Phytoplankton Biomass and Composition in Apalachicola Bay, a Subtropical River Dominated Estuary in Florida

MISSING IMAGE

Material Information

Title:
Phytoplankton Biomass and Composition in Apalachicola Bay, a Subtropical River Dominated Estuary in Florida
Physical Description:
1 online resource (123 p.)
Language:
english
Creator:
Viveros Bedoya, Paula Andrea
Publisher:
University of Florida
Place of Publication:
Gainesville, Fla.
Publication Date:

Thesis/Dissertation Information

Degree:
Doctorate ( Ph.D.)
Degree Grantor:
University of Florida
Degree Disciplines:
Fisheries and Aquatic Sciences, Forest Resources and Conservation
Committee Chair:
PHLIPS,EDWARD J
Committee Co-Chair:
HAVENS,KARL
Committee Members:
BAKER,SHIRLEY M
BRENNER,MARK
EDMISTON,HENRY L

Subjects

Subjects / Keywords:
biomass -- composition -- estuary -- phytoplankton -- subtropical
Forest Resources and Conservation -- Dissertations, Academic -- UF
Genre:
Fisheries and Aquatic Sciences thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract:
The integrity of estuaries throughout the world is being impacted by human-driven changes in the ecosystems including their watersheds. The Apalachicola River estuary is an example of a major ecosystem in jeopardy of significant change as a consequence of reduced river discharge, which is a key regulator of physical-chemical processes such as salinity, nutrient concentrations, and water residence time. The overall goal of this study was to describe how changes in river discharge influence phytoplankton community structure, biomass, and dynamics. Phytoplankton composition and physical-chemical variables were determined on a monthly basis for two years (June 2008-June 2010) at 12 sampling sites within the bay. Seasonality of phytoplankton biomass was determined using a longer pre-existing data set (2002-2012). Mean salinities in the Apalachicola Bay varied significantly between the low- and high-discharge periods, which caused salinity to double at some of the sites. Mean total soluble phosphorus (TSP) concentrations also varied seasonally and spatially due to the influence of both the Apalachicola River and the Gulf of Mexico in providing phosphorus for the estuary. In terms of nitrogen The Apalachicola River was a major source for the estuary independent of the season. Nutrient limitation bioassays indicated that phosphorus was the primary limiting nutrient for the bay. Mean chlorophyll a concentrations and mean phytoplankton biovolumes were higher in the low-discharge season than in the high-discharge season at most sampling sites. The phytoplankton community exhibited seasonal changes, with diatoms being the dominant group throughout most of the year, but with some biovolume peaks caused by dinoflagellates. Cyanobacteria were more abundant during periods of low discharge and warmer temperatures. Results indicated that seasonal patterns in river discharge affect salinity and nutrient concentrations, and were correlated to phytoplankton abundance, biovolume, and composition.
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 Paula Andrea Viveros Bedoya.
Thesis:
Thesis (Ph.D.)--University of Florida, 2014.
Local:
Adviser: PHLIPS,EDWARD J.
Local:
Co-adviser: HAVENS,KARL.

Record Information

Source Institution:
UFRGP
Rights Management:
Applicable rights reserved.
Classification:
lcc - LD1780 2014
System ID:
UFE0046670:00001


This item is only available as the following downloads:


Full Text

PAGE 1

1 PHYTOPLANKTON BIOMASS AND COMPOSITION IN APALACHICOLA BAY, A SUBTROPICAL RIVER DOMINATED ESTUARY IN FLORIDA By PAULA A. VIVEROS BEDOYA A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIA L FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 201 4

PAGE 2

2 201 4 Paula Viveros Bedoya

PAGE 3

3 To my beloved parents and grandparents who worked really hard so I could bec ome the first doctor in the family To Alejandro my daily source of motivation and inspiration.

PAGE 4

4 ACKNOWLEDGMENTS T his research was supported by the NSF SEAGEP fellowships program, a Graduate Research Fellowship from the Estuarine Reserves Division, Of fice of Ocean and Coas tal Resource Management at the National Oceanic and Atmospheric Administration (NOAA), a Research Assistantship Match from the University of Florida a Delores Auzenne Dissertation Award and the Supplemental Retention Award program of the Office of Graduate Minority Programs at the University of Florida. Invaluable field assistance was generously provided by personnel from the Apalachicola National Estuarine Research Reserve (ANERR). I would like to thank Nikki Dix, Loren Mathews, Ba iley Trump and Ake Srifa from the Phlips Lab for their help during different stages of this research. Special thanks to Jynessa Dutka Gi anelli for her support with GIS, and Nikolay Bliznyuk for offering statistical support for this research. I would als o like to thank Shirley Baker Mark Brenner Lee Edminston and Karl Havens for their feedback and support during the development of this research I give special thanks to my advisor Ed Phlips for giving me this opportunity and for his constant guidance an d advice. I want to express my gratitude to my family, specially my pare nts Tina y Julio and my brothers Andres y Felipe for always believing in me and offering me their love. I thank my husband Luke for his patience and unconditional support through thi s journey and my son Alejandro for giving me additional inspiration. Thanks also to my parents in law Nancy y Norris for their encouragement and support Last but not least I would like to thank my wonderful friends for helping me keep a smile and a positi ve attitude. Thank you all I would have not done it without you.

PAGE 5

5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ ...... 4 LIST OF TABLES ................................ ................................ ................................ ................ 7 LIST OF FIGURES ................................ ................................ ................................ .............. 9 ABSTRACT ................................ ................................ ................................ ........................ 12 CHAPTER 1 INTRODUCT ION ................................ ................................ ................................ ........ 14 2 SPATIAL AND TEMPORAL DYNAMICS OF PHYTOPLANKTON BIOMASS A ND RIVER DISCHARGE IN THE APALACHICOLA ESTUARY, FLORIDA, USA ................................ ................................ ................................ ............................. 18 Methods ................................ ................................ ................................ ...................... 19 Site Description ................................ ................................ ................................ .... 19 Field Procedures ................................ ................................ ................................ .. 20 Water Chemistry ................................ ................................ ................................ .. 21 Statistical Analyses ................................ ................................ .............................. 22 Results ................................ ................................ ................................ ........................ 22 Physical Chemical Variables ................................ ................................ .............. 22 River discharge ................................ ................................ .............................. 22 Salinity patterns ................................ ................................ ............................. 23 Temperature ................................ ................................ ................................ .. 23 Nutrient patterns ................................ ................................ ............................ 24 Phytoplankton Biomass Patterns ................................ ................................ ........ 25 Changes in Phytoplankton Biomass ................................ ................................ .... 27 Discussion ................................ ................................ ................................ ................... 28 Salinity and Nutrient Ecoclines ................................ ................................ ............ 29 Temporal Variability in Physical and Biological Factors ................................ ..... 32 3 SPATIAL AND TEMPORAL PATTERNS OF PHYTOPLANKTON COMPOSITION IN A SUBTROPICAL ESTUARY, APALACHICOLA BAY, FLORIDA, USA ................................ ................................ ................................ ........... 57 Methods ................................ ................................ ................................ ...................... 58 Site Description ................................ ................................ ................................ .... 58 Field Procedures ................................ ................................ ................................ .. 59 Water Chemistry ................................ ................................ ................................ .. 59 Nutrient Limitation Bioassays ................................ ................................ .............. 60 Phytoplankton Analysis ................................ ................................ ........................ 61 Statistical Analyses ................................ ................................ .............................. 62

PAGE 6

6 Results ................................ ................................ ................................ ........................ 63 Physical Chemical Variables ................................ ................................ ............... 63 River discharge ................................ ................................ .............................. 63 Nutrients ................................ ................................ ................................ ......... 63 Salinity ................................ ................................ ................................ ........... 64 Temperature ................................ ................................ ................................ .. 64 Co lor ................................ ................................ ................................ .............. 65 Secchi depth ................................ ................................ ................................ .. 65 Nutrient limitation bioassays ................................ ................................ ......... 66 Cluster analysis ................................ ................................ ............................. 66 Phytoplankton abundance ................................ ................................ ............. 67 Seasonality of Phytoplankton Biovolume ................................ ............................ 68 Relationships Between Phytoplankton Community Assemblages and Environmental Variables ................................ ................................ ................... 71 Discussion ................................ ................................ ................................ ................... 74 4 SUMMAR Y ................................ ................................ ................................ ................ 116 LIST OF REFERENCES ................................ ................................ ................................ 119 BIOGRAPHICAL SKETCH ................................ ................................ .............................. 123

PAGE 7

7 LIST OF TABLES Table page 2 1 Summary characteristics of sampling sites for nutrient and chlorophyll a in the Apalachicola NERR SWMP. ................................ ................................ ............ 36 2 2 ange Test for salinity during high discharge and low discharge ................................ ................................ ................................ ................ 36 2 3 discharge ................................ ................................ ................................ ............... 36 2 4 discharge and low discharge ................................ ................................ ................ 37 2 5 e nitrogen (TSN) during high discharge and low discharge ................................ ................................ ................ 37 2 6 a during high discharge and low discharge ................................ ................................ ................................ ......... 38 2 7 Spearman rank correlation coefficients (top) and p values (bottom) for selected variables at differen t sites across Apalachicola Bay ............................. 38 2 8 Results from t Test s used to compare the significance of mean values for the four variables during high discharge and low discharge. ................................ ...... 39 2 9 Spearman rank correlation coefficients (top) and p values (bottom) betw een Chlorophyll a TSP and TSN at different sites across Apalachicola Bay.. ........... 39 2 10 Summary statistics during high discharge for variables measured monthly at eight selected sites from March 2 007 September 2012. ................................ ..... 40 2 11 Summary statistics during low discharge for variables measured monthly at eight selected sites from March 2007 September 2012. ................................ ..... 41 3 1 D uncan tests for total phosphorus (TP) in Apalachicola Bay during low and high river discharge ................................ ................................ ................................ 83 3 2 Duncan tests for total nitrogen (TN) in Apalachicola B ay during low and high river discharge ................................ ................................ ................................ ........ 83 3 3 Duncan tests for silica (Si) in Apalachicola Bay duri ng low and high river discharge ................................ ................................ ................................ ................ 84 3 4 Duncan tests for salinity during low and high discharge. Concentrations expressed as psu. Letters indicate groups based on mean values. .................... 84

PAGE 8

8 3 5 Summary statistics for physical variabl es in Apalachicola Bay during high and low river discharge. LD= low discharge (left), HD= high discharge (right) .......... 85 3 6 Percent of limitation by different treatments in the six bioassay exper iments conducted at six selected sites ................................ ................................ .............. 85 3 7 Duncan tests for chlorophyll a in Apalachicola Bay during low and high river discharge. ................................ ................................ ................................ ............... 86 3 8 Duncan tests for phytoplankton biovolume in Apalachicola Bay during low and high river discharge ................................ ................................ ......................... 86 3 9 Summary statistics for variables measured monthly at the twelve sampling si tes in Apalachicola Bay during high and low river discharge ............................. 87 3 10 Major phytoplankton blooms at the twelve sampling sites in Apalachicola Bay form June 2008 to June 2010. ................................ ................................ ............... 90 3 11 List of Species observed in the Apalachicola Estuary, Florida, USA from June 2008 to 2010. ................................ ................................ ................................ .......... 91

PAGE 9

9 LIST OF FIGURES Figure page 2 1 Map showing the Apalachicola Bay estuary and the location of the sites of study. ................................ ................................ ................................ ...................... 42 2 2 Average monthly river discharge for the Apalachicola River from January 2000 to December 2012 at the Sumatra gauge ................................ ................... 43 2 3 Time series plots of salinity (gray) vs river discharge (black line) at six selected sites across Apalachicola Bay. ................................ ............................... 44 2 4 Seasonal distribution of salinity (bars) vs river discharge (black line) at six selected sites across Apalachicola Bay ................................ ................................ 45 2 5 Time series plots sh owing temperature at three selected sites in Apalachicola Bay. ................................ ................................ ................................ ......................... 46 2 6 Time series plots of TSP (gray) vs river discharge (black line) at eight selected sites across Apalachicola Bay. ................................ ............................... 47 2 7 Seasonal distribution of TSP (bars) vs river discharge (black line) at eight selected sites across Apalac hicola Bay from March 2007 to September 2012. .. 48 2 8 Time series plots of TSN (gray) vs river discharge (black line) at eight selected sites across Apalachicola Bay. ................................ ............................... 49 2 9 Seasonal distribution of TSN (bars) vs river discharge (black line) at eight selected sites across Apalachicola Bay from March 2007 to September 2012. .. 50 2 10 Relationship between salinity and phytoplankton biomass (CHL a [ g L 1 ]) at six selected sites across Apalachicola Bay. ................................ .......................... 51 2 11 Time series plots of chlorophyll a (gray) vs discharge (black line) at six selected sites across Apalachicola Bay. ................................ ............................... 52 2 12 Relationship between chlorophyll a and discharge at six different sites in Apalachicola Bay from April 2002 to September 2012. ................................ ........ 53 2 1 3 Seasonal distribution of chlorophyll a (bars) vs discharge (black line) at eight selected sites across Apalachicola Bay from March 2007 to September 2012 ... 54 2 14 Chlorophyll trends under hig h and low discharge at four different sites in Apalachicola Bay from April 2002 to September 2012 ................................ ......... 55 2 15 Chlorophyll trends under high and low discharge at four different sites in Apalachicol a Bay from April 2002 to September 2012 ................................ ......... 56

PAGE 10

10 3 1 Average monthly river discharge for the Apalachicola River from June 2008 to June 2010. Line indicates the calculated grand mean (532 m 3 s 1 ). ................ 97 3 2 Temperature at three selected sites (231, 161 and 201) from June 2008 to June 2010. ................................ ................................ ................................ .............. 97 3 3 Cluster analysis grouping of the sampling sites during low discharge based on physical, chemical, and biological characteristics. ................................ ........... 98 3 4 Cluster analysis grouping of the sampling sites during high discharge based on physical chemical, and biological characteristics. ................................ ........... 9 9 3 5 Monthly concentrations of total nitrogen (TN, light gray) and dissolved inorganic nitrogen (DIN, dark gray), at six representative sampling s ites ......... 100 3 6 Temporal variation in monthly concentrations of total phosphorus (TP, light gray) and soluble reactive phosphorus (SRP, dark gray) ................................ ... 101 3 7 Mean total phosphorus (TP), total nitrogen (TN) and Silica (Si) from June 2008 to June 2010 for eight selected sites in Apalachicola Bay ........................ 102 3 8 Mean chlorophyll a (Ch l a ), phytoplankton biovolume (BV) and carbon (C) from June 2008 to June 2010 for eight selected sites in Apalachicola Bay ....... 103 3 9 Time series plots of chlorophyll a (gray) vs discharge (black line) at six selected sites in Apalachicola Bay, from June 2008 to June 2010. ................... 104 3 10 Phytoplankton biovolume (10 6 m 3 ml 1 ) subdivided into major groups at the river, north estuary (site 17 1), East Bay (site 191), and Mid Bay (site 161) ...... 105 3 11 Phytoplankton biovolume (10 6 m 3 ml 1 ) subdivided into major groups at the west (sites 141 and 143) and east (sites 221 and 223) ................................ ..... 106 3 12 Phytoplankton biovolume (10 6 m 3 ml 1 ) subdivided into major groups at the outer estuary (sites 131, 151 and 211) and the gulf region (site 201) .............. 107 3 13 Canonical correlation analysis plots of the major phytoplankton groups at four selected sites in Apalachicola Bay ................................ ................................ ...... 108 3 14 Distribution of total phytoplankton in the Apalachicola estuary with relationship to total phosphorus (TP) and total nitrogen (TN). ........................... 110 3 15 Distribution of total phytoplankton in the Apalachicola estuary with relationship to sali nity and temperature. ................................ .............................. 111 3 16 Distribution of small phytoplankton (<20 m), large phytoplankton (>20 m) and chain forming centric diatoms across salinity gradients .............................. 112

PAGE 11

11 3 17 Distribution of common bloom forming species in relationship to salinity in the Apalachicola estuary ................................ ................................ ............................ 113 3 18 Distribution of common bloom formin g species in relationship to temperature ( C) in the Apalachicola estuary ................................ ................................ .......... 114 3 19 Distribution of phycocyanin rich and phycoerythrin rich cyanobacteria in the Apalachicola estuary with relati onship to salinity ................................ ................ 115

PAGE 12

12 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy PHYTOPLANKTON BIOMASS AND COMPOSITION IN APALACHICOLA BAY, A SUBTROPICAL RIVER DOMINATED ESTUARY IN FLORIDA By Paula A. Viveros Bedoya May 2014 Chair: Edward Phlips Major: Fisheries and Aquatic Sciences The integrity of estuaries throughout the world is being impac ted by human driven changes in the ecosystems including their watersheds. The Apalachicola River estuary is an example of a major ecosystem in jeopardy of significant change as a consequence of reduced river discharge, which is a key regulator of physical chemical processes such as salinity, nutrient concentrations and water residence time. The overall goal of this study was to describe how changes in river discharge influence phytoplankton community structure, biomass and dynamics. Phytoplankton composit ion and physical chemical variables were determined on a monthly basis for two years (June 2008 June 2010) at 1 2 sampling sites within the bay. Seasonality of phytoplankton biomass was determined using a longer pre existing data set (2002 2012). M ean salin ities in the Apalachicola Bay varied significantly between the low and high discharge periods which cause d salinity to double at some of the sites Mean total soluble phosphorus (TSP) concentrations also var ied seasonally and spatially due to the influen ce of bo th the Apalachicola River and the Gulf of Mexico in providing phosphorus for the estuary In terms of nitrogen The Apalachicola River was a major source for the estuary independent of the season. Nutrient limitation bioassays indicated that phospho rus was

PAGE 13

13 the primary limiting nutrient for the bay. Mean chlorophyll a concentrations and mean phytoplankton biovolumes were higher in the low discharge season than in the high discharge season at most sampling sites. The phytoplankton community exhibited s easonal changes, with diatoms being the dominant group throughout most of the year, but with some biovolume peaks caused by dinoflagellates. Cyanobacteria were more abundant during periods of low discharge and warmer temperatures. Results indicated that s e asonal patterns in river discharge affect salinity and nutrient concentrations and were correlated to phytoplankton abundance biovolume, and composition.

