( 1995) pointed out that although the eelgrass transplants in San Francisco Bay, CA were partia lly successful, transplant survival could have been improved by taking into acc ount the role of carbon reserves when timing a transplant event (Zimmerman et al. 1995). Hauxwell et al. (2003) suggested that similar transplant experiments should run for 1-2 years to ensure natural growth responses from the transplants. The four-week experimental period chosen for this study wa s necessary due to the high human use and disturbance of the system during the summer mo nths. Subsequent efforts to determine the effects of periphyton accumulati on on macrophyte growth in the Ichetucknee River will likely require some intervention to lessen such impacts. In addition to transplant duration and timing, it should be noted that experimental plants in the main stem of the river were maintained at depths of approximately 1.5 m whereas plants in the feeder springs were maintained at appr oximately 0.75 m. Although water clarity in the Ichetucknee system is superb, it is possible that slight differences in water depth contributed to plant loss in the main river as a consequence of increased light attenua tion. The topography of the Ichetucknee River dictated the depth at which the translocated plants would be placed and so no depth standardization was possible. It is uncl ear whether differences in depth influenced the experimental outcome, but light attenuation has a strong influence on the distribution and abundance of aquatic macrophytes and many studies have shown a negative relationship between increased light attenuation and the biomass of aquatic macrophytes (e.g., De Boer 2007, Loiselle et al. 2007). Despite the problems associated with plant transplant and translocation, the surviving plants from this study did provided a natural subs trate for a first order approximation of the rate of periphyton accumulation. The periphyton load s on macrophytes in the Ichetucknee River 35

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36 after only a four-week period were similar to st anding crop values previously reported in the river by Kurz et al. (2004). In 2004, mean periphyton abundance was 0.15 mg chl a gWW-1 in the main stem of the Ichetuc knee River and 0.61 mg chl a gWW-1 in the feeder springs. In 2007 (this study), mean periphyton a bundance was 0.09 mg chl a gWW-1 in the main stem of the Ichetucknee River a nd 0.52 mg chl a gWW-1 in the feeder springs. In terestingly, average rates of stream velocity in the main stem of the Ichetucknee River during 2007 (0.133 ms-1) were lower than those in 2004 (0.160 ms-1) as a consequence of a regiona l drought that affected spring discharge. Despite these slight differences, my stream velocity and periphyton abundance results are consistent with previous work relating the two variables (Kurz et al. 2003 and 2004). Results from this investigation reinforce the need fo r additional studies on flow rates and periphyton accrual in this system and how th ese factors might interact with others such as changes in nutrient loads, oxygen con centrations, light availa bility and grazing to a ffect the structure and function of the ecological community.

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LIST OF REFERENCES APHA (American Public Health Association) (1995) Standard me thods for the examination of water and wastewater. 19th edition. American Public Health Association, American Water Works Association, and Water Polluti on Control Federation, Washington DC Arnon S, Packman AI, Peterson CG, Gray KA (2007) Effects of overlying current velocity on periphyton structure and denitrification. Journal of Geophysical Research Biogeosciences 112(G1): Art No G01002 Barko JW, Smart RM (1986) Sediment related m echanisms of growth limitation in submerged macrophytes. Ecology 67(5): 1328-1340 Birkett C, Tollner EW, Gattie DK (2007) Total suspended solids and flow regime effects on periphyton development in a laboratory cha nnel. Transactions of the Asabe 50(3): 10951104 Caccia VG, Boyer JN (2007) A nutrient loading budget for Biscayne Bay, FL. Marine Pollution Bulletin 54(7): 994-1008 Canfield DE, Hoyer MV (1988) Th e nutrient assimilation capacity of the Little Wekiva River: Final Report District of Public Work s, City of Altamonte Springs, FL. 288pp Chambers PA, Prepas EE, Hamilton HR, Bothwell ML (1991) Current velocity and its effect on aquatic macrophytes in flowing waters. Ecological Applicat ions 1(3): 249-257 De Boer WF (2007) Seagrass-sediment interactio ns, positive feedbacks a nd critical thresholds for occurrence: a review. Hydrobiologia 591: 5-24 Dormsjo KK (2007) Oxygen mediated grazer impacts in Florida springs. Dissertation University of Florida, Gainesville, FL USA Duarte CM (1995) Submerged aquatic vegetation in relation to different nutrient regimes. Ophelia 41: 87-112 Ghosh M, Gaur JP (1991) Regulatory influence of water current on alga l colonization in an unshaded stream at Shillong (Meghalaya, India). Aquatic Botany 40(1): 37-46 Giorgi A, Feijoo C, Tell G (2005) Primary producers in a Pampean stream: temporal variation and structuring role. Biodivers ity and Conservation 14(7): 1699-1718 Hauxwell JA, Frazer TK, Osenberg CW (2003) E ffects of herbivores and competing primary producers on Vallisneria Americana in Kings Bay: implications for restoration and management. Final report for the SWFWMD 68 pp 37

