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The quantity, characteristics, source and nutrient input of groundwater seepage into the Indian River Lagoon, FL


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THE QUANTITY, CHARACTERISTICS, SOURCE AND NUTRIENT INPUT OF GROUNDWATER SEEPAGE INTO THE INDIAN RIVER LAGOON, FL By MARY K. LINDENBERG A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2001

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Copyright 2001 by Mary K. Lindenberg

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To my family

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iv ACKNOWLEDGMENTS I wish to express my appreciation to Dr. Jonathan Martin for giving me the opportunity to share in the research of this project and for his guidance and editorial assistance with my thesis writing. I also wish to express my gratitude to the other members of my committee, Dr. Elizabeth Screaton and Dr. Louis Motz, for their time and advice. I wish to thank the St. Johns River Water Management District for its financial support. A special thank you goes to the two other principal investigators on this project, Dr. Jaye Cable and Dr. Pete Swarzenski, who made working in the field fun, as well as a major learning experience. Others have contributed their time and, most of all, their patience. I would like to thank William Kenney and Dr. C. Schelske for their hospitality and guidance at the Fisheries Department; Jason Curtis for his unending assistance in the stable isotope lab; Kevin Hartl for design and construction of many devices used in the field including the seepage meters and the multisamplers (beautiful job!). I would also like to thank those who supported me through their friendship. Lastly, the greatest thank you goes to Kevin Caster, for without his support I would have given up a long time ago.

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v TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES............................................................................................................vii LIST OF FIGURES...........................................................................................................ix ABSTRACT....................................................................................................................... xi CHAPTERS 1 INTRODUCTION...........................................................................................................1 Significance of Submarine Groundwater Seepage.........................................................1 Importance of Groundwater Seepage and Nutrient Loading into Estuaries...................1 Indian River Lagoon.......................................................................................................2 Previous Studies..............................................................................................................5 Purpose........................................................................................................................ ....8 2 REGIONAL SETTING...................................................................................................9 Location....................................................................................................................... ...9 Physiographic Features.................................................................................................12 Regional Hydrostratigraphy..........................................................................................13 Climate and Hydrologic Components...........................................................................21 3 METHODS....................................................................................................................24 Seepage Measurements Methods Review and Background Theory.............................24 Field Sampling..............................................................................................................25 Seepage Meter Construction, Deployment and Seepage Measurements..................25 Multisamplers...........................................................................................................30 Water Sample Collection..........................................................................................31 Analytical Techniques..................................................................................................32 Field Measurements..................................................................................................32 Laboratory Measurements........................................................................................33

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vi 4 RESULTS......................................................................................................................35 Precipitation and Recharge...........................................................................................35 Seepage Rates...............................................................................................................39 Northern Study Area.................................................................................................39 Southern Study Area.................................................................................................41 Tracers........................................................................................................................ ...44 Nutrients...................................................................................................................... ..48 5 DISCUSSION................................................................................................................52 Seepage Rates...............................................................................................................52 Seasonal Relationship of Seepage Rates...................................................................52 Spatial Heterogeneity of Seepage Rates...................................................................54 Chloride....................................................................................................................... ..57 Seasonal Variation....................................................................................................58 Fraction of Fresh Groundwater in Seepage Water....................................................61 Effects of Seepage Water on Water Column Chemistry..........................................67 Evidence of Mixing Pore Water Chemistry..............................................................70 Evaporation and Surficial Runoff.............................................................................75 Nutrients...................................................................................................................... ..79 Nitrogen....................................................................................................................81 Phosphorus................................................................................................................83 Nutrient Loading.......................................................................................................83 Limiting Nutrients.....................................................................................................86 6 CONCLUSIONS............................................................................................................88 APPENDICES A STATION LOCATIONS..............................................................................................91 B SEEPAGE RATES........................................................................................................94 C WATER CHEMISTRY DATA....................................................................................96 LIST OF REFERENCES.................................................................................................111 BIOGRAPHICAL SKETCH...........................................................................................117

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vii LIST OF TABLES Table Page 1-1. Previous studies measuring groundwater discharge into marine environments............6 2-1. Sampling, times, measurements and locations..............................................................11 2-2. Lithologic and hydrogeologic information taken from wells in the coastal areas of Volusia, Brevard and Indian River Counties, FL................................................15 3-1. Blank and duplicate seepage flux values.......................................................................29 4-1. Average, median, minimum, maximum and standard deviation of seepage flux rates for the northern study area...................................................................................40 4-2. The minimum and maximum seepage rates and the corresponding % change between the dry and rainy seasons of the northern study area.............................40 4-3. Average, median, minimum, maximum and standard deviation of seepage flux rates for the southern study area...................................................................................42 4-4. The minimum and maximum seepage rates and the corresponding % change between the dry and rainy seasons of the southern study area............................42 4-5. The average, minimum, maximum and standard deviation of tracer concentrations of the water column, seepage water and groundwater measured during the dry season in the northern study area.........................................................................44 4-6. The average, minimum, maximum and standard deviation of tracer concentrations in the water column, seepage water and groundwater measured during the rainy season in the northern study area.........................................................................45 4-7. The average, maximum, minimum and standard deviation of tracer concentrations in the water column, seepage water, groundwater, surface water and pore water measured during the dry season in the southern study area.................................47 4-8. The average, minimum, maximum and standard deviation of tracer concentrations in the water column, seepage water, groundwater, surface water and pore water measured during the rainy season in the southern study area..............................48

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viii 4-9. Average, minimum, maximum and standard deviation of nutrient concentrations in seepage water, water column and groundwater during the dry season in the northern study area...............................................................................................49 4-10. Average, minimum, maximum and standard deviation of nutrient concentrations in seepage water, water column and groundwater during the rainy season in the northern study area...............................................................................................50 4-11. Average, minimum, maximum and standard deviation of nutrient concentrations of seepage water, water column, groundwater, surface water and pore water during the dry season in the southern study area.................................................50 4-12. Average, minimum, maximum and standard deviation of nutrient concentrations of seepage water, water column, groundwater, surface water and pore water during the dry season in the southern study area.................................................51 5-1. Normal average monthly recharge values for the entire Indian River Lagoon.............60 5-2. Average monthly recharge for the northern study area.................................................60 5-3. Average monthly recharge for the southern study area.................................................61 5-4. The chloride concentrations of seepage water, water column and groundwater used to calculate the percentage groundwater found in the seepage water..................63 5-5. Time of water column circulation through sediments of the entire lagoon...................70 5-6. The minimum chloride concentration in pore water and depth in multisamplers from the southern study area.........................................................................................71 5-7. The percent of pore water with low chloride concentrations in seepage water in the southern study area..............................................................................................73 5-8. Chloride concentrations of surface water measurements of dry and rainy season in both study areas....................................................................................................76 5-9. Mean monthly streamflow of four major surficial discharges in the southern study area.......................................................................................................................77 5-10. The average percent of inorganic and organic nutrient concentrations in total soluble nitrogen and phosphorus concentrations for the dry and rainy seasons of the northern and southern study areas.............................................................82 5-11. The average nutrient concentration, nutrient flux and nutrient loading of total nitrogen and total phosphorus in the northern and southern study areas.............85 5-12. Nutrient concentrations and flux in each study area and nutrient loading quantity to the Indian River Lagoon......................................................................................87

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ix LIST OF FIGURES Figure Page 2-1. The Indian River Lagoon System (including the Indian River Lagoon, the Banana River Lagoon and the Mosquito lagoon) located in east Central Florida............10 2-2. Map and stations of the (a) northern study area and of the (b) southern study area......11 2-3. A hydrostratigraphic cross-section below the IRL from the Volusia/ Brevard County line in the north to Sebastian Inlet in the south....................................................14 2-4. Contours of the potentiometric surface of the Upper Floridan Aquifer during (a) May 1999, (b) September 1999, (c) May 2000, (d) September 2000..................17 2-5. Average monthly precipitation for the Indian River Lagoon region. The precipitation values are based on the monthly mean of 17 stations in and around the IRL from 1951 to 1980......................................................................22 2-6. Average monthly potential evaporation for the Indian River Lagoon region. The potential evaporation values are based on the monthly mean of 17 stations in and around the IRL from 1951 to 1980...............................................................23 2-7. Average monthly recharge for the Indian River Lagoon region. The recharge values are based on the monthly mean of 17 stations in and around the IRL from 1951 to 1980........................................................................................................23 3-1. A depiction of a seepage meter placed in the sediment under the water column. .......26 3-2. A time series experiment showing 5 seepage rates from station IRL 6........................27 3-3. An example of a multisampling device.........................................................................30 4-1. The total monthly precipitation and potential evaporation values for the northern IRL from May, 1998 to December, 1999............................................................36 4-2. Recharge values between May 1998 and December 1999 for the northern study area study area (grey bars) and average recharge values taken from average data over 30 years from 17 stations (black bars).........................................................36

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x 4-3. The location of climate stations (squares) and surficial discharge stations (triangles) in both the northern and southern study areas.....................................................37 4-4. The total monthly precipitation and potential evaporation values for the southern study area between May, 1999 to July, 2000 FL.................................................38 4-5. Recharge values between May 1999 and August 2000 for the southern study area (grey bars) and average recharge values taken from average data of 30 years and 17 stations (black bars)..................................................................................38 4-6. Histogram of seepage flux for the dry season in the northern study area.....................40 4-7. Histogram of seepage flux for the rainy season in the northern study area...................41 4-8. Histogram of seepage flux for dry season in the southern study area...........................43 4-9. Histogram of seepage flux for rainy season in the southern study area........................43 4-10. The profile of chloride concentrations for 3 multisamplers measured during December, 1999 in the northern study area.........................................................46 5-1. The changes in salinity and temperature with depth in the water column for station IRL16 during the rainy season in the northern study area. Sampled on August 16, 1999................................................................................................................64 5-2. Plot of seepage water chloride concentrations against the corresponding water column chloride concentrations for the northern study area dry and rainy seasons.................................................................................................................68 5-3. Plot of seepage water chloride concentrations against the corresponding water column chloride concentrations for the southern study area dry and rainy seasons.................................................................................................................69 5-4. The multisample profiles of chloride concentrations for the (A) dry and (B) rainy seasons of the southern study area.......................................................................72 5-5. The average chloride concentrations of seepage water (italics) and the water column (mM) for each transect during the dry season (A) and rainy season (B) in the Indian River Lagoon compared with chloride concentrations of surficial discharge..............................................................................................................78 5-6. The constituents of total nitrogen..................................................................................80 5-7. The constituents of total phosphorus.............................................................................81

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xi Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science THE QUANTITY, CHARACTERISTICS, SOURCE AND NUTRIENT INPUT OF GROUNDWATER SEEPAGE INTO THE INDIAN RIVER LAGOON, FL By Mary K. Lindenberg December 2001 Chairman: Dr. Jonathan Martin Major Department: Geological Sciences The importance of groundwater seepage into estuaries is poorly understood, but it may be a significant part of nutrient cycling. Groundwater seepage also can add nutrient pollutants to an estuary, thereby changing the ecosystem to a state of eutrophic conditions. One estuary where groundwater seepage may be important is the Indian River Lagoon, located on the east coast of Florida. The Indian River Lagoon is home to 40 rare or endangered species, has great potential for economic resources and is rapidly being developed increasing the potential threat of pollution from groundwater seepage. Groundwater seepage was measured in two separate study areas of the lagoon; the northern study area is located between N28 50 and N28 40, and the southern study area is located between N28 25 and N28 00. Each study area was sampled at the end of the dry season (May) and near the end of the rainy season (August). Using seepage meters to measure seepage flux, average groundwater seepage into the Indian River Lagoon was found to be 40 ml/m2/min and 63 ml/m2/min during the dry and rainy season,

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xii respectively, in the northern study area and 28 ml/m2/min and 39 ml/m2/min during the dry and rainy season, respectively, in the southern study area. Seepage rates increased between the dry and rainy seasons in the northern study area by 58% and in the southern study area by 41%. This seasonal increase in seepage rates may be related to the increase in precipitation between the dry and rainy seasons. The chloride concentrations in seepage water are very similar to the chloride concentration in lagoon water, indicating that lagoon water cycles through the sediments possibly because of a density dependent fluid flow. Using a mass balance equation of chloride concentrations, the percentage of groundwater constitutes only 1%4% of seepage water discharged into the lagoon. The chloride concentrations in pore water profiles reflect this mixing of lagoon water into the pore water. Assuming that nutrients in groundwater seepage can be differentiated from recycled lagoon water, nutrient loading of total nitrogen and total phosphorus in seepage water was 11 to 17 times the total nitrogen and 14 to 23 times the total phosphorus of surface water discharge from drainage areas surrounding the lagoon. Nutrient loading from seepage water may also affect the limiting nutrient for primary production in each study area. This implies that seepage water may provide an important control on nutrient distribution to the Indian River Lagoon.

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1 CHAPTER 1 INTRODUCTION Significance of Submarine Groundwater Seepage Submarine groundwater seepage refers to the diffuse discharge of groundwater to a marine water body. Seepage water may include both seawater that circulates through shallow sediments and groundwater discharging from aquifers (Bokuniewicz, 1980; Cable et al., 1996 a, b; Church, 1996). Consequently, groundwater seepage is a collective mixing of salt water from recirculated seawater and fresh water from aquifer groundwater. Submarine groundwater seepage is also referred to as groundwater discharge in the literature. Compared to runoff, precipitation and evaporation, however, little is known of the magnitude of groundwater seepage to estuaries and the coastal ocean (Johannes, 1980; Bokuniewicz, 1980; Connor and Belanger, 1981; Capone and Bautista, 1985; Simmons, 1992; Bugna et al., 1996; Cable et al., 1996a, b; Church, 1996). Groundwater seepage is important because it may represent a significant portion of the hydrologic cycle in estuaries. Importance of Groundwater Seepage and Nutrient Loading into Estuaries Fresh water concentrations define estuaries. The fresh water concentration of estuaries is determined by the amount of fresh water inflow and the extent of evaporation. Fresh water inflow controls circulation, mixing and flushing in estuaries. These processes help to remove pollutants, as well as mix, distribute and recycle nutrients

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2 (Stickney, 1984). Groundwater may be a large component of the total fresh water input to estuaries, although this component of the estuarine hydrologic budget is poorly known. The potential for groundwater to add nutrients to aquatic habitats is particularly important for ecological reasons (Belanger and Mikutel, 1985). For example, submarine spring discharge was found to produce excess nitrogen to a coral reef system in Discovery Bay, Jamaica (DElia et al., 1981). More importantly, Valiela et al. (1978) noted that groundwater contributes 20 times or more the amount of nutrients brought in by precipitation to the Great Sippewissett Marsh, Massachusetts. Just as pristine groundwater represents a significant, but natural, contribution of nutrients to a healthy habitat, it may bring excessive nutrients if polluted. Excess nutrients cause eutrophication, excess algal growth and destructive changes in community structure (Day et al., 1989). For example, this problem was identified in Waquoit Bay, Massachusetts, and the Florida Keys, Florida, where anthroprogenically derived nutrients in the groundwater were shown to cause eutrophication of the aquatic systems (Lapointe and Clark, 1992; Valiela et al., 1992). Indian River Lagoon The Indian River Lagoon is an important place to study groundwater discharge because of the diverse range of animal species living in and around the lagoon, its potential economic resources and rapid human development in the area surrounding the lagoon. The Indian River Lagoon is the most biodiverse estuary in North America, with 2,200 plant and 2,100 animal species living within its ecosystem (IFASHabitat). Forty of the animal species are rare or endangered. The decline in animal and plant species,

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3 seagrass and habitat loss in the Indian River Lagoon is the foci of the National Estuary Program (Indian River Lagoon Program[IRLP], 1999). Pollution, sedimentation from surface water and sediment runoff as well as discharge of agricultural and industrial wastewater into the lagoon cause species decline in the Indian River Lagoon. In a conference held on September 1, 1998, the Indian River Lagoon Program (IRLP) formed an outline for restoration of the lagoon. On the top of the list for the restoration plan is reduction of fresh water and storm water discharges into the lagoon (IRLP, 1999). This restoration plan neglected groundwater seepage as another possible source of pollution, and consequently this potentially important source of nutrients was not included in the restoration plan for the lagoon. It is important to correctly quantify the seepage water source that contributes to a polluted area by measuring nutrient loading and pollutants from groundwater seepage. In addition to the wide biodiversity, the Indian River Lagoon is critical to the local economy. The coastal waters and the lagoon warm the surrounding farmland during the winter, allowing a more predictable harvest for the citrus growing industry (Woodward-Clyde, 1994). Throughout the lagoon, 21 species of finfish and 4 species of shellfish support local commercial fisheries (Woodward-Clyde, 1994; IRLNEP, 1998). The Indian River Lagoon is also used for recreational and tourist activities such as fishing and boating. Boat access facilities, marinas, fishing supplies, bait, and marine stores support a thriving tourist industry by providing recreational activities. Restaurants and hotels also profit from aesthetic features of the lagoon. Consequently, the Indian River Lagoon supports the sustenance and growth of industry and population in the region.

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4 Protection of the lagoon and its link to the local economy requires identifying the extent that nutrients and possible pollutants are added to the lagoon through groundwater seepage. Eutrophic conditions resulting from excess nutrients could cause mass algal blooms that block sunlight or phytoplankton blooms that deplete bottom waters of dissolved oxygen. These eutrophic scenarios would diminish seagrass beds, which aquatic animals use for food and habitat. Without such environments, levels of those species would no longer support the fishing and tourist industries. Pressures from urban and commercial development have detrimental effects on the habitat of the lagoon. The human population around the lagoon has increased by almost 124% from 1970 to 1990. By the year 2010, the human population is projected to increase another 60% (IRLNEP, 1995). This population growth raises the concern for contaminant input into the lagoon (Trochine and Trefry, 1996). In addition, population growth could cause excessive groundwater withdrawal, because in Brevard County groundwater is the largest source of potable water. Excessive groundwater withdrawal may reduce groundwater flow into the lagoon or cause salt water intrusion in coastal aquifers. If groundwater is a natural pathway for nutrients to flow into the lagoon, a reduction of groundwater flow into the lagoon may reduce important nutrient input. Salt water intrusion will degrade the quality of local potable water. Understanding the impacts on the lagoon caused by changes in the water budget as population grows will depend on a correct quantification of all the parts of the hydrologic budget, including groundwater seepage.