PAGE 14

14 CHAPTER 1 INTRODUCTION Estuaries are biotically rich and highly productive ecosystems along eart coastal zone s where there is interaction between the ocean, the land and the atmosphere (Odum, 1971 ; Day et al. 1989). Estuaries provide more ecosystem services per unit surface area than any other biome on the planet (Costanza et al., 1997) T he integrity of estuaries throughout the world is however, being compromised by human driven changes in the ecosystems including their watersheds. Most estuaries in the US and worldwide currently face challenges assoc iated with increased human development. Nutrient enrichment from agricultur al, urban and industrial development can lead to increased harmful algal blooms (HABs). Additionally, changes in temperature, precipitation and hydrology can impact estuarine system s and affect their biota. One major class of estuaries is those influenced by inputs of large rivers. This study focused on one such ecosystem, Apalachicola Bay, located in the subtropical Gulf of Mexico. Estuaries are subject to a high degree of environm ental variability including daily, seasonal and inter annual changes in temperature, light, hydrology, and chemistry (Livingston 1983). Some examples of the physical/chemical factors that regulat e estuaries are river discharge, nutrient inputs (mainly ni trogen, phosphorus, and silica), light availability, temperature, turbidity and seasonality (Eyre et al. 1999). The biotic composition of estuaries is strongly influenced by these regulating factors. Historically the re have been many ecological studies in temperate estuaries , whereas subtropical and tropical estuaries have received less attention. Unlike temperate estuaries, tropical and subtropical estuaries are subject to less pronounced

PAGE 15

15 seasonality, highly variable rainfall patterns, larger inter an nual variation in nutrient inputs, higher annual total light availability and higher average temperature (Eyre et al. 1999). Consequently, the principles governing ecological relationships in temperate estuaries are not necessarily the same as those in su btropical and tropical estuaries, and the biotic communities found in temperate estuaries differ from those observed in tropical and subtropical ones. Subtropical estuaries, such as Apalachicola Bay are important both ecologically and economically They serve as a spawning ground and nursery for aquatic wildlife and support shellfish and fin fish industries in many regions worldwide. The study of ecological interactions between phytoplankton, water quality variables and environmental factors in subtropical estuaries is particularly relevant today There is a need to improve the level of knowledge on how the food web, and in particular, primary producers are affected by physical chemical changes occurring in these estuaries and their watersheds. Phytoplankt on are the major primary producers in most estuarine systems throughout the world (Day et al. 1989). The relative influence of environmental factors on estuarine phytoplankton production varies from one estuary to another. It is therefore important to unde rstand the factors that regulate phytoplankton production and biomass in estuaries (Mortazavi et al. 2000a). The Apalachicola Bay is noteworthy because of the strong influence of the Apalachicola River on the ecology of the B ay (Livingston, 1983 ; Mortazavi et al., 2000 ; Mortazavi et al., 2000 ; Edmiston et al., 2008 ; Edmiston, 2008 ; Putland et al., 201 3) It is the major source of freshwater for the bay, which is dependent on these hydrologic

PAGE 16

16 inputs to sustain the integrity of the ecosystem, including a large and economically important oyster industry (Wilber, 1992 ; Edmiston, 2008 ; Wang et al., 2008) The inflow of t he Apalachicola River has been reduced in recent years, as a consequence of both drought conditions and increased upstream anthropogenic water withdrawal (L ivingston 2001). Consequently, the integrity of the estuary is currently endangered, including the structure and function of the main primary producer community in the bay, phytoplankton. The rapid increase in water withdrawals from the river to supply i ncreasing human development in the watershed has raised serious concerns about the potential impacts of changes in flow on phytoplankton and the overall ecology of the bay (Mortazavi et al., 2000 ; Huang and Spaulding, 2002 ; Livingston, 2007 ; Putland and Iverson, 2007 ; Edmiston, 2008 ; Wang et al., 2008 ; Huang, 20 10 ; Putland et al., 2013) Among the major concerns is the relation between river discharge and the phytoplankton community, which represent s a large fraction food web. The specific impacts of water withdrawal are not fully unders tood. Nevertheless, it can be hypothesized that alteration of salinity regimes and nutrient loads will change including the phytoplankton community Some studies have already show n that continuing reductions in flow from the Apalachicola River will significantly reduce productivity in the B ay thereby negatively affecting critical fish and oyster populations (Livingston, 1997; Putland 2007a; Wilber 1992). The overall goal of this study was to describe how spatial and temporal patterns in the structure and abundance of estuarine phytoplankton are related to changes in river discharge and

PAGE 17

17 related shifts in key physical and chemical variables such as salinity, nutrient concentrations and water residence times

PAGE 18

18 CHAPTER 2 SPA TIAL AND TEMPORAL DYNAMICS OF PHYTOPLANKTON BIOMASS AND RIVER DISCHARGE IN THE APALACHICOLA ESTUARY, FLORIDA, USA Phytoplankton composition and biomass in estuaries is affected by numerous physical, chemical and biological factors. S ite specific mechanist ic understanding of phytoplankton dynamics is required to address the driving factors for shifts in composition and biomass (Cloern, 2001, 2010) Historically temperate estuaries ha ve been the focus of more studies than subtropical and tropical estuaries Compared to temperate ecosystems tropical and subtropical environments are typically subject to less pronounced seasonal variab ility in temperature and solar light flux, but can exhibit wide swings in rainfall associated with tropical storms, which in t urn impact nutrient loading (Eyre et al. 1999). Consequently, the ecological principles ruling phytoplankton dynamics in temperate estuaries are not necessarily the same for subtropical and tropical estuaries Phytoplankton c ommunities found in tropical and subtropical estuaries can also differ substantially from those in temperate systems (Reynolds 2006) The purpose of this study was to examine phytoplankton dynamics in Apalachicola Bay, a sub tropical river dominated estuary that is experiencing major anthropogenica lly driven changes in hydrology The overall objective was to examine the relationship between trends in river discharge and phytoplankton biomass. T he specific objectives were to identify phytoplankton biomass trends during high and low disc harge regimes over a ten year period i.e. 2002 2012 and to describe the relationship between river discharge, nutrient concentrations and chlorophyll a a proxy for phytoplankton biomass Th e objectives were pursued within the context of the following c ontrasting hypotheses:

PAGE 19

19 1. Periods of below average river discharge result in higher phytoplankton biomass levels because of the combination of longer water residence time higher and more stable salinit y and warm er temperature s 2. Periods of above average r iver discharge result in lower phytoplankton biomass l evels because the combination of shorter water residence time large swings in salinity and cooler temperature s Methods Site Description This study was carried out in the Apalachicola Bay National Es tuarine Research Reserve (ANERR) located in the Florida panhandle on the north coast of the Gulf of Mexico (Figure 2 1 ). Due to its latitude Apalachicola Bay is considered a subtropical estuary (between 23 and 30 north) and is strongly influenced by the current s of the Gulf of Mexico, which r eplenish the system with warm waters from the Caribbean Sea. The Apalachicola River is the main source of fresh water for the Apalachicola estuary, and consists of a tri river drainage system, including approxima tely 19,200 square miles (~49,730 km 2 ) in Georgia, Alabama, and Florida. The confluence of the Chatahoochee and Flint rivers forms the headwaters of the Apalachicola system, which drains about 1,030 square miles (~2670 km 2 ) (Livingston 1983). ANERR is par t of a coordinated national monitoring program called the System Wide Monitoring Program (SWMP) that was established in 1995 with the goal of identifying and tracking short term variability and long term changes in representative estuarine ecosystems and c oastal watersheds. The SWMP was designed to be a phased monitoring approach that focused on three different ecosystem characteristics, abiotic factors, biological monitoring, and watershed and land use classifications (Edmiston et al., 2008) T he main goal of implementing the SWMP for the ANERR was

PAGE 20

20 to examine the relationship among short term variability, long term change, and other environmental factors on the productivity of the Apalachicola Bay system. As part of the SWMP monthly grab samples a re collected at 11 sites located across Apalachicola Bay to monitor spatial and te mporal fluctuations in nutrients and chlorophyll a concentrations in diverse areas of the bay. The stations were chosen to help determine the impact on these water variables Sampling sites are located in the lower Apalachicola River, in the coastal area, offshore of the barrier islands, at the SWMP datalogger locations, and thr oughout the bay. Field Procedures Monthly grab samples we re collected at the eleven stations (Table 2 1 ) within and adjacent to Apalachicola Bay. In most cases all grab samples were collected on the same day because of bad weat her Water temperature, salinity, and dissolved oxygen were measured at surface and bottom depths for each station with a YSI 85 handheld meter. Only surface measurements for temperature and salinity were considered in this study A horizontal Van Dorn st yle sampler was used to collect 2.2 liters of water from a depth of 0.5 meters at all stations not associated with a SWMP datalogger site. At the Cat Point and Dry Bar SWMP datalogger stations, water samples were collected at depth s of approximately 2 and 1.5 meters ( 0.5 m from the bottom) respectively, depth s equivalent to the probes of the dataloggers deployed at these sites. At the East Bay datalogger station water samples were collected from surface (0.5 meters) and bottom (1.5 meters) depths, equiva lent to the depths of the two dat aloggers deployed at this site. Triplicate samples were collected each month at one station, rotating through all

PAGE 21

21 station locations. Replicate samples were collected with separate dips of the horizontal sampler. Water from the Van Dorn sampler was delivered into a polyethylene graduated cylinder. The water sample was then filtered through glass f iber filters (0.7 size) f or soluble inorganic nutrients and chlorophyll a (CHL) determination. The glass fiber filter for chlorophyll a analysis and the water s amples were transported on ice to the University of Florida laboratory in Gainesville for subsequent proce ssing. Water Chemistry Nitrite (NO 2 ) concentrations were determined by mixing the sample with color reagent (phosphoric acid, sulfanilalimide, and N 1 naphthylethylene diamine dihidrochloride) to form a purple azodye (APHA, 1998). Colorimetric quantificati on was completed on a Bran + Luebbe Autoanalyzer 3 system. C oncentrations of nitrate (NO 3 ) and ammonium (NH 4 ) were first reduced to NO 2 and then measured as described above. NO 3 was reduced to NO 2 through a copperized cadmium redactor (APHA, 1998). NH 4 was oxidized to NO 2 with hypochlorite in an alkaline medium using potassium bromide as a catalyst (Strickland and Parsons, 1972). Dissolved inorganic nitrogen (DIN) was calculated by summing NH 4 + NO 3 + NO 2 Soluble reactive phosphorus (SRP) concentrations we re determined by mixing the sample with color reagent (sulfuric acid, ammonium molybdate, ascorbic acid, and antimony potassium tartrate) to form a blue dye (APHA, 1998). Colorimetric quantification was completed on a Hitachi U 2810 (Tokyo, Japan) dual bea m scanning spectrophotometer. CHL was processed using the Sartory and Grobbelaar (1984) hot ethanol extraction method and concentrations (not corrected for pheophytin) were determined spectrophotometrically according to Standard Methods (APHA, 1998). All p rocessing and analytical methods

PAGE 22

22 Accre ditation Program certification Statistical Analyses The SAS Enterprise Guide statis tical package for PCs (Version 4 .3) was used to carr y out statistical analyses. Distributions of most variables were non normal (determined by the Shapiro Wilk and Kolmogorov Smirnov goodness of fit tests), n ecessitating the use of non parametric Spearman rank correlation analysis to explore relationships b means of the different variables among sites. T tests were used to evaluate the significance of the seasonal differences between means in low and high discharge for the physical chemical v ariables Results Physical Chemical Variables River d ischarge A twelve year ( January 200 0 December 2012 ) monthly average river discharge for the Apalachicola River at the Sumatra gauge (about 30 km above the river mouth) was calculated with data from t he USGS National Water Information System ( http://waterdata.usgs.gov ) D uring th at time span discharge maxima occurred during late winter and early spring, wh ereas summer months were characterized by discharge min ima (Figure 2 2 ). The grand mean for the twelve years of river discharge data was 532 m 3 s 1 The minimum discharge value was 159 m 3 s 1 and the maximum 2358 m 3 s 1

PAGE 23

23 Salini ty p atterns A wide range of salinities was observed across the different sites (Tab le 2 2 ). During low discharge, mean salinities ranged from 0.1 psu at Site 231 in the river to 33.3 psu in the gulf at Site 201. During high discharge, mean salinities ranged from 0.0 psu at Site 231 in the river to 32.3 psu in the gulf at Site 201 (Table 2 2 ). The results from the Spearman rank correlation coefficients showed a significant negative correlation between river discharge and mean salinities at most sites, except Site 231 in the river and Site 201 in the g ulf (Table2 7 ). In general, salinity values exhibited a gradient that increased with distance from the river mouth highlighting the importance of discharge from the Apalachicola River in controlling this variable throughout the bay. The results from the t test show ed a signifi cant difference in the mean salinities between high and low discharge at most sites, except the river and the gulf, Sites 231 and 201 respectively (Table 2 8 ). Salinities at Site 231 in the r iver and Site 201 in the g ulf were steady because of the sampling regime used f or these two sites, which consisted of sampling once a salinity reading of a given value was reached (0.1 ppt or less for the rive r; 32 ppt or more for the gulf). Temperature Spearman rank correlation coefficients demonstrate a strong negative correlation between river discharge and temperature (Table 2 7 ). During low discharge temperature ranged from 24.4 C at Site 141 in Dry Bar to 25.1 C Site 201 in the gulf. During high discharge temperature ranged from 17.2 C at Site 231 in the river to 19.3 C at Site 191 in East Bay. (Table 2 3 ). Time series plots showed that water

PAGE 24

24 temperatures exhibited a seasonal trend, with higher temperatures usually occurring from May to October and lower temperatures occurring in January and February ( Figure 2 5 ). Nutrient p atterns Nutrient concentrations for the study period were analyzed under both high discharge and low discharge periods Mean TSP concentrations were generally higher during periods of low discharge than periods of high discharge (Table 2 4 and Figure s 2 6 and 2 7 ). The t test showed that the difference between mean TSP concentrations measured during high and low discharge was not significant at most sites, except Site 231 in the river (Table2 8 ) During low discharge m ean TSP concentrations ranged from 11 g P L 1 at Site 171 near the East Bay Bridge to 22 g P L 1 at Site 201 in the gulf (Table 2 4 ). During high discharge m ean TSP concentrations ranged from 12 g P L 1 at Site 191 in East Bay to 18 g P L 1 at Site 231 in the river (Table 2 4 ). Time ser ies plots show an inverse relationship between river discharge and TSP concentrations at most sites (Figure 2 6 ), with the highest concentration peaks o ccurring during periods of extended low discharge at most sites, except Site 231 in the river T he Spear man rank correlation coefficients (Table 2 7 ) show ed no significant correlation b etween TSP and river discharge at most sites, except Site 231 in the river and Site 201 in t he g ulf. In the low discharge period TSP concentrations increased with distance fr om the river to the g ulf (Table 2 3), but conversely in the high discharge period TSP concentrations decreased with distance from the river to the gulf Mean TSN concentrations were generally higher during periods of high discharge than periods of low dis charge at most sites, exce pt Site 201 in the gulf, where m ean

PAGE 25

25 TSN concentrations were lower during high discharge (Table 2 5 and Figure s 2 8 and 2 9 ). During both high and low discharge m ean TSN concentrations followed a gradient that decreased with dista nce from the river towards Site 151 in Pilots Cove, near the barrier islands (Table 2 5 ) During low discharge m ean TSN concentrations ranged from 136 g N L 1 at Site 201 in the gulf to 546 g N L 1 at Site 231 in the river (Table 2 5 ). During high disc harge m ean TSN concentrations ranged from 119 g N L 1 at Site 201 in East Bay to 614 g N L 1 at Site 231 in the river (Table 2 5 ). Regardless of the season Site 231 in the river always displayed the highest mean concentrations of TSN and Site 201 in th e gulf the lowest. Time series plots showed a positive relationship between river discharge and TSN concentrations (Figure 2 8 ). The results of the t test for TSN showed a significant difference between mea ns during high and low discharge at most sites, ex cept the river and the gulf, Sites 231 and 201 respectively (Table 2 8 ). Spearman rank correlation coefficients showed a significant correlation between TSN and river discharge at most sites (Table 2 7 ), but again sites 231 in the river and 201 in the gul f were exception s Phytoplankton Biomass Patterns a during both high and low discharge periods (Table 2 6 ). Chlorophyll a concentrations were higher in low discharge than in high discharge at mo st sites, except at gulf, Site 201, where chlorophyll a concentrations were slightly more elevated during high discharge. During low discharge chlorophyll a concentrations ranged from 4.9 g Chl a L 1 at Site 201 in the gulf to 19.1 g Chl a L 1 at site 191 in East Bay. During high discharge chlorophyll

PAGE 26

26 a concentrations ranged from 3.8 g Chl a L 1 at Site 231 in the river to 17.1 g Chl a L 1 at site 191 in East Bay. Although differences in mean chlorophyll a concentrations between high and low disc harge were observed the t test results showed a lack of significance between the differences in means at most sites (Table 2 8 ) The differences in mean chlorophyll a concentrations were only significant at three sites, 231 in the River, and those sites l ocated near the oyster bars, Site 141 in Dry Bar and Site 221 in Cat Point (Table 2 8 ). Chlorophyll a and river discharge were negatively correlated at site 231 in the river, site 171 in East Bay Bridge, and in the oyster bars, site s 141 ( Dry Bar ) and 221 ( Cat Point ) (Table 2 7 ). At the rest of the sites a lack of correlation between chlorophyll a and river discharge was observed ( Table 2 7 ). Time series plots showed that the re is an inverse relationship between river discharge and chlorophyll a (Figure 2 11 ). D uring periods of prolonged high discharge, such as spring 2005 and 2010, chlorophyll a concentrations through out the bay fell below 5 g Chl a L 1 at most sites (Figure 2 12 ). Conversely, during periods of extended low discharge, like summer/fall 20 10 and 2011, chlorophyll a levels tended to peak at the different sites, particularly at S ite 191 in East Bay, located i n the northeast portion of the bay. In general Site 191 stood out because it exhibited the highest mean phytoplankton biomass during bo th periods, with concentrations of 17.1 g Chl a L 1 in high discharge and 19.1 in low discharge. A closer look at the relationship between discharge and chlorophyll a indicated that m ost sites exhibited chlorophyll optima at discharges < 1000 m 3 s 1 but there were

PAGE 27

27 regional differences in the way discharge affects chlorophyll patterns at the different locations (Figure 2 12 ). The relationship between salinity and phytoplankton biomass varied at the different locations in the estuary (Figure 2 10 ). Site 1 71 near the East Bay Bridge displayed maximum chlorophyll a concentrations between 10 and 20 psu. Site 191 in East Bay displayed maximum chlorophyll a concentrations between 3 and 20 psu. In the middle of the bay, Dry Bar ( S ite 141) and Cat Point ( Site 221 ) which are located close to the main oyster bars, and site 161 in the center of the bay, displayed maximum chlorophyll a concentrations between 10 and 30 psu. At site 151 Pilots Cove, located near the barrier islands the optimum salinity range for maxim um chlorophyll a concentrations varied from about 15 to 35 psu. Changes in Phytoplankton Biomass There are empirical indications that change s may have occurred in the chlorophyll a concentration s in Apalachicola Bay in the last ten years (Figures 2 14 and 2 15 ). Chlorophyll levels show ed a long term increase at all sites in the bay under both high and low discharge regimes (Figures 2 8 and 2 9 ). Although the s e relationships were not statistically significant (R 2 < 0.25), there we re a few sites such as 191 i n East Bay, 141 in Dry Bar, and 221 in Pilots Cove, where the steepness of the slopes indicate d increases in chlorophyll a concentrations, especially after 2005. These increases in phytoplankton biomass were more pronounced during low discharge than during high discharge

PAGE 28

28 Discussion River dominated estuaries frequently exhibit significant variation in environmental conditions which affect phytoplankton composition and biomass (Smayda, 1978 ; Malone et al., 1988 ; Eyre and Balls, 1999 ; Mortazavi et al., 2000 ; Murrell et al., 2007 ; Quinlan and Phlips, 2007 ; Paerl et al., 2010) The variab ility can take the form of spatial gradients in key variables such as salinity and nutrient concentrations, sometimes referred to a s ecoclines (Attrill and Rundle, 2002 ; Murrell et al., 2007 ; Quinlan and Phlips, 2007) An ecocline represents a grad ient of change in key variables (both spatial and ecological) between two systems (e.g. river to ocean) ; it is a response to gradual difference s in at least one major environmen tal factor Additional factor s can influence the gradient and the character of transitional states ( Attrill and Rundle, 2002 ). Ecoclines are important features of Apalachicola Bay and t he specific character and dynamics of these ecoclines are strongly i nfluenced by river discharge. The central goal of this study was to determine whether the abundance of phytoplankton in the estuary is linked to discharge from the Apalachicola River. C ertain regions of the Apalachicola Bay estuary manifest links between r iver discharge, ecoclines in key environmental variables and phytoplankton biomass, wh ereas other regions exhibit different or lesser relationships likely because of mitigating factors such as water residence time temperature, or grazing pressure. I ex amine d the major ecolines with in the bay with respect to salinity, nutrient level, water residence times) and explored their potential links to variability in phytoplankton biomass. I found that river discharge exerts some control over phytoplankton bioma ss (Table 2 6 and Figures 2 11, 2 12 and 2 13) however the effects should be considered within the context of related factors that regulate losses

PAGE 29

29 and gains in algal biomass such as salinity, nutrient concentrations, temperature, zooplankton grazing wat er residence time and tidal water exchange with the Gulf of Mexico. Salinity and Nutrient Ecoclines The most obvious ecocline directly associated with river discharge in Apalachicola Bay is salinity (Livingston 1984). Salinity values increase with distan ce from the river mouth, and from west to east, reflecting the predominant flow of gulf water from the eastern inlet of the bay toward the western outlet (Edmiston, 2008) The relative influences of the river and gulf on salinity in the bay depend on the amount of discharge This is illustrated by differences in mean salinity at Site 141 in the middle of the bay during high and low discharge periods. During high discharge, the mean salinity was 12.8 psu whereas during low discharge it was 24.5 psu, reflecting the importance of higher salinity water coming from the Gulf of Mexico during the latter period. A previous study of Apalachicola Bay reported that the concentration of chlorophyll a peaked in waters with saliniti es between 5 and 25 psu (Putland et al., 2013) however my results indicate that the optimal salinity ranges vary by region in the bay (Figure 2 10) At bay sites close to river inflow (i.e. Sites 171 and 191) salinit ies commonly fall below 5 psu. Peaks in phytoplankton biomass associated with prolonged periods of low salinity, which are common in this region, are dominated by freshwater species of algae ( Chapter 3 ). Conversely, peaks in phytoplankton biomass associa ted with prolonged periods of mesohaline (i.e. 5 20 psu) conditions in the same region are dominated by marine phytoplankton taxa ( Chapter 3 ).

