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Phytoplankton bloom dynamics in a nitrogen-limited subtropical lake

Permanent Link: http://ufdc.ufl.edu/UFE0042189/00001

Material Information

Title: Phytoplankton bloom dynamics in a nitrogen-limited subtropical lake
Physical Description: 1 online resource (53 p.)
Language: english
Creator: Dong, Linghan
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: bloom, cyanobacteria, dynamics, limited, nitrogen, phytoplankton, subtropical, succession
Interdisciplinary Ecology -- Dissertations, Academic -- UF
Genre: Interdisciplinary Ecology thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: The focus of this study was Lake George, a eutrophic lake in Florida, which has experienced major algal blooms for decades. Phytoplankton blooms in the lake are typically dominated by cyanobacteria. The goal of the study was to examine the dynamics of a major bloom event within the context of variations in physical, chemical and biological conditions. A temporally intensive sampling regime was used to reveal successional patterns in phytoplankton composition and abundance at scales appropriate to the growth of phytoplankton. Two major bloom periods were observed over the study period. The first bloom was dominated by a mix of diatoms and several nitrogen-fixing species of cyanobacteria, including Anabaena spp., Aphanizomenon spp. and Anabaenopsis spp. The second, and larger, bloom was dominated by the nitrogen-fixing cyanobacterium Cylindrospermopsis sp. These observations demonstrate the importance of nitrogen fixation in supplying the nitrogen needed to support primary production in the lake. Statistical correlation analyses showed relationships between phytoplankton structure and environmental factors, emphasizing the impact of bioavailable nitrogen concentrations, Si concentrations and temperature. The results of this research hav significant implications for future efforts to manage the ecology of Lake George, in an effort to prevent the continued proliferation and intensification of cyanobacterial blooms.
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.
Statement of Responsibility: by Linghan Dong.
Thesis: Thesis (M.S.)--University of Florida, 2010.
Local: Adviser: Phlips, Edward J.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2011-02-28

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0042189:00001

Permanent Link: http://ufdc.ufl.edu/UFE0042189/00001

Material Information

Title: Phytoplankton bloom dynamics in a nitrogen-limited subtropical lake
Physical Description: 1 online resource (53 p.)
Language: english
Creator: Dong, Linghan
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: bloom, cyanobacteria, dynamics, limited, nitrogen, phytoplankton, subtropical, succession
Interdisciplinary Ecology -- Dissertations, Academic -- UF
Genre: Interdisciplinary Ecology thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: The focus of this study was Lake George, a eutrophic lake in Florida, which has experienced major algal blooms for decades. Phytoplankton blooms in the lake are typically dominated by cyanobacteria. The goal of the study was to examine the dynamics of a major bloom event within the context of variations in physical, chemical and biological conditions. A temporally intensive sampling regime was used to reveal successional patterns in phytoplankton composition and abundance at scales appropriate to the growth of phytoplankton. Two major bloom periods were observed over the study period. The first bloom was dominated by a mix of diatoms and several nitrogen-fixing species of cyanobacteria, including Anabaena spp., Aphanizomenon spp. and Anabaenopsis spp. The second, and larger, bloom was dominated by the nitrogen-fixing cyanobacterium Cylindrospermopsis sp. These observations demonstrate the importance of nitrogen fixation in supplying the nitrogen needed to support primary production in the lake. Statistical correlation analyses showed relationships between phytoplankton structure and environmental factors, emphasizing the impact of bioavailable nitrogen concentrations, Si concentrations and temperature. The results of this research hav significant implications for future efforts to manage the ecology of Lake George, in an effort to prevent the continued proliferation and intensification of cyanobacterial blooms.
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.
Statement of Responsibility: by Linghan Dong.
Thesis: Thesis (M.S.)--University of Florida, 2010.
Local: Adviser: Phlips, Edward J.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2011-02-28

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0042189:00001


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PHYTOPLANKTON BLOOM DYNAMICS IN A NITROGEN-LIMITED SUBTROPICAL
LAKE



















By

LINGHAN DONG


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

UNIVERSITY OF FLORIDA

2010

































2010 Linghan Dong

































To my Mom









ACKNOWLEDGMENTS

I thank my parents for supporting my writing mentally. I appreciate the academic

instruction from Dr. Edward Phlips, Dr. Mark Brenner and Dr. Karl Havens. Special

thanks are given to Dr. Mary Cichra for algal taxonomy training. I also appreciate the

help offered by people working in Phlips lab.









TABLE OF CONTENTS


page

A C KNO W LEDG M ENTS ................................................ ................... .......

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

L IS T O F F IG U R E S ................................................................................ 7

LIST O F A B B R EV IA T IO N S ........................................... .................... ... ............ 9

A B S T R A C T ....................................................................................... 10

CHAPTER

1 IN T R O D U C T IO N ................................................................... ................ 12

2 M E T H O D S ....................................................................... ................ 15

S ite D e s c rip tio n ................................................................................. 1 5
S a m p lin g R e g im e ............................................................................... 15
S am pling C collection and A analysis ...................................... ......................... .......... 16
S statistic a l A n a lys is .............................................................................. 17

3 R E S U LT S ...................................... ................................................... 18

4 D IS C U S S IO N ....................................................... ............................................... 4 4

C yanobacterial D om finance ............ .................................................. ................ 46
S success ion P atte rns .................................... ............................................ 4 8

LIS T O F R E F E R E N C E S ................................................................................ .... 50

B IO G R A P H IC A L S K E T C H ................................................................................. .. ..... 53









LIST OF TABLES


Table page

3-1 Pearson's correlation between day time total phytoplankton biovolume and
different environmental variables, LAG and LEO.......... ...... ... ................ 43

3-2 Pearson's correlation between nitrogen fixing cyanobacteria biovolume and
nitrogen related chemical parameters, LAG and LEO.................... ................43









LIST OF FIGURES


Figure page

3-1 M a p of La ke G eo rg e ................................................................. ....... ........ 22

3-2 Rainfall in the Lake George Basin .......................... ............. .... ............ 22

3-3 Day time water depths at LAG and LEO ................................. ....... ............ 23

3-4 Day time water temperature at LAG and LEO .................................. ................ 23

3-5 Day time colored dissolved organic matter (CDOM) levels at LAG and LEO......24

3-6 Day time water turbidity at LAG and LEO ......... ............. .... ................ 24

3-7 Secchi depth at LAG and LEO ......... .... ......... ....................... ..... ........... 25

3-8 Day time total nitrogen concentrations at LAG and LEO................ ................ 25

3-9 Day time nitrate+nitrite (NOx) concentration at LAG and LEO ................................26

3-10 Day time ammonium concentrations at LAG and LEO................................ ...26

3-11 Day time total phosphorus concentrations at LAG and LEO.............................. 27

3-12 Day time soluble reactive phosphorus (SRP) concentrations at LAG and LEO.. 27

3-13 Day time silica concentrations at LAG and LEO................ ..... ............... 28

3-14 Day time phytoplankton biovolume at LAG and LEO. ................................ ....29

3-15 Day time cyanobacteria biovolume at LAG and LEO ............... ............... ....30

3-16 Relative biovolume of Cyanobacteria in phytoplankton community at LAG
and LEO ........... ...... ................. ......... ........ .. ... .... ......... 31

3-17 Relationship between biovolume of Cyanobacteria and total phytoplankton
biovolum e, LA G and LEO ..... ...................................................... ............ 32

3-18 Day time trends of diatom and cyanobacteria biovolume and silica
concentrations, LAG and LEO ........ .. .............. ................ ........ ........ 33

3-19 Trends of biovolume of three groups of cyanobacteria: Anabaena
spp. +Anabaenopsis spp.+Aphanizomenon spp.; Cylindrospermopsis sp.;
other non-heterocystous cyanobacteria, LAG and LEO ................................... 34









3-20 Trends of temperature and bivolume of three groups of cyanobacteria:
Anabaena spp.+Anabaenopsis spp. +Aphanizomenon spp.;
Cylindrospermopsis sp.; other non-heterocystous cyanobacteria, LAG and
L E O ...................... .. .. ......... .. .. ........................................... 3 5

3-21 Trends of total phytoplankton biovolume, nitrogen fixing cyanobacteria
biovolume and total nitrogen concentrations, LAG and LEO ............................ 36

3-22 Trends of total phytoplankton biovolume and nitrate+nitrite (NOx)
concentrations, LA G and LEO ........................................ ......................... 37

3-23 Trends of total phytoplankton biovolume, nitrogen fixing cyanobacteria
biovolume and ammonium concentrations, LAG and LEO.............................. 38

3-24 Trends of total phytoplankton biovolume, nitrogen fixing cyanobacteria
biovolume and total phosphorus concentrations, LAG and LEO ....................39

3-25 Trends of total phytoplankton biovolume and soluble reactive phosphorus
(SRP) concentration, LAG and LEO...... ..................... ................40

3-26 Ratios of estimated phytoplankton phosphorus and SRP to total phosphorus,
LAG and LEO ................................................... ........ ..... ......... 41

3-27 Ratio of estimated phytoplankton nitrogen and DIN to total nitrogen, LAG and
L E O ................. ....................................... ........................... 42









LIST OF ABBREVIATIONS

DIN Dissolved inorganic nitrogen

NOx Nitrate and nitrite

SRP Soluble reactive phosphorus

TN Total nitrogen

TP Total phosphorus









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

PHYTOPLANKTON BLOOM DYNAMICS IIN A NITROGEN-LIMITED SUBTROPICAL
LAKE

By

Linghan Dong

August 2010

Chair: Edward Phlips
Major: Interdisciplinary Ecology

The focus of this study was Lake George, a eutrophic lake in Florida, which has

experienced major algal blooms for decades. Phytoplankton blooms in the lake are

typically dominated by cyanobacteria. The goal of the study was to examine the

dynamics of a major bloom event within the context of variations in physical, chemical

and biological conditions. A temporally intensive sampling regime was used to reveal

successional patterns in phytoplankton composition and abundance at scales

appropriate to the growth of phytoplankton. Two major bloom periods were observed

over the study period. The first bloom was dominated by a mix of diatoms and several

nitrogen-fixing species of cyanobacteria, including Anabaena spp., Aphanizomenon

spp. and Anabaenopsis spp. The second, and larger, bloom was dominated by the

nitrogen-fixing cyanobacterium Cylindrospermopsis sp. These observations

demonstrate the importance of nitrogen fixation in supplying the nitrogen needed to

support primary production in the lake. Statistical correlation analyses showed

relationships between phytoplankton structure and environmental factors, emphasizing

the impact of bioavailable nitrogen concentrations, Si concentrations and temperature.









The results of this research hav significant implications for future efforts to manage the

ecology of Lake George, in an effort to prevent the continued proliferation and

intensification of cyanobacterial blooms.