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5 Previous Studies There have been many attempts worldwide to measure groundwater seepage into surface water environments (Table 1-1). Seepage meters have been used to quantify submarine groundwater seepage flux into estuaries, bays, oceans and coral reef systems (Bokuniewicz, 1980; Lewis, 1987; Belanger and Walker, 1990; Belanger and Montgomery, 1992; Reay et al., 1992; Simmons, 1992; Gallagher et al., 1996; Cable et al., 1997a, b; Rutkowski et al., 1999). Seepage meters are limited to measuring only pore water flow across the sediment-water interface and cannot be used to determine the source of groundwater, for example fresh groundwater or recirculated water, because without the additional measurement of natural chemical or isotopic tracers, the fresh groundwater component cannot be differentiated from the recycled seawater component of seepage water. Bokuniewicz (1980) found typical seepage rates of 27.8 ml/m2/min within 30 m of shore in the Great South Bay, New York. Although streamflow is the principle source of fresh water in the Bay, groundwater seepage accounts for 10 20 % of the total fresh water inflow. Bokuniewicz (1980) did not differentiate the components of the seepage water. Without differentiating the components of the seepage water, Bokuniewicz (1980) assumed the seepage water was fresh groundwater. Other studies have used isotopic and chemical tracers such as Rn and Ra radioisotopes and CH4 concentrations to measure fresh groundwater seepage into nearshore marine environments (Bugna et al., 1996; Cable et al. 1996a, b; Moore, 1996; Corbett et al., 1999). With the use of these tracers, groundwater was found to flow into marine environments such as Florida Bay (Corbett et al., 1999), northeastern Gulf of Mexico (Bugna et al., 1996; Cable et al., 1996a, b) and the South Atlantic Bight (Moore,

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6 1996). These studies measure only the discharge of fresh groundwater and do not include important seepage components such as circulated seawater. Table 1-1. Previous studies measuring groundwater discharge into marine environments. Indian River Lagoon; Jensen Beach, FL -2.17 920 /83 Seepage Meter Belanger and Walker, 1990 Indian River Lagoon; Port St. Lucie, FL Net GW*: 0.29 5.90 Finite Element Model Pandit and ElKhazen, 1990 Great South Bay, NY6.9 27.8 Seepage MeterBokuniewicz, 1980 Florida Keys3.75 6.1 Seepage MeterSimmons, 1992 Onslow and Long Ba y s, NC 4.1 13.89 Seepage MeterSimmons, 1992 Chesapeake Bay Inlet, VA 0.3 61.5 Seepage MeterReay et al., 1992 Chesapeake Bay0 50.0 / 10.5 Seepage Meter Gallagher et al., 1996 Chesapeake BayNet GW*: 2 Seepage Meter/Calculation Robinson et al., 1998 Chesapeake BayNet GW*: 1 Calculation Robinson et al., 1998 Chesapeake Bay0 35 Numerical Model Robinson and Gallagher, 1999 NE Gulf of Mexico-6.9 166 / 80 Seepage Meter/ CH4 Concentrations Bugna et al., 1997 NE Gulf of Mexico8.0 55.0 Seepage MeterCable et al., 1997 NE Gulf of Mexico10 100 Seepage Meter Rutkowski et al., 1999 Coral reef; Barbados, West Indies 0.85 1.22 Seepage MeterLewis, 1987 South Atlantic Bight65.1226Ra Moore, 1996 South Atlantic BightNet GW*: 48.0 Calculation based on Moore, 1996 Li and Barry, 1999*Net GW values only measure discharge of fresh groundwater.METHOD OF MEASUREMENT SEEPAGE FLUX RANGE/AVERAGE ml/m2/min LOCATIONREFERENCE Recently, numerical modeling and calculation were used to calculate groundwater seepage and, in some cases, fresh or net groundwater seepage. Based on Moores (1996)

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7 study, Li and Barry (1999) calculated that approximately 92% of total groundwater seepage was produced from wave setup and tidal pumping and 8% resulted from fresh groundwater. Robinson and Gallagher (1999) modeled the groundwater seepage process based on density dependent fluid flow, the water table and changing tidal boundary conditions in the Chesapeake Bay. They found that the fresh groundwater comprised 6.2% of the total groundwater seepage. Although calculations and groundwater modeling can help to quantify the fresh groundwater component of seepage, these methods require assumptions of hydrologic and geologic characteristics, such as hydraulic conductivity, uniform sediment type and hydraulic head gradients (Belanger and Walker, 1990). Previously, two groundwater seepage studies were completed in areas of the Indian River Lagoon: Port St. Lucie, Florida (Pandit and El-Khazen, 1990), and Jensen Beach, Florida (Belanger and Walker, 1990; Belanger and Montgomery, 1992). Belanger and Walker found total seepage flux varied by a factor of two (-2.17 920 ml/m2/min) across a seepage meter transect traversing the 3.084 km width of the lagoon near Jensen Beach, FL. Pandit and El-Khazen (1990) calculated that fresh groundwater seepage rates ranged between 0.29 5.90 ml/m2/min, using a unsteady groundwater flow, finite element numerical model. The finite element numerical model was used to calculate seepage rates based on a 2D idealized cross-section of the lagoon between the water table divide on the mainland and the ocean, assuming the Hawthorn Formation is impermeable and the groundwater source is from the Surficial Aquifer. Pandit and El-Khazen (1990) assumed the hydraulic conductivity (Kxx = 381 cm/day, Kzz = .762 cm/day) is the same the entire width of their defined transect. The difference between the two studies shows the range in fresh groundwater seepage rates from Pandit and El-Khazens (1990) study

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8 was 6.5% of the range in seepage rates found by Belanger and Walker (1990). This difference may result from a conservative estimate of hydraulic conductivity values in groundwater seepage rates modeled by Pandit and El-Khazen (1990). The average groundwater seepage rate (3.80 ml/m2/min) calculated by Pandit and El-Khazen (1990) was 4.5 % of the average seepage rate (83 ml/m2/min) measured by Belanger and Walker (1990). The low flow rate measured by Pandit and El-Khazen (1990) takes into account only fresh or net groundwater, whereas the larger flow rates measured by Belanger and Walker (1990) include all of the water components in seepage water. Purpose There were three main objectives to this study. The first was to measure the groundwater seepage to the Indian River Lagoon using seepage meters (Lee, 1977). Ancillary objectives included determining how seepage rate fluctuations were caused by seasonality of precipitation and if spatial variability of seepage rates is controlled by aquifer composition and hydraulic properties. The second objective was to find the source of the seepage water (e.g., the proportions of lagoon and groundwater) using natural and environmental tracers such as chloride concentrations. The final objective was to estimate the extent of nutrient loading to the estuaries from groundwater seepage.

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9 CHAPTER 2 REGIONAL SETTING Location Located on the eastern margin of Florida, the Indian River Lagoon spans 251 kilometers from its northern end near Ponce De Leon Inlet to Jupiter Inlet in the south (Figure 2-1) totaling 922 km2 in surface area (Woodward-Clyde, 1994; IRLNEP, 1998). The water depth ranges between 1 and 3 m, and the average depth is 1.7 m (Smith, 1993). The Indian River Lagoon System is made up of three interconnected water bodies, i.e., the Mosquito Lagoon, the Banana River Lagoon and the Indian River Lagoon proper (Figure 2-1). The system is classified as a lagoonal estuary. The Indian River Lagoon does not depend on one single river, but on many rivers for its source of fresh water. In addition, its source of ocean water is from four small inlets, Sebastian, Ft. Pierce, St. Lucie and Jupiter Inlets, that are located in the southern half of the lagoon. The ocean connects to the Mosquito Lagoon through the Ponce De Leon Inlet and to Banana River Lagoon through a system of locks in the Port Canaveral Inlet (Woodward-Clyde, 1994). During this project, two separate areas of the Indian River Lagoon system were studied (Figure 2-2a,b). The northern 16 km of the Indian River Lagoon was sampled during 1999. To the south of the first site, between Cocoa and Melbourne, FL, the Indian River Lagoon and Banana River Lagoon were sampled during 2000. Table 2-1 shows the dates and the type of measurements recorded. The northern study site is predominantly surrounded by citrus agriculture and government reserve lands of the Canaveral National

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10 Seashore and the National Wildlife Refuge, while the southern study area is surrounded by urban and commercial development. The northern Indian River Lagoon, including both study areas, has small diurnal tides of 4 cm, and consequently wind-driven currents are responsible for much of the water movement. Figure 2-1. The Indian River Lagoon System (including the Indian River Lagoon, the Banana River Lagoon and the Mosquito lagoon) located in east Central Florida. Boxes show the 1999/northern (figure 2-2a) and 2000/southern (figure 2-2b) study sites.

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11 Table 2-1. Sampling, times, measurements and locations. May (Dry Season)August (Rainy Season)December (Dry Season) Seepage meter, water column, surface water and groundwater Seepage meter, water column, surface water and groundwater Multisample ports and water column May (Dry Season)August (Rainy Season) Seepage meter, water column, surface water, groundwater and multisam p le p orts Seepage meter, water column, surface water, groundwater and multisam p le p orts Northern Study Area (1999) Southern Study Area (2000) a Figure 2-2. Map and stations of the (a) northern study area and of the (b) southern study area. Seepage meter, surface water and groundwater well samples are denoted with squares, circles and triangles, respectively.

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12 b Figure 2-2. Continued. Physiographic Features The Indian River Lagoon is part of a drainage basin (5795 km2 in area) bordered by barrier islands to the east and the Atlantic Coastal Ridge on the west (WoodwardClyde, 1994). The Atlantic Coastal Ridge was formed from sand dune-type topography and ranges in elevation to 55 feet above sea level. The Atlantic Coastal Ridge acts as a drainage divide between the St. Johns River Valley and the Indian River Lagoon basin. The barrier islands are a series of troughs and ridges that formed from paleobeach environments (Brown et al., 1962). Paleobeach ridges on the barrier islands reach 3 meters above sea level (Brown et al., 1962).

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13 Regional Hydrostratigraphy More groundwater is available in Florida than any other state (Conover et al., 1984). Five aquifers occur in the state of Florida. Two aquifers, the Sand and Gravel and the Biscayne, occur only in the western panhandle and in the southeastern region of Florida, respectively. The other three aquifers from bottom to top include the Floridan, the Intermediate and the Surficial. These aquifers contain most of Floridas groundwater because of their large aerial extent. The largest of the three is the Floridan Aquifer. The Floridan Aquifer covers 128,748 km2 including the entire state of Florida and extending into the coastal plains of Alabama, Georgia and South Carolina. The Floridan Aquifer is an assemblage of permeable limestones and dolostones with small amounts of clay, sand and marl (Conover et al., 1984). Above the Floridan Aquifer lies the Intermediate Aquifer or the intermediate confining unit. This unit retards the exchange of water between the overlying Surficial Aquifer and the underlying Floridan Aquifer (Scott, 1990). The confining unit is comprised of siliciclastic deposits interlayered with carbonates (Scott, 1990). Above the Intermediate Aquifer is the Surficial Aquifer. As a water table aquifer, the Surficial Aquifer system is composed of limestone beds, unconsolidated sands, shells, shelly sands and occasional clay beds (Miller, 1997). Figure 2-3 and table 2-2 describe the hydrostratigraphy of the region (Toth, 1988). In northern study area, the lithology of the Surficial Aquifer is composed of two units: a marl which ranges from 15.24 to 45.72 m thick and an overlying sand which ranges from 0 to 15.24 m thick. The marl unit is Pleistocene in age and consists of sands, shells, clays and sandy clays. The lower marl formed in environments such as beach, lagoonal, tidal flat and channels systems. The upper sand unit was formed as dunes, and it is clean with some shell fragments (Williams, 1995). In the southern study area the lower Surficial

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14 Aquifer system is composed of Pliocene and Miocene-aged Tamiami Limestone, also known as the shallow rock aquifer. These bioclastic coquiniod lenses and beds are Figure 2-3. A hydrostratigraphic cross-section below the IRL from the Volusia/ Brevard County line in the north to Sebastian Inlet in the south. overlain in some areas by the Caloosahatchee Formation, which is composed of undifferentiated sediments of clay sand and coquina. These sediments are overlain by the Anastasia Formation, which contains Pleistocene-aged sandy coquina held together loosely with calcareous cement. The Surficial undifferentiated sediments and the Anastasia Formation compose the shallow sand and the shallow water table aquifer (Toth, 1988). The Surficial Aquifer is a water-table aquifer where water tables can fluctuate rapidly with rainfall, evapotranspiration and local streamflow. The Surfical

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15 Aquifer holds significant amounts of fresh water in the Atlantic Coastal Ridge, which supplies many homes with potable water (Williams, 1995). Table 2-2. Lithologic and hydrogeologic information taken from wells in the coastal areas of Volusia, Brevard and Indian River Counties, FL (Toth, 1988). EpochSurficial Sediments (north)Sands, coquina, clay and organic materialFt. Thomson Formation (southwest)Sands, coquina, limestone and organic materialGray Sand Zone (southwest) Tamiami Formation (east) Gray Sand Aquifer Shallow Rock AquiferSands with some coquina and some clay Recrystallized limestones and bioclastic co q uinoidsMiocene Secondary Artesian Eocene Suwannee Limestone Ocala Limestone Avon Park Limestone Lake City Limestone Hawthorn Group Intermediate Aquifer System or Confining UnitPhosphatic dolosilts, sands, clays and carbonate bedsOligocene Floridan Aquifer Systembioclastic, chalky or recrystallized limestone bioclastic, recrystallized or dolmitic limestone dolostone; bioclastic or recrystallized limestone limestone or dolostone Coquina with sand, silt, limestone and organic materialPliocene Miocene Callosahatchee Formation Undifferentiated SedimentsClay, sands and coquinaSurficial Aquifer SystemHolocene Pleistocene Anastasia Formation (coastal) Shallow Sand and Shallow Water Table AquifersLithologic Unit (location) Aquifer UnitCharacteristics The confining unit in east-central Florida consists of interbedded siliciclastic and carbonate sediments of the Hawthorn Group (Scott, 1990). The intermediate confining unit and Intermediate Aquifer system increase in thickness from less than 3 m to greater than 150 m from the northern study area to the southern study area (Figure 2-3). The Hawthorn Group sediments are missing in areas that include the northern study area (Scott, 1990) resulting in unconfined or semi-confined (the Surficial Aquifer can act as a confining unit) conditions for the Floridan Aquifer, which may hydraulically connect to the Surficial Aquifer system (Toth, 1988; Scott, 1990; Williams, 1995). The Hawthorn

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16 Group is composed of interbedded clay, silt, sand and carbonate beds of Miocene age. These sediments make up two zones of the Hawthorn Group. The upper zone is composed of green clays and silts, whereas clays and carbonate materials comprise the lower zone. The Floridan Aquifer system is composed of Eocene and Oligocene aged limestone units. The lower Lake City Limestone unit, a white, fossiliferous, recrystalized limestone with some dolostone, is overlain by the Avon Park Limestone unit. The two zones of the Eocene aged Avon Park Limestone comprise a lower distinct lithology of low porosity dolostone and an upper interbedded limestone and dolostone region. Overlying the Avon Park limestone is the late Eocene aged Ocala Limestone. The Ocala Limestone is a light colored, weak to hard cemented, recrystalized, foraminiferal, coquiniod limestone. Between the Ocala Limestone and the Hawthorn Group lies the Oligocene-aged bioclastic to chalky limestone of the Suwannee Limestone. The Suwannee Limestone is generally thin to absent in the study area but is present in the southern areas of Brevard County and increases in thickness to the south (Toth, 1988). Where the Floridan Aquifer is confined in the Indian River Lagoon study area, its potentiometric surface can reach heights ranging from 1.5 to 10 m above sea level (Figure 2-4). Groundwater should thus flow from the Floridan into the Surficial Aquifer and ultimately into the lagoon. The rate of upward flow will depend on the hydraulic conductivity of the overlying confining unit as well as differences between the heads of the two aquifers.

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17 a Figure 2-4. Contours of the potentiometric surface of the Upper Floridan Aquifer during (a) May 1999, (b) September 1999, (c) May 2000, (d) September 2000 (Bradner and Knowles, 1999). Contour interval is 5 ft.

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18 b Figure 2-4. Continued.

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19 c Figure 2-4. Continued.

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20 d Figure 2-4. Continued.

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21 Climate and Hydrologic Components The Indian River Lagoon is located in a transition region between sub-tropic and temperate climates, and consequently its climate is influenced by its latitude. Climate is also influenced by the proximity of the Atlantic Ocean and the Gulf Stream, which passes the full length of the lagoon approximately 50 to 100 km from the shore. From 1951 to 1980, the Indian River Lagoon basin received an annual average of 127 cm of rainfall. Figure 2-5 shows the average monthly rainfall for a thirty-year period. The lows and highs for annual rainfall amounts range from 113 cm to 144 cm (Woodward-Clyde, 1994). A Class A pan evaporation station in Vero Beach, FL supplied values since 1952. Using a pan coefficient factor of 0.78, the calculated annual potential evaporation was 124.5 cm. Figure 2-6 shows the potential evaporation rates are greatest between the months of March through September (Rao, 1987). For a 30-year period the average annual temperature for the Indian River Lagoon system was 23 C. Maximum temperatures were as high as 38 C during the summer and minimal temperatures were as low as -8 C during the winter (Woodward-Clyde, 1994). Mean temperatures for the summer months do not vary significantly along the length of the lagoon, but mean temperatures during the winter months can be 4 to 5 C warmer in the south than the north (Rao, 1987). Recharge to the Surficial Aquifer system is primarily from precipitation (Figure 2-7), minor amounts of irrigation water and upward leakage from the Upper Floridan Aquifer (Williams, 1995). For east-central Florida, 50% of the precipitation occurs during the summer months of June through September (the wet season), which means recharge is relatively higher during the summer months (Williams, 1995). When the water table is high during the wet season, the water table response to rainfall may occur

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22 within minutes in low lying areas (Williams, 1995). Discharge from areas of the Surficial Aquifer, which include seepage, springflow, well discharge, flow to drainage ditches and evapotranspiration, will increase due to increased rainfall and recharge during the summer months (Williams, 1995). 0 2 4 6 8 10 12 14 16 18 20January February March April May June July August September October November DecemberMonthPrecipitation (cm) Dry Season Dry Season Rainy Season Figure 2-5. Average monthly precipitation for the Indian River Lagoon region. The precipitation values are based on the monthly mean of 17 stations in and around the IRL from 1951 to 1980 (Rao,1987).