PAGE 30

30 In the mid bay, the highest phytoplankton biomass peaks are associated with mesohaline/polyhaline conditions (i.e 10 30 psu) which are most commonly related to periods of low moderate river discharge conditions (Figure 2 10) during which phytoplankton communities are dominated by marine taxa ( Chapter 3 ). Salinities below 10 psu in the mid bay are generally associa ted with relatively low phytoplankton biomass (Figure 2 10) reflecting the effect of reduced water residence times and increased osmotic stress experienced during periods when large freshwater inflows from the river result in low and variable salinities. The latter condition is a feature of some river dominated estuaries in which there is a region of the ecocline at which salinities are frequently high enough to cause mortality of freshwater species, but to o low and variable to support high biomass of mari ne species (Eyre and Balls, 1999 ; Murrell et al., 2007) To evaluat e the role of salinity in defining phytoplankton biomass potential it is worthwhile to keep in mind that salinity is impor tant, but may be associated with a broad range of other variables such as nutrient availability, water residence time, light transmission through the water column and grazing activity which in Apalachicola Bay includes both benthic and planktonic grazing Nutrient concentration gradients are important ecocline s in Apalachicola Bay. Previous studies highlighted the importance of the Apalachicola River in adding nutrients to the estuary which enhance s phytoplankton production (Livingston, 1983 ; Mortazavi et al., 2000 ; Mortazavi et al., 2001 ; Edmiston, 2008) In many river dominated estuaries peak phytoplankton biomass is found between t he light limited

PAGE 31

31 oligohaline (i.e. 0.5 5 psu) upper estuary and nutrient limited mixoeuhaline (i.e. >30 psu) marine dominated region The spatial distribution of phytoplankton maxima in Apalachicola Bay deviates somewhat from this pattern, in part becaus e of barrier islands that affect tidal water exchange and in part because of the unique character of the Apalachicola River discharge. The impacts of discharge on nutrient concentrations in the bay vary by region and nutrient type. The positive correlatio n between river discharge and total soluble nitrogen concentration in the river is matched by positive correlations between river discharge and total soluble nitrogen ( DI N) at all sites in the bay (Tables 2 5 and 2 7 and Figures 2 8 and 2 9) By contrast, the positive relationship between discharge and total soluble phosphorus concentrations in the river is not seen in the bay (Figures 2 6 and 2 7 ) where the correlation is negative (Tables 2 4 and 2 7). These contrasting relationships with respect to river discharge and nutrients ( DI N and TS P) indicate that the river is a source of nitrogen enrichment for the bay, but the situation for phosphorus is more complicated, possibly because of nutrient contributions from the Gulf of Mexico and advective and diffus ive fluxes of nutrients from bottom sediments in the bay In terms of sources of phosphorus to support phytoplankton production in Apalachicola Bay, it is noteworthy that mean TSP concentrations in the Apalachicola River are highest during high discharge periods, wh ereas mean concentrations in the Gulf of Mexico are comparatively low. Conversely, during the summer when mean river discharge is low, mean TSP levels are also low in the ri ver, but concentrations in the g ulf are high relative to the river an d bay. The latter relationships suggest that the g ulf may be a source of phosphorus for phytoplankton production in the summer.

PAGE 32

32 Phosphorus budgets for Apalachicola Bay (Mortazavil et al., 2000) estimated that 78 % of annual total phosphorus input to the bay comes from the Apalachicola River and 22% from the Gulf of Mexico, of which 41% is in soluble form. The TSP gradients observed in the current study (Table 2 4, Figures 2 6 and 2 7) suggest that the influence of the Gulf of Mexico on phosphorus supply to the bay is strongest during summer. The importance of the latter observation is highlighted by the results of nutrient limitation bioassays which show a predominance of phosphorus limitation ( C hapter 3 ). A lon g standing paradigm in aquatic science is that primary production in freshwater systems is often limited by phosphorus availability whereas the primary limiting nutrient in most marine systems is nitrogen (Boar d, 2000) There are of course many exceptions to this general rule ( Howarth 1988 ; Myers and Iverson 1982 ), and Apalachicola Bay is a case in point (Mortazavi et al. 2000 ; Myers and Iverson 1982 ). R esults of bioassays in the bay indicate that phospho rus is more often the primary limiting nutrient for phytoplankton production (Viveros et al. 2014), in part a result of the relatively low phosphorus levels in the Apalachicola River, as indicated by the high DIN/SRP ratios (i.e. >80) (Putland et al. 201 3). The high nitrogen to phosphorus ratios may reflect the relatively small amount of human disturbance in the watershed in terms of nutrient enrichment (Howarth, 1988 ; Board, 2000) T emporal Variability in Physical and Biological Factors The effects of temporal shifts in salinity and nutrient ecoclines in Apalachicola Bay on phytoplankton biomass must be viewed within the context of variation in key physical and biological factors, suc h as temperature, light flux, water residence times and grazing rates. These factors play a major role in defining the relationships between nutrient load and phytoplankton biomass (Reynolds, 2006) Elevated nitrogen and

PAGE 33

33 phosphorus loads to the bay from the river particularly during the winter and early spring enhance the potential for increased biomass, but low temperatures, reduced water residence times and high salinity variability have a negative effect on the attainment of that potential (Mortazavi et al., 2000) Similarly, spring peaks in benthic grazer activity can exacerbate the loss of biomass. Water temperatures in Apalachicola Bay are highly correlated with air temperature because the bay is shall ow and the water column is frequently wind mix ed Only incipient t hermal stratification has been detected because of frequent mixing in the bay (Livingston, 1983) Temperature ranges from 5 to 33 C within a ye ar with peak temperatures generally occurring in July and August and lowest temperatures occurring from December through February (Livingston, 1984) During the period this study was conducted mean temperature in the estuary was 18 C during high discharge and 24.6 C during low discharge. Spearman rank correlation coefficients demonstrate a strong negative correlation between river discharge and temperature (Table 2 7 ). This relationship could be seen as an a utocorrelation given that the high discharge period occurs in the winter and spring months Therefore, the combination of lower temperature and high discharge may act to control phytoplankton biomass during the high discharge season. Conversely, the combi nation of higher temperature and low discharge could facilitate phytoplankton growth during the summer and fall T his study demonstrate d that river discharge plays a major role in controlling phytoplankton biomass. Previous studies found that export from Apalachicola Bay provided a significant control on phytoplankton biomass during winter months, but on an annual basis grazing by zooplankton and oysters accounted for 80% of the chlorophyll

PAGE 34

34 a loss from the estuary (Mortazavi et al., 2000) T he present study d id not evaluate the role of grazers in controlling phytoplankton biomass and the limited temporal scope of previous studies made it difficult to assess quantitatively the impact of zooplankton grazing Altho ugh large oyster populations in the bay undoubtedly have an impact on phytoplankton biomass, little research has been done to quantify that impact. Apalachicola Bay exhibits higher chlorophyll a concentrations during late spring and summer months when ri ver discharge is low and water residence time is high. Previous studies have found similar patterns in other subtropical estuaries. In Escambia Bay, near Pensacola, Florida, chlorophyll a concentrations generally were also higher during the summer and lowe r during the winter and spring and freshwater flow appear s to be an important driver of phytoplankton dynamics (Murrell et al., 2007) In the Matanzas River Estuary (MRE) near St. Augustine, Florida, phytoplank ton biomass in the winter was relatively low mainly because of the combination of low temperature and light availability consistent tidal water exchange and bivalve grazing throughout the year. Relatively low levels of phytoplankton standing stock and sma ll inter annual variability within the MRE reflect a balance between gain and loss processes (Dix et al., 2013) Similar studies in Australian tropical estuaries found suppressed phytoplankton biomass as a consequence of increased turbidity from freshwater floods (Eyre and Balls, 1999) Results from this study support the hypothesis that p eriods of below average river discharge are associated with higher phytoplankton biomass leve ls It is possible to hypothesize that this may be a result of longer water residence time, higher and more stable salinity and warmer temperatures Ecoclines were important features of

PAGE 35

35 Apalachicola Bay, and the specific character and dynamics of these eco clines is influenced by changes in river discharge. Discharge from the Apalachicola River has an effect on salinity and TSN concentrations.

PAGE 36

36 Table 2 1. Summary characteristics of sampling sites for n utrient and chlorophyll a in the Apalachicola NERR SWMP Site number Site name Water depth average (m) Bottom habitat 141 Dry Bar 1.7 Oyster bar 151 Pilot's Cove 1.8 Patchy seagrass 161 Mid Bay 2.2 Sandy silt 171 East Bay Bridge 1.6 Silty clay 181 East Bay Surface 1.7 Clayey sand 201 Sikes Cut Offshore 5 Sand 221 Cat Point 1.8 Oyster bar 231 River 3.5 Sandy silt Table 2 2 discharge from March 2007 to September 2012. Concentrations expressed as psu. Letters indicate groups based o n mean values. Low discharge salinity High discharge salinity Duncan Grouping Mean SITE Duncan Grouping Mean SITE A 33.4 201 A 32.3 201 B 29.2 151 B 17.5 151 C 24.8 221 C 12.8 141 C 24.5 141 C 12.6 221 C 24.2 161 C 10.3 161 D 12.7 171 D 3.5 191 D 11.8 191 D 3.2 171 E 0.1 231 D 0.1 231 Table 2 3 discharge from March 2007 to September 2012. Concentrations expressed as C Letters indicate groups based on mean values. Low discharge temperature High discharge temperature Duncan Grouping Mean SITE Duncan Grouping Mean SITE A 25.1 201 A 19.3 191 A 24.9 231 A 18.4 201 A 24.9 171 A 18.4 171 A 24.7 151 A 17.9 161 A 24.6 191 A 17.8 151 A 24.6 2 21 A 17.8 221 A 24.5 161 A 17.6 141 A 24.4 141 A 17.2 231

PAGE 37

37 Table 2 4 discharge and low discharge from March 2007 to September 2012. Concentrations expressed as g P L 1 Letters indicate groups based on mean values. Low discharge TSP High discharge TSP Duncan Grouping Mean SITE Duncan Grouping Mean SITE A 22 201 A 18 231 B A 17 151 B A 14 171 B A C 16 221 B A 1 4 221 B A C 16 141 B A 13 161 B C 14 161 B A 13 201 B C 13 231 B 12 141 B C 1 3 191 B 1 2 151 C 11 171 B 1 2 191 Table 2 5 discharge and low discharge from March 2007 to September 2012. Concentrations expresse d as g N L 1 Letters indicate groups based on mean values. Low discharge TSN High discharge TSN Duncan Grouping Mean SITE Duncan Grouping Mean SITE A 547 231 A 61 4 231 B 35 6 171 B A 549 171 B 31 4 191 B C 506 191 C 2 60 221 D C 42 6 161 C 233 1 61 D 36 1 221 C 22 8 141 D E 340 141 D 168 151 E 25 5 151 D 13 6 201 F 11 9 201

PAGE 38

38 Table 2 6 a during high discharge and low discharge from March 2007 to September 2012. Concentrations expressed as g L 1 Letters indicate groups based on mean values. Low discharge chlorophyll High discharge chlorophyll Duncan Grouping Mean SITE Duncan Grouping Mean SITE A 19.1 191 A 17.1 191 B 10.7 141 B 8.4 161 C B 9.4 221 B 7.7 171 C B 9.1 171 C B 7 .0 141 C B 9 .0 161 C B 6.6 221 C D 6.9 151 C B 6.6 151 D 5.3 231 C B 5.1 201 D 4.9 201 C 3.8 231 Table 2 7 Spearman rank correlation coefficients (top) and p values (bottom) for selected variables at different sites across Apalachicola Bay. Data from March 2007 to December 2012. Discharge m 3 s 1 141 151 161 171 191 201 221 231 TSP 0.24 0.09 0.10 0.05 0.20 0.05 0.04 0.46 0.05 0.52 0.41 0.68 0.10 0.70 0.76 <.0001 TSN 0.48 0.26 0.58 0.66 0.47 0.12 0.24 0.33 <.0001 0.05 <.00 01 <.0001 <.0001 0.40 0.05 0.01 Chlorophyll a 0.30 0.01 0.16 0.32 0.12 0.04 0.27 0.39 0.01 0.96 0.20 0.01 0.34 0.79 0.03 0.00 Temperature 0.49 0.50 0.48 0.45 0.39 0.53 0.47 0.56 <.0001 0.00 <.0001 0.00 0.00 <.0001 <.0001 <.0001 Salinit y 0.67 0.60 0.71 0.78 0.57 0.36 0.67 0.38 <.0001 <.0001 <.0001 <.0001 <.0001 0.01 <.0001 0.00

PAGE 39

39 Table 2 8 Results from t Tests used to compare the significance of mean values for the four variables during high discharge and low discharge from M arch 2007 to September 2012. Site CHLa g L 1 Salinity (psu) TSN g L 1 TSP g L 1 141 Dry Bar 0.0476 0.0001 0.0002 0.1478 151 Pilots Cove 0.6967 0.0001 0.0245 0.1559 161 Mid Bay 0.6083 0.0001 0.0001 0.8091 171 East Bay Bridge 0.2995 0.0001 0.0001 0. 0511 191 East Bay 0.4097 0.0001 0.0003 0.4651 201 Sike's Cut 0.7985 0.041 0.4357 0.0202 221 Cat Point 0.0049 0.0001 0.0133 0.3537 231 River 0.0414 0.0215 0.1356 0.0001 Table 2 9 Spearman rank correlation coefficients (top) and p values (bottom) bet ween Chlorophyll a TSP and TSN at different sites across Apalachicola Bay. Data from March 2007 to December 2012. TSP Site 141 151 161 171 191 201 221 231 Chlorophyll a 0.05465 0.0524 0.03093 0.1876 0.0009 0.19495 0.027 0.3119 0.6605 0.7016 0.8 052 0.1376 0.9942 0.1538 0.8286 0.0102 TSN _______________________________________________________________________ Chlorophyll a 0.4142 0.1777 0.3511 0.3457 0.1347 0.0827 0.1706 0.1633 0.0005 0.1902 0.0038 0.0051 0.2773 0.5483 0.1675 0.1866

PAGE 40

40 Table 2 10 Summary statistics during high discharge for variables measured monthly at eight selected sites from March 2007 September 2012. High Discharge Site Variable Mean Median Std Dev Minimum Maximum N 141 TSP g P L 1 12 10 7 0 27 22 TSN g N L 1 340 349 129 159 528 22 CHLa g L 1 7.0 5.6 3.9 2.0 19.2 22 TEMP C 17.6 17.5 6.0 5.7 28.0 21 SAL (psu) 12.8 11.8 8.2 2.4 31.9 22 151 TSP g P L 1 12 10.5 9.4 0.0 47.0 20 TSN g N L 1 255 208 151 44 581 20 CHLa g L 1 7 7 3 2 11 19 TEM P C 17.8 17.0 5.9 6.2 27.6 19 SAL (psu) 17.5 16.8 9.2 2.5 32.1 20 161 TSP g P L 1 13 10 11 4 51 22 TSN g N L 1 426 390 185 226 1053 22 CHLa g L 1 8.4 6.0 5.7 1.1 24.4 22 TEMP C 17.9 18.0 5.6 6.4 27.5 22 SAL (psu) 10.3 10.8 6.8 0.3 23.4 22 171 TSP g P L 1 14 14 7 2 26 22 TSN g N L 1 549 554 155 285 893 22 CHLa g L 1 7.7 5.3 6.2 1.6 23.9 22 TEMP C 18.4 18.4 6.1 6.4 28.9 20 SAL (psu) 3.2 2.0 3.9 0.0 16.9 21 191 TSP g P L 1 12 11 6 3 28 22 TSN g N L 1 506 484 199 227 954 22 CHLa g L 1 17.1 17.4 11.0 2.3 48.3 22 TEMP C 19.3 18.1 5.5 11.8 29.9 19 SAL (psu) 3.5 2.9 3.3 0.1 11.3 20 201 TSP g P L 1 13 14 5 3 22 18 TSN g N L 1 119 95 78 0 300 18 CHLa g L 1 5.1 3.6 3.6 1.5 15.5 18 TEMP C 18.4 16.9 4.9 10.6 27.6 18 SAL (psu) 32.3 32.0 1.5 30.2 35.3 18 221 TSP g P L 1 14 11 8 5 44 22 TSN g N L 1 361 371 174 10 746 22 CHLa g L 1 6.6 6.6 2.9 2.4 14.0 22 TEMP C 17.8 17.7 5.4 6.2 27.2 21 SAL (psu) 12.6 12.6 6.7 0.5 24.4 22 231 TSP g P L 1 18 18 5 11 3 1 22 TSN g N L 1 614 626 178 228 953 22 CHLa g L 1 3.8 3.4 2.6 1.5 13.6 22 TEMP C 17.2 16.5 5.6 6.2 26.6 21 SAL (psu) 0.1 0.1 0.0 0.0 0.1 22