CHAPTER 1
INTRODUCTION

One common symptom of eutrophication in aquatic systems is algal blooms. Many

ecosystems around the world are experiencing increased rates of eutrophication due to

rapid agricultural and industrial development, population expansion and urbanization

(Paerl and Huisman, 2009). The essential role of nutrient load in eutrophication has

focused attention on the relative importance of different macronutrients in controlling

phytoplankton productivity, with nitrogen and phosphorus generally receiving the most

attention. One long standing paradigm is that phosphorus is more often limiting in lakes

than nitrogen (Einsele, 1941; Schindler, 1977; Schindler et al., 2008; Vollenweider,

1971; Vollenweider and Kerekes, 1982). Evidence for the importance of phosphorus

includes stoichiometric relationships between nitrogen and phosphorus (Hutchinson,

1957; Pearsall, 1930) and the correlation between total phosphorus (TP) and

chlorophyll-a (Chl-a) (Dillon and Rigler, 1974; Sakamoto, 1966). The importance of

phosphorus limitation has been further supported through whole lake fertilization

experiments by Schindler (Schindler, 1974; Schindler, 1977). Despite the evidence for

the role of phosphorus as a limiting factor, other researchers have shown that nitrogen

availability also impacts phytoplankton dynamics in many freshwater ecosystems (Lewis

Jr and Wurtsbaugh, 2008; Paerl and Huisman, 2009). For instance, many tropical and

subtropical lakes have low N: P ratios, an indicator of nitrogen limitation (Ryding and

Rast, 1989). The results of nutrient limitations bioassay experiments also support the

existence of nitrogen limitation in phosphorus-rich eutrophic lakes in Florida, such as

Lake Okeechoobee (Aldridge et a/., 1995; Phlips et al., 1997), Lake Griffin (Phlips et al.,

2004) and Lake George (Piehler et al., 2009). In these Florida lakes, nitrogen-fixing









cyanobacteria are often prominent members of the phytoplankton community, a

response to nitrogen limitation. Questions remain about whether nitrogen fixation can

provide sufficient nitrogen input to phosphorus enriched ecosystems to ultimately induce

phosphorus limitation of phytoplankton growth and biomass, making nitrogen limitation

a short-term phenomenon, ultimately leading to phosphorus limitation in the long term. If

so, management of nitrogen input to lakes would not aid in the reduction of trophic state

(Schindler et al., 2008). Some, however, argue that nitrogen fixation cannot fully make

up for nitrogen limitation in many ecosystems due to physical, biological and chemical

limitations on the process (Lewis Jr and Wurtsbaugh, 2008; Paerl and Huisman, 2009),

leading to the conclusion that it is important to consider both nitrogen and phosphorus

loads in management efforts. The goal of this study was to examine the dynamics of

phytoplankton bloom events in a lake subject to nitrogen-limiting conditions, and follow

the dynamics of key physical and chemical parameters, in an effort to evaluate the

response of the phytoplankton community.

A subtropical eutrophic lake in Florida, Lake George, was the focus of the study

because of the existence of a long record for nutrient and phytoplankton composition

and a demonstrated history of cyanobacterial blooms under nitrogen-limiting conditions

(Piehler et al., 2009). Given its shallow depth and long water residence times, Lake

George falls into the category of a number of large phosphorus-rich lakes in Florida,

such as Lake Okeechoobee (Aldridge et al., 1995; Phlips et al., 1997), Lake Apopka

and Lake Griffin (Phlips et al., 2004), and in other subtropical regions around the world,

e.g., Lake Taihu and Donghu in China and Lake Kasumigaura in Japan (Havens et al.,

2001). Along with a historical record of intense cyanobacteria blooms, nitrogen limitation









seems to be an important factor in phytoplankton dynamics in Lake George (Piehler et

al., 2009). A temporally intensive sampling regime was employed in this study, to

provide a detailed view of the dynamics of blooms in Lake George.

Several hypotheses were examined in this study:

1. Large phosphorus loads to Lake George from the watershed are sufficient to
support high algal biomass.

2. High phytoplankton biomass favors dominance of cyanobacteria.

3. Low bioavailable nitrogen load relative to bioavailable phosphorus load increases
the potential for nitrogen limitation of algal growth, leading to prominence of
nitrogen-fixing cyanobacteria.

4. Succession of phytoplankton species is correlated to shifts in key environmental
conditions, including temperature, light flux and biologically available nitrogen,
phosphorus and silica.









CHAPTER 2
METHODS

Site Description

The St. Johns River is the longest blackwater river in Florida. It is unique for its low

elevation drop (8m) from its headwaters to mouth, resulting in low river flow rates (1-2

km day-l). The gentle slope of the river bed has resulted in the creation of many wide,

shallow pools, which are called "lakes" of the St. Johns River (Livingston, 1990). The

largest lake is Lake George, with an area of 18,934 ha (Piehler et al., 2009). Located

210 km from the river mouth, Lake George is the upstream lake, which is most

susceptible to tidal forces. Tidal forces and shallow river slope result in prolonged water

retention times in Lake George, which can exceed one month (Livingston, 1990).

The upper St. Johns River is the dominant source of water for Lake George. High

concentrations of nitrogen and phosphorus in the source water result in eutrophic

conditions in Lake George (Livingston, 1990). The rich nutrient supply, coupled with

long residence time, particularly in spring and summer (April-July) (Piehler et al., 2009),

provide conditions conducive to the formation of phytoplankton blooms (Phlips et al.,

2007).

Sampling Regime

Water samples were collected twice per week during the day time and once per

week at night from two sites, LAG and LEO, which are situated in the southern and

central region of the lake channel. Sampling was conducted from March 25th to June

23rd 2009. Biweekly sample collection was suspended from Mar 26th to April 14th and

from May 15th to 25th









Sampling Collection and Analysis

Secchi depth was measured at every day-time sample collection. Parameters,

including temperature, conductivity, dissolved oxygen (DO), and pH, were measured by

Hydrolab probe from the water surface to just above the bottom at 0.5m intervals.

Five poles of depth-integrated samples were collected around the boat and then

combined in a plastic bucket. After complete agitation, lake water was transferred to

individual sample containers, 1000 ml brown plastic bottles for phytoplankton samples

and 100 ml white plastic bottles for water chemistry samples. Lugols-solution was used

for phytoplankton preservation, pipets for each bottle, followed by complete mixing.

Phytoplankton composition was determined using the Utermohl method (Utermohl,

1958). Lugol solution preserved samples were settled in 19mm inner diameter

cylindrical chambers. Phytoplankton cells were identified and counted at 400X and

10OX with a Nikon phase contrast inverted microscope. At 400X, a minimum of 100

cells of a single taxon and 30 grids were counted. If 100 cells were not counted by 30

grids, up to a maximum of 100 grids were counted until one hundred cells of a single

taxon was reached. At 100X, a total bottom count was completed for taxa > 30 microns.

Biovolume (im3 ml-1) is used as the primary measure phytoplankton biomass (Smayda,

1978).

Total nitrogen was colorimetrically determined using the persulfate digestion

method (APHA, 1989) with a Bran-Luebbe AutoAnalyzer. Nitrate, nitrite and ammonium

were colorimetrically determined using standard methods (APHA, 1989) with a Bran-

Luebbe AutoAnalyzer. Total phosphorus was colorimetrically determined using the

persulfate digestion method (APHA, 1989), with a Hitachi scanning spectrophotometer.









Soluble reactive phosphorus was colorimetrically determined using standard methods

(APHA, 1989) with a Hitachi scanning spectrophotometer. Chlorophyll a concentration

was colorimetrically determined after extraction of the filtered samples with 90% warm

ethanol (Sartory and Grobbelaar, 1984), with a Hitachi scanning spectrophotometer.

Water color was determined from filtered station water (0.7[tm glass-fiber filter).

Samples were analyzed using platinum cobalt standards from protocols described in

Standard Methods (APHA, 1989) on a Hitachi scanning spectrophotometer. Turbidity

was determined with a La Motte turbidity meter.

Statistical Analysis

SAS 9.2 was used for Pearson's Correlation Coefficient calculation. Graphs

showing trends and linear relationships were created by Microsoft Office Excel 2007.









CHAPTER 3
RESULTS

Several small peaks in rainfall in the Lake George (Figure 3-1) region were

recorded from March 29th through May 13th (Figure 3-2). A major rainfall event

occurred in late May, followed by smaller events in June.

Water depth remained stable around 3.0 m at LAG and 3.4 m at LEO until a near 1

m raise from May 16th to 20th (Figure 3-3). Water temperatures during the sampling

period increased gradually from 20 to near 30 oC from March 25th to May 10th at both

sites (Figure 3-4). Colored dissolved organic matter (CDOM) declined gradually from

100 PCU on March 25th to near 50 PCU on May 27th at both stations before increasing

again (Figure 3-5). The increase in CDOM was greater at LAG than LEO. Turbidity

ranged between 4 to 10 NTU at both stations (Figure 3-6), with several peaks in value.

Peaks in turbidity were higher at LAG than LEO. Secchi depth at both stations ranged

between 0.6 and 1.0 m (Figure 3-7). The deepest Secchi depths were observed in the

April and early May (Figure 3-7).

Total nitrogen (TN) concentration increased over the study period from 0.8 to over

1.2 mg L-1 at both stations. Peaks in TN concentration were generally higher at LEO

than LAG in the last half of the study period (Figure 8). Nitrate + nitrite concentration

(NOx) declined gradually from 0.014 mg L -on March 25th to below 0.005 mg L-1 on

May 1st at both stations, before increasing in early June (Figure 3-9). The June

increase in NOx concentration was greater at LAG than LEO. Ammonium concentration

increased over the study period from near 0.05 mg L-1 to greater than 0.15 mg L-1 at

both LAG and LEO (Figure 3-10).









TP concentrations remained near 0.05 mg L-1 until June at both LAG and LEO,

before increasing substantially. LAG showed greater variability than LEO (Figure 3-11).

Soluble reactive phosphorus (SRP) concentrations remained near 0.010 mg L-1 at both

stations until June then increased substantially reaching 0.100 mg L-1 at LAG and 0.05

at LEO (Figure 3-12).

Silica concentrations showed a trend similar to SRP, remaining low concentrations

below or near 0.5 mg L-1 at both stations until a significant increase in late May (Figure

3-13).

Total phytoplankton biovolume at the two stations showed two peaks, a smaller

one in mid-April and larger one extending through most of May (Figure 3-14). At LEO

the second bloom period extended into early June and reached 50% higher biovolume

than the second bloom at LAG. During the first bloom period, the relative contributions

of cyanobacteria and diatoms to total biovolume were similar. However, the second

bloom period was dominated by cyanobacteria (Figure 3-14).

Within the cyanobacteria community, the first bloom period was dominated by the

nitrogen-fixing taxa Anabaena spp., Anabaenopsis spp. and Aphanizominon spp.

(Figure 3-15). During the second bloom period, the former taxa were initially important

but progressively gave way to increased dominance by another heterocystous

cyanobacterium, Cylindrospermopsis sp.and other non-nitrogen-fixing cyanobacteria,

particularly Oscillatoria spp. (Figure 3-15).

The relative contribution of cyanobacteria to total phytoplankton biovolume

increased significantly at both LAG and LEO from March 25th through April (Figure 3-

16). From the end of April through the beginning of June, cyanobacteria generally









represented over 80% of total phytoplankton biovolume. In June, cyanobacteria

dominance declined somewhat at LAG, but remained high at LEO (Figure 3-16).

For both stations, high linear regression was shown between biovolume of

cyanobacteria and total phytoplankton biovolume, with r2 above 0.95(Figure 3-17).

Diatoms showed a drop in biovolume immediately after the decrease of silica

concentrations in April and remained at low levels for the rest of the study period,

despite a sharp increase in silica concentrations at the beginning of June. (Figure 3-18)

Within the cyanobacteria assemblage, the major groups of taxa had distinct

temporal patterns of abundance. The heterocystous species Anabaena spp.,

Aphanizomenon spp. and Anabaenopsis spp. had two distinct peaks in abundance in

mid-April and early May at both stations (Figure 3-19). The biovolume of the

heterocystous species Cylindrospermopsis sp. increased dramatically in mid-May,

reaching peak levels in early June at both sites (Figure 3-19). Non-heterocystous

cyanobacteria, most prominently Oscillatoria spp. (Planktothrix spp.), gradually

increased in biovolume until June at both sites (Figure 3-19)

The emergence of Cylindrospermopsis sp. and crash of Anabaena spp.

+Aphanizomenon spp. +Anabaenopsis spp. group coincided with the maximum rate of

increase in temperature (Figure 3-20).

The relationship between temporal trends in phytoplankton biovolume and trends

in nutrient concentrations varied according to forms of nitrogen and phosphorus. Total

nitrogen concentrations increased coincident with increasing biovolume of both total

phytoplankton and nitrogen-fixing cyanobacteria until the dissipation of the second

bloom in June (Figure 3-21), which was accompanied by a decline in TN. By contrast,









NOx concentrations declined to near detection levels at both stations from March to the

end of May (Figure 3-22). Concentrations showed a sharp increase after the collapse of

the second phytoplankton bloom in June (Figure 3-22). Ammonium concentrations were

highly variable at both stations, but generally increased over the study period (Figure 3-

23).