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23 Figure 2-6. Average monthly potential evaporation for the Indian River Lagoon region. The potential evaporation values are based on the monthly mean of 17 stations in and around the IRL from 1951 to 1980 (Rao, 1987). Figure 2-7. Average monthly recharge for the Indian River Lagoon region. The recharge values are based on the monthly mean of 17 stations in and around the IRL from 1951 to 1980 (Rao, 1987). -8 -6 -4 -2 0 2 4 6 8January February March April May June July August September October November DecemberMonthRecharge (cm) Dry Season Rainy Season Dry Season 0 2 4 6 8 10 12 14 16January February March April May June July August Septmember October November DecemberMonthPotential Evaporation (cm) Dry Season Dry Season Rainy Season

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24 CHAPTER 3 METHODS Seepage Measurements Methods Review and Background Theory The seepage meter (Figure 3-1) was first devised by Israelson and Reeve (1944) to study seepage outflow from irrigation canals (Fellows and Brezonik, 1980). Since then, seepage meters have been used to study groundwater discharge into lakes (Lee, 1977; Downing and Peterka, 1978; Fellows and Brezonik, 1980; Connor and Belanger, 1981; Belanger and Mikutel, 1985; Cherkauer and Nader, 1989; Hirsh, 1998) rivers/ canals, estuarine/coastal regions (Bokuniewicz, 1980; Capone and Bautista, 1985; Simmons, 1992; Cable et. al, 1996a, b) and coral reef habitats (Lewis, 1987). Several laboratory-scale tests experiments have been conducted to test the accuracy of seepage meters. Lee (1977) tested seepage water by varying the hydraulic gradient in a rectangular tank and measuring the flow. Lees (1977) study showed a linear correlation between changes in seepage rate and hydraulic gradient. The slopes of the regression lines differed per location which was attributed to heterogeneity of sediment type throughout the test tank (Lee, 1977). Belanger and Montgomery (1992) also used a series of laboratory experiments to test the seepage meter device under known conditions. Belanger and Montgomery (1992) found seepage rates varied per location which they inferred to be a function of heterogeneous permeability. Shaw and Prepas (1989) discovered that empty seepage bags would fill rapidly because of a difference in

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25 hydraulic gradient between the water column and the bags. This result led to a modification of the technique where seepage bags were pre-filled with 1000 ml of water. Field Sampling Seepage Meter Construction, Deployment and Seepage Measurements Seepage meters were constructed from 55 gallon steel drums. The drums were cut 15 cm from the ends to form a cup-like container. One half inch diameter ports were drilled into the flat top, 6 cm from the edge of the meter. Two screw-sized holes were drilled into one side of the meter to attach rubber handles. The meters were sanded and painted with two coats of two-part marine epoxy paint. A male garden hose fitting was inserted into the port and made watertight using rubber washers and silicon caulking. Rubber handles were screwed into the side of the meter using washers and silicon caulking. Seepage meters were placed into the sediment like an upside-down cup (Figure 31). The sides were pushed into the sediment to prevent water from flowing into the meter under the rim. The side with the port was tilted slightly upward to prevent an accumulation of gases, which could lead to backpressure and lift the meter free of the sediment. The arrangement of stations differed between the northern and southern study areas. In the northern study area, seepage was measured over five short transects containing 2 to 8 seepage stations and six individual seepage stations in deep water sites (Figure 2-2a). In the southern study area, four transects extended in an east west direction across the lagoon (Figure 2-2b). The northern two transects traverse both the

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26 Indian River Lagoon and the Banana River Lagoon and the southern two transects were confined to the Indian River Lagoon. Figure 3-1. A depiction of a seepage meter placed in the sediment under the water column. Receptacle bag is connected and the valve is open in order to allow flow through the port. Arrows indicate direction of groundwater discharge. After installation, the meters were left to equilibrate for at least 24 hours, which allowed enough time to eliminate any effects that may be caused by backpressure during deployment of the meters (Figure 3-2). Polyethylene seepage bags were used to collect water that flowed from the port. Two sizes of polyethylene bags were used; 5 liter bags had wall thickness of 4 mm while 4 liter bags had wall thickness of 1.5 mm. The

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27 different size wall thickness of each bag did not alter the measured seepage rates. Seepage bags were attached to the male garden hose fitting using zip ties and electrical tape. The male fitting was attached to a female garden hose fitting with a ball valve. 0 10 20 30 40 50 60 70 80 90 100 8/17/99 7:12 8/17/99 8:24 8/17/99 9:36 8/17/99 10:48 8/17/99 12:00 8/17/99 13:12 8/17/99 14:24 8/17/99 15:36 8/17/99 16:48 8/17/99 18:00 8/17/99 19:12 8/17/99 20:24TimeSeepage Flux (ml/m2/min) Figure 3-2. A time series experiment showing 5 seepage rates from station IRL 6. Error bars show the length of time the bags were left on the meter. Stabilization of seepage flux rates resolve around 90 ml/m2/min within 12 hours of placing the seepage meter into the sediment. Seepage rates were measured by adding 1000 ml of lagoon water to the bags prior to deployment in order to prevent pressure anomalies (Shaw and Prepas, 1989). After the 1000 ml of water was added, the valve was closed, then connected to the port of the seepage meter. Once installed on the meter, the valve was opened to allow flow of water either into or out of the bag. After a sufficient amount of time (approximately 1 to 2 hours), the valve was closed, the bag was removed from the seepage meter and the volume of water in the bag was measured using either a 1000 ml or a 2000 ml graduated

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28 cylinder. This process was repeated sequentially for three measurements at each seepage meter site. The seepage flux was calculated by dividing the volume of water that flowed into the bag by the amount of time the bag was on the meter and by the area of the meter (0.28 m2). Control experiments, termed blank seepage measurements, were set up to measure seepage in an environment where seepage was blocked from flowing from the sediments below the lagoon floor. Blank seepage rates were measured in the simulated non-seepage flow environment. A non seepage flow environment was made by placing a small, 2.5 m diameter, plastic, childrens wading pool on the floor of the lagoon and filling it with sediment ~0.5 m deep. The wading pool simulated a non seepage flow environment by blocking seepage from flowing from sediments below the pool to the sediments in the pool. Once 24 hours had passed after deploying a seepage meter in the pool, seepage rates were measured in the same way seepage rates were measured from seepage meters deployed on the floor of the lagoon. The average, standard deviation, minimum and maximum blank seepage flux were calculated for all measurements in both study areas (Table 3-1). The average blank seepage flux was 10.9 ml/m2/min with 1 of 4.9 ml/m2/min. The minimum blank seepage flux was 5.8 ml/m2/min, measured at station IRL3 during the rainy season in the northern study area. The maximum blank seepage flux was 17.6 ml/m2/min, measured at station IRL7 during the rainy season in the northern study area. Blank seepage flux measurement were not conducted during the dry season in the northern study area. Seepage meters were deployed in duplicate to find the relative difference of seepage rates measured from closely spaced seepage meters. Duplicate seepage meters

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29 were deployed within a few meters of each other at a station. The average, minimum and maximum percent difference of seepage rates measured from duplicate seepage meters were calculated for all duplicate stations in both study areas. The average percent difference of duplicate seepage rates was 61.9% (Table 3-1). The minimum percent difference between duplicate seepage rates was 7.4%, measured from station BRL1 during the dry season in the southern study area. The maximum percent difference between duplicate seepage rates was 84.9%, measured from BRL1 during the rainy season in the southern study area. Duplicate seepage measurements were not conducted during the dry season in the northern study area. Table 3-1. Blank and duplicate seepage flux values. Bl ankDupl i cat eDupl i cat e SeepageSeepageSeepage Fl uxFl uxFl ux ml / m2/ mi nml / m2/ mi n % DifferenceNorthern IRL3 13. 416. 8BRL6a 59. 619. 8 72.5Study5. 85. 2BRL6c 102. 813. 9AreaIRL7 14. 51. 4 17. 65. 1SouthernBRL1 7. 75. 2BRL1a43. 116. 9 7.4StudyBRL1b 40. 18. 7AreaBRL3a13. 15. 4 75.3 BRL3b23. 09. 4 BRL1 6. 37. 2BRL1a 30. 311. 3 84.9 BRL1b 56. 038. 4 BRL3a 8. 89. 0 69.2 BRL3b 15. 010. 3 Average10.9 6.861.9 Minimum5.87.4 Maximum17.684.9 St. Deviation4.9Rainy SeasonRainy Season Dry Season Station Station

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30 Multisamplers Multiple level samplers (multisamplers) were used to sample pore waters at depths up to 2 m below the lagoon floor (Pickens et al., 1981; Fetter, 1994). Multisamplers are made of a PVC pipe with smaller PVC tubes that extend inside the pipe from the top to screened ports at several depths (Figure 3-3). The bottom end of each tube is screened with 250 m spectra mesh screening to prevent sediments from clogging the tubes. Figure 3-3. An example of a multisampling device. Modified from Fetter, 1994.

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31 Two different types of multisamplers were used in the northern area and southern study areas. Sampling tubes of multisamplers in the northern area extended along the outside of the PVC pipe, while sampling tubes of multisamplers used in the southern area were fed through the inside the PVC pipe. The way the multisamplers were deployed also differed in the northern and southern areas. In the northern study area, a hole was augured and the multisampler was inserted into it. In the southern study area, the multisamplers were pounded into the sediment. Water Sample Collection Seepage water was collected using a technique similar to that used to measure seepage rates, except that dry seepage bags were deployed on the seepage meters. The bags were attached to the seepage meter until approximately 1 liter of water filled the bags. The water was filtered through a 0.45 m filter while transferred from the bag into two 125 ml HDPE Nalgene bottles using a 60 ml syringe. Except for the May 1999 sampling trip, another HDPE Nalgene sample bottle was used to collect unfiltered water. The bottles were labeled with the station and date and wrapped with parafilm to protect the notation. Throughout the day, the Nalgene bottles were stored on ice. At the end of the day, 16 N optima grade HCl was added to one of the filtered sample bottles and all bottles were refrigerated. The samples were kept refrigerated until analyzed. One water column sample was collected from each transect and from individual sites in the northern study area. In contrast, water column samples were collected at every station in the southern study area. Water column samples were either collected by immersing a 1000 ml graduated cylinder just below the water surface of the lagoon or by pumping water ~ 50 cm above the lagoon floor. The sample from the water column were

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32 stored and preserved in the same manner as samples of seepage water. An unfiltered sample was not collected for the dry season (May) of the 1999 northern study area. Groundwater samples were taken from wells surrounding the two lagoon field areas. Water was pumped from the wells using 12 V powered electric pump and a garden hose. While pumping the water, temperature and conductivity were monitored until they stabilized, then the samples were stored and preserved the same way as samples of seepage water and water column. An unfiltered sample was not collected for the dry season (May) of the 1999 northern study area. The ports on each multisampler were pumped using a peristaltic pump and flowed through a liter sized container. Conductivity and dissolved oxygen were monitored until stabilized, then afterwards water was collected and filtered using a syringe or stored unfiltered in HPDE bottles in a manner similar to the seepage water sampling techniques. Not all multisampler ports provided water, but those that did continually would pump unlimited volumes of water. The volumes that were actually pumped were not monitored, but were generally less than one liter. Analytical Techniques Field Measurements While on site, conductivity, salinity, temperature, dissolved oxygen and pH were measured on all samples with portable field meters. An Orion model #250A meter was used to measure pH. Conductivity, temperature and salinity were measured with an Orion model #130 conductivity meter. Dissolved oxygen was measured with a YSI model #55 oxygen meter. At the beginning of each day, the dissolved oxygen and pH meters were calibrated using manufacturer directions. The conductivity meter was

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33 calibrated at the beginning of each sampling trip. To measure seepage water, the probes were either placed directly into the seepage bags after they were cut open or the seepage sample was first transferred to a 1 L graduated cylinder and then measured. Water column measurements of conductivity, salinity, temperature and dissolved oxygen were obtained by placing the probes into the water column in the immediate vicinity of the seepage meter. Water column measurements of pH were made by measuring the water column sample collected in a 1 L graduated cylinder for water analysis. Conductivity, salinity, temperature and pH were measured on the groundwater as water was pumped into a 1 liter plastic bucket. Multisampler pore water from each port was collected in a 1 liter container, then measurements were taken inside the container. Laboratory Measurements Chloride. The Clconcentrations were measured by titrating with AgNO3 at the University of Florida (Gieskes and Peretsman, 1986). Measurements of an internal standard (St. Augustine Seawater or SAS) yields a reproducibility of less than 0.5%. Sulfate. Sulfate concentrations were measured from the filtered samples using an Automated Dionex model 500 Ion Chromatograph. Measurements of an internal standard (St. Augustine Seawater or SAS) yields a reproducibility of less than 0.8%. Ammonium. Ammonium (NH4 +) was analyzed for samples from the northern study area using a Spectronic 401 Spectrophotometer by Milton Roy (Gieskes and Peretsman, 1986). Samples from the southern study area were measured using the oxidation method of determining ammonia with an Bran and Luebe auto analyzer (Strickland and Parsons, 1972).

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34 Nitrate and nitrite. Nitrate was measured using a copper-cadmium reducing column with an Bran and Luebe auto analyzer (Strickland and Parsons, 1972). Nitrite measurements were measured without the cadmium column. Total nitrogen. Total soluble nitrogen and total nitrogen (a difference of filtered and unfiltered samples, respectively) were measured on the Bran and Luebe autoanalyzer using a persulfate digestion technique (DElia et al.., 1976). Phosphate. Phosphate or SRP (soluble reactive phosphorus) was measured using a colorimetric method on the Spectronic 401 Spectrophotometer by Milton Roy (Gieskes and Peretsman, 1986) for samples from the northern study area. The samples from the southern study area were measured on the Bran and Luebe auto analyzer (Wetzel and Likens, 1991). Total phosphorus. Total soluble phosphorus and total phosphorus (a difference of filtered and unfiltered samples, respectively) were measured by using a persulfate digestion solution, then autoclaved before they were measured on the Bran and Luebe auto analyzer (Wetzel and Likens, 1991).

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35 CHAPTER 4 RESULTS Precipitation and Recharge Precipitation data for the northern study area was taken from Titusville and Big Flounder rain stations in the northern study area (NOAA Southeastern Regional Climate Center Columbia, SC,Tabitha White, pers. comm. St. Johns River Water Management District) (Figure 4-1). Evaporation data was taken from either the Vero Beach or the Fort Pierce stations (NOAA Southeastern Regional Climate Center Columbia, SC). The potential recharge for the northern study area is calculated as the value of precipitation minus potential evaporation that are shown in figure 4-1. The recharge for the northern study area is shown along with the average monthly recharge for the IRL region for comparison in figure 4-2 (Rao, 1987). The position of each climate station is located in figure 4-3. Precipitation data for the southern study area was taken from the Melbourne station in the southern study area (NOAA Southeastern Regional Climate Center Columbia, SC) (Figure 4-4). Evaporation data was taken from either the Vero Beach or the Fort Pierce stations (NOAA Southeastern Regional Climate Center Columbia, SC). The recharge for the southern study area is calculated as the value of precipitation minus potential evaporation that are shown in figure 4-4. The recharge for the southern study area is shown along with the average monthly recharge for the IRL region for comparison in figure 4-5 (Rao, 1987).

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36 0 5 10 15 20 25 30 35 40May-98 Jun-98 Jul-98 Aug-98 Sep-98 Oct-98 Nov-98 Dec-98 Jan-99 Feb-99 Mar-99 Apr-99 May-99 Jun-99 Jul-99 Aug-99 Sep-99 Oct-99 Nov-99 Dec-99Date(cm) Precipitation Evaporation Wet Season Wet Season Dry Season Figure 4-1. The total monthly precipitation and potential evaporation values for the northern IRL from May, 1998 to December, 1999 (NOAA Southeastern Regional Climate Center Columbia, SC, Tabitha White, pers. comm. St. Johns River Water Management District). -15 -10 -5 0 5 10 15 20 25 30May-98 Jun-98 Jul-98 Aug-98 Sep-98 Oct-98 Nov-98 Dec-98 Jan-99 Feb-99 Mar-99 Apr-99 May-99 Jun-99 Jul-99 Aug-99 Sep-99 Oct-99 Nov-99 Dec-99DateRecharge (cm) Northern Study Area Recharge Average IRL Recharge Rainy Season Dry Season Rainy Season Figure 4-2. Recharge values between May 1998 and December 1999 for the northern study area study area (grey bars) and average recharge values taken from average data over 30 years from 17 stations (black bars) (Rao, 1987).

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37 Figure 4-3. The location of climate stations (squares) and surficial discharge stations (triangles) in both the northern and southern study areas.

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38 0 5 10 15 20 25 30 35 40 45 50 May99 Jun99 Jul99 Aug99 Sep99 Oct99 Nov99 Dec99 Jan00 Feb00 Mar00 Apr00 May00 Jun00 Jul00 Aug00Date(cm) Precipitation Evaporation Rainy Season Rainy Season Dry Season Figure 4-4. The total monthly precipitation and potential evaporation values for the southern study area between May, 1999 to July, 2000 FL (NOAA Southeastern Regional Climate Center Columbia, SC). -20 -10 0 10 20 30 40 May99 Jun99 Jul99 Aug99 Sep99 Oct99 Nov99 Dec99 Jan00 Feb00 Mar00 Apr00 May00 Jun00 Jul00 Aug00DateRecharge (cm) Southern Study Area Recharge Average Monthly Recharge Rainy Season Rainy Season Dry Season Figure 4-5. Recharge values between May 1999 and August 2000 for the southern study area (grey bars) and average recharge values taken from average data of 30 years and 17 stations (black bars) (Rao, 1987).

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39 Seepage Rates Northern Study Area In the northern area, the average, minimum and maximum seepage rate increased between the dry and rainy seasons (Table 4-1). None of the reported seepage rate values are corrected for the values of blank seepage flux measurements. The average of all measured seepage fluxes was 39.91 ml/m2/min with 1 of 21.66 ml/m2/min during the dry season. The average of all measured seepage fluxes was 63.08 ml/m2/min with 1 of 30.99 ml/m2/min during the rainy season. The minimum seepage flux for the dry season of 2.91 ml/m2/min occurred at station IRL25. The minimum seepage flux for the rainy season of 22.00 ml/m2/min also occurred at station IRL25. The maximum seepage flux for the dry season of 103.66 ml/m2/min occurred at station IRL23. The maximum seepage flux for the rainy season of 144.40 ml/m2/min occurred at station IRL7. Between dry and rainy season of the northern study area there was a 58% increase in average seepage rates (Table 4-2). Minimum values for both the dry and rainy season occurred at station IRL25 and increased by 652%, whereas the maximum increase in seepage rates from May to August was 697% at IRL7. The station with the maximum seepage rate during the dry season was IRL23 and during the rainy season was IRL7. Out of the 28 stations, seven stations including IRL 5, 12, 15, 18, 23, 27 and 28, decreased in seepage rates from dry to the rainy season. The average decrease in seepage rate is -11%, where the greatest decrease was -19% at station IRL12. Both the rainy and dry seasons exhibit a rightward skewness or positively skewed frequency curve (Figure 4-6, 4-7).

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40 Table 4-1. Average, median, minimum, maximum and standard deviation of seepage flux rates for the northern study area. AverageMedianMin ValueStationMax ValueStationSt. Dev.* Season ml/m2minml/m2minml/m2minml/m2minml/m2min Dry 37.642.93IRL25103.66IRL2321.66 Rainy 53.1522.00IRL25144.40IRL730.99 *Standard deviation of all measured seepage rates39.91 63.08 Table 4-2. The minimum and maximum seepage rates and the corresponding % change between the dry and rainy seasons of the northern study area. StationDry Season Rainy Season ml/m 2 minml/m 2 min % Increase Average 39.9163.0858.1 IRL 7 18.1144.4697.0 IRL 25 2.922.0652.0 % Decrease IRL 12 92.174.3-19.3 IRL 23 103.789.9-13.3 0 2 4 6 8 10 12 14 0-14.9915-29.9930-44.9945-59.9960-74.9975-89.9990-104.99Seepage Flux (ml/m2/min)Number of Obs. Average value of 39.9 ml/m2/min Figure 4-6. Histogram of seepage flux for the dry season in the northern study area.