PAGE 41

41 Table 2 1 1 Summary statistics during low discharge for variables measured monthly at eight selected sites from March 2007 September 2012. Low Discharge Site Variable Mean Median Std Dev Minimum Maximum N 141 TSP g P L 1 16 9 16 2 71 45 TSN g N L 1 227 220 99 21 500 45 CHLa g L 1 10.7 9.3 10.8 0.6 76.5 45 TEMP C 24.4 27.4 6.5 8.7 31.5 45 SAL (psu) 24.5 24.4 6.6 12.4 35.2 45 151 TSP g P L 1 17 11 14 0 65 37 TSN g N L 1 168 177 78 17 346 37 CHLa g L 1 6.9 6.4 3.5 0.6 17.3 37 TEMP C 24.7 27.2 6.5 8.5 31.4 37 SAL (psu) 29.2 29.0 4.7 15.9 35.4 37 161 TSP g P L 1 14 11 10 3 46 44 TSN g N L 1 233 242 98 33 416 44 CHLa g L 1 9.0 8.5 4.5 0.8 21.7 44 TEMP C 24.5 27.3 6.6 9.3 32.1 44 SAL (psu) 24.2 24.9 6.1 8.8 35.2 44 171 TSP g P L 1 11 10 6 2 28 42 TSN g N L 1 356 352 133 114 614 42 CHLa g L 1 9.1 9.0 4.4 0.4 26.0 42 TEMP C 24.9 28.1 6.8 6.9 33.1 42 SAL (psu) 12.7 12.2 6.4 1.2 30.7 42 191 TSP g P L 1 13 11 5 5 27 45 TSN g N L 1 314 298 131 121 707 45 CHLa g L 1 19.1 18.6 7.8 0.8 36.7 45 TEMP C 24.6 26.7 6.9 5.0 33.5 43 SAL (psu) 11.8 10.8 6.9 0. 1 29.8 43 201 TSP g P L 1 22 12 20 1 81 37 TSN g N L 1 136 128 76 3 315 37 CHLa g L 1 4.9 4.3 3.5 0.6 16.9 37 TEMP C 25.1 28.3 5.9 11.4 30.8 37 SAL (psu) 33.4 33.8 1.9 29.8 37.0 37 221 TSP g P L 1 16 13 12 3 49 45 TSN g N L 1 260 228 141 90 731 45 CHLa g L 1 9.4 8.5 4.9 0.4 21.8 45 TEMP C 24.6 26.9 6.5 7.0 31.4 45 SAL (psu) 24.8 24.3 5.5 11.1 35.2 45 231 TSP g P L 1 13 12 5 5 31 44 TSN g N L 1 547 522 168 185 1042 45 CHLa g L 1 5.3 4.9 2.8 0.6 12.6 45 TEMP C 24.9 27.3 6.4 9.7 32.3 45 SAL (psu) 0.1 0.1 0.0 0.1 0.1 45

PAGE 42

42 Figure 2 1. Map showing the Apalachicola Bay estuary and the location of the sites of study.

PAGE 43

43 Figure 2 2 Average monthly river discharge for the Apalachicola River from January 2000 to De cember 2012 at the Sumatra gauge Line indicates calculated grand mean (532 m 3 s 1 ).

PAGE 44

44 Figure 2 3 Time series plots of salinity (gray) vs river discharge (black line) at six selected sites across Apalachicola Bay

PAGE 45

45 Figure 2 4 Seasonal distribution of salinity ( bars ) vs river discharge (black line) at six selected sites across Apalachicola Bay from March 2007 to September 2012

PAGE 46

46 Figure 2 5 Time series plots showing temperature at three selected sites in Apalachicola B ay.

PAGE 47

47 Figure 2 6 Time ser ies plots of TS P (gray) vs river discharge (black line) at eight selected sites across Apalachicola Bay

PAGE 48

48 Figure 2 7 Seasonal distribution of TS P ( bars ) vs river discharge (black line) at eight selected sites across Apalachicola Bay from March 2007 to September 2012

PAGE 49

49 Figure 2 8 Time series plots of TS N (gray) vs river discharge (black line) at eight selected sites across Apalachicola Bay

PAGE 50

50 Figure 2 9 Seasonal distribution of TS N ( bars ) vs river discharge (black line) at eight selected sites across Apalachicola Bay from March 2007 to September 2012

PAGE 51

51 Figure 2 10 Relationship between salinity and phytoplankton biomass (CHL a [ g L 1 ]) at six selected sites across Apalachicola B ay

PAGE 52

52 Figure 2 11 Time series plots of chlorophyll a (gray) vs discharge (black line) at six selected sites across Apalachicola B ay

PAGE 53

53 Figure 2 1 2 Relationship between chlorophyll a and discharge at six different sites in Apalachicola Bay from April 2002 to September 2012

PAGE 54

54 Figure 2 1 3 Seasonal distribution of chlorophyll a ( bars ) vs discharge (black line) at eight selected sites across Apalachicola B ay from March 2007 to September 2012.

PAGE 55

55 Figure 2 1 4 Chlorophyll trends under high an d low discharge at four different sites in Apalachicola Bay from April 2002 to September 2012 (HD =high discharge; LD= low discharge).

PAGE 56

56 Figure 2 1 5 Chlorophyll trends under high and low discharge at four different sites in Apalachicola Bay from April 2002 to September 2012 (HD =high discharge; LD= low discharge)

PAGE 57

57 CHAPTER 3 SPATIAL AND TEMPORAL PATTERNS OF PHYTOPLANKTON COMPOSITION IN A SUBTROPICAL ESTUARY, APALACHICOLA BAY, FLORIDA, USA The combination of land and ocea nic influences in estuaries results in high spatial and temporal variability of key environmental factors, such as salinity, nutrient concentrations, light attenuation and water residence time. All of these factors are potentially important in regulating phytoplankton community structure, biomass and function ( Eyre et al. 1999). The biotic composition of estuaries is strongly influen ced by these regulating factors. The relative influence of environmental factors on the phytoplankton community depends on the specific character and location (e.g. climatic zone) of individual systems. The influences of watersheds associated with estuaries are particularly pronounced in semi enclosed systems subject to inputs from large rivers. In such systems, changes asso ciated with human development can play major roles in ecosystem structure and function, including phytoplankton communities. Apalachicola Bay is an example of such a system in the subtropical environment of study. T he Apalachicola River is the main source of fresh water for Apalachicola Bay and consists of a watershed of approximately 19,200 square miles ( ~49,730 km 2 ) encompassing parts of Georgia, Alabama and Florida (Edmiston, 2008) The watershed has been subject to rapid human development over the past century, including the growth of Atlanta, the largest metropolitan area in the southeastern United States. Whereas much of the watershed has escaped extensive indu strialization, the burgeoning consumptive water demand has created a serious issue with respect to flows needed to service the needs of the estuary, particularly during drought years (Huang, 2010 ; Putland et al., 2013) Significant reductions in freshwater discharge to

PAGE 58

58 the bay during low rainfall years are implicated in mass mortalities of oysters, which are a keystone species and supp ort a large shellfish industry (Livingston, 1983 ; Mortazavi et al., 2000 ; Huang and Spaulding, 2002 ; Edmiston, 2008 ; Huang, 2010) There are also serious concerns about the consequen ces of low discharge on the phytoplankton availability for the food web (Putland and Iverson, 2007 ; Putland et al., 2013 ) It has recently been hypothesized that prolonged period s of low river discharge result in low levels of primary production and undesirable changes in the structure of phytoplankton communities (Putland et al. 2013). The specific objectives of this s tudy were (1) to characterize the composition and abundance of the phytoplankton community within different regions of Apalachicola Bay ; (2) to describe temporal trends in composition and abundance; and (3) to compare phytoplankton assemblage s under high a nd low discharge. The results of the study are discussed within the context of the aforementioned hypotheses regarding the impacts of changes in discharge on phytoplankton abundance Methods Site Description This study was carried out in the Apalachicola estuary, located in the Florida panhandle on the northern coast of the Gulf of Mexico (Figure 2 1 ). T he Apalachicola River is the main source of freshwater for the Apalachicola estuary, and consists of a tri river drainage system, including approximately 19,200 square miles ( ~49,730 km 2 ) in Georgia, Alabama, and Florida. The confluence of the Chatahoochee and Flint rivers forms the headwaters of the Apalachicola system, which drains about 1,030 square miles (~2,670 km 2 ) (Livingston 1983). The estuary may be divided into four sections

PAGE 59

59 based on both natural bathymetry and artificial structural alterations: East Bay (North East) St. Vincent Sound (West side) Apalachicola Bay (Middle) and St. George Sound (East). Apalachicola Bay is behind a well developed barrier island complex composed of four islands: St. Vincent, Cape St. George, St. George, and Dog Island, lying roughly parallel to the mainland (Edmiston, 2008) Field Procedures Twelve sampling sites were selected for this study ( Figure 2 1), with the intention of obtaining extensive coverage of the different geographic regions of the estuary Collections were made monthly for a two year period, from June 2008 to June 2010. The primary phytoplankton samples were c ollected with a vertically integrating sampling tube (integrated pole) which collects water evenly from the surface to 0.1 m from the bottom. Samples were split into two subsamples, one preserved with and the other with glutaraldehyde in 0.1 M so dium cacodylate buffer. Basic water column characteristics (depth, salinity, and temperature) were obtained in situ in cooperation with the on going ANERR monitoring program, at the same time that samples were taken for analyses of chemical variables such as chlorophyll a concentrations and nutrient concentrations (total soluble phosphorus, total soluble nitrogen, and soluble reactive phosphorus). Additional analyses were carried out on samples collect ed under this project: total phosphorus (TP), total nitr ogen (TN), silica (Si), total suspended solids (TSS), turbidity, and c olor dissolved organic matter (CDOM) Water Chemistry Whole water samples were used to determine concentrations of TN, TP, Si, and Chl a To determine TN and TP, samples were digested and measured colorometrically on a Bran Luebbe autoanalyzer (TN) and a dual beam scanning spectrophotometer

PAGE 60

60 (TP; APHA, 1998). Chlorophyll a was processed from filters using the Sartory and Grobbelaar (1984) hot ethanol extraction method and concentrations were determined spectrophotometrically according to Standard Methods (APHA, 1998). Si concentrations were corrected for turbidity and measured on a dual beam scanning spectrophotometer following Standard Methods (APHA, 1998). For soluble nutrient and C DOM analyses, whole water was filtered through glass fiber filters (0.7 m pore size). NH 4 and NO 3 +NO 2 concentrations were determined by conversion to NO 2 and read colorometrically on a Bran Luebbe autoanalyzer (Strickland and Parsons, 1972; APHA, 1998). Dissolved inorganic nitrogen (DIN) was calculated by summing NH 4 +NO 3 +NO 2 SRP concentrations were measured via the ascorbic acid method on a dual beam scanning spectrophotometer following Standard Methods (APHA, 1998). Color dissolved organic matter (CD OM) values were measured against a platinum cobalt standard using a dual beam scanning spectrophotometer (APHA, 1998). Nutrient Limitation Bioassays For each nutrient limitation experiment, 5 L of water were collected using an integrated sampling pole at e ach of six sites: 231 in the River, 171 near The East Bay Bridge, 143 in St Vincent Sound, 223 in St. George Sound, 161 in Mid Bay and 201 in the gulf. Water was transported to the lab in a large clear carboy covered with a white plastic bag (to best si mulate natural light conditions) and closed with a foam stopper (to allow gas exchange). At the lab, water was transferred to a large mixing tank and stirred continuously during experimental set up. Water from each site was divided into 300 ml aliquots and poured into 15 Erlenmeyer flasks ( 500 ml ) to create five treatment groups (control, N addition, P addition, N+P addition, and N+P+Si addition) in triplicate.

PAGE 61

61 Nutrients were added to obtain final concentra 3 N L 1 1 4 P L 1 Flasks were incubated in temperature controlled water baths illuminated from the bottom. Temperatures were set at ambient levels measured on the day of sampling and l ight flux was fixed at 80 E m 2 s 1 To correspond with seasonal differences in day length p hotoperiods were set at 12 hours light, 12 hours dark in November and February, and 14 hours light, 10 hours dark in May, June, July and September Flasks were swirled and sampled for algal biomass every 24 hours for seven days. Algal biomass was estimated us ing in vivo fluorescence of Chl a using a Turner Designs TD 700 Fluorometer (Sunnyvale, CA) at fixed time intervals over a 6 8 day incubation period. Phytoplankton Analysis Picoplankton ic cyanobacteria were counted after a subsample was filtered onto 0.2 m Nuclepore filters and mounted between microscope slides and coverslips with immersion oil. Samples were kept frozen, and within 48 h of sampling cells were counted with a Nikon resear ch microscope equipped with autofluorescence (green and blue light excitation). N u merical abundances of cyanobacterial cells were determined by counting a minimum of five grids of the ocular micrometer at 1,000 X magnification After five grids, the number of additional grids counted was dependent on cell density, until reaching a count of 100 cells of the dominant taxon (Phlips et al., 1999) Biovolumes were determined using the closest shape method (Smayda, 1978) General p hytoplankton composition was determined for integrated samples from all the sites on a monthly basis using the Utermohl method (Utermohl 1958). S amples preserved in were settled in 19 mm diameter cyli ndrical glass chambers, and counted. Phytoplankton cells were identified and counted at 400X and 100X with a

PAGE 62

62 Nikon phase contrast inverted microscope. At 400X, a minimum of 100 cells of a single tax on and 30 grids were counted. If 100 cells were not counte d within 30 grids, up to a maximum of 100 grids were counted, or until 100 cells of a single tax on was reached. At 100X a total bottom count was completed for taxa >30 mm. Counts for individual taxa were converted to cell volumes using the closest geometr ic shape method (Smayda 1978). Mean volume was calculated for each species from specific phytoplankton dimensions measured for a minimum of 30 randomly selected cells or as many as possible for rare species. Statistical Analyses The SAS Enterprise Guide statistical package for PCs (Version 4.3) was used to carry out statistical analyses. Distributions of most variables were non normal (determined by the Shapiro Wilk and Kolmogorov Smirnov goodness of fit tests), necessitating the use of non parametric Spe arman rank correlation analysis to explore relationships between variables among sites. Canonical Correlation Analyse s ( CCA ) were performed in R using the CCA package to evaluate the statistical relationships between phytoplankton composition and abundance and environmental variables ( nutrients, chlorophyll a temperature and salinity ) For c lustering the sites with respect to discharge and salinity values Cluster Analysi s was performed in R using the principal components method and the hclust function

PAGE 63

63 Results Physical Chemical Variables River d ischarge Discharge trends in the Apalachicola estuary from January 2000 to December 2012 were discussed in C hapter 2 (Figure 2. 2 ). During the two years of this study four low discharge periods and three high discharge periods were indentified (Figure 3 1 ) The longer low discharge periods began in the month of June and extended until November in 2008 and September in 2009. Additi onally, February 2009 and June 2010 were characterized as short duration, low discharge periods. The first high discharge period was short and occurred during December 2008 and January 2009, t he second one ran from March through June 2009, and the third on e, which was also longest, went from October 2009 through May 2010. Nutrients Mean total nitrogen (TN) total phosphorus (TP) and Silica (Si) varied slightly from between low and high discharge periods (Tables 3 1 3 2 3 3 and Figure 3 7) Nutrient distrib ution portrays the influence of both the Apalachicola River and the Gulf of Mexico in nourishing the Bay on a seasonal basis D uring low discharge mean TP concentrations ranged from 19.4 g P L 1 at Site 171 near the East Bay Bridge to 42.5 g P L 1 at S ite 221 in Cat Point (Table 3 1 Figure 3 7 ). D uring high discharge TP concentrations ranged from 21.1 g P L 1 at Site 201 in the gulf to 41.4 g P L 1 at S ite 231 in the river (Table 3 1 Figure 3 7 ). TN concentrations tended to be higher in sites near the river mouth and lower in sites near outlets to the gulf during both high and low discharge (Table 3 2 Figure 3 7 ) During low discharge mean TN concentrations ranged from 221.9 g N L 1 at Site 201

PAGE 64

64 in the g ulf to 617.29 g N L 1 at Site 191 in East Bay. During high discharge mean TN concentrations ranged from 169.64 g N L 1 at Site 201 in the g ulf to 514.81 g N L 1 at East Bay (191). Silica (Si) concentrations were strongly influenced by river discharge, and were higher in sites adjacent to the Apalachicola River, decreasing with proximity to the barrier islands and the gulf (Table 3 3 Figure 3 7 ) During low discharge mean Si concentrations ranged from 1495 g Si L 1 at S ite 221 in Cat Point to 7474 g Si L 1 at Site 231 in the river. During h igh discharge, mean Si concentrations ranged from 819 g Si L 1 at S ite 201 in the gulf to 6534 g Si L 1 at Site 231 in the river. Salinity Measurements at the 12 sampling sites revealed a salinity gradient that decreases with distance from the river to t he gulf (Table 3 4 ) Salinities at S ite 231 in the river and Site 201 in the g ulf we re constant because of the sampling strategy used for these two sites, which consisted of taking the sample only after a certain salinity value was reached ( 0.1 ppt for th e rive r; 3 2 ppt for the gulf). M ean salinities in Apalachicola Bay vary significantly between the low and high discharge periods (Table 3 4 ) During low discharge salinities ranged from 9 .9 psu at Site 171 near the East Bay Bridge to 28.8 psu at Site 13 1 in West Pass (Tables 3 4 and 3 9 ) During high discharge salinities ranged from 1.9 psu at Site 171 in Eas t Bay Bridge to 16.8 psu at Site 151 in Pilots Cove (Tables 3 4 and 3 9). Temperature Temperature variations in the estuary from June 2008 to J une 2010 were similar to those described in Chapter 2 for the period M arch 2007 to September 2012 (Figures 2 4 and 3 2). From June 2008 to June 2010 w ater temperatures exhibited inter season

PAGE 65

65 variability with higher temperatures usually occurring from May to October and lower temperatures occurring from December to February ( Table 3 5 Figure 3 2). Mean water temperatures were higher during low discharge and ranged from 25.7 C at S ite 223 in St. Vincent Sound to 27.8 C at S ite 191 in East Bay. Mean water temperatures were lower during high discharge and ranged from 17.7 C at Site 231 in the river to 20.2 C at Site 191 in East Bay. Site 191 in East Bay displayed the highest mean temperature among all the sites d uring both low and high discharge (Tables 3 5 and 3 9 ) Color C olor dissolved organic matter (C DOM ) values reflected proximity to the river inflow. The CDOM pattern was similar during both low and high discharge (Tables 3 5 and 3 9) In general m ean CDOM values were higher at sites 191 in East Bay and 231 in the river and decreased with distance from the river, with the lowest mean values displayed at site 201 in the gulf During low discharge CDOM ranged from 6.8 PCU at Site 201 in the gulf to 47 PCU at S ite 191 in East Bay. During high discharge CDOM values ranged from 6.8 PCU at Site 201 in the gulf to 120 PCU at Site 191 in East Bay and 1 32 PCU at Site 143 in St. Vincent Sound The high mean CDOM concentrations displayed at Site 143 in St. Vincent Sound in April 2009 (1392 PCU) were the resul t of an exceptionally high discharge event Secchi d epth Light transmission through the water column was on average slightly higher d uring low discharge than during high discharge (Table 3 5) Site 191 in East Bay displayed the lowest mean Secchi depth v alues during both seasons, 0.6 m during low