Total phosphorus concentrations remained near 0.05 mg L-1 at both stations

through most of the study period until the dissipation of the second phytoplankton bloom

period in June (Figure 3-24), which was accompanied by a sharp increase in TP. TP

concentrations were more variable at LAG than at LEO. Soluble reactive phosphorus

concentrations remained near 0.010 mg L-1 at both stations from March to the end of

May and then increased substantially after the dissipation of the second phytoplankton

bloom in June (Figure 3-25).

Pearson's correlation analyses showed that log phytoplankton biovolume was

significantly correlated to SRP, NOx, TN, Turbidity and TN: TP ratio at LAG. At LEO, log

biovolume was significantly correlated to NOx, TN, Turbidity and Secchi Depth (Table 3-

1). Correlations between nitrogen-fixing cyanobacteria biovolume and nitrogen

compounds were also examined (Table 3-2). At LAG, log nitrogen-fixing cyanobacteria

biovolume was negatively correlated with NH4 and NOx. At LEO, log nitrogen-fixing

cyanobacteria biovolume was negatively correlated with NOx and positively correlated

with TN (Table 3-2).










































Figure 3-1. Map of Lake George






E6
8 -
7 -


5 -



2
1
0 -






Figure 3-2. Rainfall in the Lake George Basin















3.5

3

2.5

2

1.5

1


0.5

0

,,, -,y 4 > ^' ,,,> /> ,.,\ 4", ^ .



Figure 3-3. Day time water depths at LAG and LEO

35
LAG
30 1

25 -

20 -
LEO
5 15
E
S10 -
I--
5

0






Figure 3-4. Day time water temperature at LAG and LEO


LAG


LAG


I











250


200

u LAG
150

0
o 100


50
LEO








Figure 3-5. Day time colored dissolved organic matter (CDOM) levels at LAG and LEO


12

10 LAG
8--





4-
LEO
2





Figure 3-6. Day time water turbidity at LAG and LEO


Figure 3-6. Day time water turbidity at LAG and LEO












1.2


E 1 LAG
C 0.8

-0 0.6 -
U LEO
u 0.4 -
/)
0.2








Figure 3-7. Secchi depth at LAG and LEO


1.8
1.6 -
LEO
1.4 -
1.2


z 0.8 LAG
0.6 -
0.4
0.2




Figure 3-8. Day time total nitrogen concentrations at LAG and LEO


Figure 3-8. Day time total nitrogen concentrations at LAG and LEO











0.06

0.05

0.04
oo LAG
E 0.03 -












Figure 3-9. Day time nitrate+nitrite (NOx) concentration at LAG and LEO


0.25


0.20
SLELEO











o 0.15 LAG
z 0.10
0.01 -





















0.00
Figure 3-10. Day time ammonium concentrations at LAG and LEO


Figure 3-9. Day time nitrate+nitrite (NOx) concentration at LAG and LEO


0.25 -


0.20 -


tM 0.15 LAG


z 0.10 v




0.00





Figure 3-10. Day time ammonium concentrations at LAG and LEO











0.16
0.14
0.12
L 0.10 -LAG
E 0.08

0.04
0.04 LEO
LEO
0.02
0.00






Figure 3-11. Day time total phosphorus concentrations at LAG and LEO


0.12

0.10

0.08

0.06

0.04


0.02 L

0.00






Figure 3-12. Day time soluble reactive phosphorus (SRP) concentrations at LAG and
LEO












5

-4 -

.0 LAG
E3
Lz
2

*1 LEO

0 __

Figure 3-13. Day time silica concentrations at LAG and LEO



Figure 3-13. Day time silica concentrations at LAG and LEO













7 18

E 16 LAG

: 14
12 -
E
= 10 -
0
> 8
.2
- 6

4


0








18

E 16 LEO
E
: 14

S12 -
E
-3 10 -
10


0
C 6
0
S4

0 2

a- 0


* Other
Green
* Diatoms
SCyanobacteria








A











* Other
Green
* Diatoms
SCyanobacteria


.\01`~ \


B


Figure 3-14. Day time phytoplankton biovolume at LAG (A) and LEO (B). The
community is divided into four groups, cyanobacteria, diatoms, green algae
and other phytoplankton taxa














S12 "
E
S10
E


E 6 -

> 4

2

0

0, 0, 1%0' 0, NO' eQ~ e e e< ee
40'0 QP3 d-\' Q? o Zbe d<\y dl\>* < 61>' <^ 0o'


14
12 LEO

10 -

8

) 6
E
0 4
0
2

0

CP I. Cd ?d-\ ^' CvO^ gO^ 001 Ob O^ O^ O^ v- ^\<^ CO v


* Other Cyano
Ana+Aphan
* Oscil
SCyl


* Other Cyano
Ana+Aphan
* Oscil
SCyl


Figure 3-15. Day time cyanobacteria biovolume at LAG (A) and LEO (B). The
cyanobacteria community is divided into four groups, Cylindrospermopsis sp.;
Oscillatoria spp.; Anabaena spp.+ Anabaenopsis spp.+Aphanizomenon spp.;
other cyanobacteria











100
S90 -
E
= 80
0 LEO




40 LAG
0
I 30
u 20
10
0





Figure 3-16. Relative biovolume of Cyanobacteria in phytoplankton community at LAG
and LEO

















E 12
E

010




.2 6
.Q

3 4



S0
u 0


0 5 10
Phytoplankton biovolume, 106 tm3 ml-'


14
E
12
E

010
a,
E8



2

--
4
Cu
-QD-
C
0
U 0


5 10
Phytoplankton biovolume, 106 l m3 ml'


Figure 3-17. Relationship between biovolume of Cyanobacteria and total phytoplankton
biovolume, LAG (A) and LEO (B)


y = 0.971x 928565
R2 = 0.9713































S0U1 d _\_ \< i iZ01






14

12 LEO

10

8

6

4 A


6


5


4
Si, mg L-1
3 Diatom
Cyanobacteria
2 si

1


0







- 6


-5


-4


- 3 Si, mg L-1
Diatom
_2 Cyanobacteria
Si

-1


-0


Figure 3-18. Day time trends of diatom and cyanobacteria biovolume and silica
concentrations, LAG (A) and LEO (B)


6\, d,< ?Z lz"d Z ,,\6" -Z" ,I(? ,< zov d
v'' OV \'' \ *,; ^3\ dO^ vT' (O'\^'v















S LMU
E
E 8


o
0 6

E
2 4
0
0 2
o 2i ---- ^ --- *-V

0< ?,\


li& a ^\^^\<^^^


Ana+Aph
- Cylindrospermopsis

Non Het


/


- Ana+Aph
- Cylindrospermopsis
Non Het


Figure 3-19. Trends of biovolume of three groups of cyanobacteria: Anabaena
spp.+Anabaenopsis spp.+Aphanizomenon spp.; Cylindrospermopsis sp.;
other non-heterocystous cyanobacteria, LAG (A) and LEO (B)


12

-10
E
S8

4 6-

E
S 4
0
0
o 2


0 -I .

,~~d~"~\
















oC
20
_Ana+Aph

15 Cylindrospermopsis
Non Het


- Temperature


t, t.\ t 4 b S


oC
- Ana+Aph
- Cylindrospermopsis
Non Het
- Temperature


Figure 3-20. Trends of temperature and bivolume of three groups of cyanobacteria:
Anabaena spp.+Anabaenopsis spp. +Aphanizomenon spp.;
Cylindrospermopsis sp.; other non-heterocystous cyanobacteria, LAG (A) and
LEO (B)


I,, I i


LAG




--000_ 1


e e e e e e e e e e\ e e
^~~~~ 4 AY<<<\ ^\











16 1.8

14 LAG 1.6

12 1.4
1.2
10
1
8 TN, mg L-1
0.8
6 Nitrogen fixing
0.6 Total phytoplankton

4 0.4 TN

2 0.2

0 0


^'~ ~ ~ ~ ,\ ^^c\^c^^<


16

14 LEO

12 -
E
10

86


E
5 4
0
m 2
i, / i i i i i


1.8

1.6

1.4

1.2

1 TN, mg L-1

0.8
Nitrogen fixing
0.6 Total Phytoplankton

0.4 TN

0.2

0


Figure 3-21. Trends of total phytoplankton biovolume, nitrogen fixing cyanobacteria
biovolume and total nitrogen concentrations, LAG (A) and LEO (B)













-16

S14 LAG
E
S12
0
o
a 10
E
0 8

S6

S4-


2 -0 .

ol.,, ,,, ,,,,


16

S14 LEO
E 12
E
12 -

0
10 -

I 8 -
o


4-
C
2
0 i i i i i i i i. i i .i


0.06


0.05


0.04


0.03 NOx, mg L-1

Biovolume
0.02
NOX

0.01


0.00


0.06


-0.05


-0.04


-0.03 NOx, mg L-1

-Biovolume
0.02
-NOX

-0.01


0.00


B


Figure 3-22. Trends of total phytoplankton biovolume and nitrate+nitrite (NOx)
concentrations, LAG (A) and LEO (B)













14 LA

2 12 -
E
E 10 -
0 8


E 6

0
> 4

2/

0 i i i i i i i i i --i-- -






16

14 LEO

_ 12 -
E
E 10 -





Co
E



2

0 l


q?V Z^' Z9 IV ^v dlV 41\oV


0.20


0.15


NH4, mg L-1

0.10
Nitrogen fixing
Total Phytoplankton
0.05 -NH4


0.00


0.25


0.2


0.15

NH4, mg L-1
0.1
1 Nitrogen fixing
Total Phytoplankton

0.05- NH4


0


Figure 3-23. Trends of total phytoplankton biovolume, nitrogen fixing cyanobacteria
biovolume and ammonium concentrations, LAG (A) and LEO (B)











16 0.18

14 LAG 0.16
0.14
-12
0- 0.12

0.10
08 0 TP, mg L1
S0.08
E 6 Nitrogen fixing
-2 0.06
006 1 Total phytoplankton
.4 0.04 TP
2 V 0.02

0 .. 0.00



A


16 0.18

14 LEO 0.16
12 0.14
12 -
E
S- 0.12
E 10 -
0.10
I 8 TP, mg L-1
S0.08
E 6 Nitrogen fixing
E60.06
S 0.06 1 Total Phytoplankton
0.04 TP
2 0.02

0 I-- 0.00
,I ,< ,< ,< ,< ,< ,< .0


B

Figure 3-24. Trends of total phytoplankton biovolume, nitrogen fixing cyanobacteria
biovolume and total phosphorus concentrations, LAG (A) and LEO (B)













18

E 16 LAG
E
S14
0
S12

E 10
0
> 8



.A
4o
C.
0 2









16 1

E 14 LEO

E
ai 12 -
0
0
r-







`e 4
E 14 LEO











2 -2
c 0 -



o z

a- 0 .----


0.12


0.10


0.08

SRP, mg L-1
0.06
Biovolume

-SRP
0.04


0.02


0.00


- 0.12


- 0.10


- 0.08
SRP, mg L-1

- 0.06 Biovolume
-SRP
-0.04


- 0.02


0.00


0 _B '.3\3~d3 o.\d o6


Figure 3-25. Trends of total phytoplankton biovolume and soluble reactive phosphorus
(SRP) concentration, LAG (A) and LEO (B)


i















Phyto-P/TP Ratio

-SRP/TP Ratio


Phyto-P/TP Ratio

-SRP/TP Ratio


Figure 3-26. Ratios of estimated phytoplankton phosphorus and SRP to total
phosphorus, LAG (A) and LEO (B)


\
*< oC^<^Co~Y~7 ob^ <^o\~


Io lA < A ^ -Z 4 4x C dl z 'P\ IZI I\














0.2


0.15


0.1


0.05 -


oI






0.18

0.16 LEO

0.14

0.12 -

0.1 -

0.08 -

0.06 -

0.04 -

0.02

01


Phyto-N/TN Ratio
-DIN/TN Ratio


Phyto- N/TN Ratio
-DIN/TN Ratio


B

Figure 3-27. Ratio of estimated phytoplankton nitrogen and DIN to total nitrogen, LAG
(A) and LEO (B)