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41 0 2 4 6 8 10 12 14 0-14.9915-29.9930-44.9945-59.9960-74.9975-89.9990-104.99Seepage Flux (ml/m2/min)Number of Obs. Average Value of 63.1 ml/m2/min Figure 4-7. Histogram of seepage flux for the rainy season in the northern study area. Southern Study Area In the southern study area, the average and maximum seepage rates increased between the dry and rainy seasons, but the minimum seepage flux decreased (Table 4-3). None of the reported seepage rate values are corrected for the values of blank seepage flux measurements. The average of all measured seepage fluxes was 27.3 ml/m2/min with 1 of 13.1 ml/m2/min during the dry season. The average of all measured seepage fluxes was 39.5 ml/m2/min with 1 of 23.5 ml/m2/min during the rainy season. The minimum seepage flux for the dry season of 10.1 ml/m2/min occurred at station IRL41. The minimum seepage flux for the rainy season of 8.8 ml/m2/min occurred at station BRL3. The maximum seepage flux for the dry season of 57.7 ml/m2/min occurred at

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42 station IRL40. The maximum seepage flux for the rainy season of 94.3 ml/m2/min occurred at station IRL39. The increase in average seepage rate was 41% from the dry to the rainy season. The largest increase at an individual station was 245% at IRL29 (Table 4-4). Out of 20 stations measured in the southern study area, seven stations including BRL 1, 3, 4, IRL 31, 36, 38, and 42 decreased in seepage rate from the dry to rainy season. The average decrease for these stations was -19% and the largest decrease was -37%. The dry and rainy season seepage rates produced a left and a rightwardly skewed frequency curve, respectively (Figure 4-8 and 4-9). Table 4-3. Average, median, minimum, maximum and standard deviation of seepage flux rates for the southern study area. AverageMedianMin ValueStationMax ValueStationSt. Dev.* Season m l/m2/m inm l/m2/m inm l/m2/m inm l/m2/m inm l/m2/m in Dry 24.5710.11IRL4157.71IRL40*12.86 Rainy 35.928.85IRL395.97IRL3923.22*Standard deviation of all measured seepage rates27.69 39.11 Table 4-4. The minimum and maximum seepage rates and the corresponding % change between the dry and rainy seasons of the southern study area. StationDry SeasonRainy Season ml/m 2 /minml/m 2 /min % Increase Average 27.6939.1141.3 IRL41 10.1116.6264.0 IRL29 14.4549.91245.0 IRL39 30.3794.31210.5 % Decrease BRL3 13.108.85-32.5 BRL4 41.9826.55-36.8

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43 0 1 2 3 4 5 6 7 8 9 0-14.9915-29.9930-44.9945-59.9960-74.9975-89.9990-104.99Seepage Flux (ml/m2/min)Frequency of Values Average value of 26.9 ml/m2/min Figure 4-8. Histogram of seepage flux for dry season in the southern study area. 0 1 2 3 4 5 6 7 8 0-14.9915-29.9930-44.9945-59.9 960-74.9975-89.9990-104.99Seepage Velocity (ml/m2/min)Frequency of Values Average value of 39.1 ml/m2/min Figure 4-9. Histogram of seepage flux for rainy season in the southern study area.

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44 Tracers All average, minimum, maximum and standard deviation for tracer concentrations are posted in the following tables for the dry season of the northern study area (Table 45), the rainy season for the northern study area (Table 4-6), the dry season for the southern study area (Table 4-7) and the rainy season for the southern study area (Table 48). Northern study area. During the dry season, the average chloride concentration in the seepage water and water column was 588 mM with 1 of 16.2 mM and 595 mM with 1 of 11.4 mM, respectively (Table 4-5). Chloride concentrations of four groundwater well samples that penetrate the Floridan Aquifer, range between 3 and 18 mM, however GW3 and GW-6 were 153 mM and 219 mM, respectively. The well that provided GW-3 is in a different hydrologic basin (Figure 2-2a). The well that Table 4-5. The average, minimum, maximum and standard deviation of tracer concentrations of the water column, seepage water and groundwater measured during the dry season in the northern study area. SalinityCond.OxygenpH Cl-SO4(ppt)(mS/cm ) (mg/L)(mM)(mM) Ave Water Column 40.2660.469.488.3359531.48 Max 41.4063.1010.758.4361032.48 Min 38.0058.608.248.2456729.35 St. Deviation 0.931.310.860.0811.40.91 Ave Seepage Wate r 39.8360.124.387.4558831.15 Max 41.4063.409.847.7761632.22 Min 37.5047.701.167.2256029.04 St. Deviation 1.083.442.050.1316.200.90 Ave Groundwater 6.35.60.57.167.13.02 Max 14.515.71.07.5219.09.96 Min 0.40.10.36.83.20.00 St. Deviation 6.78.70.40.394.54.68

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45 provided GW-6 penetrates the Surficial Aquifer on the coastal side of the lagoon. Surface water samples from the Haulover Canal (HOC) were similar in concentration to the water column. Turnbull Creek (TBC), with a value of 514 mM, had a lower chloride concentration than average seepage water and average water column values. During the rainy season, the average chloride concentration in the seepage water and the water column was 565 mM with 1 of 20.6 mM and 554 mM with 1 of 14.9 mM, respectively (Table 4-6). The chloride concentrations of four groundwater samples range between 5 mM and 21 mM, however, GW3 and GW-6 were 154 mM and 282 mM, respectively. The surface water samples, TBC and HOC, were similar to the average water column samples. Table 4-6. The average, minimum, maximum and standard deviation of tracer concentrations in the water column, seepage water and groundwater measured during the rainy season in the northern study area. SalinityCond.OxygenpH Cl-SO4(ppt)(mS/cm ) (mg/L)(mM)(mM) Ave Water Column 37.7062.305.418.1355429.43 Max 40.3065.508.238.6357131.70 Min 35.5060.601.348.0152827.40 St. Deviation 1.361.601.830.1814.91.17 Ave Seepage Wate r 37.9562.912.187.4056529.39 Max 41.9067.806.127.7162131.70 Min 35.6060.400.226.9553325.60 St. Deviation 1.521.971.550.2020.61.29 Ave Groundwater 5.6613.50N/A7.55801.53 Max 17.1027.98N/A9.502829.10 Min 0.400.87N/A6.7450.00 St. Deviation 7.3612.25N/A1.121153.71 During the dry season, the water column chloride concentrations are greater than the seepage water chloride concentrations, while during the rainy season the opposite is

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46 true. Overall, the chloride concentrations of the dry season samples are greater than those of the rainy season samples. Multisamplers were sampled during December 1999 in the northern study area, four months after the rainy season sampling trip. Profiles from the water column down into the sediment water interface show chloride concentrations that were ~100-200 mM lower than the seepage water and water column concentration measured during the rainy season (Figure 4-10). -220 -170 -120 -70 -20 30 300350400450500550600Chloride (mM)Depth into sediment (cm) IRL4 IRL22 IRL5 Sediment water interface Average Water Column Chloride Concentrations Dry Season Rainy Season Average Seepage Water Chloride Concentrations Figure 4-10. The profile of chloride concentrations for 3 multisamplers measured during December, 1999 in the northern study area. Southern study area. During the dry season, the average chloride concentration in the seepage water and the water column was 341 mM with 1 of 26.4 mM and 348 mM with 1 of 33.6 mM, respectively (Table 4-7). The chloride concentration of six

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47 groundwater samples range between 4 mM and 34 mM and surface waters samples (including canals and streams) range from 228 mM to 531 mM during the dry season. Table 4-7. The average, maximum, minimum and standard deviation of tracer concentrations in the water column, seepage water, groundwater, surface water and pore water measured during the dry season in the southern study area. SalinityCond.OxygenTemp.pH Cl-SO4(ppt)(mS/cm ) (mg/L)(oC)(mM)(mM) Ave Water Column 21.3133.867.0227.998.4034817.12 Min 19.0030.705.4726.908.0631315.01 Max 26.8041.109.1529.308.7743021.61 St. Deviation 2.183.090.770.700.18341.93 Ave Seepage Wate r 21.6934.590.7827.787.5134115.97 Min 19.0030.600.1326.407.1931413.16 Max 26.5043.603.0028.607.9440125.35 St. Deviation 2.454.490.930.620.23262.96 Ave Groundwater 1.132.160.6526.047.09191.11 Min 0.100.200.1124.504.3340.00 Max 2.003.812.3331.507.86342.04 St. Deviation 0.731.360.772.461.26120.73 Ave Surface Water 25.2242.816.4428.968.2635920.22 Min 18.0032.575.5226.608.1122811.10 Max 36.0056.307.2730.408.3753131.11 St. Deviation 7.059.480.791.450.111138.45 During the rainy season, the average chloride concentration in the seepage water and the water column was 449 mM with 1 of 18.7 mM and 457 mM with 1 of 22.6 mM, respectively, (Table 4-8). The chloride concentration of five groundwater samples range between 6 mM and 31 mM and surface water samples (including canals and streams) range from 228 mM to 531 mM during the rainy season. Chloride concentrations in the seepage water and water column of the dry season are lower than seepage water and water column of the rainy season.

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48 Table 4-8. The average, minimum, maximum and standard deviation of tracer concentrations in the water column, seepage water, groundwater, surface water and pore water measured during the rainy season in the southern study area. SalinityCond.OxygenTemp.pH Cl-SO4(ppt)(mS/cm ) (mg/L)(oC)(mM)(mM) Ave Water Column 28.544.27.4288.345723.3 Min 25.840.34.278.042221.3 Max 29.846.229.1298.649325.3 St. Deviation 1.21.75.050.222.61.3 Ave Seepage Wate r 28.945.61.3307.444923.0 Min 25.843.80.2307.042221.6 Max 38.547.74.0328.248325.3 St. Deviation 3.01.31.100.418.71.0 Ave Groundwater 1.12.31.4287.5211.2 Min 0.00.60.3266.760.0 Max 1.83.52.1327.8312.1 St. Deviation 0.61.10.830.49.20.7 Ave Surface Water 21.934.17.2317.934817.6 Min 0.20.93.9307.5110.6 Max 33.751.08.6328.257029.6 St. Deviation 11.417.31.810.3185.39.5 In the southern study area, multisamplers were measured during both the dry and rainy seasons. The minimum chloride concentration in the pore water was 337 mM during the dry season and 324 mM during the rainy season. The maximum chloride concentration in the pore water was 443 mM during the dry season and 477 mM during the rainy season. Nutrients All average, minima, maxima and standard deviations for nutrient concentrations are posted in the following tables for the dry season of the northern study area (Table 49), the rainy season for the northern study area (Table 4-10), the dry season for the southern study area (Table 4-11) and the rainy season for the southern study area (Table 4-12). All posted concentrations of NO3 include concentrations of both NO3 and NO2 -.

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49 Northern study area. The concentration of TSN in the water column, seepage water and groundwater increased between the dry and rainy seasons. The concentations of TSP in the water column and groundwater decreased between the dry and rainy seasons. However, TSP concentrations increased in the seepage water between the dry and rainy seasons. Southern study area. The concentrations of TSN increased in the water column, seepage water, groundwater and surface water between the dry and rainy seasons. The concentrations of TSP increased in the water column, seepage water, groundwater and surface water between the dry and rainy seasons. However, TSP concentrations decreased in the seepage water between the dry and rainy seasons. Table 4-9. Average, minimum, maximum and standard deviation of nutrient concentrations in seepage water, water column and groundwater during the dry season in the northern study area. NO3 NH4 TSNSRPTSP SiO2 ( m g /L ) ( m g /L ) ( m g /L ) ( m g /L ) ( m g /L ) ( m g /L ) Ave Water Column 0.0060.0990.9190.0060.0170.47 Max 0.0130.1251.0380.0080.0221.39 Min 0.0010.0690.7900.0060.0150.15 St. Deviation 0.0040.0170.0760.0010.0020.31 Ave Seepage Wate r 0.0062.5632.6250.0690.1085.11 Max 0.0176.3084.0230.2590.41210.10 Min 0.0010.6891.3750.0000.0172.72 St. Deviation 0.0051.4370.8310.0780.1081.79 Ave Groundwater 0.0020.6320.8930.0900.1480.02 Max 0.0100.9192.1860.3000.6100.03 Min 0.0000.4590.3000.0140.0140.01 St. Deviation 0.0040.1560.7030.1200.2350.01

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50 Table 4-10. Average, minimum, maximum and standard deviation of nutrient concentrations in seepage water, water column and groundwater during the rainy season in the northern study area. NO3 NH4 TSNTNSRPTSPTPSiO2(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L) Ave Water Column 0.0550.1351.0891.3240.0000.0160.0371.71 Max 0.1020.2511.2511.4710.0000.0170.0454.00 Min 0.0270.0420.9301.2320.0000.0140.0310.66 St. Deviation 0.0280.0610.0970.0680.0000.0010.0050.93 Ave Seepage Wate r 0.0483.8582.6983.0080.0930.1530.2345.05 Max 0.11330.6239.35812.1760.8182.3182.63510.27 Min 0.0080.3441.1601.7160.0000.0150.0401.67 St. Deviation 0.0255.0921.3721.7530.1500.3900.4431.98 Ave Groundwater 0.0241.0261.0061.0740.0760.1250.1290.02 Max 0.0592.4722.6462.7940.4240.6630.6220.03 Min 0.0010.4790.3520.3460.0000.0010.0000.01 St. Deviation 0.0240.7710.8750.9520.1700.2640.2440.01 Table 4-11. Average, minimum, maximum and standard deviation of nutrient concentrations of seepage water, water column, groundwater, surface water and pore water during the dry season in the southern study area. NO3 NH4 TSNTNSRPTSPTPSiO2(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L) Ave Water Column 0.0020.0310.3020.3290.0420.0440.0321.32 Min 0.0000.0070.0810.2500.0010.0020.0010.00 Max 0.0060.0920.3800.4300.6020.6280.0516.49 St. Deviation 0.0020.0220.0620.0490.1260.1310.0111.28 Ave Seepage Wate r 0.0070.3790.5982.1141.0460.7150.69411.50 Min 0.0010.0010.0030.0200.0360.0000.0000.00 Max 0.0140.8263.14311.3584.1803.1143.00431.06 St. Deviation 0.0030.2270.7052.9131.2220.9400.8439.21 Ave Groundwater 0.0050.4850.4360.7140.1250.0850.08115.62 Min 0.0000.3860.0000.1410.0010.0000.00012.15 Max 0.0090.6340.6192.2500.7590.5570.56417.72 St. Deviation 0.0040.0890.2470.6950.2810.2090.2131.74 Ave Surface Water 0.0170.0330.2680.2580.0400.0170.0733.44 Min 0.0030.0170.1220.0610.0010.0000.0210.43 Max 0.0510.0470.3490.4040.1020.0450.1608.47 St. Deviation 0.0200.0130.0930.1290.0370.0190.0563.11

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51 Table 4-12. Average, minimum, maximum and standard deviation of nutrient concentrations of seepage water, water column, groundwater, surface water and pore water during the dry season in the southern study area. NO3 NH4 TSNTNSRPTSPTPSiO2(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L) Ave Water Column 0.0030.0270.4410.4750.0320.0480.0602.43 Min 0.0000.0080.3030.3290.0040.0190.0261.74 Max 0.0440.0560.6350.7230.0660.0750.0843.51 St. Deviation 0.0090.0160.1020.1220.0220.0190.0180.44 Ave Seepage Wate r 0.0030.6351.5911.5210.4600.3950.4428.73 Min 0.0010.0500.5820.5180.0220.0200.0292.28 Max 0.0121.8973.1692.9171.9131.6052.01720.37 St. Deviation 0.0030.5280.6430.6230.4710.3950.4845.44 Ave Groundwater 0.0040.3830.6920.7080.1260.1060.11915.62 Min 0.0000.1820.4300.4440.0020.0020.00011.75 Max 0.0160.5911.3281.3390.7420.6190.71018.17 St. Deviation 0.0060.1460.3220.3200.3020.2510.2892.12 Ave Surface Water 0.0160.0360.4270.5110.0480.0590.0774.19 Min 0.0010.0140.0700.1240.0110.0200.0240.44 Max 0.0660.0811.0000.9880.0890.0890.11412.76 St. Deviation 0.0250.0240.3110.2810.0290.0280.0364.41

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52 CHAPTER 5 DISCUSSION Seepage Rates Groundwater seepage measured from seepage meters in the northern and southern study areas reflect flow of water across the sediment water interface that was greater than seepage rates measured from blank experiments. In both the northern and southern study areas, seepage rates increased from the dry to the rainy seasons based on the average seepage rate. In addition, seepage rates vary spatially across each study area during each season. The following discussion of seepage rates will focus on two questions. The first part of the discussion will focus on whether the seasonal increase in seepage rates was a direct result of increased precipitation from the dry to the rainy season. The second part of the discussion will focus on the cause of spatial variation of seepage rates. Seasonal Relationship of Seepage Rates Temporal variations in seepage rates measured using seepage meters have been found in studies of coral reef, nearshore and estuarine environments (Lewis, 1987; Cable et al., 1997b; Robinson et al., 1998). Along the Barbados coast, seepage rates were twice as high during the rainy season than the dry season because the Barbados aquifer, a highly permeable and transmissible aquifer, is recharged during the rainy season, thus increasing the flow of groundwater (Lewis, 1987). Cable et al. (1997b) found that mean monthly integrated seepage rates to decrease from 21.4 L/m/min to 3.6 L/m/min from August 1992 to March of 1993 off shore of the panhandle of Florida. The decrease in

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53 seepage rate corresponds to a decrease in monthly precipitation from ~35 cm to ~15 cm from August 1992 to March 1993 in the study area. Seepage rates increased from the dry to the rainy season in both study areas. On average, seepage rates increased by 58% from the dry to rainy seasons of the northern study area, although seven stations show decreasing seepage rates (Table 4-2). On average, seepage rates increased by 41% from the dry to rainy seasons of the southern study area, although eight stations show decreasing seepage rates (Table 4-4). All seepage rates were compared using the Wilcoxon signed rank test. The Wilcoxon signed rank test is a nonparametric test that compares probability distributions of sampled data sets and can be used with skewed data similar to the sets of this study (Figure 4-5, 4-6, 47, 4-8). The Wilcoxon signed rank was used to show that there is a significant difference with 95% confidence in the distributions of the seepage rates between the two seasons of both study areas. One possible cause for the observed increased seepage is from an increase in discharge from the Surficial Aquifer. Discharge from the Surficial Aquifer will increase when precipitation recharge to the aquifer increases. The dry season average monthly precipitation value (October, 1998 through April, 1999) was 3.96 cm, while the rainy season average monthly precipitation value was 8.60 (May through August, 1999) for the northern study area (Figure 4-1). The dry season average monthly precipitation value (October, 1999 through April, 2000) was 5.24 cm, while the rainy season average monthly precipitation value (May through August 2000) was 11.2 cm in the southern study area (Figure 4-4). Precipitation recharge increased 2-fold between the dry and the

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54 rainy seasons in both the northern and southern study areas. A two-fold increase may provide enough recharge to aquifers, which is then discharged into the lagoon as seepage. Spatial Heterogeneity of Seepage Rates Seepage rates varied spatially throughout the northern and southern study areas. In the northern study area, seepage rates ranged from 3 ml/m2/min to 104 ml/m2/min during the dry season and from 22 ml/m2/min to 144 ml/m2/min during the rainy season (Table 4-1). In the southern study area, seepage rates ranged from 10 ml/m2min to 58 ml/m2min during the dry season and from 9 ml/m2min to 96 ml/m2min during the rainy season (Table 4-3). This range in seepage rate is not surprising considering the average difference was 61% at stations with duplicate seepage measurements (Table 3-1). Many factors may have caused these observed variations of seepage rates. These factors include the spatial heterogeneity of hydraulic properties and composition of the aquifers that lie below the Indian River Lagoon, the presence of benthic dwelling organisms in sediments and the composition of sediments below each station. The variability of hydraulic properties of the Floridan Aquifer may have caused the spatial changes in measured seepage rates. The Upper Floridan Aquifer is a cavernous limestone system known for its heterogeneous hydraulic properties (Tibbals, 1990). Assuming groundwater is the cause of the seepage, vertical conduits in the system would allow increased upward groundwater flow. Increased upward groundwater flow would produce faster seepage rates. However, the Floridan Aquifer is partially overlain by a confining unit in the northern study area and fully overlain by the confining unit in the southern study area. Consequently, the confining unit and the Surficial Aquifer may control the spatial variation of seepage rates, rather than the Floridan Aquifer.