PAGE 66

66 discharge and 0.5 m during high discharge. Site 201 in the gulf displayed the largest mean Secchi depth values during both seasons, 2.0 m during low discharge and 1.8 m during high discharge (Tables 3 5 and 3 9 ) Mean Secchi depth at site 231 (River) doubled from 0.6 m during high discharge to 1.2 m during low discharge (Table 3 5 ) Nutrient l imitation b ioassays B i oassays (Table 3 6) showed that phosphorus was the primary limiting nutrient for ph ytoplankton growt h in the river, in the north and in the ce nter of the bay (sites 231, 171 and 161 ), except when the presence of surplus nutrients was indicated by significant growth in the control groups (i.e., no added nutrients). Even in cases for which the bioassays sh owed no initial nutrient limitation, the mesocosms eventually shifted to phosphorus limitation or phosphorus nitrogen co limitation, as biomass levels peaked in the incubations from these sites (Table 3 6 ). Conversely, nitrogen or a combination of nitrogen and phosphorus limited phytoplankton growth in the west and east portions of the bay, as well as in the gulf (Table 3 6 ). Phytoplankton growth was never limited by s ilica (Si) during any of the incubations. Cluster a nalysis Cluster analyses based on physi cal chemical variables ( nutrients, chlorophyll a temperature and salinity ) were performed during low and high discharge periods from March 2007 to September 2012 (Figure s 3 3 and 3 4 ). C luster analyses illustrated the influence of river discharge in str ucturing temporal and spatial patterns in physical chemical variables In general Site 231 in the river and adjacent sites such as 191 in East Bay and 171 near the East Bay Bridge tend ed to group together independent of discharge. Site 143 in St. Vincent Sound tended to group with th e s e lower salinity sites during periods

PAGE 67

67 of low discharge, but during periods of high discharge it group ed with the bay sites, especially with Site 223 in St. George S ound (Figures 3 3 and 3 4). S ites located with in the bay su ch as 141 in Dry Bar, 161 in Mid Bay, 221 in Cat tend ed to form a large cluster that varied acc ording to the discharge period (Figures 3 3 and 3 4). Site 151 in Pilots Cove is close t o the barrier islands and is greatly influenced by the marine waters of the gulf. This site merge d with the bay cluster during high discharge h owever during low discharge it grouped with Site 201 in the gulf (Figures 3 3 and 3 4). Site 201 was in a separa te cluster during both high and low discharge. Phytoplankton a bundance M ean chlorophyll a concentrations were higher at S ite 191 in East Bay and lower at Site 231 in the river and at Site 201 in the gulf (Table 3 7, Figure 3 8). During low discharge m ean chlorophyll a concentrations ranged from 5.5 g L 1 at Site 201 in the gulf to 20.8 g L 1 at Site 191 in East Bay During high discharge m ean chlorophyll a concentrations ranged from 4.0 g L 1 at Site 231 in the river to 14.4 g L 1 at Site 191 in East Bay Mean values were slightly higher in the low discharge season than in the high discharge season at the 12 sampling sites. The average mean chlorophyll a concentrations for the bay increased from 7.6 g L 1 in the high discharge season to 9.9 g L 1 in the low discharge season In general chlorophyll a patterns from June 2008 to June 2010 were similar to those observed for the longer data set discussed in Chapter 2 Time series plots showed that river discharge and chlorophyll a are inverse ly related ( Figure 3 9 ). D uring periods of prolonged high discharge, such as October 2009 through May 2010 chlorophyll a concentrations remained low at most sites (Figure 3 9 ). Conversely, during

PAGE 68

68 periods of extended low discharge, like June to September 2008 chlorop hyll a levels tended to peak at the different sites, particularly at S ite 191 in East Bay. During the two years this study was carried out Site 191 in East Bay displayed the highest mean phytoplankton biomass during both low and high discharge. Similar t o chlorophyll a phytoplankton biovolumes were highe r during low discharge than during high discharge (Table 3 8 Figure 3 8 ) T he average mean phytoplankton biovolume for the entire bay double d from high discharge (1.6 x 10 6 m 3 ml 1 ) to low discharge sea son (3.3 x 10 6 m 3 ml 1 ) h owever the spatial and temporal trends observed for phytoplankton biovolume were different from those observed for chlorophyll a (Figures 3 8, 3 10, 3 11 and 3 12 ) Mean phytoplankton biovolume tends to be higher at Site 201 in the gulf and lower at sit e 231 in the river independent of the season (Figure 3 8 ) Spatial trends in the distribution of phytoplankton biovolume were similar to those observed for carbon (Figure 3 8 ). Sites 191 in East Bay, 151 in Pilots Cove and 201 in the gulf displayed the highest values for both phytoplankton biovolume and carbon. Seasonal ity of Phytoplankton Biovolume Phytoplankton blooms for the Apalachicola Bay were established using a 10% exceeda nce criterion, i.e. the biovolume level that was ex ceeded on <10% of the sampling events Bloom conditions within the bay sites ( e.g. 141, 151, 161, 171, 221 ), East B ay (191) and the g ulf (201) corresponded to total individual biovolumes exceeding 3 x 10 6 m 3 ml 1 At site 231 i n the river phytoplankton blooms under this definition were not observed and phytoplankton biovolumes were low and steady Seasonal patterns of phytoplankton biovolume i n the estuary varied be tween the two years of sampling, and t here were more phytoplankton blooms during the firs t low

PAGE 69

69 discharge season (June November 2008) than in any other season (Figures 3 10 3 11 and 3 12 ). T he first low discharge season included in the study exhibited moderate to high peaks in phytoplankton biovolume which varied temporally and spatially and were mostly dominated by diatoms In the northern area of the bay, more specifically at Site 171 near the East Bay Bridge and at Site 191 in East Bay Leptocylindrus danicus Cerataulina p elagica and Thalassionema nitzschioide s were the dominant species. L danicus was particularly important because it formed the greatest bloom observed during the period of study (13.86 x 10 6 m 3 ml 1 ) at Site 191 in East Bay At Site 161 in Mid Bay moderate peaks in biovolume of T n itzschioide s L danicus Pseudosolenia calcar avis and F ragilaria spp. were observed In the west, at Site 141 in Dry Bar and 143 in St. Vincent Sound, Thalassiosira spp. L danicus and P calcar avis dominated peaks of phytoplankton biovolume. In the outer portion of estuary, a t s ite s 131 i n West Pass, 151 in Pilots Cove, Fragilaria spp. Hemialus hauckii L s danicus T nitzschioide s and Rhabdonema adriaticum were the major bloom formers. A t Site 201 in the gulf, the phytoplankton community was dominated by the diat oms L danicus P calcar avis and F ragilaria spp. In the east part of the estuary, a t s ite s 221 in Cat Point and 223 in St. George Sound, L danicus and P calcar avis were the predominant species. November 2008 was an outstanding month in that blooms of various species occurred at 10 of the 12 sampling sites. The first high discharge season occurred in December 2008 January 2009, and coincided with a general pattern of low biovolumes at most sites in the estuary. Three sites 191 in East Bay, 151 in P ilots Cove, and 223 in St. George Sound were the exception and displayed moderate to intermediate biovolumes dominated by diatoms

PAGE 70

70 at Pilots Cove and St. George Sound, and dinoflagellates of the genus Protoperidinium at East Bay. During the low discharge period of February 2009, elevated biovolume levels and some exceptional blooms were observed in seven of the twelve sites, including Site 191 in East Bay and other sites located in the middle and outer estuary and the gulf (161, 221, 151, 223, 131 and 201 ). In this period the dinoflagellate Prorocentrum minimum was in bloom at East Bay and the diatoms C p elagica Skeletonema costatum R adriaticum and Fragilaria spp were the main contributors to the blooms in the middle and outer estuary. The second hi gh discharge season (March June 2009) followed the February low discharge event. During that time noticeable reductions in phytoplankton biovolume occurred across the estuary especially in April 2009 when biovolume s throughout the estuary reached dramat ic low levels S ite 201 in the gulf was the exception, where a bloom of P calcar avis was recorded. Also, during May and June 2009 cyanobacteria reached high biovolume levels at s ite s 191 in East Bay 151 in Pilots Cove and 211 in Phytoplank ton biovolumes remained low in the east and middle estuary during the third low discharge period (June September 2009), but was moderate at East Bay ( S ite 191 ) in the outer estuary ( Sites the western part of the estuary ( S ite 143 in St. Vincent Sound ) and the gulf ( S ite 201 ). At these sites a combination of cyanobacteria and diatoms dominated the community. During the third and longest high discharge period (October 2009 May 2010 ) eight of the 12 sites (171, 19 1, 161, 141, 143, 131, 223, and 201) displayed blooms in

PAGE 71

71 November 2009, which were composed of a mix of dinoflagellates, diatoms, cyanobacteria and other groups. These blooms covered the north, west and east portions of the estuary and were followed by si gnificant reductions in phytoplankton biovolumes at all sites. Later in the season, d iatoms of the genus F r agilaria formed blooms at Site 201 in the gulf ( 4 x 10 6 m 3 ml 1 ) during January 2010 and at Site 131 in West Pass (16.4 x 10 6 m 3 ml 1 ) during Mach 2010. This latter bloom was the th ird largest one detected in the estuary during the study period. Also, a phytoplankton bloom of the dinoflagellate P minimum was recorded at Site 161 in Mid Bay in April 2010. River discharge was low in the last month o f s ampling for this study (June 2010), h owever phytoplankton biovolumes were low at most sites Site s 161 in Mid Bay and 131 in West Pass were the exception, as a combination of cyanobacteria and diatoms of the genus Fragilaria reached bloom levels in the se regions Relationships Between Phytoplankton Community Assemblage s and Environmental Variables The major algal groups observed within the Apalachicola estuary during the study period included: diatoms (88 taxa), dinoflagellates (58 taxa), cyanobacte ria (9 taxa), green algae (35 taxa), euglenoids (4 taxa), cryptophytes (4 taxa), and prasinophytes (7 taxa) ( Table 3 12 ) The dominant phytoplankton species varied temporally and spatially at the different sites. Bloom forming species included centric diat oms, pennate diatoms and dinofla gellates. T he relationship between the major phytoplankton groups and environmental variables was explored at four selected sites using Canonical Correlation Analysis (CCA) (Figure 3 13). I n the river (Site 231) cyanobact eria were positively correlated with temperature and diatoms were correlated with chlorophyll a At Site 161 in Mid Bay

PAGE 72

72 dinoflagellates were positively correlated with Secchi depth, and again diatoms were correlated with chlorophyll a and cyanobacteria wi th temperature. At Site 151 in Pilots cove dinoflagellates were positively correlated with Secchi depth, and cyanobacteria and diatoms correlated with temperature and salinity respectively. At Site 201 in the gulf cyanobacteria correlated positively wit h temperature and diatoms with total phosphorus (TP). Although no obvious relationship with phosphorus was detected (Figure 3 1 4 ) concentrations in the range of 10 to 90 g L 1 seemed to be optimal for phytoplankton biolvolume peaks. P hytoplankton biovolu me showed the highest bloom intensities at concentrations of nitrogen between 200 and 600 g L 1 (Figure 3 1 4 ). T otal phytoplankton biovolume optima were observed at salinities between 15 and 25 psu (Figure 3 15 ). Total phytoplankton biovolumes were also a ffected by temperature, with most of the peaks occurring between 15 and 25 C (Figure 3 1 5 ). Moderate amounts of small phytoplankton ( biovolume 20 00 m 3 ) were observed over a broad spect rum of salinities (0 to 35 psu), however peak concentrations were more common in salinities between 5 and 27 psu (Figure 3 1 6 ). Large phytoplankton ( biovolume 20 00 m 3 ) were also abundant at different saliniti es, but noticeable peaks in biovolume tended to occur at salinities between 15 and 35 psu (Figure 3 1 6 ). Chain forming centric diatoms were a conspicuous component of the phytoplankton biovolume, with several species forming medium to large bloom s at salin i ties between 15 and 25 psu (Figure 3 1 6 ). T hree species of centric diatoms were abundant throughout the study, L. danicus C p elagica and P calcar avis These species were present at different salinity ranges,

PAGE 73

73 however C. pelagica reached bloom levels w hen salini ty was ~ 20 psu (Figure 3 1 7 ). The other two species, L danicus and P. calcar avis reached bloom conditions frequently at salinities between 18 and 34 psu. T he most prominent pennate diatom taxa forming blooms were species belonging to genera Fr agilaria Amphiprora and Pleurosigma as well as T nitzchioides (Figure 3.1 7 ). The most conspicuous blooms of pennate diatoms were formed by T nitzchioides at salinities of about 15 to 32 psu, and Fragilaria sp. at salinities between 25 and 3 5 psu (Figur e 3. 17 ). The dinoflagellates P minimum Gyrodinium spirale and Akashiwo sanguin ea were observed over a wide range of salinities. P. minimum showed somewhat different salinity preferences in terms of small magnitude bloom events (Figure 3 1 7 ). Temperatur e was another key factor correlated with the distribution of certain species of centric diatoms. L. danicus C p elagica and P calcar avis had different preferences in terms of temperature (Figure 3 18). Peaks in biovolume of C. pelagica were observed ar ound 15 C, whereas P calcar avis tended to prefer temperatures around 20 C. In the case of L. danicus the range in temperature preferences was larger (18 to 32 C), and high biovolumes for this species were recorded at 18, 25 and 30 32 C (Figure 3 18) Some pennate diatoms also showed preferred ranges in temperature (Figure 3 18). Peaks in biovolume of Fragilaria spp. were recorded at a wide range of temperatures from 10 to 32 C, whereas species of the genus Pleurosigma were restricted to temperature s between 18 and 2 5 C. T nitzchioides was observed over a broad spectrum of temperatures, however major blooms of this species tended to be

PAGE 74

74 restricted to temperatures around 30 C. The dinoflagellate P minimum exhibited higher biovolumes between 15 and 25 C. A sanguinea also a dinoflagellated had higher biovolumes were observed around 20 C and 28 C (Figure 3 18). Cyanobacteria also were a major component of the phytoplankton biovolume in the estuary, especially during low discharge (Figures 3 10, 3 11, 3 12 and 3 19). Phycocyanin rich cyanobacteria exhibited a wide range of salinity distribution, with biovolume peaks occurring at salinities between 3 and 20 psu (Figure 3 19). Phycoerythrin rich cyanobacteria on the other hand tended to display peak s in biovolume at salinity ranges between 25 and 35 psu (Figure 3 19). Discussion This study revealed spatial differences in phytoplankton composition and biovolume in the Apalachicola estuary S ampling sites included in the study can be roughly organize d into five groups; 1) The river (Site 231) and the site close to the river discharge (Site 171) 2) East Bay in the northeast corner of Apalachicola Bay (Site 191) 3) the central bay and oyster bars (Sites 143, 141, 161, 221, and 223), 4) the outer bay ( Sites 131, 151, and 211), and 5 ) Site 201 in the Gulf of Mexico. S ites near the river outflow had the lowest mean phytoplankton biovolume values in part reflecting the high light attenuation and short water residence times in the river. The latter regio n also showed strong temporal changes in composition attributable to shifts in salinity from fresh to saline conditions related to levels of river discharge (Figure 3 10) Site 191 in East Bay stood apart from other regions in the study because it display ed the greatest variability in dominant species. Peaks in phytoplankton biovolume were at different times dominated by diatoms, dinoflagellates and

PAGE 75

75 picoplanktonic cyanobacteria (Figure 3 10) The site also exhibited high chlorophyll a levels These obse rvations may be attributable to several unique characteristics of East Bay, including longer water residence times than the other sites in the bay and influences of allochthonous inputs from small creeks in the region, which discharge colored waters of rel atively high nutrient content. I n the central bay where large oyster bars are located mixing of river and marine waters provide conditions more conducive to high phytoplankton biovolume s and proliferation of marine phytoplankton species, including increa sed light availability in the water column and more consistent mid range salinities (i.e. >5 psu). These findings are in agreement with previous studies in the Apalachicola estuary (Putland and Iver son, 2007 ; Putland et al., 2013) which point out that during the summer months (defined as May to October) the highest concentrations of chlorophyll a occur in samples from sites with salinities between 5 and 23 psu. Similar spatial trends are observed in other estuaries associated with discharges from turbid or highly colored rivers, such as the Amazon River in Brazil (Smith Jr and Demaster, 1996 ; Santos et al., 2008) the Pearl (Dai et al., 2006) and Huange ( Turner et al., 1990) Rivers in China, the Mississippi (Liu et al., 2004 ; Rabalais et al. 2004) and Suwannee (Bledsoe et al., 2004 ; Quinlan and Phlips, 2007) Rivers in the Gulf of Mexico and the Nile River in Africa (Oczkowski et al., 2009) Phytoplankton maxima in these systems often occur in the nearshore transition zone between light limited river water and the nutrient limited offshore water. The location and magnitude of the phytoplankton maxima are dictated by the rates of disch arge from the river and its light

PAGE 76

76 attenuation properties, which in turn can influence the productivity of higher trophic levels, as well as the potential for and distribution of hypoxia. In terms of phytoplankton composition, Site s 161 141, and 221 prov ide an example of the pattern s in the central bay and oyster bars. Site 161 exhibited hig her mean phytoplankton biovolume, 3 .7 4 x 10 6 m 3 ml 1 during low discharge, and lower phytoplankton biovolume 2.3 x 10 6 m 3 ml 1 during high discharge Bloom events w ere often dominated by one or more species of centric chain forming diatoms, including L danicus P calcar avis and C p elagica P ennate diatom species in the genus Fragilaria were also common bloom formers in the region Some dinoflagellate blooms we re observed at this site, as well as other sites in the mid and outer bay, most prominently A sanguinea and P minimum Understanding the factors that regulat e blooms of A. sanguinea and P. minimum is important, because of their potential for forming har mful algal blooms (Phlips et al., 2002 ; Heil et al., 2005 ; Phlips et al., 2012) Earlier studies report that a mong harmful algal bloom species, P. minimum is important for the following reasons: it is widely distributed geographically in temperate and subtropical waters; it is p otentially harmful to humans via shellfish poisoning; it has detrimental effects at both the organismal and broader environmental levels; blooms app ear to have undergone a geographic expansion over the past several decades; and, a relationship appears to exist between blooms of this species and changing environments in coastal systems (Heil et al., 2005) Altho ugh it was beyond the scope this study to determine the particular conditions that may trigger harmful algal blooms (HABs) of specific taxa the dinoflagellate P. minimum was found frequently in