Table 3-1. Pearson's correlation between day time total phytoplankton biovolume (log
transformation of phytoplankton biovolume is used for the third column) and
different environmental variables, LAG (top) and LEO (bottom)
LAG Correlation Correlation(log(biov))
SRP -0.45 (0.06) -0.48 (0.04)
TP -0.45 (0.06) 0.11 (0.68)
NH4 -0.12(0.63) 0.40(0.10)
NOX -0.55 (0.02) -0.49 (0.04)
TN 0.42 (0.08) 0.67 (0.002)
DIN -0.23 (0.35) 0.30 (0.22)
Turbidity 0.54 (0.02) 0.69 (0.002)
Color -0.53 (0.02) -0.29 (0.24)
TN/TP 0.45 (0.06) 0.53 (0.02)
Secchi depth -0.04 (0.88) -0.01 (0.97)
DO(top) 0.44 (0.09) 0.35 (0.19)
DO(bottom) 0.28 (0.28) 0.23 (0.37)
Temperature 0.16(0.53) 0.15(0.55)
LEO Correlation Correlation(log(biov))
SRP 0.13(0.61) 0.16(0.54)
TP 0.07 (0.79) 0.11 (0.68)
NH4 0.32(0.19) 0.40(0.10)
NOX -0.49 (0.04) -0.49 (0.04)
TN 0.66 (0.003) 0.67 (0.002)
DIN 0.23 (0.36) 0.30 (0.22)
Turbidity 0.64 (0.004) 0.69 (0.002)
Color -0.28 (0.26) -0.29 (0.24)
TN/TP 0.44 (0.07) 0.44 (0.07)
Secchi depth -0.50 (0.04) -0.54 (0.02)
DO(top) 0.31 (0.22) 0.28 (0.28)
DO(bottom) 0.22 (0.40) 0.10(0.70)
Temperature 0.28 (0.26) 0.37 (0.13)

Table 3-2. Pearson's correlation between nitrogen fixing cyanobacteria biovolume and
nitrogen related chemical parameters, LAG (top) and LEO (bottom)
LAG Correlation Correlation(log(biov))
NH4 -0.11 (0.65) -0.47 (0.05)
NOX -0.48 (0.05) -0.78 (0.0001)
TN 0.44 (0.07) 0.10(0.68)
LEO Correlation Correlation(log(biov))
NH4 0.36 (0.14) 0.19(0.45)
NOX -0.44 (0.07) -0.61 (0.008)
TN 0.71 (0.0009) 0.57 (0.01)









CHAPTER 4
DISCUSSION

High phytoplankton biomass was observed during our sampling period in Lake

George. Phytoplankton blooms are a regular wet season phenomenon in Lake George

(Phlips et al., 2000), as they are in many eutrophic lakes in subtropical and tropical

regions of the world (Havens et al., 2001). Both edaphic and anthropogenic factors

contribute to the high phosphorus loads that support blooms in Lake George

(Hendrickson et al., 2003). External nitrogen loads are relatively smaller than

phosphorus loads (Hendrickson et al., 2003). This is illustrated by the more than two-

fold increase in TP concentrations at LAG following the rainfall-induced increase in

water inputs from the upper St. Johns River to Lake George in late May, compared to

only a 30% increase in TN concentration. The consequences of the excess phosphorus

load are reflected in several structural and functional characteristics of the

phytoplankton community in Lake George.

One important functional feature is the common observation of nitrogen-limiting

conditions for phytoplankton growth in the lake (Piehler et al., 2009). The existence of

nitrogen-limiting conditions explains the important role that heterocystous cyanobacteria

play in the phytoplankton community of Lake George, as revealed in this study and in

previous studies (Piehler et al., 2009). As might be expected, the blooms of

heterocystous cyanobacteria have been shown to be associated with high rates of

nitrogen fixation (Doron, 2010). Nitrogen fixation rates observed during the summer of

2008 were sufficient to account for all of the deficits in nitrogen load to Lake George

estimated by nutrient load modeling carried out by the St. Johns River Water

Management District (Doron, 2010).









In terms of the potential for phosphorus limitation, SRP concentrations remained

relatively constant between 0.010 and 0.020 mg P L-1 through most of both bloom

periods, suggesting that phosphorus was not a limiting nutrient for phytoplankton

growth. In addition, the increasing ratio of estimated phytoplankton phosphorus to TP

showed that as phytoplankton biomass increased, more phosphorus was incorporated

into algal cells. Along with the trend of phytoplankton phosphorus to TP ratios, the ratios

of SRP to TP showed a similar increasing trend, which indicates a lack of phosphorus-

limitation of phytoplankton growth during the study period. Unfortunately, the bloom

observed during the study period was cut short by a freshwater flushing event

subsequent to high rainfall at the end of May. Without the disruption of the bloom

caused by dilution, phosphorus limitation might eventually have been observed. The

potential for periods of phosphorus limitation is indicated by the combination of high

phytoplankton phosphorus to TP and low SRP to TP ratios during some other major

bloom peaks observed over the historical data record (Phlips, unpublished data).

The results of this study also highlight the importance of rainfall conditions on

bloom dynamics. The influences of precipitation on phytoplankton dynamics are multi-

faceted and depend on the intensity, duration and timing of the events (Phlips et al.,

2007). Large rainfall events, such as the one observed in late May during this study,

substantially increased inputs of water to Lake George containing high phosphorus

concentration, but relatively low nitrogen levels. Such events cause a dilution of

phytoplankton biomass in the lake and displacement of the bloom water downstream

into the lower St. Johns River, thereby reducing water residence times in the lake and

river (Phlips et al., 2000; Phlips et al., 2007). More moderate rainfall events, as









observed in April, can introduce pulses of bioavailable nutrients to the lake, but do not

substantially reduce water residence time, allowing for a bloom response within the

lake.

Cyanobacterial Dominance

The phytoplankton blooms observed in Lake George during the study period were

dominated by cyanobacteria, which matches the historical record in the St. Johns River

System (Phlips et al., 2007). Strong correlations between cyanobacterial biomass and

total algal biomass have been observed in Florida lakes (Canfield et al., 1989). The

same pattern was found in Lake George. Strong linear regression relationships were

observed for both stations, with r2 values above 0.95. Several environmental conditions

in Lake George favor dominance by cyanobacteria. Factors that may be responsible for

the dominance of cyanobacteria at high phytoplankton biovolumes include their

preference for high temperature, ability to compete for inorganic carbon at high pH,

adaptability to environments with high light attenuation, and lack of requirement for

silica.

Cyanobacteria generally exhibit optimal growth rates at higher temperatures than

many other phytoplankton groups, usually in excess of 250C (Paerl and Huisman,

2009). Therefore, at high temperatures, cyanobacteria have a competitive advantage

over many eukaryotic phytoplankton species (De Senerpont Domis et al., 2007; Elliott et

al., 2006; Joehnk et al., 2007). In other words, as the growth rate of other groups

declines with temperatures greater than 250C, cyanobacteria growth rates go up (Paerl

and Huisman, 2009). The temperature in Lake George increased over the study period,

which might favor the dominance of cyanobacteria. Since the temperature preferences









of the cyanobacteria and eukaryotic algae in Lake George are not known, it is difficult to

confirm this hypothesis.

Planktonic cyanobacteria grow at near optimal rates at high pHs (i.e. 7-9) (Kratz

and Myers, 1955). The high pH values (i.e., 8-9.5) observed during our study, reflect

high photosynthetic activity. At high pH, soluble C02 in water is low, which places a

premium on the ability of algae to use bicarbonate as a source of carbon for

photosynthesis. The ability of many cyanobacteria to efficiently use bicarbonate has

been proposed as one explanation for the dominance of cyanobactria in eutrophic

ecosystems (Shapiro, 1973; Shapiro, 1990; Shapiro, 2007).

Secchi depths in Lake George are shallow, ranging from 0.6 to 1 m during the

study period. The largest contributors to light attenuation in Lake George are CDOM,

tripton (none algal suspended solids), and phytoplankton (Phlips et al., 2000). Based on

Secchi disk values, the depth of the euphotic zone in the lake is about half the depth of

the mixed-layer, indicating that light availability may contribute to the competition

between algal species and successional patterns. The ability of many planktonic

cyanobacteria to adjust their position in the water column using the regulation of gas

vesicles, represent a selective advantage in shallow euphotic zones (Oliver et al.,

2000), particularly during the summer when average wind intensities are relatively low in

Florida. In addition, low light flux also favors dominance of cyanobacteria, because of

their lower light requirements for growth compared to many other algal groups (Smith,

1986).

A possible reason for cyanobacteria dominance over diatoms in Lake George is

the potential for silica limitation. The drop in diatom biovolume observed immediately









after the decrease of silica concentrations was then followed by the sharp increase in

cyanobacteria biovolume, which might support this hypothesis.

Succession Patterns

Historical data for the lower St. Johns River ecosystem, including Lake George,

demonstrate recurring aspects of blooms includes: increases in diatom abundance in

the early spring followed by increasing dominance of cyanobacteria, with a succession

of cyanobacteria dominance from Anabaena spp., Anabaenopsis spp. and

Aphanizomenon spp. (A-Group) to Cylindrospermopsis sp. (C-Group) (Phlips et al.,

2007). The successional pattern has been observed in other ecosystems(Ryding and

Rast, 1989). Successional patterns can be controlled by allogenic factors, such as

nutrient supply, ambient temperature, light income, CO2 availability and turbulence, or

autogenic factors, such as physiological and life-history characteristics of individual

species.

In terms of nutrient supply, low concentration of dissolved inorganic nitrogen (DIN)

before the bloom events was undoubtedly a factor in the dominance of nitrogen fixing

cyanobacteria. Coincident with the increase in phytoplankton biomass during the

blooms, NH4 and TN concentrations increased, probably linked to the input of

atmospheric nitrogen to Lake George via nitrogen fixation (Doron, 2010).

The DIN: SRP ratio ranged from 2 to 12, with more than 50% of values falling

below 7, which is generally considered the threshold for distinguishing phosphorus from

nitrogen limitation. SRP concentration showed no evident change with the A-Group

peak, but an increase associated with the increase in C-Group biovolume. This might be

explained by the relatively high affinity phosphorus-uptake of Cylindrospermopsis, in









consort with its relatively low thresholds for phosphorus-uptake, high phosphorus-

storage capacity and its ability to mobilize internal P sources (Padisak, 1997).

The collapse of the A-Group and the significant increase in C-Group biomass were

both coincident with an evident increase in Secchi Depth, that is to say, an increase in

light penetration in water column. The increase in Secchi Depth might be an indicator of

calm conditions in the water column, with more bioavailable P settling to the bottom.

The different P uptake ability and buoyancy characteristics of these two groups could

contribute differently to their response to the changing environmental conditions, which

might be the reason for their alternating dominance.

The steady increase in temperature over the study period could be one factor

favoring the dominance of the C-Group over the A-Group. The former group became

increasingly dominant when water temperature exceeded 28 OC.









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Shapiro, J. (1984) Blue-green dominance in lakes: the role and management
significance of pH and CO2. Int. Rev. Gesamten Hydrobiol., 69, 765-780.

Shapiro, J. (1990) Current beliefs regarding dominance by blue-greens: the case for the
importance of CO2 and pH. Verh. Int. Ver. Limnol. 24: 38-54.

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Manual (Sournia, A., ed.). UNESCO, Paris, FR.

Smith, V.H. (1986) Light and nutrient effects on the relative biomass of blue-green algae
in lake phytoplankton. Can. J. Fish. Aquat. Sci., 43, 148-153.

Utermohl, H. (1958) Zur vervoll kommnung der quantitativen phytoplankton-methodik.
Mitt. Int. Ver. Theor. Angew. Limnol., 9, 1-38.

Vollenweider, R.A. (1971) Scientific Fundamentals of the Eutrophication of Lakes and
Flowing Waters, with Particular Reference to Nitrogen and Phosphorus as Factors
in Eutrophication. OECD, Paris, FR.

Vollenweider, R.A. and Kerekes, J. (1982) Eutrophication of Waters, Monitoring,
Assessment and Control. OECD, Paris, FR.