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55 The presence of the Hawthorn Group confining layer is not well mapped throughout the northern study area. Toth (1988), Tibbals (1990) and Scott (1990) suggest that the Hawthorn Group is missing in northern Brevard County, although the location of the boundary is not clearly defined because of limited well coverage. Pockets of the confining unit could be scattered throughout the area. Where the confining units are missing in the northern study area water flows upward from the Floridan Aquifer to the Surficial Aquifer (Toth, 1988). In areas where the confining unit is breached, seepage rates would be expected to increase due to increased groundwater flow from the Floridan Aquifer, except where there is a confining layer in the Surficial Aquifer. The confining unit thickens to the south and ranges between 30.5 m to 45.7 m in thickness in the southern study area. The confining unit retards upward flow of groundwater from the Floridan Aquifer to the Surficial Aquifer. Low upward flow from the Floridan Aquifer may result in slower seepage flux in the southern study area than the northern study area. Seepage rates may have decreased from the northern study area to the southern study area due to the increased thickness of the confining unit in the southern study area, assuming precipitation recharge remained constant. The average seepage rates decreased by 44% between the dry season in the northern study area and the dry season in the southern study area (Table 4-1, 4-3). The average seepage rates decreased by 61% between the rainy season in the northern study area and the rainy season in the southern study area (Table 4-1, 4-3). In addition, because the confining layer is uniformly distributed, it would not have a significant effect on the variability of the seepage rates in the southern study area. Where the confining unit is present, the Surficial Aquifer is likely to control the spatial variation in seepage rates.

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56 The hydraulic properties of the Surficial Aquifer, such as transmissivity and hydraulic conductivity, vary throughout the study area. The transmissivities range from 2.5 L/d/m to 98.7 L/d/m in Brevard and Indian River Counties (Toth, 1988). The hydraulic conductivity can range by two orders of magnitude in east-central Florida (Toth, 1988). The Surficial Aquifer contains beds of fine-grained materials that act as confining units and these beds may lead to changes in measured seepage rates (Toth, 1988). The presence of minor confining units would slow the rate of flow in the Surficial Aquifer and the rate of seepage measured above the local confining unit. The presence of benthic dwelling organisms in sediments may increase or decrease seepage rates by altering sediment characteristics. Sediments are altered by organisms through bioturbation, biodeposition and production of cementing by-products such as shells and mucous (Day et al., 1989). Through bioturbation, organisms burrow into sediments forming conduits. The presence of conduits alters the hydraulic properties of sediments by increasing porosity and permeability. Elevated porosity and permeability would increase seepage water flow rates. Biodeposition is the buildup of macroinfaunal feces and the deposit of bacterial mucous in sediments. The mucous and feces act as cementing agents and bind sediment particles together (Day et al., 1989). Cemented particles reduce porosity and permeability in the sediments. Reduced porosity and permeability would reduce seepage water flow rates. The variation of composition in the sediments may effect the spatial distribution of seepage rates. Sediments range from mud to sand sized particles in the northern and southern study areas of the lagoon. Mud and clay sized particles may have low permeabilities of 10-6 to 10-3 darcys while, sand sized particles may have increased

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57 permeabilities of 10-2 to 102 darcys (Fetter, 1994). Increased permeability in sediments will allow increased seepage rates compared to areas of low permeability. Spatial variability of seepage rates was more likely controlled by changes in hydraulic properties and composition of sediments and the upper stratigraphy of the Surficial Aquifer, where seepage flow was locally defined beneath each seepage station. The presence of the Hawthorn Group confining unit and the Floridan Aquifer more likely control seepage rates on a regional scale between the northern and southern study areas. Chloride Chloride concentrations were measured to determine the source of seepage water based on concentrations of groundwater, seepage water and the water column of the lagoon. Chloride concentrations in seepage water and the water column decreased between the dry and rainy seasons in the northern study area and increased between the dry and rainy seasons in the southern study area. In addition, chloride concentrations in the seepage water and water column were greater in the northern study area than the southern study area. The following discussion of chloride concentrations will focus on three questions. The first part of the discussion will focus on the cause of the variation in chloride concentrations from the dry to the rainy season in each study area. The second part of the discussion will focus on tracing the source of seepage water using chloride concentrations. The third part of the discussion will focus on how evaporation and surficial runoff directly effects chloride concentrations in the water column and indirectly effects chloride concentrations in seepage water.

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58 Seasonal Variation Average chloride concentrations in the seepage water decreased from the dry to rainy season in the northern study area and increased from the dry to rainy season southern study area. In the northern study area, the percent decrease of the average chloride concentration was 4% in seepage water from the dry to the rainy season. In the southern study area the percent increase in average chloride concentration was 31% in the water column and 32% in the seepage water from the dry to the rainy season. The total normal average monthly recharge is 9.67 cm during the dry season (October through April) and 7.0 cm during the rainy season (May through August) (Table 5-1) (Rao, 1987). The total average monthly recharge was -26.1 cm during the dry season (October 1998 through April 1999) and 8.0 cm during the rainy season (May 1999 through August 1999) in the northern study area (Table 5-2). The total monthly recharge was 7.5 cm during the dry season (October 1999 through April 2000) and 0.1 cm during the rainy season (May 2000 through August 2000) in the southern study area (Table 5-3). The changes in chloride concentrations may have been caused by precipitation recharge to the lagoonal basin or a lack of normal precipitation leading to evaporation. The total monthly recharge increased from the dry season to the rainy season in the northern study area. An increase in recharge may have controlled the decrease in chloride concentrations of the seepage water between the dry and rainy seasons of the northern study area, by diluting the seepage water. In contrast, the total monthly recharge decreased from the dry to rainy season of the southern study area. The decrease in recharge from the dry to the rainy season may be attributed to increased precipitation from a hurricane, which increased normal precipitation by a factor of two during the dry

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59 season. Two hurricanes contributed excessive amounts of rain when they passed through the study areas at the end of the rainy season and the beginning of the dry season in 1999. Assuming the hurricane precipitation was so extensive that it caused a change in water column chloride concentrations, the chloride concentrations of pore water profiles measured in the northern study area during December, 1999, were ~ 100 to 200 mM less in the water column than the average chloride concentrations of the dry and rainy season water column (Figure 4-10). The southern study area received 10 cm more rainfall than the northern study area for September 1999. The extensive recharge during the dry season was caused by significant precipitation during Hurricane Irene that passed through in October 1999. The excessive precipitation increased the total recharge value for the rainy season to over 2 times the normal average dry season. The southern study area may have undergone the same dilution process as the northern study area. The chloride concentrations in the water column measured during the dry season may not have been indicative of natural conditions due to dilution of the lagoon from increased recharge. Chloride concentrations may have increased between the dry and rainy seasons in the southern study area as the lagoon returned to natural conditions after the hurricanes. In addition, chloride concentrations may have increased due to a lack of normal recharge from the dry to the rainy seasons. The total monthly recharge during the rainy season was 7 cm less than the normal monthly recharge during the rainy season. The recharge during the rainy season may have been insufficient to dilute chloride concentrations in the water column; leading to evaporation as a factor that increased the chloride concentrations measured during the rainy season.

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60 Table 5-1. Normal average monthly recharge values for the entire Indian River Lagoon. Normal Average Values for the Entire LagoonPrecipitation*Potential*Recharge Month(cm)Evaporation (cm)(cm) January5.55.7-0.2 February6.97.6-0.7 March7.410.8-3.4 April6.113.0-6.9 May11.014.4-3.4 June17.513.63.9 July16.713.63.1 August16.012.63.4 September18.211.17.1 October13.09.73.2 November5.46.8-1.4 December5.15.4-0.3 *Rao Report, 1987 Table 5-2. Average monthly recharge for the northern study area. Northern Study Area PrecipitationaPotentialbRecharge Month(cm)Evaporation (cm)(cm) May-982.710.8-8.0 Jun-982.19.9-7.8 Jul-9812.7N/AN/A Aug-9818.016.02.0 Sep-9822.15.816.3 Oct-982.87.0-4.1 Nov-985.07.4-2.4 Dec-985.17.9-2.9 Jan-997.05.61.4 Feb-992.36.3-4.0 Mar-991.99.5-7.5 Apr-993.610.2-6.6 May-996.611.1-4.5 Jun-9910.79.80.9 Jul-991.211.5-10.2 Aug-9915.910.15.8 Sep-9933.96.327.6aTitusville and Scotsmoor weather stns.(NOAA, SJRWMD)bVero Beach and Ft.Pierce weather stns.(NOAA)

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61 Table 5-3. Average monthly recharge for the southern study area. Southern Study AreaPrecipitationaPotentialbRecharge Month(cm)Evaporation (cm)(cm) May-9916.511.15.4 Jun-9914.49.84.6 Jul-993.011.5-8.4 Aug-9917.310.17.3 Sep-9943.48.135.4 Oct-9934.07.726.3 Nov-996.310.3-4.0 Dec-996.17.2-1.0 Jan-005.96.00.0 Feb-000.96.9-6.1 Mar-005.59.4-3.9 Apr-006.710.5-3.8 May-001.012.6-11.5 Jun-0017.911.56.3 Jul-0017.110.17.0 Aug-008.810.5-1.7aMelbourne weather stn. (NOAA)bVero Beach and Ft.Pierce weather stns.(NOAA) Fraction of Fresh Groundwater in Seepage Water It is important to determine the percentage of groundwater in seepage water to assess the hydrologic budget of the region in order to confirm numerical models of groundwater seepage such as the one developed by Pandit and El-Khazen (1990). The source of groundwater seepage is also an important control on its chemical composition. The concentration of chloride in the groundwater, seepage water and water column was used to find the percentage of groundwater flowing into the seepage meters. Groundwater has low chloride concentrations, ranging from 3 mM to 33 mM because of its source from precipitation. In addition, there is no source of chloride in the upper Floridan, Intermediate and Surficial aquifers, although in some coastal areas groundwater may contain chloride that originates as seawater intrusion. Nonetheless, the low chloride concentration of groundwater means that chloride should be a useful tracer of

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62 groundwater in the seepage water. Assuming two-end member mixing, the fraction of lagoon and aquifer water can be calculated from the following equation: fgw = (C1-Cm)/(Cl-Cgw) Eq. (1) Where fgw is the fraction of groundwater that enters the seepage meter, C1 is the value of the tracer in the lagoon water, Cgw is the value of the tracer in the groundwater and Cm is the value of the tracer in the seepage water. The percentage of groundwater flowing into the lagoon was calculated for the dry and rainy seasons in the northern and southern study areas using equation (1). Using average values of chloride, the fraction of groundwater flowing into the lagoon during the dry season in the northern study area was calculated to be 4.0 %, 0.0 %, 0.0 %, -0.2 %, 1.4 % and 0.8 % for transect stations IRL1-8; IRL9,10,16; IRL17-20; IRL21-24; IRL11, 25-28, respectively (Table 5-4). Using average values of chloride, the fraction of groundwater flowing into the lagoon during the rainy season in the northern study area was calculated to be -0.2 %, -11.7 %, -3.7 %, -1.5 %, -1.3 % and 0.0 % for transect stations IRL1-8; IRL9,10,16; IRL17-20; IRL21-24; IRL11, 25-28, respectively. Using average values of chloride, the fraction of groundwater flowing into the lagoon during the dry season in the southern study area was calculated to be 2.5 %, -0.3 %, -1.3 %, 0.7 %, 2.6 % and 2.4 % for transect stations IRL29-31; BRL1-5; IRL32-34; BRL6-7; IRL35-38 and IRL39-42, respectively. Using average values of chloride, the fraction of groundwater flowing into the lagoon during the rainy season in the southern study area was calculated to be 3.7 %, 1.4 %, 1.9 %, 1.6 %, 2.9 % and 0.5 % for transect stations IRL29-31; BRL1-5; IRL32-34; BRL6-7; IRL35-38 and IRL39-42, respectively. The groundwater percentage calculated for transects IRL9, 10,16; IRL12-15 and IRL17-20

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63 Table 5-4. The chloride concentrations of seepage water, water column and groundwater used to calculate the percentage groundwater found in the seepage water. TransectGroundwaternSeepage waternWater columnn% Groundwater IRL1-8 7.75a4579860314.0 IRL9,10,16 7.75a4591359120.0 IRL12-15 7.75a4602460220.0 IRL17-20 7.75a456845671-0.2 IRL21-24 7.75a460745991-1.4 IRL11,25-28 7.75a4591559650.8 TransectGroundwaternSeepage waternWater columnn% Groundwater IRL1-8 10.25a457285711-0.2 IRL9,10,16 10.25a459215311-11.7 IRL12-15 10.25a459245711-3.7 IRL17-20 10.25a453645281-1.5 IRL21-24 10.25a454445371-1.3 IRL11,25-28 10.25a4554555450.0 TransectGroundwaternSeepage waternWater columnn% Groundwater IRL29-31 19a,b734223342-2.5 BRL1-5 19a,b732053195-0.3 IRL32-34 19a,b733633323-1.3 BRL6-8 19a,b7324332630.7 IRL35-38 19a,b7354236322.6 IRL39-42 19a,b7392340132.4 TransectGroundwaternSeepage waternWater columnn% Groundwater IRL29-31 21a,b6462347933.7 BRL1-5 21a,b6431443741.4 IRL32-34 21a,b6480248921.9 BRL6-8 21a,b6448345531.6 IRL35-38 21a,b6456446942.9 IRL39-42 21a,b6427342930.5aWells sampled from the Floridan AquiferbWells sampled from the Surficial Aquifer n = number of samplesDr y Season 2000 Chloride Concentrations ( mM ) Rainy Season 2000 Chloride Concentrations (mM) Northern Study Area Dry Season 1999 Average Chloride Concentrations (mM) Rain y Season 1999 Chloride Concentrations ( mM ) Southern Study Area during the rainy season in the northern study area produced lower negative values than the dry season because of precipitation that diluted chloride concentrations of the lagoon water to values lower than the seepage waters. An example of this dilution was observed while sampling the water column on the 16th during the August sampling trip of 1999. A gradient of temperature and salinity (Figure 5-1) was measured and indicated a cooler and less saline surface of the water column caused by a passing storm earlier in the day.

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64 Consequently, the seepage water, although possibly diluted by fresh groundwater, was more saline than the overlying water column. In addition, negative values indicate that the chloride concentrations in the sampled groundwater wells are not indicative of Cgw endmember values. Therefore, in order to calculate the fraction of groundwater in the seepage water, it is important to have high resolution measurements of the chloride concentrations in the water column. It is also important to measure the vertical distribution of chloride concentrations in the water column. In the northern study area, the water column was sampled from ~30 cm below the surface. While in the southern study area, high resolution measurements and vertical distribution of chloride concentrations in the water column were taken into account by sampling the water column ~50 cm above the sediment water interface and by measuring the gradient of temperature and salinity in the water column at each station. 0 0.5 1 1.5 2 3737.53838.53939.54040.541 Salinity (ppt)Depth of Lagoon (m)29.429.629.83030.230.430.630.8 Salinity TemperatureTemperature oC Figure 5-1. The changes in salinity and temperature with depth in the water column for station IRL16 during the rainy season in the northern study area. Sampled on August 16, 1999.

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65 Assuming groundwater samples from wells was the correct Cgw endmember value of seepage water, then the 1 4 % groundwater in seepage water may reflect the volume of fresh water that seeps into the lagoon based on the Pandit and El-Khazen (1990) study. Pandit and El-Khazen (1990) calculated 34 38 million m3 of fresh groundwater from the Surficial Aquifer flows into the lagoon annually. The annual groundwater seepage into the lagoon calculated by Pandit and El-Khazen (1990) is 0.002 % the minimum and 0.0005 % the maximum annual seepage rates into the lagoon measured for this study. Based on Pandit and El-Khazen (1990), the percent groundwater contribution in seepage is much smaller than the percent of groundwater calculated with chloride concentrations. The difference between the two calculations suggest that fresh groundwater inflow into the lagoon from the Surficial Aquifer is smaller than total seepage flow measured with seepage meters (Motz and Gordu, 2001). The groundwater percentages calculated for this study indicate that only a small fraction of fresh groundwater flows into the Indian River Lagoon. Low fresh groundwater percentages may have resulted from at least two causes. First, the source of seepage water might be from regions of the aquifers that have undergone salt-water intrusion. If this is the case, then groundwater well chloride concentrations are not valid for equation 1. Increased chloride concentrations in the Surficial and Floridan aquifers result from lateral seawater intrusion which results from overpumping of fresh water and subsequent infiltration of seawater (Toth, 1988; Tibbals, 1990). Alternatively, seawater that remains in an aquifer because the aquifer was previously inundated with seawater during times of higher stands of sealevel may upwell into the fresh water lens (Toth, 1988; Tibbals, 1990).

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66 Second, lagoon water may have circulated into the sediment to become the primary component of seepage water. Many studies have concluded that seawater circulates through sediments. Seawater circulation is believed to be caused by fresh groundwater hydraulic head (Simmons, 1992). As less dense fresh groundwater flows upward, the more saline pore waters flow downward into the sediment to displace the fresh groundwater. Bokuniewicz (1992) describes this physical phenomenon as density driven salt fingering, after analyzing the salinity distribution of pore water in cores taken from Great South Bay, New York. The salt-fingering results from an unstable density gradient of saline pore waters that overlie fresh pore waters, resulting in narrow plumes of salt water dipping into the fresh water region. The density inversion only accounts for mixing when increased chloride concentrations in the water column overly lower chloride concentrations in the sediment pore water. When lower chloride concentrations in the water column overly increased chloride concentrations in the sediment pore water another mechanism must control mixing between the two. The concept that the circulating lagoon water constitutes the majority of seepage water is inconsistent with the idea that the source of seepage water is directly from aquifer groundwater. Therefore, seepage rate variations that were said to be caused by increased precipitation to aquifer groundwater from the dry to rainy seasons is also inconsistant with this finding because fresh aquifer groundwater was not the source of seepage water. Changes in chloride concentrations in seepage water and the water column from dry to rainy season may be controlled by direct recharge to the water column based on the idea that seepage is primarily composed of lagoon water, which is

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67 opposite of the idea that changes in recharge to aquifers will control changes is chloride concentrations of seepage water and the water column. Effects of Seepage Water on Water Column Chemistry The chloride concentrations of the water column correlate directly to the seepage water chloride concentrations for the dry and rainy seasons of the northern and the southern study areas (Figures 5-2, 5-3). Although, there was one instance of known density layering in the water column, in general, the density was uniform with depth. The chloride concentration of seepage water may directly effect the concentration in the water column by diluting or concentrating the chloride concentrations in the water column. If chloride concentrations in the seepage water control the chloride concentrations in the water column then the source of the seepage water would have to derive from aquifers that have undergone salt-water intrusion and not from circulating lagoon water. Assuming seepage water is largely composed of circulated lagoon water, the relationship shown in figure 5-2 and 5-3 suggest that the water column chloride concentrations may control seepage concentrations. The regression lines of the dry and rainy seasons measured in both study areas are offset from the line representing seepage water concentration equals water column concentrations (Figures 5-2, 5-3). This offset may result from water column chloride concentrations that were affected by other factors such as meteoric water or evaporation. For example, the regression lines that offset to the left of the line indicating seepage water concentrations equal water column concentrations suggest that water column chloride concentrations increased compared to seepage water concentrations. The water column chloride concentrations may have increased compared to seepage water concentrations due to evaporation. Alternatively, the regression lines that offset to the

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68 y = 0.527x + 282.94 R2 = 0.4824 Dry Season y = 0.623x + 204.34 R2 = 0.7183 Rainy Season520 530 540 550 560 570 580 590 600 610 520540560580600Seepage Water Chloride Concentration (mM)Water Column Chloride Concentration (mM) Dry Season Rainy Season Linear (Dry Season) Linear (Rainy Season) Y=X Y=X is the line representing seepage water concentrations equal water column Figure 5-2. Plot of seepage water chloride concentrations against the corresponding water column chloride concentrations for the northern study area dry and rainy seasons. right of the line indicating seepage water concentrations equal water column concentrations suggest that water column chloride concentrations decreased compared to seepage water concentrations. The water column chloride concentrations may have decreased because precipitation directly on the lagoon diluted the chloride concentrations of the water column. The regression lines of the dry season in the northern study area and both the dry and rainy seasons in the southern study area are offset to the left of the line indicating seepage water concentrations equal water column concentrations. This ofset suggests that the water column chloride concentrations increased compared to seepage water concentrations due to evaporation. The regression line of the rainy season in the northern study area is offset to the right of the line indicating seepage water concentrations equal water column concentrations. This offset suggests that the water

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69 column chloride concentrations decreased compared to seepage water concentrations due to precipitation. y = 1.0547x 15.988 R2 = 0.8029 Rainy Season y = 1.1293x 42.9 R2 = 0.9563 Dry Season300 320 340 360 380 400 420 440 460 480 500 300320340360380400420440460480500Seepage Water Chloride Concentration (mM)Water Column Chloride Concentration (mM) Dry Season Rainy Season Linear (Rainy Season) Linear (Dry Season) Y=XY=X is the line representing seepage water concentrations equal water column Figure 5-3. Plot of seepage water chloride concentrations against the corresponding water column chloride concentrations for the southern study area dry and rainy seasons. Assuming that most of the seepage water is recirculated lagoon water, it is possible to calculate the time it takes for entire volume of lagoon water column to circulate through the sediments. This calculation can be made by dividing the volume of lagoon water by the seepage rate (Table 5-5). This calculation indicates it would take 29.6 days during the dry season and 18.7 days during the rainy season for the lagoon water to circulate through the sediments of the entire lagoon using seepage rates from the northern study area. Using seepage rates from the southern study area this calculation indicates it would take 42.6 days during the dry season and 30.2 days during the rainy season for total volume of the water in the lagoon to circulate through the sediments.