PAGE 77

77 temperatures between 15 to 25 C and at different salinity re gimes (Table 3 10 and Figure 3 17). A sanguinea has also been reported to have the potential to develop blooms under conditions of increased water residence time and high temperature in San Francisco Bay (Cloern et al., 2005) In Apalachicola Bay A sanguine a was often found to form medium size blooms (Table 3 10) in waters with temperatures around 20 C and was tolerant of a wide range of salinities (Figures 3 17 and 3 18). P icoplanktonic cyanobacteria were frequ ently abundant and dominant in the central bay and oyster bars especially during periods of low discharge and warm temperatures (Figure 3 10). These findings highlight the often overlooked importance of considering the role of these species in the ecology of estuaries (Phlips et al., 1999 ; Murrell and Lores, 2004 ; Putland et al., 2013) Sites 141 in Dry Bar and 221 in Cat Point are located at major oyster bars (Figure 3 11). In a similar way to Site 161, b loom events were often dominated by one or more species of centric chain forming diatoms, including L s danicus P calcar avis and C p elagica P ennate diatom species of the genus Fragilaria however, were not very c ommon at these two sites. Phytoplankton biovolumes at these sites were slightly lower than at site 161, possibly because of constant grazing from the oyster bars. Although it was beyond the scope of this study to evaluate the impact of grazers on phytoplan kton abundance, a previous study reported that up to 80% of phytoplankton biomass is consumed by grazers in the water column ( (Mortazavi et al., 2000) Sites 131 and 151 provide examples of the outer estuary. Th is region is greatly influenced from the Gulf of Mexico and w ith respect to species composition some of

PAGE 78

78 the dominant species recorded in this region were similar to those found in the central estuary (e.g. L danicus P calcar avis and Fragilaria spp.) However, marine species such as R adriaticum and H hauckii were also major bloom formers. This could have been the result of increased influence of marine phytoplankton species coming from the Gulf of Mexico through West Pass. The fifth region examine d in the study was outside the bay in the open waters of the Gulf of Mexico (S ite 201). Like much of the mid and outer bay, biovolume peaks at S ite 201 were dominated by marine diatoms. Although many of the same species observed in the bay were important at Site 201, the cosmopolitan species S costatum was added to the list of bloom formers. Mean biovolume levels were relatively high, reflecting the high productivity of the near shore shelf environment of the northern Gulf of Mexico, which receives h igh nutrient inputs from numerous large rivers, such as the Mississippi (Rabalais et al., 2004) In comparison with the first year of sampling (June 2008 May 2009), the second year (June 2009 June 2010) was characteri zed by a generalized reduction in phytoplankton biovolumes throughout all regions in the estuary, except for Site 131 in West Pass, next to the gulf. The phytoplankton community was mostly dominated by diatoms. A previous study conducted in the estuary fou nd similar results (Estabrook, 1973) However a transition from a mostly diatom dominated community during the first year to a heterogenous mix including diatoms, dinoflagellates and cyanobacteria was obse rved during the second year (Figures 3 10, 3 11, and 3 12). This was possibly the result of interactions among numerous environmental factors, including a longer and

PAGE 79

79 more pronounced high discharge period from October 2009 to May 2010 (Figure 3 1) which re sulted in shorter residence times and highly variable salinities. One of the central issues facing the ecology of Apalachicola Bay is the impact of anticipated futu re declines in river discharge (Mortazavi et al., 2001 ; Huang and Spaulding, 2002 ; Livingston, 2007 ; Edmiston, 2008 ; Huang, 2010 ; Putland et al., 2013) In 2012 widespread mass mortalities of oysters in the bay were attributed to persistent high salinity conditions caused by drought induced low river discharge. The resulting negative effects on the important oyster industry in the bay heightened concerns about the effects of low river dischar ge on the overall ecology of the bay, including the phytoplankton community, which forms a large portion of primary production in the bay. Putland et al. (2013) hypothesized that persistent low river discharge will reduce phytoplankton production and bioma ss because of diminished nutrient loads from the river. They also suggested that the structure of the phytoplankton community will change from one in which smaller phytoplankton species (< 20 m) are major components to one dominated by larger species (> 20 m), in particular diatoms. This study present s a more complex picture of the relationships between discharge and phytoplankton biomass, although there is support for aspects of the aforementioned hypothesis. One of the princip al expectations associate d with the latter hypothesis is that peak phytoplankton biomass should occur at salinities between 5 and 25 psu, because th e s e areas represent a water column where river inflows have contributed significantly to the surface mixed layer. Phytoplankton biom ass peaks in the mesohaline to lower polyhaline (i.e. 5 25 psu) regions of estuaries are common because the area possesses a combination of nutrient rich river water with relatively

PAGE 80

80 clear marine water, yielding an optimal blend for primary production (Quinlan and Phlips, 2007) In Apalachicola Bay many of the highest peaks in phytoplankton biovolume were observed at salinities between 15 and 27 psu, although there were also peaks in the upper polyhaline (27 35 psu) or oligohaline range (0.1 5 psu). The results of this study indicate somewhat variable trends in the relative importance of small and large celled phytoplankton across the salinity gradient in Apalachicola Bay. Small celled phytoplankton did not indicate dramatically higher peaks in biovolume in the mesohaline lower polyhaline salinity range, except for picoplanktonic cyanobacteria (Figures 3 16 and 3 19) As observed by Putland et al. (2013), biovolume peaks of phycocyanin rich picoplanktonic cyanobacter ia were abundant in the mesohaline lower polyhaline salinity range (Figure 3 19) Large celled phytoplankton showed a relatively wide range of salinity over which biovolume peaks were observed, i.e. 10 33 psu (Fig ure 3 16 ). The group that show ed the mos t dramatic trend in biovolume peaks in the upper mesohaline to lower polyhaline range was cha in forming centric diatoms (Figure 3 16 ). Most of the highest peaks in biovolume were observed during the late fall or early spring when temperatures were relative ly low (near 20 C) (Figure 3 18) P rominence of chain forming centric diatoms under the aforementioned conditions is in part attributable to several features common to these species, including their high growth rates (Stolte and Garcs 2006) and toleranc e of a wide range of salinities and temperatures (Smayda 1980 ; Reynolds 2006). T hese traits help explain the ir cosmopolitan global distribution (Smayda 1980 ; Reynolds 2006).

PAGE 81

81 The larger question of whether low river discharge results in low phytoplankton primary production and biomass is complicated by the need to define the relative role of the Gulf of Mexico as a source of nutrients compared to the role of the Apalachicola River. During periods of high river discharge (i.e. winter and early spring) pho sphorus and nitrogen levels in the river are elevated compared to low discharge periods. Wh ereas the elevated nutrient loads during the latter periods represent a potential for increased phytoplankton biomass, high discharge can also reduce water residenc e time and increase salinity variability, both of which have a negative effect on biomass. The other complicating factor is the role of nutrients from the Gulf of Mexico in support ing phytoplankton production. Previous studies (Mortazavi et al., 2000, 2001) estimated that only 23% of annual nutrient load to A palachicola Bay comes from the g ulf, with the rest coming from the river. However, it is possible that this approximation underesti mates the gulf contribution which depend s on specific environmental conditions that vary from year to year. The northern Gulf of Mexico is a relatively nutrient rich region, at least compared to many open ocean environments, because of the numerous region al inputs from major eutrophic rivers, such as the Mississippi River ( Rabalais et al. 2004) and Suwannee River (Quinlan and Phlips 2007). These regional river influences are reflected in the fact that average total phosphorus concentrations in the Gulf of Mexico just outside of Apalachicola Bay are twice as high as in the Apalachicola River during the spring summer low discharge period (Table 2 3) Because phosphorus appears to be the dominant limiting nutrient for phytoplankton growth in the bay, the g ulf could represent an important nutrient source during the latter period. This possibility needs to be further explored to evaluate more accurately the

PAGE 82

82 overall consequences of future reductions in river discharge on phytoplankton p rimary production and biomass. In summary r esults from this study indicate d regional differences in the composition and abundance of phytoplankton in the estuary, which had a strong connection to changes in river discharge and salinity gradients. River discharge alone played a n important role in decreasing water residence time and, as a consequence, decreased phytoplankton biomass and biovolume due to osmo tic stress and rapid flushing. However phytoplankton blooms are highly dynamic and drawing major conclusions from a two year study would be a precipitate action.

PAGE 83

83 Table 3 1 Duncan tests for total phosphorus (TP) in Apalachicola Bay during low and high river discharge Concentrations expressed as g P L 1 Letters indicate groups based on mean values. Low discharge TP High d ischarge TP Duncan Grouping Mean N SITE Duncan Grouping Mean N SITE A 43 11 221 A 41 14 231 B A 38 11 131 B A 39 14 171 B A 37 11 201 B A 38 14 191 B A C 35 11 191 B A 38 13 131 B A C 34 11 211 B A 37 14 161 B A C 33 11 161 B A 37 12 143 B A C 32 8 223 B A C 34 14 221 B A C 30 11 151 B A C 31 14 141 B A C 30 8 143 B A C 28 13 211 B C 24 11 231 B A C 28 13 223 B C 22 11 141 B C 25 13 151 C 19 11 171 C 21 13 201 Table 3 2 Duncan tests for total nitrogen (TN) in Apalachic ola Bay during low and high river discharge Concentrations expressed as g N L 1 Letters indicate groups based on mean values. Low discharge TN High discharge TN Duncan Grouping Mean N SITE Duncan Grouping Mean N SITE A 617 10 191 A 515 14 191 A 600 10 231 A 512 14 171 B A 505 10 171 A 472 14 231 B C 402 10 141 B A 427 14 161 B C D 378 10 221 B A 415 14 221 B C D 376 7 143 B A 407 12 143 B C D 373 10 161 B A 392 14 141 C D 343 10 131 B A 377 12 223 C D 310 10 211 B A 370 13 211 C D 299 7 223 B C 299 13 151 C D 285 10 151 B C 285 13 131 D 222 10 201 C 170 10 201

PAGE 84

84 Table 3 3 Duncan tests for silica (Si) in Apalachicola Bay during low and high river discharge Concentrations expressed as g Si L 1 Letters indicate groups b ased on mean values. Low discharge Si High discharge Si Duncan Grouping Mean N SITE Duncan Grouping Mean N SITE A 7474 11 231 A 6535 14 231 B 5424 11 191 B A 6121 14 171 B 4745 11 171 B C 5083 14 191 C 2790 8 143 D C 4531 14 161 C 2572 11 141 D C E 4224 14 221 C 2472 11 161 D C E 4095 14 141 D C 2197 11 131 D E 3591 12 143 D C 2062 8 223 D E 3541 13 211 D C 1828 11 221 D E 3278 13 223 D C 1531 11 151 E 2933 13 151 D C 1495 11 211 E 2849 13 131 D 989 11 201 F 820 13 201 Table 3 4 Duncan tests for salinity during low and high discharge Concentrations expressed as psu. Letters indicate groups based on mean values. Low discharge salinity High discharge salinity Duncan Grouping Mean N SITE Duncan Grouping Mean N SITE A 32. 9 11 201 A 32.4 13 201 B A 28.8 11 151 B 16.8 13 131 B C 26.2 8 223 B 16.7 13 151 B C D 25. 9 11 211 C B 13.5 12 143 B C D 24. 8 11 221 C B 13.2 13 223 B C D 24.7 11 131 C B 11.7 13 211 E C D 23.9 11 161 C B 11.6 14 141 E D 21.3 11 141 C B 11.2 14 221 E 19.9 8 143 C D 8.3 14 161 F 10.7 11 191 E D 3.1 12 191 F 9.9 11 171 E 1.8 14 171 G 0.1 11 231 E 0.0 14 231

PAGE 85

85 Table 3 5 Summary statistics for physical variables in Apalachicola Bay during high and low river dischar ge. LD= low discharge (left), HD= high discharge (right) SITE Temp LD Temp HD Secchi LD Secchi HD C DOM LD CDOM HD 231 26.3 17.7 1.2 0.6 31.2 66.6 171 27.1 18.8 1.1 0.7 19.8 57.3 191 27.8 20.2 0.6 0.5 47.0 120.6 131 26.8 18.6 1.0 0.9 10.8 21.1 141 2 6.8 18.2 1.0 0.8 11.6 26.4 143 25.7 17.9 0.9 0.7 14.1 132.1 151 26.7 18.7 1.3 1.0 8.1 20.4 161 26.8 18.3 1.2 1.0 10.8 40.3 211 27.0 18.6 1.3 0.9 10.4 31.3 221 27.0 18.3 0.9 0.9 13.9 42.8 223 25.7 18.9 1.2 1.1 14.6 33.6 201 26.6 19.2 2.0 1.8 6.8 6.8 Average 26.7 18.6 1.1 0.9 16.6 49.9 Table 3 6 Percent of limitation by different treatments in the six bioassay experiments conducted at six selected sites. U= unlimited, P= phosphorus limited, N= nitrogen limited, NP= co limited by nitrogen and phosp horus. Site Season Initial Primary 231 (River) Low U 100% P 100% High P 50%, U 50% P 100% 171 (North) Low NP 25%, P 75% NP 25%, P 75% High P 50%, U 50% P 100% 161 (Center) Low P 50%, NP 50% P 50%, NP 50% High NP 50%, U 50% NP 50% P 50% 143 (West) Low N 50%, P 25%, NP 25% N 50%, P 25%, NP 25% High N 50%, U 50% N 50%, P 5 0 % 223 (East) Low P 50%, NP 50% P 50%, NP 50% High N 50%, U 50% N 50% P 50% 201 (Gulf) Low NP 50 %, N 50% NP 50 %, N 50% High NP 100% NP 100%

PAGE 86

86 Table 3 7 Duncan tests for chlorophyll a in Apalachicola Bay during low and high river discharge Concentrations expressed as g L 1 Letters indicate groups based on mean values. Low discharge chlorophyll High discharge chlorophyll Duncan Grouping Mean N SITE Duncan Grouping Mean N SITE A 20.8 11 191 A 14.4 14 191 B 13.0 8 143 B A 11.0 12 143 C B 11.1 11 221 B C 8.0 14 161 C B D 10.0 11 141 B C 7.5 12 223 C B D 9.8 11 161 B C 6.9 13 131 C B D 9.3 11 131 B C 6.9 14 171 C B D 8.8 11 171 B C 6.6 12 151 C B D 8.5 11 211 B C 6.6 14 141 C D 8.4 8 223 B C 6.3 12 211 C D 7.2 11 151 B C 6.1 14 221 C D 6.9 11 231 C 5.8 13 201 D 5.5 11 201 C 4.0 14 231 Table 3 8 Duncan tests for phytoplankton biovolume in Apalachicola Ba y during low and high river discharge Concentrations expressed as 10 6 m 3 ml 1 Letters indicate groups based on mean values. Low discharge biovolume High discharge biovolume Duncan Grouping Mean N SITE Duncan Grouping Mean N SITE A 4.7 8 143 A 2.8 13 131 A 4.4 11 201 B A 2.5 13 201 A 4.2 11 191 B A 2.3 14 161 A 4.2 7 223 B A C 2.0 13 151 B A 3.7 11 161 B A C 1.9 14 191 B A 3.6 11 131 B A C 1.6 12 143 B A 3.2 11 141 B A C 1.5 13 223 B A 3.1 11 221 B A C 1.3 13 211 B A 3.0 11 151 B A C 1 .2 14 141 B A 2.9 11 211 B C 1.0 14 171 B A 2.2 11 171 B C 1.0 14 221 B 0.9 11 231 C 0.4 14 231

PAGE 87

87 Table 3 9 Summary statistics for variables measured monthly at the twelve sampling sites in Apalachicola Bay d uring high and low river discharge from June 2008 to June 2010. Site Variable Mean (Low) Mean (High) Std Dev (Low) Std Dev (High) Min. (Low) Min. (High) Max. (Low) Max. (High) 231 CHL a 6.9 4.0 3.3 3.2 2.6 1.5 12.6 13.6 TP g 24 41 6 13 9 23 32 63 TN g 600 472 218 150 268 263 875 711 Si g 7474 6535 642 1474 6254 3098 8278 8800 TEMP 26.3 17.7 5.8 6.3 12.3 6.2 30.8 26.6 SAL 0.1 0.1 0.0 0.0 0.1 0.0 0.1 0.1 SECCHI 1.2 0.6 0.3 0.3 0.8 0.3 1.7 1.2 CDOM 31.2 66.6 22.6 39.6 16.1 27.3 96.1 186.1 171 CHL a 8.8 6.9 3.0 5.2 4.3 1.6 13 .7 17.7 TP g 19 39 7 14 10 18 27 66 TN g 505 512 127 141 319 365 776 793 Si g 4745 6121 1372 1575 3151 3102 7015 9757 TEMP 27.1 18.8 5.2 6.8 15.2 6.4 31.6 28.9 SAL 9.9 1.9 4.1 2.5 4.4 0.0 16.3 9.1 SECCHI 1.1 0.7 0.4 0.2 0.7 0.4 2.1 0.9 CDO M 19.8 57.3 20.5 45.1 8.9 21.8 81.0 187.7 191 CHL a 20.8 14.4 5.7 9.9 14.6 2.3 32.6 35.1 TP g 35 38 14 13 16 19 57 64 TN g 617 515 155 144 431 231 973 799 Si g 5424 5083 2492 1328 604 2366 8880 7671 TEMP 27.8 20.2 5.1 6.3 16.7 13.0 31.4 29.9 SAL 10.7 3.2 6.5 3.9 1.3 0.1 21.4 11.3 SECCHI 0.6 0.5 0.2 0.2 0.3 0.2 1.0 1.0 CDOM 47.0 120.6 41.3 134.4 16.1 20.3 140.1 496.6 161 CHL a 9.8 8.0 3.6 5.9 5.1 1.1 15.5 24.4 TP g 33 37 18 22 22 20 85 108 TN g 373 427 203 172 202 109 918 717 Si g 2472 4531 1665 2014 801 1864 6247 9335 TEMP 26.8 18.3 5.5 6.7 14.4 6.4 30.5 27.5 SAL 24.0 8.3 4.0 6.8 20.5 0.3 31.5 23.4 SECCHI 1.2 1.0 0.4 0.6 0.4 0.2 1.8 2.6 CDOM 10.8 40.3 6.3 40.1 1.6 9.3 27.4 145.8 141 CHL a 10.0 6.7 3.6 3.1 3.5 2.8 17.9 12. 8 TP g 22 31 11 16 10 10 47 72 TN g 402 392 138 164 180 210 697 798 Si g 2572 4095 1392 1645 443 1971 4355 7209