BIOGRAPHICAL SKETCH

The author is originally from China, received her bachelor's degree in biological

science from Nanjing Agricultural University in the summer of 2008. In the United

States, she received her master's degree in interdisciplinary ecology from the University

of Florida in the summer of 2010.





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1 PHYTOPLANKTON BLOOM DYNAMICS I N A NITROGEN-LIMITED SUBTROPICAL LAKE By LINGHAN DONG A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2010

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2 2010 Linghan Dong

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3 To my Mom

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4 ACKNOWLEDGMENTS I thank my parents for supporting my writing mentally. I appreciate the academic instruction from Dr. Edward Phlips, Dr. Mark Brenner and Dr. Karl Havens. Special thanks are given to Dr. Mary Cichra for algal taxonomy training. I also appreciate the help o ffered by people working in Phlips lab.

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5 TABLE OF CONTENTS ACKNOWLEDGMENTS ...................................................................................................... 4 page LIST OF TABLES ................................................................................................................ 6 LIST OF FIGURES .............................................................................................................. 7 LIST OF ABBREVIATIONS ................................................................................................ 9 ABSTRACT ........................................................................................................................ 10 CHAPTER 1 INTRODUCTION ........................................................................................................ 12 2 METHODS .................................................................................................................. 15 Site Description ........................................................................................................... 15 Sampling Regime ....................................................................................................... 15 Sampling Collection and Analysis .............................................................................. 16 Statistical Analysis ...................................................................................................... 17 3 RESULTS .................................................................................................................... 18 4 DISCUSSION .............................................................................................................. 44 Cyanobacterial Dominance ........................................................................................ 46 Succession Patterns ................................................................................................... 48 LIST OF REFERENCES ................................................................................................... 50 BIOGRAPHICAL SKETCH ................................................................................................ 53

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6 LIST OF TABLES Table page 3 -1 Pearsons correlation between day time total phytoplankton biovolume and different environmental variables, LAG and LEO .................................................. 43 3 -2 Pearsons correlation between nitrogen fixing cyanobacteria biovolume and nitrogen relat ed chemical parameters, LAG and LEO .......................................... 43

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7 LIST OF FIGURES Figure page 3 -1 Map of Lake George .............................................................................................. 22 3 -2 Rainfall in the Lake George Basin ......................................................................... 22 3 -3 Day time water depths at LAG and LEO ............................................................... 23 3 -4 Day time water temperature at LAG and LEO ...................................................... 23 3 -5 Day time colored dissolved organic matter (CDOM) levels at LAG and LEO ...... 24 3 -6 Day time water turbidity at LAG and LEO ............................................................. 24 3 -7 Secchi depth at LAG and LEO ............................................................................... 25 3 -8 Day time total nitrogen concentrations at LAG and LEO ...................................... 25 3 -9 Day time nitrate+nitrite (NOx) concentration at LAG and LEO ............................. 26 3 -10 Day time ammonium concentrations at LAG and LEO ......................................... 26 3 -11 Day time total phosphorus concentrations at LAG and LEO ................................ 27 3 -12 Day time soluble reactive phosphorus (SRP) concentrations at LAG and LEO .. 27 3 -13 Day time silica c oncentrations at LAG and LEO ................................................... 28 3 -14 Day time phytoplankton biovolume at LAG and LEO. .......................................... 29 3 -1 5 Day time cyanobacteria biovolume at LAG and LEO ........................................... 30 3 -16 Relative biovolume of Cyanobacteria in phytoplank ton community at LAG and LEO .................................................................................................................. 31 3 -17 Relationship between biovolume of Cyanobacteria and total phytoplankton biovolume, LAG and LEO ...................................................................................... 32 3 -18 Day time trends of diatom and cyanobacteria biovolume and silica concentrations, LAG and LEO ............................................................................... 33 3 -19 Trends of biovolume of three groups of cyanobacteria: Anabaena spp. + Anabaenopsis spp + Aphanizomenon spp ; Cylindrospermopsis sp ; other non-heterocystous cyanobacteria, LAG and LEO ...................................... 34

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8 3 -20 Trends of temperature and bivolume of three groups of cyanobacteria: Anabaena spp + Anabaenopsis spp + Aphanizomenon spp ; Cylindrospermopsis sp ; other non-heterocystous cyanobacteria, LAG and LEO ......................................................................................................................... 35 3 -21 Trends of total phytoplankton biovolume, nitrogen fixing cyanobacteria biovolume and total nitrogen concentrations, LAG and LEO ............................... 36 3 -22 Trends of total phytoplankton biovolume and nitrate+nitrite (NOx) concentrations, LAG and LEO .............................................................................. 37 3 -23 Trends of total phytoplankton biovolume, nitrogen fixing cyanobacteria biovolume and ammonium concentrations, LAG and LEO ................................... 38 3 -24 Trends of total phytoplankton biovolume, nitrogen fixing cyanobacteria biovolume and total phosphorus concentrations, LAG and LEO ......................... 39 3 -25 Trends of total phytoplankton biovolume and soluble reactive phosphorus (SRP) concentration, LAG and LEO ...................................................................... 40 3 -26 Ratios of estimated phytoplankton phosphorus and SRP to total phosphorus, LAG and LEO ......................................................................................................... 41 3 -27 Ratio of estimated phytoplankton nitrogen and DIN to total nitrogen, LA G an d LEO ......................................................................................................................... 42

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9 LIST OF ABBREVIATION S DIN Dissolved inorganic nitrogen NOx Nitrate and nitrite SRP Soluble reactive phosphorus TN Total nitrogen TP Total phosphorus

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10 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 PHYTOPLANKTON BLOOM DYNAMICS IIN A NITROGEN-LIMITED SUBTROPICAL LAKE By Linghan Dong August 2010 Chair: Edward Phlips Major: Interdisciplinary Ecology The focus of this study was Lake George, a eutrophic lake in Florida, which has experienced major algal blooms for decades. Phytoplankton blooms in the l ake are typically dominated by cyanobacteria. The goal of the study was to examine the dynamics of a major bloom event within the context of variations in physical, chemical and biological conditions. A temporally intensive sampling regime was used to rev eal successional patterns in phytoplankton composition and abundance at scales appropriate to the growth of phytoplankton. Two major bloom periods were observed over the study period. The first bloom was dominated by a mix of diatoms and several nitrogen -fixing species of cyanobacteria, including Anabaena spp., Aphanizomenon spp. and A nabaenopsis spp. The second, and larger, bloom was dominated by the nitrogen -fixing cyanobacterium Cylindrospermopsis sp. These observations demonstrate the importance of nitrogen fixation in supplying the nitrogen needed to support primary production in the lake. Statistical correlation analyses showed relationships between phytoplankton structure and environmental factors, emphasizing the impact of bioavailable nitrogen concentrations, Si concentrations and temperature.

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11 The results of this research hav significant implications for future efforts to manage the ecology of Lake George, in an effort to prevent the continued proliferation and intensification of cyanobacterial blooms.

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12 CHAPTER 1 INTRODUCTION One common symptom of eutrophication in aquatic systems is algal blooms. Many ecosystems around the world are experiencing increased r ates of eutrophication due to rapid agricultural and industrial development, population expansion and urbanization (Paerl and Huisman, 2009) The essential role of nutrient load in eutrophication has focused attention on the relative importance of different macronutrients in controlling phytoplankton productivity, with nitrogen and phosphorus generally receiving the most attention. One long standing paradigm is that phosphorus is more often limiting in lakes than nitrogen (Einsele, 1941; Schindler, 1977; Schindler e t al. 2008; Vollenweider, 1971; Vollenweider and Kerekes, 1982) Evidence for the importance of phosphorus include s stoich iometric relationships between nitrogen and phosphorus (Hutchinson, 1957; Pearsall, 1930) and the correlation between total phosphorus ( TP ) and c hlorophyll a ( Chl a ) (Dillon and Rigler, 1974; Sakamoto, 1966) The importance of phosphorus limitation has been further supported through whole lake fertilization experiments by Schindler (Schindler, 1974; Schindler, 1977) Despite the evidence for the role of phosphorus as a limiting factor, other researchers have shown that nitrogen availability also impa cts phytoplankton dynamics in many freshwater ecosystems (Lewis Jr and Wurtsbaugh, 2008; Paerl and Huisman, 2009). For instance, many tropical and subtropical lakes have low N: P ratios, an indicator of nitrogen limitation (Ryding and Rast, 1989) The results of nutrient limitations bioassay experiments also support the e xistence of nitrogen limitation i n phosphorus -rich eutrophic lakes in Florida, such as Lake Okeechoobee (Aldridge et al. 1995; Phlips et al. 1997) Lake Griffin (Phlips et al. 2004) and Lake George (Piehler et al. 2009) In these Florida lakes, nitrogen-fixing

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13 cyanobacteria are often prominent members of the phytoplankton community, a response to nitrogen limitation. Questions remain about whether nitrogen fixation can provide sufficient nitrogen input to phosphorus enriched ecosystems to ultimately induce phosphorus limitation of phytoplankt on growth and biomass, making nitrogen limitation a short -term phenomenon, ultimately leading to phosphorus limitation in the long term. If so, management of nitrogen input to lakes would not aid in the reduction of trophic state (Schindler et al. 2008) Some, however, argue that nitrogen fixation cannot fully make up for nitrogen limitation in many ecosystems due to physical, bi ological and chemical limitations on the process (Lewis Jr and Wurtsbaugh, 2008; Paerl and Huisman, 2009) le ading to the conclusion that it is important to consider both nitrogen and phosphorus loads in management efforts. The goal of this study was to examine the dynamics of phytoplankton bloom events in a lake subject to nitrogenlimiting conditions, and follow the dynamics of key physical and chemical parameters, in an effort to evaluate the response of the phytoplankton community. A subtropical eutrophic lake in Florida, Lake George, was the focus of the study because of the existence of a long record for nut rient and phytoplankton composition and a demonstrated history of cyanobacterial blooms under nitrogenlimiting conditions (Piehler et al. 2009) Given its shallow depth and long water residence times, Lake George falls into the category of a number of large phosphorus -rich lakes in Florida, such as Lake Okeechoobee (Aldridge et al. 1995; Phlips et al. 1997) Lake Apopka and Lake Griffin (Phlips et al. 2004) and in other subtropical regions around the world, e.g., Lake Taihu and Donghu in China and Lake Kasumi gaura in Japan (Havens et al. 2001) Along with a historical record of intense cyanobacteria blooms, nitrogen limitation

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14 seems to be an important factor in phytoplankton dynamics in Lake George (Piehler et al. 2009) A temporally intensive s ampling regime was employed in this study, to provide a detailed view of the dyn amics of blooms in Lake George. Several hypotheses were examined in this study: 1 Large phosphorus loads to Lake George from the watershed are sufficient to support high algal bi omass. 2 High phytoplankton biomass favors dominance of cyanobacteria. 3 Low bioavailable nitrogen load relative to bioavailable phosphorus load increases the potential for nitrogen limitation of algal growth, leading to prominence of nitrogen -fixing cyanobac teria. 4 Succession of phytoplankton species is correlated to shifts in key environmental conditions, including temperature, light flux and biologically available ni trogen, phosphorus and silica.

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15 CHAPTER 2 METHODS Site D escription The St. Johns River is the longest blackwater river in Florida. It is unique for its low elevation drop (8m) from its headwater s to mouth, resulting in low river flow rates ( 1 -2 km day1). The gentle slope of the river bed has resulted in the creation of many wide, shallow pools, which are called lakes of the St. Johns River (Livi ngston, 1990) The largest lake is Lake George, with an area of 18,934 ha (Piehler et al. 2009) Located 210 km from the river mouth, Lake George is the upstream lake, which is most susceptible to tidal forces. Tidal forces and shallow river slope result in prolonged water retention times in Lake George, which can exceed one month (Livingston, 1990) The upper St. Johns River is the dominant source of water for Lake George. High concentrations of nitrogen and phosphorus in the source water result in eutrophic conditions in Lake George (Livingston, 1990) The rich nutrient supply, coupled with long residence time, particularly in spring and summer (April -July) (Piehler et al. 2009) provide conditions conducive to the formation of phytoplankton blooms (Phlips et al. 2007) Sampli ng R egime Water samples were collected twice per week during the day time and once per week at night from two sites, LAG and LEO, which are situated in the southern and cent ral region of the lake channel Sampling was conducted from March 25th to June 23rd 2009. Biweekly sample collection was suspended from Mar 26th to April 14th and from May 15th to 25th.