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70 Therefore, when the water column chemistry changes, it takes up to a month before the same changes are reflected in the chemistry of the sediment pore water. Table 5-5. Time of water column circulation through sediments of the entire lagoon. Area 922 km2Volume 1.57 km3Northern Seepage FluxFlux for Total LagoonCirculation Study Area ml/m2/min Area (ml/min)Time (days) Dry Season 39.91 3.68 x 101029.6 Rainy Season 63.08 5.82 x 101018.7 Southern Seepage FluxFlux for Total LagoonCirculation Study Area ml/m2/min Area (ml/min)Time (days) Dry Season 27.69 2.55 x 101042.6 Rainy Season 39.11 3.61 x 101030.2For Entire Lagoon Evidence of Mixing Pore Water Chemistry Chloride concentrations in pore waters at certain depths were lower than chloride concentrations of seepage water and water column of the dry and rainy seasons of the southern study area. Chloride concentrations decrease to a minimum of 287 mM to 313 mM at a depth of 50 cm to 84 cm in the multisampler profiles of stations BRL7, 6, 2 and IRL32 during the dry season (Figure 5-4a, Table 5-6). The minimum values in each profile are lower than the average chloride concentration of seepage water (341 mM) and water column (348 mM) measured during the dry season (Figure 5-4B, Table 5-8). Chloride concentrations decrease to a minimum of 324 mM to 409 mM at a depth of 80 cm to 150 cm in the multisampler profiles of station IRL29, BRL2, 1, 6 and 5 during the rainy season (Figure 5-4b, Table 5-6). The minimum values in each profile were lower than the average chloride concentration of seepage water (449 mM) and water column

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71 (457 mM) measured during the rainy season. The low chloride concentrations in the pore waters range between 70 cm and 150 cm depth into the sediment during the rainy season. Table 5-6. The minimum chloride concentration in pore water and depth in multisamplers from the southern study area. Depth intoConcentration StationSediments (cm)(mM) BRL774287 BRL684289 BRL250298 IRL3273313 Average297 Depth intoConcentration StationSediments (cm)(mM) IRL2980324 BRL280329 BRL1110349 BRL6150349 BRL570409 Average352Lowest Pore Water Chloride Concentrations (Rainy Season) Lowest Pore Water Chloride Concentrations (Dry Season) Multisampler profiles may show mixing of chloride concentrations of lagoon water that circulated into sediments to mix with pore water. The low chloride concentrations in the pore water at the 50 cm to 150 cm horizon layer would have a lower density than the water column at each station. This density inversion may drive water upward, exchanging with the higher density lagoon water. The mixed pore waters and lagoon waters would be sampled as seepage water. The percent of pore water that contributed to the seepage water was calculated using equation (1) for the dry and rainy season in the southern study area. The average chloride concentration in the pore water (Cgw) was calculated by averaging the

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72 -250 -200 -150 -100 -50 0 50 280300320340360380400420440460480Chloride (mM)Depth into Sediment (cm) BRL2 BRL6 BRL7 IRL32 Average Water Column Average Seepage WaterA -250 -200 -150 -100 -50 0 50 280300320340360380400420440460480Chloride (mM)Depth into Sediment (cm) IRL29 BRL1 BRL2 BRL5 BRL6 Average Water Column Average Seepage WaterB Figure 5-4. The multisample profiles of chloride concentrations for the (A) dry and (B) rainy seasons of the southern study area. Values plotted at the sediment water interface indicate seepage water collected from the same station. Values plotted 30 cm above sediment water interface symbolizes water column collected from the same station.

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73 lowest chloride concentration in each multisampler profile of the 50 cm to 150 cm layer. The average chloride concentration in the seepage water and the water column of each season was used to calculate the percent of pore water contribution to seepage water. With these values, equation (1) indicates that seepage water was composed of 13.0% pore water during the dry season and 7.6% pore water during the rainy season in the southern study area (Table 5-5). Using low pore water concentrations as the Cgw endmember in Eq. 1 suggests that pore water 50 to 150 cm below the sediment-water interface is not a significant source of seepage water. This furthur suggests that the source of seepage water is likely from the circulation of lagoon water into the sediments and not a significant source from pore water below. The change from the dry to the rainy season of the contribution of pore water to seepage water implies that the source of the low chloride concentrations in the pore water may be ephemeral without sufficient dilution of the circulating lagoon water, such as when large storms drop heavy precipitation. The contribution of pore water, that originated from lagoon water, to seepage water further supports the idea that seepage water is largely composed of circulating lagoon water. Table 5-7. The percent of pore water with low chloride concentrations in seepage water in the southern study area. Dry Season % Pore Water in Seepage Water Pore WaternSeepage waternWater columnn% Pore Water 297*4341203472013.0Rainy Season % Pore Water in Seepage Water Pore WaternSeepage waternWater columnn% Pore Water 352*544920457207.6*Average concentrations calculated from the lowest pore water chloride concentrations measured in each multisampler profile from 50 cm to 150 cm depth

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74 The sediment horizon layer retaining lower chloride concentrations than other depths into the sediment may have resulted from dilution of the lagoon after two hurricanes dropped extensive precipitation over the study area in September and October of 1999 (Table 5-3). After the lagoon water was diluted from extensive rainfall, it circulated into the sediments to provide the 50 cm to 150 cm horizon layer with lower chloride concentrations. Over the extent of the dry season, chloride concentrations in the water column increased due to evaporation. Assuming the water column circulates into the sediments within 43 days (Table 5-7) after increasing in concentration, the chloride concentrations in the 50 cm to 150 cm horizon layer should increase to values similar to the water column within that time. The average low pore water chloride concentration measured during the rainy season (352 mM) did increase from the dry to the rainy season to values greater than the average water column chloride concentrations measured during the dry season (347 mM). The increase in low pore water chloride concentration suggests the water column circulated into the sediments within the time of sampling from the dry to the rainy season (~90 days). If the lowest pore water chloride concentrations increased to concentrations similar to the water column within 43 days from time the water column was measured during the dry season, then the pore water chloride concentrations would have increased by 1.16 mM/day. Using the same rate of increase, lowest pore water chloride concentrations should have increased to an average of 401.7 mM for the rainy season, because the chloride concentrations in the water column continued to increase from the dry to the rainy season by 1.22 mM/day. From the dry to the rainy season, the lowest pore water chloride concentration did not increase by 1.16 mM/day because the 50 cm to 150 cm sediment horizon may be low in permeability or

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75 circulating lagoon water may not recirculate as quickly into sediment depths greater than 50 cm than depths less than 50 cm. Evaporation and Surficial Runoff The difference in chloride concentrations of the water column was 520 610 mM and 310 480 mM between the northern and southern study areas, respectively. The high chloride concentrations in the northern study area when compared with the southern study area may have resulted from extensive evaporation. Increased evaporation can occur where the surface area to volume ratio of a water body increases. The surface area to volume ratio is two times higher in the northern study area than the southern study area because the average depth increases from the north to the south. The deepest water depth in the northern study area is 2 m, while the average water depth is ~1 m. In contrast, the deepest water depth in the southern study area is 3.80 m and the average depth is ~2.32 m. Consequently, the fraction of evaporation relative to the total volume of the lagoon is less in the southern study area than the northern study area, because the southern study area provides a lower surface area to volume. In areas of the lagoon where the surface area to volume ratio increases, then the chloride concentrations of the water column will increase, thus increasing the chloride concentrations in the seepage water after circulation of the water column into the sediments. Surface water runoff may reduce chloride concentrations directly in water column and indirectly in seepage water in the southern study area. Surficial discharges are more common in the southern study area than in the northern study area. There is little surface water runoff to the northern study area except during major precipitation (Rao, 1987). The chloride concentration in Turnbull Creek is similar to those of the water column (Table 5-8), although the stream was never sampled following a rainstorm. The creeks

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76 and rivers near the southern study area (EauGallie River, Crane Creek, Turkey Creek and Sebastian River) contribute major discharges (Figure 4-3, Table 5-9) (Rao, 1987). The chloride concentrations in the water column were higher in the northern study area compared with the southern study area (Table 5-8). The surficial discharge in the southern study area may reduce chloride concentrations through dilution of the lagoon water. The surficial discharge in the northern study area may have been too small to effect the chloride concentrations in the lagoon water, allowing evaporation to have a greater effect on chloride concentrations. Table 5-8. Chloride concentrations of surface water measurements of dry and rainy season in both study areas. Dry SeasonRainy Season ChlorideChloride ConcentrationConcentration (mM)(mM)%DifferenceTurnbull Creek5145415.3 Haulover Canal601582-3.3 Average Water Column595554-7.4 Eau Gallie River29543447.4 Crane Creek3583826.6 Turkey Creek22811-2021.0 Saint Sebastian River531355-49.6 Sebastion Inlet38457048.4 Average Water Column34845731.3Northern Study Area Southern Study Area Chloride concentrations would be expected to decrease during the rainy season because rainfall would dilute chloride concentrations of the tributaries. Although Turkey Creek and St Sebastian River decreased in chloride concentration by -2000% and -50%, respectively, Crane Creek and EauGallie River increased in chloride concentrations, by 7% and 47% respectively, between the dry and rainy seasons. Furthermore, chloride concentrations in the water column increased from the dry to the rainy season in the

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77 southern study area. The chloride concentrations in the water column may have increased due to lower than normal precipitation recharge and high evaporation (Table 51, 5-3). The observed increase in chloride concentrations of EauGallie River and Crane Creek may result from smaller drainage areas and discharge rates than those for Turkey Creek and St. Sebastian River (Table 5-9). The drainage areas are larger because the C-1 Canal and the Fellsmere Canal drain the marshlands of the St. Johns River and marshlands into the Turkey Creek and St. Sebastian River, respectively. The EauGallie River and Crane Creek thus may not have collected enough precipitation to flush the river of lagoon water near the sampling site, despite the increase in rainfall during the rainy season. Table 5-9. Mean monthly streamflow of four major surficial discharges in the southern study area. Drainage Areakm2JanFebMarAprMayJunJulAugSepOctNovDecEau Gallie River98.40.270.260.310.220.210.350.400.570.630.500.340.22Crane Creek46.80.960.991.180.820.731.061.522.012.091.911.570.99Turkey Creek/ C-1 Canal253.83.652.824.082.742.303.915.445.617.567.625.101.86St Sebastian River/ Fellsmere Canal203.11.811.722.261.741.352.722.503.544.133.373.031.82*NWISWeb U.S. Geological SurveyMean Monthly Streamflow m3/s* During the dry season, the average chloride concentration of the water column of each transect increased from the north to the south (Figure 5-5). In contrast, the average chloride concentration in the water column of each transect decreased from the north to the south during the rainy season. The chloride concentrations in the water column of the southern transect increased slightly from dry season to rainy season compared to the transects to the north. The low chloride concentration of the Turkey Creek discharge

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78 Figure 5-5. The average chloride concentrations of seepage water (italics) and the water column (mM) for each transect during the dry season (A) and rainy season (B) in the Indian River Lagoon compared with chloride concentrations of surficial discharge. may have minimized the increase of chloride concentrations in the southern transect between the dry and rainy seasons. The low chloride concentration of Turkey Creek discharge may have reduced the change of chloride concentrations in the southern transect by dilution of chloride concentrations in the water column. In addition, the chloride concentrations in the water column circulated into the sediments, reducing the change in chloride concentrations of seepage water of the southern transect. Both evaporation and surficial runoff effect chloride concentrations in the water column. By circulating into sediments, chloride concentrations in the water column control the

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79 chloride concentrations in seepage water. Ultimately, evaporation and surficial runoff indirectly effect the chloride concentrations in seepage water. Nutrients The contribution of nutrients from seepage water to the water column may be very significant when compared to nutrient contribution from surficial input to the Indian River Lagoon. The first part of the following discussion will focus on the importance of inorganic and organic nitrogen and phosphorus species in seepage water and the water column. The second part of the discussion will focus on the quantity of nutrient loading from seepage water and relative comparison to nutrient loading from surface discharge. The final part of the discussion will focus on the effects nutrient loading from seepage water may have had on the limiting nutrient of primary production for each study area. In marine environments, the concentration of organic nitrogen and phosphorus species are usually higher than inorganic nitrogen and phosphorus species in the water column, while the converse is true in the sediment pore water (Trefry et al., 1992; Herbert, 1999). In the sediment pore water, bacteria mineralize organic nitrogen and phosphorus, thereby leaving an increased concentration of inorganic nitrogen and phosphorus (Trefry et al., 1992; Herbert, 1999). When seepage water flows into the overlying water column, the inorganic species are assimilated into the food web, increasing the concentration of organic species. Nutrients are recycled back down into the sediment through the deposition and decay of organic matter and recirculation of lagoon water (Trefry et al., 1992; Herbert, 1999). Nitrogen occurs as dissolved inorganic, dissolved organic or particulate forms. Dissolved inorganic nitrogen species include NO3 -, NO2 and NH4 + (Figure 5-6).

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80 Dissolved organic nitrogen species include amino acids, urea, proteins, purines and pyrimidines etc. (Behnke, 1975; Herbert, 1999). The organic and inorganic species of dissolved nitrogen comprise the total soluble nitrogen. Total soluble nitrogen and particulate nitrogen combine to form the total nitrogen. InorganicOrganic Dissoved Organic Nitrogen (DON) Urea, Amino acids Proteins Purines and Pyrimidines Dissoved Inorganic Nitrogen (DIN) NO2 -NO3 -NH4 -Total Soluble Nitrogen (TSN) DIN and DON & Particulate Nitrogen Total Nitrogen (TN) Figure 5-6. The constituents of total nitrogen. Phosphorus also occurs as dissolved inorganic, dissolved organic or particulate species (Figure 5-7). The dissolved inorganic species is PO4 -, which is also referred to as soluble reactive phosphorus. Dissolved organic phosphorus species include proteins and sugars etc. The organic and inorganic species of dissolved phosphorus comprise the total soluble phosphorus. Total soluble phosphorus and particulate phosphorus combine to form total phosphorus. The nutrient data was interpreted based on the relative concentrations of nitrogen and phosphorus in the water column and seepage waters. The summed concentrations of the inorganic nitrogen species, NO2 -, NO3 -and NH4 +, constitutes dissolved inorganic nitrogen. The dissolved organic nitrogen was calculated as the difference between the

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81 total soluble nitrogen and dissolved inorganic nitrogen. Dissolved organic phosphorus was calculated as the difference between total soluble phosphorus and PO4 3-. InorganicOrganic Dissoved Organic Phosphorus (DOP) Proteins and Sugars Dissoved Inorganic Phosphorus (DIP) or Soluble Reactive Phosphorus (SRP) PO4 -Total Soluble Phosphorus (TSP) DIP and DOP & Particulate Phosphorus Total Phosphorus (TP) Figure 5-7. The constituents of total phosphorus. Nitrogen During both dry and rainy seasons in the northern study area and the dry season in the southern study area, the concentration of dissolved inorganic nitrogen was greater than dissolved organic nitrogen concentrations in the seepage water, while in the water column the dissolved organic nitrogen was greater than the dissolved inorganic nitrogen concentrations (Table 5-10). This relationship was different during the rainy season in the southern study area. The concentration of dissolved organic nitrogen was greater than dissolved inorganic nitrogen in both the seepage water and the water column during the rainy season. The dissolved organic nitrogen is usually greater than dissolved inorganic nitrogen in the water column, although not in the seepage water. Dissolved organic nitrogen was greater in the average seepage water (0.926 mg/L) than the average water column (0.411 mg/L) during the rainy season. Dissolved organic nitrogen may have been

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82 Table 5-10. The average percent of inorganic and organic nutrient concentrations in total soluble nitrogen and phosphorus concentrations for the dry and rainy seasons of the northern and southern study areas. Northern Study Area Dry Season 1999Rainy Season 1999DINDIPDINDIP Water column 11%35% Water column 17%0% Seepage water 98%64% Seepage water 100%59% Groundwater 70%61% Groundwater 100%64% DONDOPDONDOP Water column 89%65% Water column 83%100% Seepage water 2%36% Seepage water 0%41% Groundwater 30%39% Groundwater 0%36%Southern Study Area Dry Season 2000Rainy Season 2000DINDIPDINDIP Water column 11%95% Water column 7%67% Seepage water 65%100% Seepage water 40%100% Groundwater 100%100% Groundwater 54%100% DONDOPDONDOP Water column 89%5% Water column 93%33% Seepage water 35%0% Seepage water 60%0% Groundwater 0%0% Groundwater 46%0% increased in the seepage water during the rainy season due to shallow lagoon water circulation into the sediments or from the regeneration of dissolved organic nitrogen in lagoon water trapped below the seepage meters. Based on the average seepage flux measured during the rainy season (39.11 ml/m2/min), it would take 31.96 hours to flush the seepage meter of lagoon water after deployment, although seepage meters over the slowest seepage flux (8.85 ml/m2/min ) would take 5.9 days. Seepage water was sampled from each seepage meter from 4 to 7 days after deployment. The seepage meters measuring the slowest seepage rates may have retained some lagoon water that was sampled as seepage water. Lagoon water measured as seepage water may have increased the average concentration of dissolved organic nitrogen in seepage water to values greater than natural conditions.