PAGE 88

88 Table 3 9 Continued Site Variable Mean (Low) Mean (High) Std Dev (Low) Std Dev (High) Min. (Low) Min. (High) Max. (Low) Max. (High ) TEMP 26.8 18.2 5.3 7.0 14.9 5.7 30.8 28.0 SAL 21.3 11.6 6.4 8.3 12.4 2.4 34.1 27.6 SECCHI 1.0 0.8 0.4 0.4 0.3 0.2 1.8 1.4 CDOM 11.6 26.4 10.3 27.0 2.3 9.4 40.7 98.0 143 CHL a 13.0 11.0 7.8 11.3 3.8 1.7 23.9 39.1 TP g 30 37 15 35 7 12 54 142 TN g 376 407 133 243 248 86 598 956 Si g 2790 3591 1156 1565 1088 929 4584 5875 TEMP 25.7 17.9 5.7 7.1 15.3 5.6 30.3 28.6 SAL 19.9 13.6 5.4 10.9 11.2 0.6 26.6 31.9 SECCHI 0.9 0.7 0.4 0.3 0.3 0.2 1.5 1.2 CDOM 14.1 132.1 8.2 397.2 5.9 4.2 28.9 1 393.0 221 CHL a 11.1 6.1 5.6 2.3 2.8 2.4 21.8 11.4 TP g 43 34 17 12 22 23 83 63 TN g 378 415 146 195 251 17 740 663 Si g 1827 4224 1245 1465 134 2130 4851 6320 TEMP 27.0 18.3 5.1 6.3 15.8 6.2 31.4 27.2 SAL 24.7 11.2 5.0 7.2 19.0 0.5 33.2 24.4 SECCHI 0.9 0.9 0.3 0.3 0.4 0.4 1.4 1.7 CDOM 13.9 42.8 11.7 50.0 7.2 10.7 42.5 199.7 223 CHL a 8.4 7.5 4.9 3.7 2.6 2.5 17.2 15.3 TP g 32 28 14 10 11 17 48 55 TN g 299 377 61 181 218 63 391 612 Si g 2062 3278 1478 1648 234 767 3943 5814 TEMP 25.7 18.9 5.8 6.4 15.1 6.6 31.2 26.9 SAL 26.2 13.3 5.2 8.8 18.3 2.2 33.2 32.4 SECCHI 1.2 1.1 0.3 0.8 0.7 0.4 1.5 3.2 CDOM 14.6 33.6 9.6 38.6 5.8 9.6 36.3 153.0 131 CHL a 9.3 7.0 4.6 4.3 4.4 2.6 20.1 18.3 TP g 38 38 17 21 20 13 79 75 TN g 343 285 132 169 157 52 590 632 Si g 2197 2849 1449 1718 380 473 4335 6125 TEMP 26.8 18.6 5.4 6.4 14.7 7.4 30.6 27.3 SAL 24.7 16.8 6.2 11.1 17.2 1.8 34.4 34.9 SECCHI 1.0 0.9 0.6 0.5 0.3 0.3 2.2 2.0 CDOM 10.8 21.1 7.7 21.7 0.0 3.7 31.7 69.8 151 CHL a 7.2 6.7 3.1 3.2 4.0 2.1 13.3 11.2 TP g 30 25 21 11 6 10 86 42

PAGE 89

89 Table 3 9 Continued Site Variable Mean (Low) Mean (High) Std Dev (Low) Std Dev (High) Min. (Low) Min. (High) Max. (Low) Max. (High) TN g 285 299 115 154 120 137 569 606 Si g 1531 2933 916 1825 151 759 2777 6088 TEMP 26.7 18.7 5.2 6.8 15.1 6.2 31.4 27.6 SAL 28.8 16.7 4.3 9.8 20.1 2.5 34.5 32.1 SECCHI 1.3 1.0 0.4 0.4 0.5 0.5 2.3 2.0 CDOM 8.1 20.4 5.9 19.1 0.2 5.0 24.0 63.9 211 CHL a 8.5 6.3 4.1 3.2 3.8 1.9 18.8 13.0 TP g 34 28 21 14 11 12 83 60 TN g 310 370 159 172 192 52 743 682 Si g 1495 3541 1173 1679 268 868 4030 5552 TEMP 27.0 18.6 5.2 6.7 16.3 6.1 31.6 26.8 SAL 25.8 11.8 4.0 7.8 20.4 1.3 32.1 24.0 SECCHI 1.3 0.9 0.4 0.5 0.7 0.4 2.2 2.4 CDOM 10.4 31.3 5. 7 39.7 4.3 6.4 26.1 153.6 201 CHL a 5.5 5.9 3.4 4.0 1.7 1.5 12.9 15.5 TP g 37 21 22 10 8 3 73 35 TN g 222 170 119 67 81 71 453 256 Si g 988 820 781 738 259 0 2945 2635 TEMP 26.6 19.2 5.0 5.4 14.8 10.6 30.4 27.6 SAL 32.8 32.4 1.8 1.4 30.5 30.2 35.8 35.0 SECCHI 2.0 1.8 1.2 1.2 0.5 0.5 4.0 4.0 CDOM 6.8 6.8 4.5 3.1 0.8 1.9 15.9 14.6

PAGE 90

90 Table 3 1 0 Major phytoplankton b loom s at the twelve sampling sites in Apalachicola Bay form June 2008 to June 2010. \ Species Maximum biovolume Number of obser vations Bloom frequency Prorocentrum minimum 10,117,318.19 105 8 Protoperidinium spp 4,989,537.00 69 1 Gymnodinium c.f. 1,660,554.98 9 1 Akashiwo sanguineum >45<65 1,588,204.71 64 4 Gyrodinium spirale c.f. <80 1,131,743.34 8 3 1 Cryptophyte (>5<15) 1,368,241.20 282 1 Fragilaria sp. 17,896,284.00 30 15 Leptocylindrus danicus 13,861,936.41 78 14 Cerataulina pelagica 8,988,936.98 51 8 Pseudosolenia calcar avis 5,026,694.40 111 3 Rhabdonema adriatic um 4,800,000.00 7 4 Thalassionema nitzschioides (>30 apical) 4,212,512.04 112 6 Pleurosigma/Gyrosigma (40 transapical) 3,404,153.30 16 1 Navicula 25 3,198,427.64 24 1 Coscinodiscus 2,997,085.00 13 1 Skeletonema cf costatum 2,612,179.20 58 1 Thalassiosira 10 cell 2,608,600.50 55 1 Pleurosigma/Gyrosigma (10 20 transapical) 2,507,400.00 250 1 Aulacoseira sp 2,100,189.00 35 1 Cerataulina pelagica 1,713,123.38 51 8 Hemialus hauckii 1,706,964 .40 25 2 Centric diatom 10 1,470,302.10 246 1 Dactyliosolen fragilissimus (>10 < 20 transapical) 1,257,217.07 9 1 Synechococcus (phycocyanin) 1,623,424.11 183 3 Phycocyanin (spherical picoplankton) 1,536,614.40 281 8

PAGE 91

91 Table 3 1 1 List of Species o bserved in the Apalachicola Estuary, Florida, USA from June 2008 t o 2010. Phytoplankton Species Sites 171 191 141 221 161 151 201 231 Green algae Chlorophyceae Actinastrum hantzschii 1 . . . Ankistrodesmus convolu tus 4 6 2 2 3 2 5 Ankistrodesmus falcatus 4 4 4 2 2 11 Ankistrodesmus nannosolene 1 . 1 . 1 Chlamydomonas 8 8 7 8 8 6 3 7 Closteriopsis sp. . . . 1 Closterium (c shaped) 2 1 . 1 . Closterium (straight) 1 1 3 2 . Coela strum cambricum . . . 1 1 Coelastrum sp. . 1 . . 2 Crucigenia quadrata 1 1 2 1 1 . 3 Crucigenia rectangularis . . 1 . Crucigenia sp. 1 . 1 . 1 Crucigenia tetrapedia 1 . 1 . 2 Dictospherium puchellum . 2 . 2 Eudorina 2 . . . 1 Kirchneriella contorta . 1 . 1 Micractinium pusillum 1 . . 2 Oocystis 5 1 1 . . 4 Pandorina sp. . . . 1 Pediastrum duplex 1 1 . . 6 Pediastrum simplex 1 1 . . 5 Pleodorina 1 . . 1 Scenedesmaus bijuga 3 2 2 1 2 6 Scenedesmus acutiformis . . 1 . Scenedesmus denticulatus . . . 1 Scenedesmus dimorphus 1 . . . Scenedesmus quadricauda 11 7 3 4 5 . 14 Scenedesmus sp. 6 1 1 2 4 . 8 Staurastrum sp. . . . 2 Tetraedron minimum . . . . Tetraedron regulare var incus . . . 1 Tetrastrum . 1 . . Tetrastrum hetero . . . 1 Treubaria 1 . . . Pseudobodo tremulans 2 3 1 2 1 1

PAGE 92

92 Table 3 11 continued Phytoplankton Species Sites 171 191 141 221 161 151 201 231 Eutreptia cf. . 1 1 1 2 Eutreptia globulifera . 1 1 1 . Trachlemonas cf 1 . . . Dinoflagellates Dinophyceae Akashiwo sanguineum 7 15 5 6 7 7 5 Amphidinium crassum . . . 1 Amphidinium sp. 1 1 2 . Ceratium fusus (Steidenger) . 2 1 6 Ceratium hircus (Steidenger) . . 1 2 Ceratium lineatum 1 2 2 2 6 9 Ceratium sp. . 2 1 3 1 Cochlodinium polykrikodos 1 1 1 1 1 Cocholidium citron . 1 . . Dinophysis caudata 2 2 5 1 3 . Diplosoid . 1 . 1 Gonyaulax polygramma (Steidenger) . 1 1 2 Gonyaulax sp. . . . . Gymnodinium sp A <15 18 13 19 15 19 20 18 6 Gymnodinium sp B >15 <50 6 4 3 4 4 3 5 1 Gyrodinium >5 <25 3 2 5 2 3 2 8 Gyrodinium instriatum 3 2 1 . . Gyrodinium spirale 5 7 4 9 8 13 17 1 Hermesinum adriaticum (Sornia) 1 1 . 1 . Heterocapsa sp. 2 4 3 5 6 2 5 Karenia longicanalis . . 1 1 . Karlodinium veneficum 5 8 6 6 11 8 9 2 Katodinium >25<50 . . . . Katodinium glaucum 1 1 2 1 5 Katodinium rotundatum 1 1 3 3 1 2 1 Kryptoperidinium foliaceum cf 1 . . . Oxyphysis oxytoxides 3 2 2 4 3 5 2 Oxyrrhis marina . . . . Polykrikos hartmanni 2 2 1 1 1 1 . Polykrikos schwartzi (Steidenger) . . 1 1 1 Prorocentrum scutellum . . . . Prorocentrum balticum . . 1 . Prorocentrum compressum . . . . Prorocentrum gracile . . . 2 Prorocentrum mexicanum 1 . . 2

PAGE 93

93 Table 3 11. Continued Phytoplankton Species Sites 171 191 141 221 161 151 201 231 Prorocentrum micans 3 6 9 9 13 14 7 1 Prorocentrum minimum 11 10 10 8 13 9 9 1 Prorocentrum rathymum . . 1 2 P rorocentrum sp. . . 1 2 Protoperidinium conicum . 2 1 2 . Protoperidinium crassipes . . . . Protoperidinium divergens . . . 1 Protoperidinium excentricum . . 1 1 Protoperidinium leonis cf . 1 . . Protoper idinium oblongum . . . . Protoperidinium pallidum . . . 1 Protoperidinium pellucidium 1 . 1 . Protoperidinium quinquecorne . . . 1 Protoperidinium sp. 5 10 4 8 4 7 10 1 Pyrodinium bahamense var. bahamense 2 . . 1 Pyrophacus horologium <50u 1 1 2 1 1 1 5 Pyrophacus sp. 1 2 2 1 2 3 5 Scrippsiella sp. 5 3 5 6 4 6 4 1 Takayama pulchella . 1 . . Takayama sp 2 4 3 5 2 2 Takayama tasmanica . . 1 . Torodinium terado . . . 1 Warnowi a sp . . 1 1 Cryptophytes Cryptophyceae Cryptomonas <30 3 4 1 2 2 1 3 Cryptophytes 25 26 27 26 26 25 23 29 Hillea . 1 2 2 . Rhodomonas 1 2 1 2 1 . 1 Diatoms Bacyllariophyceae Amphiprora A 5 <50 2 2 6 10 6 4 1 Amphiprora B >50 <100 3 3 . . Asterionella glacialis (Hasle) 7 4 15 12 15 17 19 1 Asterolampra (30) . . 1 . Aulocoseira sp. 2 2 1 2 2 1 2 Bacillaria paradoxa 2 5 3 1 3 7 1 Bacteriastrum furcatum . 1 . . Bacteriastrum hylinum . 1 . 2 Bacteriastrum sp. . . 1 5 Bidduphila alternans . . 5 7

PAGE 94

94 Table 3 11. Continued Phytoplankton Species Sites 171 191 141 221 161 151 201 231 Bidduphila sp. 1 2 2 2 4 Centric chain >5 <30 19 4 6 9 9 12 13 2 6 Centric diatom A >5 < 25 60 56 66 73 66 55 55 44 Centric diatom B >30 <60 25 19 48 41 42 40 43 5 Centric diatom C >70 <100 4 4 6 4 3 7 11 2 Centric diatom D >100 <150 0 0 1 0 2 1 0 0 Cerataulina 1 . . 2 Cerataulina pelagica 4 2 8 4 5 6 7 Chaetoceros aequatorialis . 2 2 2 1 Chaetoceros affins . . . . Chaetoceros cf. costatus . . 1 1 1 Chaetoceros diadema . 1 . 1 Chaetoceros simplex (Hasle) 1 1 2 1 2 1 Chaetoceros sp. >5 <30 3 4 9 5 4 12 16 0 Ch aetoceros subtillis (Hasle) 1 1 1 1 . Chaetoceros tenuissimus 1 1 . . Corethron sp. . . . . Coscinodiscus sp. 2 2 2 2 2 3 . Cylindrotheca sp 9 11 7 12 10 10 15 4 Dactyliosolen fragilissimus 3 7 3 2 6 9 Diploneis sp. A >50< 100 . . . 1 Diploneis sp. B >25<50 1 1 3 1 1 Diploneis sp. C >5<25 1 1 1 1 1 Epithemia sp. 1 . . 1 . Eucampia sp . 1 . 3 Fragilaria gramatophora . 1 2 3 1 Fragilaria sp. . 1 1 3 2 9 Guinardia delicatata . . . 3 Guinardia flaccida 3 2 4 4 7 9 17 Guinardia striata 2 1 5 10 7 13 17 Hemiaulus hauckii 2 2 1 1 3 4 8 Hemiaulus sinensis . . . . Leptocylindrus danicus 2 3 6 6 7 10 14 Leptocylindrus minimus 9 6 8 8 8 11 13 2 Licmophor a abbreviata . . . . Licomophora sp . 2 1 . 2 Melosira granulata 3 1 . . 1 6 Melosira sp. 7 4 2 3 2 1 9 Navicula plagiotropis . . . 1

PAGE 95

95 Table 3 11. Continued Phytoplankton Species Sites 171 191 141 221 161 151 201 231 Nav icula sp. A >75 < 150 1 1 1 2 1 Navicula sp. B >5 <75 0 0 5 4 3 4 6 0 Nitchia cf. delicate 12 13 17 16 14 20 19 4 Nitzschia sp. 3 4 5 8 6 2 3 1 Odontella aurita . . . 2 Odontella moblilienis (Hasle) . 3 1 1 6 9 Odontella regia . 1 . 2 2 Odontella sp 10 15 diameter . . . . Paralia sulcata (Ricard) 3 2 5 4 6 11 15 Pennate diatom sp. A <5 transapical >5 <50 apical 43 40 51 56 40 49 57 24 Pennate diatom sp. B <5 transapical >50 <100 apical 10 2 10 7 4 8 17 4 Pennat e diatom sp. C <5 transapical >100 <250 apical 5 5 3 5 9 8 2 15 Pennate diatom sp. D <5 transapical >250 <450 apical 0 0 0 1 2 1 6 0 Pennate diatom sp. E 6 15 transapical >5 <50 apical 3 2 4 4 8 7 8 0 Pennate diatom sp. F 6 15 transapical >50 <100 apic al 7 5 2 6 3 9 8 2 Pennate diatom sp. G 6 15 transapical >100 <250 apical 9 6 5 11 4 6 3 7 Pennate diatomsp. H 6 15 transapical >250 <600 apical 1 0 1 0 2 4 2 0 Pennate diatom sp. I 30 transapical >10 <100 apical 0 4 1 2 1 4 1 0 Pennate diatom sp. J 3 0 transapical >100 <200 apical 0 1 0 1 0 0 2 1 Plagiogramma vanheurckii . 1 . 1 Pleurosigma/Gyrosigma A >5 < 20 transapical) 10 24 20 32 20 34 41 9 Pleurosigma/Gyrosigma B >30 < 40 transapical) 6 2 2 3 3 6 7 0 Pseudo nitzchia sp. 6 5 8 8 8 1 3 20 1 Pseudo nitzchia turgidula c.f. . 1 1 1 2 Pseudo nitzschia calliantha . 1 1 1 2 Pseudosolenia calcar avis 6 8 5 31 9 4 11 0 Rhabdonema adriaticum 1 . . 4 . Rhizosolenia setigera 0 0 0 4 1 1 5 0 Rhizosolenia styliformis . . 1 2 Skeletonema costatum 3 3 5 4 8 7 7 Surirella sp. A >5 <50 2 . . . Surirella sp. B >50 < 100 1 3 1 . 2 Thalassionema bacillare . 2 1 3 2 Thalassionema frauenfeldii . . . 1 Thalassionema javanicum 2 2 1 2 1 1 Thalassionema nitzschioides 18 9 23 22 20 25 25 1 Thalassiosira chain >5 <30 6 5 8 6 6 5 5 0 Triceratium . 1 . . Tropidoneis lepidoptere . . 1 .

PAGE 96

96 Table 3 11. Continued Phytoplankton Species Sites 171 191 141 221 161 151 201 231 Cyanobacteria Cyanophyceae Anabaena sp. 1 1 . 1 2 Chrococcus 4 . . 1 . Chrococcus minutus 1 2 1 2 . Merismopedia sp. 5 2 1 1 2 9 Merismopedia tennuissima 1 . . . Microcystis sp. . . . 1 Oscillator ia sp. . . 1 3 Spherical picoplankton 47 42 48 48 46 49 49 36 Synechococcus 27 26 27 22 28 30 24 21 Raphydophyceae Chatonella 1 1 . . . Generic raphidiophyceae 1 2 . . . Prasinophyceae Chrysochromulina sp. . 1 1 1 . Flagellate ovoid <15 11 12 4 7 4 5 3 7 Flagellate ovoid >15 1 1 1 2 1 1 4 Flagellate spherical 10 15 11 14 10 14 8 11 11 11 Micromonas cf. 9 5 7 3 8 4 3 4 Pyramimonas sp. 2 2 3 2 3 2 2 0 Unidentified haptophyte 1 1 1 2 2 .

PAGE 97

97 Figure 3 1 Average monthly river discharge for the Apalachicola River from June 2008 to June 201 0 Line indicates the calculated grand mean (532 m 3 s 1 ). Figure 3 2 Temperature at three selected sites (231, 161 and 201) from June 2008 to June 201 0

PAGE 98

98 Figure 3 3 Cluster analysis grouping of the sampling sites during low discharge based on physical, chemical, and biological characteristics.

PAGE 99

99 Figure 3 4 Cluster analysis grouping of the sampling sites during high discharge based on physical, chemi cal, and biological characteristics.