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16 Sampling Collection and A nalysis Se c chi depth was measured at every day time sample collection. Parameters, including temperature, conductivity, dissol ved oxygen (DO), and pH, were measured by H ydrolab probe from the water surface to just above the bottom at 0.5m intervals. Five poles of depth-integrated samples were collected around the boat and then combined in a plastic bucket. After complete agitation lake water was transferred to individual sample containers, 1000 ml brown plastic bottles for phytoplankton samples and 100 ml white plastic bottles for water chemistry samples. Lugols solution was used f or phytoplankton preservation, pipe ts for each bottle, followed by complete mixing. Phytoplankton composition was determined using the Utermhl method (Utermhl, 1958) Lugol solution preserved samples were settled in 19mm inner diameter cylindrical chambers. Phytoplankton cells were identified and counted at 400X and 100X with a Nikon phase contrast inverted microscope. At 400X, a minimum of 100 cells of a single taxon and 30 grids were counted. If 100 c ells were not counted by 30 grids, up to a maximum of 100 grids were counted until one hundred cells of a single taxon was reached. At 100X a total bottom count was completed for taxa > 30 microns. Biovolume ( m3 m l1) is used as the primary measure phyt oplankton biomass (Smayda, 1978) Total nitrogen was colorimetrically det ermined using the persulfate digestion method (APHA, 1989) with a BranLuebbe AutoAnalyzer. Nitrate, nitrite and ammonium were colorimetrically determined using standard methods (APHA, 1989) with a BranLuebbe AutoAnalyzer. Total phosphorus was colorimetrically determined using the persulfate digestion method (APHA, 1989) with a Hitachi s canning spectrophotometer.

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17 Soluble reactive phosphorus was colorimetrically determined using standard methods (APHA, 1989) with a Hitachi scanning spectrophotometer. Chlorophyll a concentration was colorimetrically determined after extraction of the filtered samples with 90% warm ethanol (Sartory and Grobbelaar, 198 4) with a Hitachi scanning spectrophotometer. Water color was determined from filtered station water (0.7 m glass -fiber filter). Samples were analyzed using platinum cobalt standards from protocols described in Standard Methods (APHA, 1989) on a Hitac hi scanning spectrophotometer. Turbidity was determined wit h a La Motte turbidity meter. Statistical A nalysis SAS 9.2 wa s used for Pearson s Correlation Coefficient calculation. Graphs showing trends and linear relationships were created by Microsoft Off ice Excel 2007.

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18 CHAPTER 3 RESULTS Several small peaks in rainfall in the Lake George (Figure 31) region were recorded from March 29th through May 13th (Figure 3 -2). A major rainfall event occurred in late May fol lowed by smaller events in June. Water depth remained stable around 3.0 m at LAG and 3.4 m at LEO until a near 1 m raise from May 16th to 20th (Figure 3 -3). Water temperatures during the sampling period increased gradually from 20 to near 30 from March 25th to May 10th at both sites (Figure 3 4 ). Colored dissolved organic matter (CDOM) declined gradually from 100 PCU on March 25th to near 50 PCU on May 27th at both stations b efore increasing again (Figure 3 5 ). The increase in CDOM was greater at LAG than LEO. Turbidity ranged between 4 to 10 NTU at both stations (Figure 3 6) with several peaks in value. Peaks in turbidity were higher at LAG than LEO. Secchi depth at bot h stations ranged between 0.6 and 1.0 m (Figure 3 -7). The deepest Secchi depths were observed in the April and early May (Fi gure 3 7 ). Total nitrogen (TN) concentration increased over the study period from 0.8 to over 1.2 mg L1 at both stations. Peaks in TN concentration were generally higher at LEO than LAG in the last ha lf of the study period (Figure 8). Nitrate + nitrite co ncentration (N Ox) declined gradually from 0.014 mg L 1on March 25th to below 0.005 mg L1 on May 1st at both stations before increasing in early June (Figure 3 9 ). The June increase in N Ox concentration was greater at LAG than LEO. Ammonium concentration increased over the study period from near 0.05 mg L1 to greater than 0.15 mg L1 at both LAG and LEO (Figure 3 10 ).

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19 TP concentrations remained near 0.05 mg L1 until June at both LAG and LEO, before increasing substantially. LAG sho wed greater variabilit y than LEO (Figure 3 -11 ). Soluble reactive phosphorus (SRP) concentrations remained near 0.010 mg L1 at both stations until June then increased substantially reaching 0.100 mg L1 at LAG and 0.05 at LEO (Figure 3 1 2 ). Silica concentrations showed a trend similar to SRP, remaining low concentrations below or near 0.5 mg L1 at both stations until a significant increase in late May (Figure 3 -13). Total phytop lankton biovolume at the two stations showed two peaks, a smaller one in mid-April and larger one ext ending through most of May (Figure 3 14). At LEO the second bloom period extended into early June and reached 50% higher biovolume than the second bloom at LAG. During the first bloom period, the relative contributions of cyanobacteria and diatoms to total biovolume were similar. However, the second bloom period was dominated by cyanobacteria (Figure 3 14). Within the cyanobacteria community, the first bloom period was dominated by the nitrogen -fixing taxa Anabaena spp. Anabaenopsis spp. and Aphan i zominon spp. (Figure 3 15). During the second bloom period, the former taxa were initially important but progressively gave way to increased dominance by another heterocystous cyanobacterium, Cylindrospermopsis sp and other non-nitrogen-fixing cyanobacteria, parti cularly Oscillatoria spp. (Figure 3 15). The relative contribution of cyanobacteria to total phytoplankton biovolume increased significantly at both LAG and LEO from March 25th through April (Figure 3 16). From the end of April through the beginning of June, cyanobacteria generally

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20 represented over 80% of total phytoplankton biovolume. In June, cyanobacteria dominance declined somewhat at LAG, but remained high at LEO (Figure 3 -16). For both stations, h igh linear regression was shown between biovolume of cyanobacteria and total phytoplankton biovolume, with r2 above 0.95(Figure 3 17). Diatoms showed a drop in biovolume immediately after the decrease of silica concentrations in April and remained at low l evels for the rest of the study period, despite a sharp increase in silica concentrations at the beginning of June. (Figure 3 -18) Within the cyanobac teria assemblage, the major groups of taxa had distinct temporal patterns of abundance. The heterocystous species Anabaena spp., Aphanizomenon spp. and Anabaenopsis spp. had two distinct peaks in abundance in mid -April and early May at both stations (Figure 3 19). The biovolume of the heterocystous species Cylindrospermopsis sp. increased dramatically in midMay reaching peak levels in ear ly June at both sites (Figure 3 -19). Non-heterocystous cyanobacteria, most prominently Oscillatoria spp. ( Planktothrix spp.) gradually increased in biovolume unt il June at both sites (Figure 3 19 ) The emergence of Cylindrospermopsis sp. and crash of Anabaena spp. + Aphanizomenon spp. + Anabaenopsis spp. group coincided with the maximum rate of increase in temperature (Figure 3 -20). The relations hip between temporal trends in phytoplankton biovolume and trends in nutrient concentrations varied according to forms of nitrogen and phosphorus. Total nitrogen concentrations increased coincident with increasing biovolume of both total phytoplankton and nitrogen-fixing cyanobacteria until the dissipation of the second bloom in June (Figure 3 21), which was accompanied by a decline in TN. By contrast,

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21 NOx concentrations declined to near detection level s at both stations from Ma rch to the end of May (Figure 3 -22 ). Concentrations showed a sharp increase after the collapse of the second phytoplankton bloom in June (Figure 3 22 ). Ammoni um concentrations were highly variable at both stations, but generally increased over the study period (Figure 3 23). Total phosphorus concentrations remained near 0.05 mg L1 at both stations through most of the study period until the dissipation of the second phytoplankton bloom period in June (Figure 3 24), which was accompanied by a sharp increase in TP. TP concentrations w ere more variable at LAG than at LEO. Soluble reactive phosphorus concentrations remained near 0.010 mg L1 at both stations from March to the end of May and then increased substantially after the dissipation of the second phytop lankton bloom in June (Figure 3 25). Pearsons correlation analyses showed that log phytoplankton biovolume was significantly correlated to SRP, NOx, TN, Turbidity and TN: TP ratio at LAG. At LEO, log biovolume was significantly correlated to NO x TN, Turbidity and Secchi Depth (Table 3 1). Correlations between nitrogen-fixing cyanobacteria biovolume and nitrogen compounds were also examined (Table 3 -2). At LAG, log nitrogen-fixing cyanobacteria biovolume was negatively correlated with NH4 and NOx. At LEO, log nitrogen -fixing cyanobacteria biovolume was negatively correlated with NOx and positively correlated with TN (Table 3 -2)

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22 Figure 31. Map of Lake George Figure 32. Rainfall in the Lake George Basin 0 1 2 3 4 5 6 7 8 9 Rain fall (cm)

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23 Figure 33. Day time water depths at LAG and LEO Figure 34. Day time water temperature at LAG and LEO 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 LEO LAGWater depth (m) 0 5 10 15 20 25 30 35 Temperature ( )LAG LEO

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24 Figure 35. Day time colored dissolved organic matter (CDOM) levels at LAG and LEO Figure 36. Day time water turbidity at LAG and LEO 0 50 100 150 200 250 CDOM (PCU) LAG LEO 0 2 4 6 8 10 12 Turbidity (NTU) LAG LEO

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25 Figure 37. Secchi depth at LAG and LEO Figure 38. Day time total nitr ogen concentrations at LAG and LEO 0 0.2 0.4 0.6 0.8 1 1.2 Secchi depth (m) LAG LEO 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 TN (mg L1) LAG LEO

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26 Figure 39. Day time nitrate+nitrite (NOx) concentration at LAG and LEO Figure 310. Day time ammonium concentrations at LAG and LEO 0.00 0.01 0.02 0.03 0.04 0.05 0.06 NOX(mg L1) LEO LAG 0.00 0.05 0.10 0.15 0.20 0.25 NH4(mg L1) LAG LEO

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27 Figure 311. Day time total phosphorus concentrations at LAG and LEO Figure 312. Day time soluble reactive phosphorus (SRP) concentrations at LAG and LEO 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 TP (mg L1) LEO LAG 0.00 0.02 0.04 0.06 0.08 0.10 0.12 SRP (mg L1) LAG LEO

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28 Figure 313. Day time silica concentrations at LAG and LEO 0 1 2 3 4 5 6 Si (mg L1) LAG LEO

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29 A B Figure 314. Day time phy toplankton biovolume at LAG (A ) and LEO ( B). The community is divided into four groups, cyanobacteria, diatoms, green algae and other phytoplankton taxa 0 2 4 6 8 10 12 14 16 18 Phytoplankton biovolume (106 m3ml1) Other Green Diatoms CyanobacteriaLAG 0 2 4 6 8 10 12 14 16 18 Phytoplankton biovolume (106 m3 ml1) Other Green Diatoms CyanobacteriaLEO

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30 A B Figure 315. Day time cya nobacteria biovolume at LAG (A ) and LEO (B ). The cyanobacteria community is divided into four groups, Cylindrospermopsis sp. ; Oscillatoria s pp ; Anabaena spp + Anabaenopsis spp + Aphani zomenon spp. ; other cyanobacteria 0 2 4 6 8 10 12 14 Biovolume (106 m3ml1) Other Cyano Ana+Aphan Oscil CylLAG 0 2 4 6 8 10 12 14 Biovolume (106 m3 ml1) Other Cyano Ana+Aphan Oscil CylLEO