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83 Phosphorus During the dry and rainy seasons of the northern study area, the concentration of dissolved inorganic phosphorus was greater than dissolved organic phosphorus in the seepage water, while the concentration of dissolved organic phosphorus was greater than the concentration of dissolved inorganic phosphorus in the water column (Table 5-10). In contrast, during the dry and rainy seasons in the southern study area, dissolved inorganic phosphorus was greater than dissolved organic phosphorus in both the water column and the seepage water. Dissolved inorganic phosphorus may have been greater than dissolved organic phosphorus in both the seepage water and the water column because dissolved organic phosphorus concentrations in the seepage water was 0.0 mg/L in the seepage water, thereby reducing its loading to the water column. Dissolved organic phosphorus concentrations were low in the water column due to no seepage loading, thus allowing dissolved inorganic phosphorus concentrations to be greater in the water column. Nutrient Loading Seepage water may provide a considerable amount of additional nutrients to the water column, because of the elevated dissolved inorganic nitrogen and phosphorus in the seepage water. To calculate the contribution of newly generated nutrients to the water column, the nutrient concentrations in lagoon water must be differentiated from the nutrient concentrations in seepage water. The nutrient concentration in lagoon water may be differentiated from the nutrient concentrations in the seepage water by subtracting all forms of nutrient concentration in the water column from all forms of nutrient concentrations in the seepage water. In order to make calculations, the average total nitrogen and total phosphorus concentrations in the water column were subtracted from

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84 the average total nitrogen and total phosphorus concentrations in the seepage water (Table 5-11). The flux of nutrients was calculated using the corresponding seepage flux measured during each season. Nutrient loading was calculated for each study area and for the entire lagoon. The annual nutrient flux value was calculated for the dry (212 days) and rainy (153 days) seasons then added together to calculate the total annual nutrients added to the water column from seepage flux. The annual nutrient loading of total nitrogen was 4.50 x 106 kg and total phosphorus was 4.59 x 105 kg in the northern study area. The annual nutrient loading of total nitrogen was 6.03 x 106 kg and total phosphorus was 2.20 x 106 kg in the southern study area. A range of annual nutrient loading values to the entire lagoon was calculated assuming nutrient fluxes of total nitrogen and total phosphorus was uniform across the entire lagoon. The average annual load of total nitrogen ranged from 2.60 x 107 kg to 4.11 x 107 based on nutrient flux measured in the northern study area and southern study area, respectively. The average annual load of total phosphorus ranged from 4.52 x 106 kg to 7.89 x 106 based on nutrient flux measured in the northern study area and southern study area, respectively. Annual loads of total nitrogen and total phosphorus from seepage water are greater than total annual loads of total nitrogen and total phosphorus from surficial discharge into the Indian River Lagoon. The annual loads of total nitrogen and total phosphorus from surficial discharge were 2.38 x 106 kg and 3.19 x 105 kg, respectively based on the Pollution Load Screening Model (Adamus and Bergman, 1993; WoodwardClyde, 1994). On the basis of these calculations, the average total annual nutrient loads from seepage water were thus greater than surficial discharge by factors of 10 to 17 for

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85 total nitrogen and 14 to 25 for total phosphorus. Because the total annual loads from the surficial discharge to the entire lagoon was calculated based on a pollution load model, it may not be representative of surficial discharge nutrient loading made from physical measurements. Assuming the pollution load model represents physical measurements of surficial discharge into the lagoon, these calculations indicate that groundwater seepage to the Indian River Lagoon may represent a previously unidentified, but important, source of nutrients. Table 5-11. The average nutrient concentration, nutrient flux and nutrient loading of total nitrogen and total phosphorus in the northern and southern study areas. Nutrient Concentration TNTP Northern Study Areamg/Lmg/L Dry Season#1.7060.091 Rainy Season 1.690.197 Southern Study Area Dry Season 1.7850.662 Rainy Season 1.0640.382 TNTP kg/yrkg/yr Minimum* 8.96 x 1069.55 x 105Average* 4.11 x 1074.52 x 106Maximum* 9.94 x 1078.43 x 106Minimum* 6.99 x 1062.57 x 106Average* 2.60 x 1077.89 x 106Maximum* 4.97 x 1071.82 x 107#Nutrient concentrations measured as TSN and TSP *Values based on average, min and max seepage fluxNutrient Loading Northern Study Area Southern Study Area

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86 Limiting Nutrients The atomic ratio of N:P can be used to determine the nutrient that limits primary production (Schelske et al., 1999). The atomic ratio of N:P, termed the Redfield Ratio, in macroalgae is 16:1 (Day et al., 1989). Using the atomic ratio of DIN:DIP, values that are less than 16 are considered nitrogen limiting and values greater than 16 are considered phosphorus limiting to the growth of macroalgae (Schelske et al., 1999). The limiting nutrient to the growth of macroalgae changes from phosphorus in the northern study area to nitrogen in the southern study area. Phosphorus was limiting in the seepage water and the water column of both seasons of the northern study area (Table 512). In contrast, nitrogen was the limiting nutrient in seepage water and the water column of both seasons in the southern study area. Similarly, Sigua et al. (2000) found the ratio of N:P in the water column to decrease from the northern to the southern end of the Indian River Lagoon, showing phosphorus as the limiting nutrient in the northern study area and nitrogen as the limiting nutrient in the southern study area. The limiting nutrient in the water column may be directly affected by nutrient loading from seepage water. The average total annual loading of total nitrogen to the entire lagoon was larger based on seepage flux and nutrient concentrations from the northern study area than the southern study area (Table 5-12). The opposite was true for total phosphorus, the average total annual loading to the entire lagoon was smaller based on seepage flux and nutrient concentrations from the northern study area than the southern study area. The shift from phosphorus limiting in the northern study area to nitrogen limiting in the southern study area may be directly related to the shift in increased loading of total phosphorus and decreased loading of total nitrogen in the

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87 southern study area. The shift from phosphorus to nitrogen as the limiting nutrient will affect primary production in each study area. Table 5-12. Nutrient concentrations and flux in each study area and nutrient loading quantity to the Indian River Lagoon. Northern Study AreaDry Season 1999Rainy Season 1999 DINDIPDIN/DIPDINDIPDIN/DIP (atoms/L)(atoms/L)ratio(atoms/L)(atoms/L)ratio Water column 4.50E+181.17E+1738 Water column 7.95E+180.00E+00* Seepage water 1.10E+202.97E+1837 Seepage water 1.68E+201.75E+1896Southern Study AreaDry Season 2000Rainy Season 2000 DINDIPDIN/DIPDINDIPDIN/DIP (atoms/L)(atoms/L)ratio(atoms/L)(atoms/L)ratio Water column 1.42E+188.17E+171.7 Water column 1.29E+186.22E+172.1 Seepage water 1.76E+192.03E+190.9 Seepage water 2.74E+198.95E+183.1 *DIP is limiting because concentrations are close to zero.

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88 CHAPTER 6 CONCLUSIONS The results of this study show that seepage flow occurs in two study areas of the Indian River Lagoon. The average seepage fluxes were 40 ml/m2/min and 63 ml/m2/min during the dry and rainy season, respectively, in the northern study area and 28 ml/m2/min and 39 ml/m2/min during the dry and rainy season, respectively, in the southern study area. The Wilcoxon signed rank test was used to show that there was a significant difference of 95% confidence in the distributions of seepage flux between the dry and rainy season of both study areas. The average seepage fluxes may differ seasonally because of increased precipitation and recharge between dry and rainy seasons. Seepage flux varied spatially and averaged 60% difference between duplicate seepage measurements. The spatial heterogeneity in seepage flux may be controlled by the spatial heterogeneity of hydraulic and compositional properties of sediments. Detailed studies of hydraulic and compositional changes in sediments and aquifers could be used to determine the controlling factor of spatial variability in seepage rates. Such local studies can be achieved by using geophysical techniques, taking core samples and performing hydraulic tests in wells placed in close proximity to each seepage station. Geophysical techniques, such as seismic profiles, would show changes in thickness and structure of sediments and rocks. An analysis of core profiles would show changes in composition of sediments and aquifer rocks. Hydraulic tests, such as pump tests and slug tests, would determine the transmissivity of sediments.

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89 Using chloride concentrations as a tracer, the seepage water was shown to contain 1% to 4% of fresh groundwater. These low amounts of fresh water indicate the principal constituents of seepage water could be recycled seawater. The water column may circulate down in the sediments due to a density dependent fluid flow. This mechanism would mix lagoon water and sediment pore water, thus changing the chloride concentration in the seepage water to concentrations similar to the water column. Alternatively, the low fraction of groundwater may result from higher groundwater chloride concentrations than those measured. Some groundwater source may have undergone saltwater intrusion resulting in chloride concentration closer to those of seepage water. Sampling wells directly below the lagoon would provide a more representative groundwater source. Chloride concentrations in pore water profiles measured deeper than profiles in this study may provide an understanding of groundwater and seepage water mixing. Dissolved inorganic nutrient species are usually greater in the seepage water than dissolved organic species. Alternatively, dissolved organic species are usually greater than dissolved inorganic species in the water column. However, dissolved organic nitrogen was greater than dissolved inorganic nitrogen in the seepage water measured during the rainy season in the southern study area and dissolved inorganic phosphorus was greater than dissolved organic phosphorus in the water column of both the dry and rainy season in the southern study area. Dissolved organic nitrogen may have been greater than dissolved inorganic nitrogen in the seepage water because of recirculated lagoon water or from regeneration of dissolved organic nitrogen trapped in the seepage meter. Dissolved inorganic phosphorus may have been greater than dissolved organic

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90 phosphorus in the water column because of low seepage loading to the water column of dissolved organic phosphorus. According to differences in total nitrogen and total phosphorus concentrations in seepage water and the water column, coupled with seepage flux measurements, nutrient loading from seepage water contributes 10-17 times more total nitrogen and 14-25 times more total nitrogen to the water column than does surficial runoff from drainage areas around the lagoon. Consequently, seepage water may be a prominent source of nutrients to the water column. Changes in nutrient concentrations in seepage water may ultimately change the primary productivity of the ecosystem in the water column. In areas where surficial discharge is low, nutrient loading may be primarily controlled by seepage water. Groundwater seepage should be included as a source of nutrients in the nutrient cycle.

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APPENDIX A STATION LOCATIONS

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92 StationLatitudeLongitudeDepth IDNW(m) IRL 1N28o45.179'W80o50.570'0.4572 IRL 2N28o45.175'W80o50.532'0.6096 IRL 3N28o45.194'W80o50.471'0.6096 IRL 4N28o45.211'W80o50.414'0.6858 IRL 5N28o45.207'W80o50.385'0.762 IRL 6N28o45.213'W80o50.347'0.9144 IRL 7N28o45.243'W80o50.208'1.6764 IRL 8N28o45.286'W80o50.039'1.8288 IRL 9N28o47.101'W80o50.764'1.07 IRL 10N28o47.116'W80o50.876'0.61 IRL 12N28o46.036'W80o48.876'0.74 IRL 13N28o46.045'W80o48.087'0.89 IRL 14N28o46.569'W80o48.683'0.94 IRL 15N28o46.577'W80o48.624'0.64 IRL 17N28o42.535'W80o49.846'0.6096 IRL 18N28o42.522'W80o49.701'0.7366 IRL 19N28o42.513'W80o49.740'0.762 IRL 20N28o42.515'W80o49.694'0.762 IRL 21N28o43.905'W80o45.739'0.9652 IRL 22N28o43.999'W80o46.054'1.1938 IRL 23N28o44.019'W80o46.244'1.0922 IRL 24N28o44.117'W80o46.546'1.016 IRL 11N28o43.624'W80o49.381'1.98 IRL 16N28o46.272'W80o50.148'1.67 IRL 25N28o 44.283 W80o 48.263 1.905 IRL 26N28o 43.079 W80o48.500 1.9812 IRL 27N28o 45.027 W80o48.554 1.4986 IRL 28N28o 43.843 W80o47.440 1.905 TBCN28o49.216 W80o51.5670.635 HOCN28o44.246 W80o45.262 N/A GW-1N28o41.481 W80o 51.505 38.1 GW-2N28o45.954 W80o 52.638 36.27 GW-3N28o39.966 W80o 56.907 1.524-4.57 GW-4N28o46.147 W80o 52.266 39.01 GW-5N28o38.511 W80o43.281'24.384 GW-6N28o42.377 W80o43.611 N/A Northern Study Area Big Flounder Transect Turnbull Creek Transect Shiloh Palm Tree Transect Groundwater Wells Tower Transect Duckroost Cove Transect Deep Sites Canals/Creek

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93 St at i onLat i t udeLongi t ude Depth I DNW (m) BRL1N28o16.496'W80o39.760'1.83 BRL2N28o16.500'W80o39.054'1.52 BRL3N28o16.491'W80o38.096'3.05 BRL4N28o16.497'W80o37.173'2.20 BRL5N28o16.503'W80o36.584'1.52 BRL6N28o14.318'W80o38.841'0.91 BRL7N28o14.320'W80o38.378'2.74 BRL8N28o14.150'W80o37.071'1.52 IRL29N28o16.379'W80o41.196'1.63 IRL30N28o16.475'W80o40.793'3.05 IRL31N28o16.513'W80o40.478'2.44 IRL32N28o13.951'W80o40.247'1.83 IRL33N28o14.108'W80o39.962'3.05 IRL34N28o14.239'W80o39.512'2.44 IRL35N28o09.975'W80o38.446'2.29 IRL36N28o10.007'W80o38.238'3.05 IRL37N28o10.073'W80o37.774'3.80 IRL38N28o10.249'W80o37.365'2.74 IRL39N28o07.000'W80o37.061'1.83 IRL40N28o07.133'W80o36.528'3.60 IRL41N28o07.292'W80o36.041'2.44 IRL42N28o07.399'W80o35.574'1.52 BHSN28o18.783'W80o41.251' GW331N28o07.815'W80o35.550'73 GW921N28o18.096'W80o36.612'11 GW1472N28o15.286'W80o41.487'6 GW1473N/AN/A85 GW1580N28o09.988'W80o38.793'18 GW1647N28o08.035'W80o37.725'107 Horse CreekN28o09.992'W80o38.737'0.97 Eau Gallie RiverN28o07.523'W80o37.520'0.91 Crane CreekN28o04.652'W80o36.138'0.61 Turkey CreekN28o02.000'W80o34.765'1.40 St. Sebastian RiverN27o50.693'W80o29.861'0.91 Sebastian InletN27o51.583'W80o26.875'1.83 Seepage Met er St at i ons Groundwater Wells Surface Water Samples Southern Study Area

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94 APPENDIX B SEEPAGE RATES AverageAverageAverageAverage StationSeepageSeepageSeepageSeepage IDRates (Flux)VelocityRates (Flux)Velocity ml/m2min (cm/day) ml/m2min (cm/day) IRL 123.5514.23.392.043.0014.56.202.1 IRL 221.600.33.110.055.3018.77.962.7 IRL 327.675.03.990.743.705.66.290.8 IRL 428.322.94.080.446.4011.66.681.7 IRL 536.685.25.280.835.505.95.110.9 IRL 649.748.47.161.2102.8013.914.812.0 IRL 718.120.62.610.1144.4010.820.800.0 IRL 847.007.26.771.0100.909.414.521.4 IRL 944.771.26.450.265.7014.69.462.1 IRL 1021.862.53.150.450.606.57.280.9 IRL 1292.104.713.260.774.3012.710.711.8 IRL 1338.592.35.560.351.0016.17.342.3 IRL 1454.674.67.870.758.1025.78.373.7 IRL 1526.643.03.840.423.404.33.360.6 IRL 1719.501.52.810.231.33.34.510.5 IRL 1850.906.77.331.043.71.26.290.2 IRL 1933.365.84.800.874.014.810.662.1 IRL 2026.454.03.810.637.11.55.340.2 IRL 2130.553.44.330.140.902.95.890.4 IRL 2250.122.37.080.384.309.212.131.3 IRL 23103.6610.414.932.189.903.512.940.5 IRL 2450.606.97.790.772.7020.510.473.0 IRL 1153.997.17.190.179.704.711.480.7 IRL 1652.404.67.550.7139.1012.520.031.8 IRL 252.930.30.400.022.009.33.161.3 IRL 2615.501.32.290.266.303.19.540.4 IRL 2741.152.05.820.339.400.55.670.1 IRL 2855.087.78.431.050.805.87.320.8 DUCKROOST COVE TRANSECT DEEP SITES Dry SeasonRainy Season TOWER TRANSECT Northern Study Area BIG FLOUNDER TRANSECT TURNBULL CREEK TRANSECT SHILOH TRANSECT

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95 AverageAverageAverageAverage StationSeepageSeepageSeepageSeepage IDRates (Flux)VelocityRates (Flux)Velocity ml/m2min (cm/day) ml/m2min (cm/day) BRL1A43.0716.96.202.430.2711.34.361.6 BRL1B 40.128.75.781.255.9838.48.065.5 BRL2 44.5012.06.411.748.103.26.930.5 BRL3A13.105.41.890.88.859.01.271.3 BRL3B 22.959.43.311.414.9710.32.161.5 BRL4 41.9815.16.052.226.5518.53.822.7 BRL5 22.5214.23.242.041.5811.45.991.6 BRL6 18.7012.62.691.835.3210.25.091.5 BRL7 23.1811.23.341.647.0910.14.524.0 BRL8 36.4614.65.252.195.9744.713.826.4 IRL2914.4511.52.081.749.918.37.191.2 IRL3014.721.82.120.328.584.94.110.7 IRL3115.2911.42.201.613.046.51.880.9 IRL3225.977.03.741.062.1232.68.954.7 IRL3326.884.13.870.643.1151.26.217.4 IRL3414.7018.12.122.6 IRL3542.434.46.110.642.783.46.160.5 IRL3619.691.82.840.315.010.72.160.1 IRL37 14.235.62.050.836.527.15.261.0 IRL3837.4215.05.392.226.185.43.770.8 IRL3930.3711.14.371.694.3112.713.581.8 IRL4057.7125.48.313.7 IRL4110.1121.21.463.116.622.42.390.3 IRL4233.9612.94.891.927.5822.23.973.2 Rainy Season Dry Season Southern Study Area

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APPENDIX C WATER CHEMISTRY DATA