PAGE 100

100 Figure 3 5 M onthly concentrations of t otal nitrogen (TN, light gray) and dissolved inorganic nitrogen (DIN, dark gray ) at six representative sampling sites in Apalachicola Bay Concentrations expressed as g N L 1

PAGE 101

101 Figure 3 6 Temporal variation in monthly concentrations of t otal phosphorus (TP, light gray) and soluble reactive phosphorus (SRP, dark gray ) at six representative sampling sites in Apalachicola Bay Concentrations expressed as g P L 1

PAGE 102

102 Figu re 3 7 M ean total phosphorus (TP) total nitrogen ( TN ) and Silica ( Si ) from June 2008 to June 2010 for eight selected sites in Apalachicola Bay Low= Low discharge, High= High discharge.

PAGE 103

103 Figure 3 8 M ean chlorophyll a (Chl a ), phytoplankton biovolume (BV) and carbon (C) from June 2008 to June 2010 for eight selected sites in Apalachicola Bay Low= Low discharge, High= High discharge.

PAGE 104

1 04 Figure 3 9 Time series plots of chlorophyll a (gray) vs discharge ( black line) at six selected sites in Apalachico la Bay, from June 2008 to June 2010.

PAGE 105

105 Figure 3 10 Phytoplankton biovolume ( 10 6 m 3 ml 1 ) subdivided into major groups at the river, north estuary (site 171) East Bay (site 191) and Mid Bay (site 161) Dominant species during blooms: Diatoms 1. Lepto cylindrus danicus 2. Pseudosolenia calcar avis 4. Cerataulina pelagica 5. Fragilaria spp., 9. Coscinodiscus 11. Thalassionema nitzschioides 12. Skeletonema costatum Dinoflagellates: 14. Akashiwo sanguinea 15. Prorocentrum minimum 16. Protoperidinium spp. Cy anobacteria : 19.Picocyanobacterium Gray boxes indicate periods of high discharge.

PAGE 106

106 Figure 3 11 Phytoplankton biovolume ( 10 6 m 3 ml 1 ) subdivided into major groups at the west (sites 141 and 143) and east (sites 221 and 223) portions of the estuary D ominant species during blooms: Diatoms 1. Leptocylindrus danicus 2. Pseudosolenia calcar avis 4. Cerataulina pelagica 6. Thalassiosira spp., 7. Pleurosigma spp., 8. Navicula spp., 9. Coscinodiscus spp. Dinoflagellates: 14. Akashiwo sanguinea 15. Prorocentrum m inimum Cyanobacteria : 19.Picocyanobacterium Gray boxes indicate periods of high discharge.

PAGE 107

107 Figure 3 12. Phytoplankton biovolume ( 10 6 m 3 ml 1 ) subdivided into major groups at the outer estuary (sites 131, 151 and 211) and the gulf region (site 201) Dominant species during blooms: D iatoms 1. Leptocylindrus danicus 2. Pseudosolenia calcar avis 4. Cerataulina pelagica 5. Fragilaria spp., 10. Rhabdonema adriaticum 11. Thalassionema nitzschioides 13. Hemialus hauckii Cyanobacteria : 19.Picocyanobacterium Combination of different diatoms. Gray boxes indicate periods of high discharge.

PAGE 108

108 Figure 3 1 3 Canonical correlation analysis plots of the major phytoplankton groups at four selected sites in Apalachicola Bay based on physical, chemical, and biologica l characteristics.

PAGE 109

109 Figure 3 13 Continued

PAGE 110

110 Figure 3 1 4 Distribution of total phytoplankton in the Apalachicola estuary with relationship to total phosphorus (TP) and total nitrogen (TN). Observations are expressed as biovolume and where taken from Ju ne 2008 to June 2010.

PAGE 111

111 Figure 3 1 5 Distribution of total phytoplankton in the Apalachicola estuary with relationship to salinity and temperature. Observations are expressed as biovolume and where taken from June 2008 to June 2010.

PAGE 112

112 Figure 3 1 6 Distribution of small phytoplankton (<20 m) large phytoplankton (>20 m) and chain forming centric diatoms across salinity gradients in the Apalachicola estuary. Observations are expressed as biovolume and where taken from June 2008 to June 2010.

PAGE 113

113 Fi gure 3 1 7 Distribution of common bloom forming species in relationship to salinity in the Apalachicola estuary Observations are expressed as biovolume and where taken from June 2008 to June 2010.

PAGE 114

114 Figure 3 1 8 Distribution of common bloom forming specie s in relationship to temperature ( C) in the Apalachicola estuary Observations are expressed as biovolume and where taken from June 2008 to June 2010.

PAGE 115

115 Figure 3 19 Distribution of phycocyanin rich and phycoerythrin rich cyanobacteria in the Apalachico la estuary with relationship to salinity. Observations are expressed as biovolume and where taken from June 2008 to June 2010.

PAGE 116

116 CHAPTER 4 SUMMARY Apalachicola Bay is a sub tropical river dominated estuary which is experiencing major anthropogenica lly driven changes in hydrology This study was conducted in Apalachicola Bay with the overall goal of describing how spatial and temporal patterns in the structure and abundance of phytoplankton are related to changes in river discharge, and shifts in ke y physical and chemical parameters, such as salinity, nutrient concentrations and water residence times. This initiative was undertaken in two different approaches under the premise that river discharge is a crucial element driving key physical chemical pa rameters and ultimately phytoplankton abundance and composition. The first approach consisted of identifying phytoplankton biomass trends during periods of below and above average discharge over a ten year period (i.e. 2002 2012) and exploring the relati onship between river discharge, nutrient concentrations, and chlorophyll a River discharge exerted significant control on phytoplankton biomass in most regions of the estuary and, in combination with nutrient gradients and salinity, acted as ecoclines for phytoplankton biomass Ecoclines were important features of Apalachicola Bay, and the specific character and dynamics of these ecoclines was strongly influenced by changes in river discharge. Discharge from the Apalachicola River had a strong effect on salinity and TSN, and was auto correlated with temperature. It also appeared to regulate TSP concentrations in regions adjacent to the river, but had little effect on TSP concentrations in regions close to the Gulf of Mexico. In Apalachicola Bay lower mean chlorophyll a concentrations were detected during high discharge, when the combination of lower temperature and high residence time limited

PAGE 117

117 phytoplankton growth. Conversely, the combination of higher temperature and low discharge, and therefore high resi dence time could have facilitated phytoplankton biomass to reaching maximum levels during the summer and fall. The second approach attempted to characterize the composition and abundance of the phytoplankton community within different regions of Apalachic ola Bay, considering temporal trends and including comparisons of the phytoplankton assemblage under different discharge regimes. Numerous species of diatoms were the main component of the community, especially during the first year of sampling. The second year was characterized by community transitions from a diatom dominated system to a more heterogeneous one, displaying a mix of diatoms, dinoflagellates, and cyanobacteria. In comparison with the first year of sampling, the second year was characterized b y a generalize reduction in phytoplankton. This was possibly the result of interactions among numerous environmental factors, including a longer and more pronounced high discharge period from October 2009 to May 2010, which resulted in shorter residence ti mes and highly variable salinities. With respect to phytoplankton size distribution, biovolume of small celled phytoplankton did not show dramatically higher peaks in biovolume in the mesohaline lower polyhaline salinity range, except for picoplanktonic cy anobacteria peaks, which were abundant in mesohaline lower polyhaline salinity range. Large celled phytoplankton showed a relatively wide range of salinity over which biovolume peaks were observed, i.e. 10 33 psu. The group showing the most dramatic trend in biovolume peaks in the upper mesohaline to lower polyhaline range was chain forming centric diatoms. In general, diatoms were the major dominant group, however

PAGE 118

118 dinoflagellates were important, including a few species with potential to develop harmful al gal blooms (HABs) such as Prorocentrum minimum In summary, r esults from this study indicate d regional differences in the composition and abundance of phytoplankton in the estuary, which had a strong connection to changes in river discharge and salinity g radients. River discharge alone played an important role in decreasing water residence time and, as a consequence, decreased phytoplankton biomass and biovolume due to osmo tic stress and rapid flushing. However phytoplankton blooms are highly dynamic and d rawing major conclusions from a two year study would be a premature action. The task of defining the factors that drive phytoplankton community assembly and succession remains a central challenge in aquatic ecology (Hutchinson, 1961, Cloern and Dufford, 2005) As Hutchinson (1961) pointed out, it is hard to understand how, in turbulent open water, many physical opportunities for niche diversification can exist, and how only a few organism s can be favored by peculiar chemical conditions at the surface. Although our results highlight the importance of factors such as salinity and river discharge in shaping the phytoplankton community in Apalachicola Bay, several additional factors (e.g. resi dence time, loss due to grazing by zooplankton and oysters, and nutrient gradients) remain to be considered in order to explain, in a more holistic fashion, the dynamics of the phytoplankton community in this estuary

PAGE 119

119 LIST OF REFERENCES Attrill, M. and Rundle, S., 2002. Ecotone or ecocline: ecological boundaries in estuaries. Estuarine, Coastal and Shelf Science 55, 929 936. Bledsoe, E.L., Phlips, E.J., Jett, C.E. and Donnelly, K.A., 2004. The relationships among phytoplankton biomass, n utrient loading and hydrodynamics in an inner shelf estuary. Ophelia 58, 29 47. Board, O.S., 2000. Clean coastal waters: understanding and reducing the effects of nutrient pollution. National Academies Press. Cloern, J.E. and Dufford, R., 2005. Phytoplankt on community ecology: principles applied in San Francisco Bay. Marine Ecology Progress Series 285, 11 28. Cloern, J.E., Schraga, T.S., Lopez, C.B., Knowles, N., Grover Labiosa, R. and Dugdale, R., 2005. Climate anomalies generate an exceptional dinoflagell ate bloom in San Francisco Bay. Geophysical Research Letters 32. Costanza, R., d'Arge, R., De Groot, R., Farber, S., Grasso, M., Hannon, B., Limburg, K., Naeem, S., O'neill, R.V. and Paruelo, J., 1997. The value of the world's ecosystem services and natura l capital. Nature 387, 253 260. Dai, M., Guo, X., Zhai, W., Yuan, L., Wang, B., Wang, L., Cai, P., Tang, T. and Cai, W., 2006. Oxygen depletion in the upper reach of the Pearl River estuary during a winter drought. Marine Chemistry 102, 159 169. Dix, N., P hlips, E. and Suscy, P., 2013. Factors Controlling Phytoplankton Biomass in a Subtropical Coastal Lagoon: Relative Scales of Influence. Estuaries and Coasts, 1 16. Edmiston, H.L., Fahrny, S.A., Lamb, M.S., Levi, L.K., Wanat, J.M., Avant, J.S., Wren, K. and Selly, N.C., 2008. Tropical storm and hurricane impacts on a Gulf Coast estuary: Apalachicola Bay, Florida. Journal of Coastal Research, 38 49. Edmiston, L., 2008. A River Meets the Bay a characterization of the Apalachicola River and Bay System. Apalachi cola: Apalachicola National Estuarine Research Reserve, Florida Department of Environmental Protection. Edmiston, L., 2008. A River Meets the Bay a characterization of the Apalachicola River and Bay System. Apalachicola: Apalachicola National Estuarine Res earch Reserve, Florida Department of Environmental Protection. Estabrook, R.H., 1973. Phytoplankton ecology and hydrography of Apalachicola Bay.

PAGE 120

120 Eugene Turner, R., Rabalais, N.N. and Nan, Z.Z., 1990. Phytoplankton biomass, production and growth limitations on the Huanghe (Yellow River) continental shelf. Continental Shelf Research 10, 545 571. Eyre, B. and Balls, P., 1999. A comparative study of nutrient behavior along the salinity gradient of tropical and temperate estuaries. Estuaries 22, 313 326. Heil, C .A., Glibert, P.M. and Fan, C., 2005. < i> Prorocentrum minimum(Pavillard) Schiller: A review of a harmful algal bloom species of growing worldwide importance. Harmful Algae 4, 449 470. Howarth, R.W., 1988. Nutrient limitation of net primary production in marine ecosystems. Annual Review of Ecology and Systematics 19, 89 110. Huang, W., 2010. Hydrodynamic modeling and ecohydrological analysis of river inflow effects on Apalachicola Bay, Florida, USA. Estuarine, Coastal and Shelf Science 86, 526 534. Huang, W. and Spaulding, M., 2002. Modelling residence time response to freshwater input in Apalachicola Bay, Florida, USA. Hydrological Processes 16, 3051 3064. Hutchinson, G.E., 1961. The paradox of the plankton. The American Naturalist 95, 137 145. Liu, H., Da gg, M., Campbell, L. and Urban Rich, J., 2004. Picophytoplankton and bacterioplankton in the Mississippi River plume and its adjacent waters. Estuaries 27, 147 156. Livingston, R.J., 2007. Phytoplankton bloom effects on a gulf estuary: water quality change s and biological response. Ecological Applications 17, S110 S128. Livingston, R.J., 1984. Ecology of the Apalachicola Bay System: an estuarine profile. Livingston, R.J., 1983. Resource atlas of the Apalachicola estuary. Florida Sea Grant College Program. Malone, T., Crocker, L., Pike, S. and Wendler, B., 1988. Influences of River Flow on the Dynamics of Phytoplankton Production in a Partially Stratified Estuary. Marine Ecology Progress Series MESEDT Vol.48, No.3, p 235 249, October 3, 1988.12 fig, 5 tab, 44 ref. Mortazavi, B., Iverson, R.L. and Huang, W., 2001. Dissolved organic nitrogen and nitrate in Apalachicola Bay, Florida: spatial distributions and monthly budgets. Marine ecology.Progress series 214, 79 91.

PAGE 121

121 Mortazavi, B., Iverson, R.L., Huang, W., Le wis, F.G. and Caffrey, J.M., 2000. Nitrogen budget of Apalachicola Bay, a bar built estuary in the northeastern Gulf of Mexico. Marine Ecology Progress Series 195, 1 14. Mortazavi, B., Iverson, R.L., Landing, W.M., Lewis, F.G. and Huang, W., 2000. Control of phytoplankton production and biomass in a river dominated estuary: Apalachicola Bay, Florida, USA. Marine Ecology Progress Series 198, 19 31. Mortazavil, B., Iversonl, R.L., Landing, W.M. and Huang, W., 2000. Phosphorus budget of Apalachicola Bay: a riv er dominated estuary in the northeastern. Mar Ecol Prog Ser 198, 33 42. Murrell, M.C., Hagy, J.D., Lores, E.M. and Greene, R.M., 2007. Phytoplankton production and nutrient distributions in a subtropical estuary: Importance of freshwater flow. Estuaries an d Coasts 30, 390 402. Murrell, M.C. and Lores, E.M., 2004. Phytoplankton and zooplankton seasonal dynamics in a subtropical estuary: importance of cyanobacteria. Journal of Plankton Research 26, 371 382. Oczkowski, A.J., Nixon, S.W., Granger, S.L., El Saye d, A.M. and McKinney, R.A., 2009. Anthropogenic enhancement of Egypt's Mediterranean fishery. Proceedings of the National Academy of Sciences 106, 1364 1367. Paerl, H.W., Rossignol, K.L., Hall, S.N., Peierls, B.L. and Wetz, M.S., 2010. Phytoplankton commun ity indicators of short and long term ecological change in the anthropogenically and climatically impacted Neuse River Estuary, North Carolina, USA. Estuaries and Coasts 33, 485 497. K., Sun, D., Viveros, P. and Yilmaz, M., 2012. Climatic influences on autochthonous and allochthonous phytoplankton blooms in a subtropical estuary, St. Lucie Estuary, Florida, USA. Estuaries and coasts 35, 335 352. Phlips, E.J., Badylak, S. and Lynch, T .C., 1999. Blooms of the picoplanktonic cyanobacterium Synechococcus in Florida Bay, a subtropical inner shelf lagoon. Limnology and Oceanography 44, 1166 1175. Phlips, E., Badylak, S. and Grosskopf, T., 2002. Factors affecting the abundance of phytoplankt on in a restricted subtropical lagoon, the Indian River Lagoon, Florida, USA. Estuarine, Coastal and Shelf Science 55, 385 402. Putland, J. and Iverson, R., 2007. Phytoplankton biomass in a subtropical estuary: distribution, size composition, and carbon: c hlorophyll ratios. Estuaries and Coasts 30, 878 885.

PAGE 122

122 Putland, J., Mortazavi, B., Iverson, R. and Wise, S., 2013. Phytoplankton Biomass and Composition in a River Dominated Estuary During Two Summers of Contrasting River Discharge. Estuaries and Coas ts, 1 16. Quinlan, E.L. and Phlips, E.J., 2007. Phytoplankton assemblages across the marine to low salinity transition zone in a blackwater dominated estuary. Journal of Plankton Research 29, 401 416. Rabalais, N.N., Atilla, N., Normandeau, C. and Eugene T urner, R., 2004. Ecosystem history of Mississippi River influenced continental shelf revealed through preserved phytoplankton pigments. Marine pollution bulletin 49, 537 547. Santos, M.L., Medeiros, C., Muniz, K., Feitosa, F.A., Schwamborn, R. and Macdo, S.J., 2008. Influence of the Amazon and Par Rivers on water composition and phytoplankton biomass on the adjacent shelf. Journal of Coastal Research, 585 593. Smayda, T.J., 1978. From phytoplankters to biomass. Phytoplankton Manual.UNESCO, Paris, 273 279. Smith Jr, W.O. and Demaster, D.J., 1996. Phytoplankton biomass and productivity in the Amazon River plume: correlation with seasonal river discharge. Continental Shelf Research 16, 291 319. Wang, H., Huang, W., Harwell, M.A., Edmiston, L., Johnson, E., Hs ieh, P., Milla, K., Christensen, J., Stewart, J. and Liu, X., 2008. Modeling oyster growth rate by coupling oyster population and hydrodynamic models for Apalachicola Bay, Florida, USA. Ecological Modelling 211, 77 89. Wilber, D.H., 1992. Associations betw een freshwater inflows and oyster productivity in Apalachicola Bay, Florida. Estuarine, Coastal and Shelf Science 35, 179 190.

PAGE 123

123 BIOGRAPHICAL SKETCH Paula Viveros grew up in the city of Armenia, Colombia. She graduated from Universidad del Quindo in July of 2001 with a B.S. in biology. Her undergraduate research focused on orchid distribution and taxonomic composition in two natural reserves of Quindo, Colombia. In May 2007 she graduated from Universidad del Quindo with her M.S. in plant biology, concen trating her studies on plant taxonomy and diversity. Her thesis examined distribution and taxonomic composition of P leurothallidinae (Orchidaceae) in the Quindo region of Colombia. In 2008 Paula began her doctoral studies on estuarine and phytoplankton ec ology at the University of Florida in Fisheries and Aquatic Sciences Her research focused on factors controlling phytoplankton abundance, species composition, and seasonality in Apalachicola Bay, a subtropical estuary in Florida. Her research and studies were funded by NOAA's National Estuarine Research Reserve Graduate Research Fellowship, South East Alliance for Graduate Education and Profes s oriate fellowships and awards, and the Delores Auzenne Dissertation Award. She received her Ph D from the Univer sity of Florida in the spring of 2014.