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Heck KL, Valentine JF, Pennock JR, Chaplin G, Spitzer PM (2006) Effects of nutrient enrichment and grazing on shoalgrass Halodule wrightii and its epiphytes : results of a field experiment. Marine Ecology Progress Series 326: 145-156 Hill WR, Ryon MG, Schilling EM (1995) Light li mitation in a stream ecosystem: responses by primary producers and consumers. Ecology 76(4): 1297-1309 Huryn A, Koebel JW, Benke AC (1994) Life hi story and longevity of the pleurocerid snail Elimia : a comparative study of eight populations. Journal of the North American Benthological Society 13(4): 540-556 JMP IN v. 5.1 (1989) SAS Institute, Inc Jowett IG, Biggs BJF (1997) Flood and velocity effects on periphyton and silt accumulation in two New Zealand rivers. New Zealand Journal of Marine and Freshwater Research 31(3): 287-300 Katano I, Mitsuhashi H, Isobe Y, Sato H, Oish i T (2005) Reach-scale distribution dynamics of a grazing stream insect, Micrasema quadriloba martynov (Brachycentridae, Trichoptera), in relation to current velocity and periphyton abundance. Zoological Science 22(8): 853860 Kirk, JTO (1994) Light and Photos ynthesis in Aquatic Ecosystems Cambridge University Press: New York 401pp Kurz RC, Sinphary P, Hershfeld WE, Krebs AB, Peery AT, Woithe DC, Notestein SK, Frazer TK, Hale JA, Keller SR (2003) Mapping and monitoring submerged aquatic vegetation in Ichetucknee and Manatee Springs. Final report for the Suwannee River Water Management District. 50 pp Kurz RC, Woithe DC, Notestein SK, Frazer TK, Hale JK, Keller SR (2004) Mapping and monitoring submerged aquatic vegetation in Ichetucknee Springs2004. Final report for the Suwannee River Water Management District. 35pp Loiselle SA, Cozar A, Dattilo A, Bracchini L, Ga lvez JA (2007) Light limitations to algal growth in tropical ecosystems. Fr eshwater Biology 52(2): 305-312 Mattson RA, Epler JH, Hein MK (1995) Description of benthic communities in karst, spring-fed streams of north central Florid a. Journal of the Kansas Entomological Society 68(2): 1841 McKinsey DM, Chapman LJ (1998) Dissolved oxygen and fish distribution in a Florida Spring. Environmental Biology of Fishes 53: 211-223 38

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39 Moss B (1981) The effect of fertilization a nd fish on community structure and biomass of aquatic macrophyte and epiphytic algae populat ions: An ecosystem experiment. Journal of Ecology 64: 313-342 Notestein SK, Frazer TK, Hoyer MV, Canfield DE (2003) Nutrient limitation of periphyton in a spring-fed, coastal stream in Florida, USA. Journal of Aquatic Plant Management 41:5760 Odum HT (1957) Trophic structure and productivity of Silver Springs, Florida. Ecological Monographs 27(1): 55-112 Rosenau JC, Faulkner GL, Hendry CW Jr., Hull RW (1977) Springs of Florida. Florida Geological Survey Geological Bulletin No 31, revised. From http://www.flmnh.ufl.edu/spring s_of_fl/aaj7320/content.html Sabater S, Armengol J, Comas E, Sabater F, Urrizalqui I, Urrutia I (200 0) Algal biomass in a disturbed Atlantic ri ver: water quality relationships and environmental implications. Science of the Total Environment 263(1-3): 185-195 Turner ER, Rabalais NN (1994) Coastal eutrophi cation near the Mississippi River delta. Nature 368: 619-621. Wright RM, McDonald AJ (1986a) Macrophyte growth in shallow streams. Field investigations. Journal of Environmental Engineering 112: 952-966 Wright RM, McDonald AJ (1986b) Macrophyte growth in shallo w streams. Biomass model. Journal of Environmental Engineering 112: 967-981 Zimmerman RC, Reguzzoni JL, Alberte RS (1995) Eelgrass (Zostera marine L) transplants in San-Francisco Bay role of light availabi lity on metabolism, growth and survival. Aquatic Botany 51(1-2): 67-86

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BIOGRAPHICAL SKETCH Vince Politano graduated summa cum laude from the University of Rhode Island with a Bachelor of Science degree in marine biology. He completed his Ma ster of Science degree at the University of Florida in the Departme nt of Fisheries and Aquatic Sciences. 40