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31 Figure 316. Relative biovolume of Cyanobacteria in phytoplankton community at LAG and LEO 0 10 20 30 40 50 60 70 80 90 100 % Cyanobacteria Biovolume LAG LEO

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32 A B Figure 317. Relationship between biovolume of Cyanobacteria and total phytoplankton biovolume, LAG ( A) and LEO ( B) y = 0.9707x 901939 R = 0.9565 0 2 4 6 8 10 12 14 0 5 10 15Cyanobacteria biovolume, 106 m3ml1Phytoplankton biovolume, 106 m3ml1LAG y = 0.971x 928565 R = 0.9713 0 2 4 6 8 10 12 14 0 5 10 15Cyanobacteria biovolume, 106 m3ml1Phytoplankton biovolume, 106 m3ml1LEO

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33 A B Figure 318. Day time trends of diatom an d cyanobacteria biovolume and silica concentrations, LAG (A) and LEO (B ) 0 1 2 3 4 5 6 0 2 4 6 8 10 12 14 Biovolume, 106 m3ml1 Diatom Cyanobacteria Si Si, mg L1LAG 0 1 2 3 4 5 6 0 2 4 6 8 10 12 14 Biovolume, 106 m3ml1 Diatom Cyanobacteria SiSi, mg L1LEO

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34 A B Figure 319. Trends of biovolume of three groups of cyanobacteria: Anabaena spp. + Anabaenopsis spp + Aph ani zomenon spp ; Cylindrospermopsis sp ; other non-heterocystous cyanobacteria, LAG (A) and LEO (B ) 0 2 4 6 8 10 12 Biovolume (106 m3 ml1) Ana+Aph Cylindrospermopsis Non Het LAG 0 2 4 6 8 10 12 Biovolume (106 m3 ml1) Ana+Aph Cylindrospermopsis Non HetLEO

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35 A B Figure 320. Trends of temperature and bivolume of three groups of cyanobacteria: Anabaena spp + Anabaenopsis spp + Aphani zomenon spp ; Cylindrospermopsis sp ; other non-heterocystous cyanobacteria, LAG ( A) and LEO ( B) 0 5 10 15 20 25 30 35 0 2 4 6 8 10 12 Biovolume, 106 m3ml1 Ana+Aph Cylindrospermopsis Non Het Temperature LAG 0 5 10 15 20 25 30 35 0 2 4 6 8 10 12 Biovolume, 106 m3ml1 Ana+Aph Cylindrospermopsis Non Het Temperature LEO

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36 A B Figure 321. Trends of total phytoplankton biovolume, nitrogen fixing cyanobacteria biovolume and total nitrogen concentrations, LAG (A) and LEO (B ) 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 0 2 4 6 8 10 12 14 16 Biovolume (106 m3ml1) Nitrogen fixing Total phytoplankton TNTN, mg L1LAG 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 0 2 4 6 8 10 12 14 16 Biovolume (106 m3ml1) Nitrogen fixing Total Phytoplankton TNTN, mg L1LEO

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37 A B Figure 322. Trends of total phytoplankton biovolume and nitrate+nitrite (NOx) concentrations, LAG (A) and LEO (B ) 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0 2 4 6 8 10 12 14 16 NOX, mg L1Phytoplankton biovolume (106 m3 ml1) Biovolume NOXLAG 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0 2 4 6 8 10 12 14 16 NOX, mg L1Phytoplankton biovolume (106 m3 ml1) Biovolume NOXLEO

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38 A B Figure 323. Trends of total phytoplankton biovolume, nitrogen fixing cyanobacteria biovolume and ammonium concentrations, LAG (A) an d LEO (B) 0.00 0.05 0.10 0.15 0.20 0.25 0 2 4 6 8 10 12 14 16 Biovolume (106 m3ml1) Nitrogen fixing Total Phytoplankton NH4NH4, mg L1LAG 0 0.05 0.1 0.15 0.2 0.25 0 2 4 6 8 10 12 14 16 Biovolume (106 m3ml1) Nitrogen fixing Total Phytoplankton NH4NH4, mg L1LEO

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39 A B Figure 324. Trends of total phytoplankton biovolume, nitrogen fixing cyanobacteria biovolume and total phosphorus concentrations, LAG (A) and LEO (B ) 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0 2 4 6 8 10 12 14 16 Biovolume (106 m3ml1) Nitrogen fixing Total phytoplankton TPTP, mg L1LAG 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0 2 4 6 8 10 12 14 16 Biovolume (106 m3ml1) Nitrogen fixing Total Phytoplankton TPTP, mg L1LEO

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40 A B Figure 325. Trends of total phytoplankton biovolume and soluble reactive phospho r us (SRP) concentration, LAG (A ) and LEO ( B) 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0 2 4 6 8 10 12 14 16 18 SRP, mg L1Phytoplankton biovolume (106 m3 ml1) Biovolume SRPLAG 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0 2 4 6 8 10 12 14 16 SRP, mg L1Phytoplankton biovolume (106 m3 ml1) Biovolume SRPLEO

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41 A B Figure 326. Ratios of estimated phytoplankton phosphor us and SRP to total phosphorus, LAG (A ) and LEO ( B ) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Phyto P/TP Ratio SRP/TP RatioLAG 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Phyto P/TP Ratio SRP/TP RatioLEO

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42 A B Figure 327. Ratio of estimated phytoplankton nitrogen and DIN to total nitrogen, LA G (A) and LEO (B) 0 0.05 0.1 0.15 0.2 0.25 Phyto N/TN Ratio DIN/TN RatioLAG 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 Phyto N/TN Ratio DIN/TN Ratio LEO

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43 Table 3 1. Pearsons correlation between day time total phytoplankton biovolume (log transformation of phytoplankton biovolume is used for the third column) and different environmental variables LAG (top) and LEO (bottom) LAG Correlation Correlation(log(biov)) SRP 0.45 (0.06) 0.48 (0.04) TP 0.45 (0.06) 0.11 (0.68) NH4 0.12 (0.63) 0.40 (0.10) NOX 0.55 (0.02) 0.49 (0.04) TN 0.42 (0.08) 0.67 (0.002) DIN 0.23 (0.35) 0.30 (0.22) Turbidity 0.54 (0.02) 0.69 (0.002) Color 0.53 (0.02) 0.29 (0.24) TN/TP 0.45 ( 0.06) 0.53 ( 0.02) Secchi depth 0.04 (0.88) 0.01 (0.97) DO(top) 0.44 (0.09) 0.35 (0.19) DO(bottom) 0.28 (0.28) 0.23 (0.37) Temperature 0.16 (0.53) 0.15 (0.55) LEO Correlation Correlation(log(biov)) SRP 0.13 (0.61) 0.16 (0.54) TP 0.07 (0.79) 0.11 (0.68) NH4 0.32 (0.19) 0.40 (0.10) NOX 0.49 (0.04) 0.49 (0.04) TN 0.66 (0.003) 0.67 (0.002) DIN 0.23 (0.36) 0.30 (0.22) Turbidity 0.64 (0.004) 0.69 (0.002) Color 0.28 (0.26) 0.29 (0.24) TN/TP 0.44 (0.07) 0.44 (0.07) Secchi depth 0.50 (0.04) 0.54 (0.02) DO(top) 0.31 (0.22) 0.28 (0.28) DO(bottom) 0.22 (0.40) 0.10 (0.70) Temperature 0.28 (0.26) 0.37 (0.13) Table 3 2. Pearsons correlation between nitrogen fixing cyanobacteria biovolume and nitrogen related chemical parameters, LAG (top) and LEO (bottom) LAG Correlation Correlation(log(biov)) NH4 0.11 (0.65) 0.47 (0.05) NOX 0.48 (0.05) 0.78 (0.0001) TN 0.44 (0.07) 0.10 (0.68) LEO Correlation Correlation(log(biov)) NH4 0.36 (0.14) 0.19 (0.45) NOX 0.44 (0.07) 0.61 (0.008) TN 0.71 (0.0009) 0.57 (0.01)

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44 CHAPTER 4 D ISCUSSION High phytoplankton biomass was observed during our sampling period in Lake George. Phytoplankton blooms are a regular wet season phenomenon in Lake George (Phlips et al. 2000) as they are in many eutrophic lakes in subtropical and tropical regions of the world (Havens et al. 2001) Both edaphic and anthropogenic factors contribute to the high phosphorus loads that supp ort blooms in Lake George (Hendrickson et al. 2003) E xternal nitrogen loads are relatively smaller than phosphorus loads (Hendrickson et al. 2003) This is illustrated by the more than two fold increase in TP concentrations at LAG following the rainfall induced increase in water inputs from the upper St. Johns River to Lake George in late May compared to only a 30% increase in TN concentration. The consequences of the excess phosphorus load are reflected in several structural and functional characteristics of the phytoplan kton community in Lake George. One important functional feature is the common observation of nitrogenlimiting conditions for phytoplankton growth in the lake (Piehler et al. 2009) The exis tence of nitrogen -limiting conditions explains the important role that heterocystous cyanobacteria play in the phytoplankton community of Lake George, as revealed in this study and in previous studie s (Piehler et al. 2009) As might be expected, the blooms of heterocystous cyanobacteria have been shown to be associated with high rates of nitrog en fixation (Doron, 2010) Nitrogen fixation rates observed during the summer of 2008 were sufficient to account for all of the deficits in nitrogen load to Lake G eorge estimated by nutrient load modeling carried out by the St. Johns Rive r Water Management District (Doron, 2010)

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45 In terms of the potential for phosphorus limitation, SRP concentrations remained relatively constant between 0.010 and 0.020 mg P L1 through mos t of both bloom periods, suggesting that phosphorus was not a limiting nutrient for phytoplankton growth. In addition, the increasing ratio of estimated phytoplankton phosphorus to TP showed that as phytoplankton biomass increased, more phosphorus was inco rporated into algal cells. Along with the trend of phytoplankton phosphorus to TP ratios, the ratios of SRP to TP showed a similar increasing trend which indicates a lack of phosphorus limitation of phytoplankton growth during the study period. Unfortunat ely, the bloom observed during the study period was cut short by a freshwater flushing event subsequent to high rainfall at the end of May. Without the disruption of the bloom caused by dilution, phosphorus limitation might eventually have been observed. T he potential for periods of phosphorus limitation is indicated by the combination of high phytoplankton phosphorus to TP and low SRP to TP ratios during some other major bloom peaks observed over the historical data record ( Phlips, unpublished data ). The results of this study also highlight the importance of rainfall conditions on bloom dynamics. The influences of precipitation on phytoplankton dynamics are multi faceted and depend on the intensity, duration and timing of the events (Phlips et al. 2007) Large rainfall events, such as the one observed in late May during this study, substantially increased inputs of water to Lake George containing high phosphorus concentration, but relatively low nitrogen levels. Such events cause a dilution of phytoplankton biomass in the lake and displacement of the bloom water downstream into the lower St. Johns River, t hereby reducing water residence times in the lake and river (Phlips et al. 2000; Phlips et al. 2007) More moderate rainfall events, as

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46 observed in April, can introduce pulses of bioavailable nutrients to the lake, but do not substantially reduce water residence time, allowing for a bloom response within the lake. Cyanobacterial Dominance The phytoplankton blooms observed in Lake George during the study period were dominated by cyanobacteria, which mat ches the historical record in the St. Johns River System (Phlips et al. 2007) Strong correlations be tween cyanobacterial bio mass and total algal biomass have been observed in Florida lakes (Canfield et al. 1989) The same pattern was found in Lake George. Strong linear regression relationships were observed for both stations, with r2 values above 0.95. Several environmental c onditions in Lake George favor dominance by cyanobacteria. Factors that may be responsible for the dominance of cyanobacteria at high phytoplankton biovolumes include their preference for high temperature, ability to compete for inorganic carbon at high pH adaptability to environments with high lig ht attenuation, and lack of requirement for silica. Cyanobacteria generally exhibit optimal growth rates at higher temperatures than many other phytoplankton groups, usually in excess of 25oC (Paerl and Huisman, 2009) T herefore, at high temp eratures, cyanobacteria have a competitive advantage over many eukaryotic phytoplankton species (De Senerpont Domis et al. 2007; Elliott et al. 2006; Joehnk et al. 2007) In other words, as the growth rate of other groups declines with temperatures greater than 25oC cyanobacteria growth rates go up (Paerl and Huisman, 2009) The temperature in Lake George increased over the study period which might favor the dominance of cyanobacteria. Since the temperature preferences

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47 of the cyanobacteria and eukaryotic algae in Lake G eorge are not known, it is difficult to confirm this hypothesis. Planktonic cyanobacteria grow at near optimal rates at high pH s (i.e. 7-9) (Kratz and Myers, 1955) The high pH values (i.e., 8 9.5) observed during our study, reflect high photosynthetic activity. At high pH, soluble CO2 in water is low, which places a premium on the ability of algae to use bicarbonate as a source of carbon for photosynthesis. The ability of many cyanobacteria to efficiently use bicarbonate has been proposed as one explanation for the dominance of cyanobactria in eutrophic ecosystems (Shapiro, 1973; Shapiro, 1990; Shapiro, 2007) Secchi depths in Lake George are shallow, ranging from 0.6 to 1 m during the study period. The largest contributers to light attenuation in Lake George are CDOM, tripton (none algal suspended solids), and phytoplankton (Phlips et al. 2000) Based on Secchi d isk values the depth of the euphotic zone in the lake is about half the depth of the mixed -layer, indicating that light availability may contribute to the competition between algal species and successional patterns. The ability of many planktonic cyanobac teria to adjust their position in the water column using the regulation of gas vesicles, represent a selective advantage in shallow e uphotic zones (Oliver et al. 2000) particularly during the summer when average wind intensities are relatively low in Florida. In addition, low light flux also favor s domina nce of cyanobacteria, because of their lower light requirements for growth compared to many other algal groups (Smith, 1986) A possible reason for cyanobacteria dominance over diatoms in Lake George is the potential for silica limitation. The drop in diatom biovolume observed immediately

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48 after the decrease of silica concentrations was then followed by the sharp increase in cyanobacteria biovolume, which might support this hypothesis. Succession Patterns Historical data for the lower St. Johns River ecosystem, including Lake George, de monstrate recurring aspects of blooms includes: increases in diatom abundance in the early spring followed by increasing dominance of cyanobacteria, with a succession of cyan obacteria dominance from Anabaena spp. Anabaenopsis spp. and Aphanizomenon spp. (A -G roup) to Cylindrospermopsis sp. (C -Group) (Phlips et al. 2007) The succession al pattern has been observed in other ecosystems (Ryding and Rast, 1989) Successional patterns can be controlled by allogenic factors, such as nutrient supply ambient temperature, light income, CO2 availability and turbulence, or autogenic factors, such as physiological and life history characteristics of individual species. In terms of nutrient supply, low concentration of dissolved inorganic nitrogen (DIN) be fore the bloom events was undoubtedly a factor in the dominance of nitrogen fixing cyanobacteria. Coincident with the increase in phytoplankton biomass during the blooms, NH4 and TN concentrations increased, probably linked to the input of atmospheric nitr ogen to Lake George via nitrogen fixation (Doron, 2010) The DIN: SRP ratio ranged from 2 to 12, with more than 50% of values falling below 7, which is generally considered the threshold for distinguishing phospho rus from nitrogen limitation. SRP concentration showed no evident change with the A -G roup peak but an increase associated with the increase in C -G roup biovolume. This might be explained by the relatively high affinity phosphorus -uptake of Cylindrospermops i s, in

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49 consort with its relatively low thresholds for phosphorus uptake, high phosphorus storage capacity and its ability to mobilize internal P sources (Padisk, 1997) The collapse of the A -G roup and the significant increase in C -G roup bioma ss were both coincident with an evi dent increase in Secchi Depth, that is to say, an increase in light penetration in water column. The increase in Secchi Depth might be an indicator of calm conditions in the water column, with more bioavailable P settling to the bottom. The different P uptake ability and buoyancy characteristics of these two gr oups could contribute differently to their response to the changing environmental conditions, which might be the reason for their alternating dominance. The steady increase in temperature over the study period could be one factor favoring the domin ance of the C -Group over the A -Group. The former group became increasingly dominant when water temperature exceeded 28 oC.

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50 L IST OF REFERENCES Aldridge, F. J. Phlips, E. J. and Schelske, C. L. (1995) The use of nutrient enrichment bioassays to test for spatial and temporal distribution of limiting factors affecting phytoplankton dynamics in Lake Okeechobee, F lorida Arch. Hydrobiol., Advances in Limnology 45 177 190. APHA. (1989) Standard Methods for the Examination of Water and W astewater 17th edition. American Public Health Association, Washington, DC. Canfield, D. E.,Jr Phlips, E. J. and Duarte, C. M (1989) Factors influencing the ab undance of blue green algae in F lorida lakes. Can. J. Fish. Aquat. Sci., 46, 1232 1237. De Senerpont Domis, L., Mooij, W. and Huisman, J. (2007) Climate-induced shifts in an experim ental phytoplankton community: a mechanistic approach. Hydrobiologia 584, 403 413. Dillon, P. J. and Rigler, F. H. (1974) The phosphorus -chlorophyll relationship in lakes. Limnol. Oceanog r. 767 773. Doron, M. (2 010) Nitrogen fixation in Lake G eorge. Master Thesis, University of Florida, Gainesville, FL Einsele, W. (1941) Die umsetzung von zugefuhrtem, anorganischen phosphat im eutrophen see und ihre ruckwirkung auf seinen gesamthaushalt. Z. Fisch 39 407 488. Elliott, J. A. Jones, I.D. and Thackeray, S. J. (2006) Testing the sensitivity of phytoplankton communities to changes in water temperature and nutrient load, in a temperate lake. Hydrobiologia 559, 401 411. Havens, K. E. Fukushima, T., Xie, P., Iwakuma, T., James, R.T. Takamura, N., Hanazato, T. and Yamamoto, T. (2001) Nutrient dynamics and the eutrophication of shallow lakes kasumigaura (Japan), donghu (PR China), and O keechobee (USA). Environ. Pollut. 111 263 272. Hendrickson, J., Lowe, E. F., Dobberfuhl, D., Sucsy, P. and Campbell, D. (2003) Characteristics of Accelerated Eutrophication in the Lower St. Johns River Estuary and Recommendation of Targets for the Achievement of Water Quality Goals to F ulfill TMDL and PLRG O bjectiv es Water Resources Department Technical Memorandum St. Johns River Water Management District, Palatka, FL. Hutchinson, G. E. (1957) A Treatise on L imnology Vol. 1. Geography, P hysics and C hemistry John Wiley and Sons N ew York NY

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51 Joehnk, K. D. Huisman, J., Sharples, J., Sommeijer, B., Visser, P.M. and Stroom, J. M (2007) Summer heatwaves promote blooms of harmful cyanobacteria. Global Change Biol. 14 495 512. Kratz, W. A. and Myers, J. (1955) Nutrition and growth of several blue -green algae. Am. J. Bot. 42, 282 287. Lewis W. M., Jr and Wurtsbaugh, W. A. (2008) Control of lacustri ne phytoplankton by nutrients: erosion of the phosphorus paradigm. Int. Rev. Hydrobiol., 93 446 465. Livingston, R. J. (1990) The R ivers of F lorida Springer -Verlag N ew York, NY Oliver, R. L. Ganf, G. G. Whitton, B. A. and Potts, M. (2000) The E cology of C yanobacteria: Their D iversity in T ime and S pace. Kluwer Academic Publishers Dordrecht NL Padisk, J. (1997) C ylindrospermopsis raciborskii (W oloszynska) Seenayya et S ubba R aju, an expanding, h ighly adaptive cyanobacterium: w orldwide distribution and review of its ecology. Arch Hydrobiol./ Suppl 107, 563 593. Paerl, H. W. and Huis man, J. (2009) Climate change: a catalyst for global expansion of harmful cyanobacterial blooms. Environ. Microbiol. Reports 1 27 37. Pearsall, W. H. (1930) Phytoplankton in the E nglish lakes: I. The proportions in the waters of some dissolved substances of biological importance. J. Eco l 18 306 320. Phlips, E. J. Cichra, M., Aldridge, F. J. Jembeck, J., Hendrickson, J. and Brody, R. (2000) Light availability and variations in phytoplankton standing crops in a nutrient -rich blackwater river. Limnol. Oceanogr 45 916 929. Phlips, E. J. Cichra, M., Havens, K., Hanlon, C., Badylak, S., Rueter, B., Randall, M. and Hansen, P. (1997) The control of phytoplankton abundance and structure by nutrient and light availability in a shallow subtropical lake. J. Plankton Res. 19 319 342. Phlips, E. J. Frost, J., Yilmaz, N. and Cichra, M. (2004) Factors Controlling the Abundance and C ompositi on of Bluegreen A lgae in Lake G riffin Final Report to the St. Johns River Water Management District St. Johns River Water Management District, Palatka, FL. Phlips, E. J. Hendrickson, J., Quinlan, E. L. and Cichra, M. (2007) Meteorological influences on algal bloom potential in a nutrient -rich blackwater river. Freshwat. Biol 52 2141 2155. Piehler, M. F., Dyble, J., Moisander, P. H. Chapman, A. D. Hendrickson, J. and Paerl, H. W. (2009) Interactions between nitrogen dynamics and the phytoplankton community in Lake George, F lorida, USA. Lake Reserv. Manage 25 1 14.

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52 Ryding, S. O. and Rast, W. (1989) Control of Eutrophication of Lakes and R eservoirs. Parthenon Publishing Group, Paris FR Sakamoto, M. (1966) Primary production by phytoplankton community in some J apanese lakes and its dependence on lake depth. Arch. Hydrobiol 62, 1 28. Sartory, D. P. and Grobbelaar, J. U. (1984) Extraction of chlorophyll a from freshwater phytoplankton for spectrophotometric analysis Hydrobiologia, 114 177 187. Schindler, D. W. (1974) Eutrophication and r ecovery in experimental lakes: i mplications for lake management. Science 184 897 899. Schindler, D. W. (1977) Evolution of phosphorus limitation in lakes. Science 195 260 262. Schindler, D. W. Hecky, R. E. Findlay, D.L. Stainton, M. P. Parker, B. R. Paterson, M. J. Beaty, K. G. Lyng, M. and Kasian, S. (2008) Eutrophication of lakes can not be controll ed by reducing nitrogen input: r esults of a 37 year wholeecosystem experiment. Proc Natl Acad. Sci U.S.A 105, 11254 11258 Shapiro, J. (1973) Bluegreen algae: w hy they become dominant. Science 179 382 384. Shapiro, J. (1984) Blue green dominance in lakes: t he role and management significance of pH and CO2. Int Rev G esamten Hydrobiol 69, 765 780. Shapiro, J. (1990) Current beliefs regar ding dominance by bluegreens: t he case for the importance of C O2 and pH Verh. Int. Ver. Limnol. 24 : 38 54 Smayda, T. J. (1978) From phytoplankters to biomass p. 273 279. In Phytoplankton Manual (Sournia, A. ed.). UNESCO, Paris FR Smith, V. H. (1986) Light and nutrient effects on the relative biomass of blue green algae in lake phytoplankton. Can. J. Fish. Aquat. Sci 43 148 153. Utermhl, H. (1958) Zur vervoll kommnung der quantitativen phytoplankton -methodik. Mitt. Int. Ver. Theor. Angew. L imnol ., 9 1 38. Vollenweider, R. A. (1971) Scientific Fundamentals of the E utroph ication of Lakes and F lowing Waters, with P articular R eference to Nitrogen and P hosphorus as Factors in E utrophication OECD Paris, FR Vollenweider, R. A. and Kerekes, J. (19 82) Eutrophication of Waters, M onitoring, Assessment and C ontrol. OECD Paris, FR

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53 BIOGRAPHICAL SKETCH The author is originally from China, received her bachelors degree in biological science from Nanjing Agricultural University in the summer of 2008 In the United States, s he received her masters degree in interdisciplinary ecology from the University of Florida in the summer of 2010