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97 Northern Study Area, Dry Season, Seepage Water StationSalinityCond.OxygenpH Cl-SO4NO3 NH4TSNSRPTSPSiO2(ppt)(mS/cm ) (mg/L)(mM)(mM)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L) IRL 140.6063.303.267.3059531.390.0012.7583.7760.1310.2015.44 IRL 239.6061.101.167.2257930.550.0026.3083.7230.0680.146N/A IRL 339.8061.102.487.3258131.050.0022.2371.8290.0140.0393.28 IRL 439.1060.103.607.3156930.210.0014.7284.0230.2590.4126.17 IRL 538.7059.404.187.2656330.370.0032.6443.5940.0680.1304.32 IRL 639.6061.703.937.4458531.320.0011.3901.4720.0140.0263.00 IRL 738.5059.304.567.3558330.630.0022.2041.9680.0190.0603.35 IRL 839.3059.503.337.4357630.840.0032.9372.7530.1610.2077.87 IRL 940.3059.10N/A7.4559431.630.0162.8392.4020.0160.0246.37 IRL 1040.2057.80N/A7.5558231.540.0021.6342.0600.0080.0174.52 IRL 1240.2063.403.317.2858731.500.0112.1882.7860.0220.0495.46 IRL 1340.8063.304.497.6159931.800.0070.9341.8130.0110.0173.98 IRL 1441.3063.404.707.5160831.990.0022.7413.1360.0490.1314.99 IRL 1541.4060.60N/A7.4161632.030.0173.4913.4260.0000.0716.34 IRL 1738.3061.704.637.3856629.530.0103.3603.5840.0160.0355.58 IRL 1838.2060.802.917.4257429.480.0081.9432.5780.0080.0212.72 IRL 1937.5060.004.177.5156029.040.0031.8782.4190.0110.0283.46 IRL 2038.2061.104.777.4657129.890.0042.8722.7930.0300.0476.20 IRL 2141.2051.209.847.5961132.220.0045.7873.7410.2400.3394.72 IRL 2240.8047.709.407.5660432.010.0163.7843.3010.1500.1634.79 IRL 2340.9061.703.467.5260732.100.0031.6672.2650.0300.0533.72 IRL 2440.8062.004.947.5260532.170.0042.0742.3560.0440.0614.22 IRL 1139.5059.701.637.3856530.800.0074.4193.5350.2400.3446.43 IRL 1640.2059.00N/A7.7759731.270.0010.6891.3750.0080.0173.67 IRL 25N/AN/AN/AN/AN/A32.020.0091.3241.9720.0740.10010.10 IRL 2639.3062.206.547.6159031.370.0161.1291.6790.0930.1225.31 IRL 2740.7061.505.957.6260331.900.0040.8031.5230.0110.0183.27 IRL 2840.3061.603.477.4959831.680.0130.9991.6120.1250.1498.72

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98 Northern Study Area, Dry Season, Water Column StationSalinityCond.OxygenpH Cl-SO4NO3 NH4TSNSRPTSPSiO2(ppt)(mS/cm ) (mg/L)(mM)(mM)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L) IRL 6WCN/A59.7010.75N/A60331.97 0.0010.1250.826 0.0080.0220.31 IRL 9WC39.8061.209.898.3158731.30 0.0100.0910.928 0.0060.0151.39 IRL 13WC40.6060.508.248.2459331.50 0.0060.0690.983 0.0060.0150.60 IRL 14WC41.2063.1010.608.43610N/A0 .0010.1080.990 0.0080.0200.25 IRL 18WC38.0058.708.92N/A56729.35 0.0060.0791.038 0.0060.0160.30 IRL 23WC40.7061.708.45N/A59931.88 0.0050.1060.790 0.0060.0150.38 IRL 11WC39.6058.609.59N/A585N/A0 .0020.1160.927 0.0060.0160.44 IRL 16WC40.2059.9010.368.3359831.07 0.0110.1000.965 0.0060.0150.37 IRL 25WC41.4061.409.49N/A598N/A0 .0040.1000.972 0.0060.0160.52 IRL 26WC40.1059.809.42N/A59331.61 0.0050.0770.885 0.0060.0160.15 IRL 27WC40.8061.209.78N/A60432.48 0.0130.1140.825 0.0060.0150.46 IRL 28WC40.5059.708.30N/A60232.16 0.0050.1040.903 0.0060.0170.45

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99 Northern Study Area, Dry Season, Groundwater and Surface Water StationSalinityCond.OxygenpH Cl-SO4NO3 NH4TSNSRPTSPSiO2(ppt)(mS/cm ) (mg/L)(mM)(mM)(mg/L)(mg/L) (mg/L)(mg/L)(mg/L)(mg/L) Ground water samples GW-11.20N/A1.026.93180.090.0000.5990.3000.0140.0220.02 GW-20.40N/A0.326.8430.000.0010.4590.4510.0190.0250.03 GW-39.2015.700.277.461539.960.0000.6690.6040.1720.1840.01 GW-4<11.04N/A7.3960.000.0000.5900.6210.0140.0350.03 GW-5N/A0.10N/A6.9040.000.0000.9191.1990.3000.6100.01 GW-614.50N/AN/A6.842198.050.0100.5572.1860.0190.0140.01 Surface water samples TBC33.00N/AN/A7.0051427.490.0160.1331.4120.0140.0400.01 HOC36.90N/AN/A7.8360132.130.0070.1000.8430.0060.0160.00

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100 Northern Study Area, Rainy Season, Seepage Water StationSalinityCond.OxygenpH Cl-SO4NO3NH4TSNTNSRPTSPTPSiO2(ppt)(mS/cm ) (mg/L)(mM)(mM)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L) IRL 139.1066.900.827.0658130.100.0412.7892.8412.0840.0840.1100.1755.80 IRL 237.9063.701.317.0856428.200.0504.0812.8412.4790.0880.1530.1488.85 IRL 338.6063.402.277.2257329.500.0443.9242.9172.2450.0230.0800.1446.21 IRL 438.7063.702.357.2757629.900.0721.8292.1502.2330.0030.0200.0774.66 IRL 538.7062.402.337.3157428.800.0606.5233.6773.9170.2350.2540.3584.45 IRL 6A38.3062.100.937.5056630.000.0281.5141.9771.9700.0390.0340.0812.99 IRL 6C38.0062.400.887.4457030.000.0280.9311.7291.8710.0230.0230.0812.82 IRL 738.3062.100.937.4957330.100.0100.7571.5101.7160.0550.0500.1014.43 IRL 838.2062.400.507.4957229.900.0322.5852.5362.7350.0750.0650.1494.13 IRL 940.0064.501.247.3559431.200.0612.6792.3162.4680.0940.0700.1126.84 IRL 1039.6065.200.737.2457930.600.0543.8923.0513.2980.2050.1790.2104.88 IRL 1238.7063.804.567.2457429.900.0553.3572.8402.9110.1200.1040.1356.36 IRL 1338.7063.801.667.3157330.100.0552.7112.7142.7870.0260.0610.0985.80 IRL 1440.6066.500.967.6360331.700.0702.5852.7252.7700.0060.0500.0745.22 IRL 1541.9067.801.217.0862130.900.1138.2082.7682.2970.0360.0860.1206.96 IRL 1735.8061.303.367.5154027.900.0286.6013.3433.2330.1820.1620.1704.70 IRL 1835.7060.703.087.5853528.000.1012.9152.7412.9790.0580.0680.1423.86 IRL 1935.8060.902.387.5353327.900.0304.6952.6572.8580.0390.0410.0935.44 IRL 2035.8060.703.337.5053728.000.0463.7983.2053.0920.0910.0890.1906.84 IRL 2137.8063.201.427.3956629.300.0195.0262.5032.7470.0320.0790.1035.46 IRL 2236.1061.101.087.2254129.000.0273.5462.9383.3600.0450.1160.1485.77 IRL 2335.9060.601.057.2653628.100.0994.3962.7142.6810.0060.0600.1084.44 IRL 2435.6060.502.336.9553326.900.0534.4753.7924.0130.0750.0810.0934.43 IRL 1138.5064.301.697.3757229.700.0084.5063.7843.5100.3060.3850.3994.97 IRL 1639.9065.201.227.6059231.100.0501.7972.0002.2480.0030.0330.1084.13 IRL 2537.5061.300.227.5555425.600.05730.6239.35812.1760.8182.3182.63510.27 IRL 2637.0062.302.487.4855129.100.0253.1042.8033.0140.0710.0700.1215.11 IRL 2737.0060.801.287.3155228.900.0282.5532.2952.6140.2410.1520.1596.31 IRL 2836.8060.501.247.3454328.300.0302.4902.2812.5380.0940.1160.1848.90

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101 Northern Study Area, Rainy Season, Water Column StationSalinityCond.OxygenpH Cl-SO4NO3NH4TSNTNSRPTSPTPSiO2(ppt)(mS/cm ) (mg/L)(mM)(mM)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L) IRL 6WC38.6062.704.278.1157130.000.0770.1661.1221.3600.0000.0150.0451.31 IRL 9WC40.3065.503.968.10N/A31.700.0740.1561.2391.4710.0000.0170.0444.00 IRL 12WC38.6063.701.348.0857130.100.1000.2511.2511.3760.0000.0160.0352.25 IRL 18WC35.5060.708.238.6352827.400.0430.1021.0951.2400.0000.0150.0330.80 IRL 22WC36.0060.605.578.0153728.100.1020.2251.1391.3590.0000.0150.0352.01 IRL 11WC38.6064.107.108.2457030.400.0390.0841.0801.3320.0000.0170.0451.09 IRL 16WC38.2062.504.638.0456129.600.0350.1281.0331.2800.0000.0140.0330.66 IRL 25WC37.8061.905.778.0155629.600.0390.1180.9971.2320.0000.0160.0331.78 IRL 26WC37.2061.906.428.0655229.100.0360.1081.0731.3300.0000.0160.0381.02 IRL 27WC37.1060.906.168.1154729.000.0350.0420.9301.3100.0000.0170.0361.85 IRL 28WC36.8060.806.088.0254528.700.0270.1001.0211.2760.0000.0150.0312.10 Northern Study Area, Rainy Season, Groundwater and Surface water StationSalinityCond.OxygenpH Cl-SO4NO3NH4TSNTNSRPTSPTPSiO2(ppt)(mS/cm ) (mg/L)(mM)(mM)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L) Ground Water Samples GW-11.2022.00N/A7.28210.100.0590.4790.3520.3460.0030.0210.0190.02 GW-2N/AN/AN/AN/A70.000.0100.5370.4440.3970.0030.0140.0140.03 GW-39.1015.57N/A9.501549.100.0010.7420.6510.7210.0000.0010.0000.01 GW-40.501.07N/A7.2780.000.0150.6050.6040.6150.0230.0360.0270.03 GW-50.400.87N/A6.7450.000.0501.3221.3361.5700.4240.6630.6220.01 GW-617.1027.98N/A6.942820.000.0092.4722.6462.7940.0060.0140.0890.01 Surface Water Samples TBCN/AN/AN/AN/A54128.800.0520.2211.3441.9950.0090.0450.179N/A HOCN/AN/AN/AN/A58231.100.0690.1121.0961.2740.0000.0180.0330.00

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102 Southern Study Area, Dry Season, Seepage Water Statio n SalinityCond.OxygenTemp.pHClSO4NO3NH4TSNTNSRPTSPTPSiO2(ppt)(mS/cm ) (mg/L)(oC)(mM)(mM)(mg/L)(mg/L)(mg/ L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L) IRL2922.2033.301.16N/A7.4634214.560. 0040.3940.4420.8661. 4400.0000.0002.60 IRL3122.5037.000.2727.57.7934215.080. 0100.0770.3350.3650. 4351.3681.26712.09 IRL3221.8031.000.32N/A7.2733714.650. 0100.0010.0035.2692. 3450.7230.6719.12 IRL3321.9031.602.26N/A7.4333314.170. 0060.8260.4600.6382. 7391.9812.00525.06 IRL3422.0036.000.2926.47.9033913.160. 0080.2630.8370.3334. 1803.1143.00431.06 IRL3623.0038.300.13N/A7.3035014.820. 0090.2730.13011.3582. 3912.2291.58224.28 IRL3823.7039.300.1928.07.2935716.420. 0140.2630.9950.8370. 5610.3980.69616.78 IRL3924.7039.500.13N/A7.1937817.480. 0100.0010.9013.8090. 6580.3790.00012.17 IRL4126.5043.300.14N/A7.2839525.350. 0070.3601.0750.2162. 3181.6431.37022.46 IRL4226.4043.603.0028.47.3940115.420. 0070.5733.1431.8510. 4410.3650.31810.36 BRL119.8031.700.5327.17.6732721.000. 0070.5230.3672.2790. 0360.0920.1033.58 BRL219.3031.000.1528.47.4531914.950. 0050.2860.2530.0200. 0590.0430.0243.26 BRL319.0030.601.2627.77.9431414.510. 0030.4350.3650.0750. 4030.0000.3130.00 BRL419.2030.700.7327.47.4031914.850. 0050.4770.1043.2480. 2850.2500.11615.09 BRL519.3030.900.3427.97.7231914.930. 0070.4380.4100.0250. 2010.1510.1297.03 BRL619.4031.102.6628.67.7232015.250. 0010.4060.2140.5940. 1040.1090.0006.13 BRL719.3031.000.2527.87.6731614.940. 0040.7960.3800.6730. 1230.0040.1840.99 BRL820.5032.700.1828.27.37335N/A0. 0030.4220.3495.5940. 1080.0290.7084.94

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103 Southern Study Area, Dry Season, Water Column StationSalinityCond.OxygenTemp.pHClSO4NO3NH4TSNTNSRPTSPTPSiO2(ppt)(mS/cm ) (mg/L)(oC)(mM)(mM)(mg/L)(mg/L)(mg/ L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L) IRL29WC20.3032.406.9628.88.43333N/A0 .0020.0620.0810.395 0.6020.6280.0016.49 IRL30WC20.4032.607.1927.98.1133416.21 0.0060.0590.3790.358 0.0050.0110.0200.23 IRL31WC20.40N/A7.2626.98.0633515.99 0.0010.0120.3110.368 0.0070.0140.0240.56 IRL32WC20.4032.407.9229.38.4333316.25 0.0020.0270.3310.385 0.0160.0200.0320.96 IRL33WC20.3032.307.8028.18.3033216.14 0.0020.0260.3800.430 0.0170.0200.0291.19 IRL34WC20.2032.207.4927.38.1733116.15 0.0010.0330.2960.386 0.0150.0160.0271.06 IRL35WC21.8034.609.1528.98.3835617.49 0.0030.0220.2840.326 0.0280.0280.0360.96 IRL36WC21.6034.307.1028.98.2935217.44 0.0010.0180.2990.391 0.0320.0290.0351.04 IRL37WC22.5035.20N/A28.18.2736518.32 0.0010.0150.3200.310 0.0250.0220.0280.59 IRL38WC22.6035.70N/A28.08.3037318.51 0.0010.0200.2980.309 0.0280.0240.0340.00 IRL39WC24.3037.806.5428.18.2838719.21 0.0010.0140.3010.338 0.0310.0290.0351.46 IRL40WC26.8041.106.7428.28.2843021.61 0.0010.0070.2510.284 0.0210.0190.0281.75 IRL41WC25.2039.406.9627.68.3141120.66 0.0000.0350.2350.250 0.0360.0310.0382.07 IRL42WC24.8038.906.8427.68.3640420.39 0.0010.0130.2590.277 0.0300.0280.0322.07 BRL1WC19.7031.507.2029.28.7732315.85 0.0060.0160.2980.336 0.0040.0040.0261.04 BRL2WC19.3030.906.6528.28.6031315.01 0.0020.0370.3380.298 0.0030.0050.0350.97 BRL3WC19.2030.806.4028.08.5431915.61 0.0030.0240.3200.345 0.0030.0060.0511.13 BRL4WC19.0030.706.7028.08.5431815.44 0.0010.0220.3250.284 0.0030.0080.0391.51 BRL5WC19.6031.406.3827.18.5232415.55 0.0020.0240.3280.298 0.0040.0080.0391.49 BRL6WC20.6032.907.6427.28.6732015.77 0.0040.0750.3550.294 0.0030.0020.0150.16 BRL7WC19.3031.006.0627.18.6331615.48 0.0010.0920.3570.260 0.0010.0060.0510.89 BRL8WC20.6032.905.4727.28.4634016.51 0.0010.0380.3070.311 0.0030.0090.0431.41

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104 Southern Study Area, Dry Season, Groundwater and Surface water StationSalinityCond.OxygenTemp pHClSO4NO3NH4TSNTNSRPTSPTPSiO2(ppt)(mS/cm ) (mg/L)(oC)(mM)(mM)(mg/L)(mg/L)(mg/L)(mg/L ) (mg/L)(mg/L)(mg/L ) (mg/L) Groundwater Wells BHSpring2.003.810.5824.87.8342.040 .0060.4370.5590.5360. 0300.0000.00015.02 (F)GW3311.402.680.2225.27.5241.140 .0010.5310.6020.5820. 0020.0000.00015.92 (S)GW9211.903.550.2726.07.9311.660 .0000.5500.6190.5860. 0010.0000.00015.74 (S)GW14720.100.200.3524.54.350.310 .0060.4160.0002.2500. 0810.0400.00016.45 (F)GW14730.300.640.7224.76.940.000 .0020.6340.1760.1410. 7590.5570.56412.15 (S)GW15801.102.082.3325.67.6191.44 0.0090.3860.4900.4040. 0010.0000.00016.33 (F)GW16471.102.170.1131.57.6201.20 0.0080.4430.6070.5020. 0010.0000.00017.72 Surface WaterEauGallie River18.0032.577.2628.88.429514.460. 0030.0420.3460.4040. 0410.0450.0983.87Crane Creek20.6036.526.0430.48.235817.570. 0130.0360.3490.2770. 1020.0000.1602.91Turkey Creek23.7040.555.5229.28.122811.100. 0170.0470.2440.3240. 0310.0220.0448.47St. Sebastian River27.8048.106.1029.88.353126.850. 0030.0170.1220.2220. 0270.0160.0411.50Sebastian Inlet36.0056.307.2726.68.338431.110. 0510.0230.2810.0610. 0010.0000.0210.43

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105 Southern Study Area, Rainy Season, Seepage Water StationSalinityCond.OxygenTemp.pHSO4ClNO3NH4TSNTNSRPTSPTPSiO2(ppt)(mS/cm ) (mg/L)(oC)(mM)(mM)(mg/L)(mg/L)(mg/ L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L) IRL29N/AN/AN/AN/A7.0524.274740.004 1.0061.0080.9510. 2560.2450.2186.73 IRL30N/AN/AN/AN/A7.4523.404590.006 1.8972.2902.6160. 6310.5600.54511.81 IRL31N/AN/AN/AN/AN/A23.514540.012 0.4571.9352.4491. 2721.0331.19816.57 IRL32N/AN/AN/AN/A6.9624.384780.002 1.3301.1811.1560. 6060.5180.5206.58 IRL33N/AN/AN/AN/A7.9525.334830.009 0.0690.5820.5180. 0550.0470.0292.28 IRL3527.8047.103.9630.87.2323.984590. 0050.4301.2931.3860. 1570.1470.1594.37 IRL3628.3047.703.1030.67.0322.864570. 0021.5503.1692.9171. 9131.6052.01720.03 IRL3738.5047.701.1030.17.2023.344510. 0030.5881.5181.7280. 1690.1530.1803.97 IRL3827.9046.800.4430.07.1523.554580. 0010.1132.0901.9740. 7290.6500.75313.02 IRL3926.0044.600.9631.57.1221.794220. 0020.3721.5611.4020. 2650.2160.2495.13 IRL4126.8045.101.8730.07.1122.834370. 0060.4091.7341.5230. 4370.3610.40012.21 IRL4225.8043.801.7830.47.1621.754230. 0011.0281.4640.9920. 3120.2520.3056.48 BRL129.2045.502.0030.48.2322.984410. 0010.0810.7590.8160. 0700.0250.0343.36 BRL328.2044.430.3030.07.8621.574240. 0060.3862.6431.8020. 8160.7350.78120.37 BRL428.8044.790.9429.87.6921.924310. 0020.5271.1091.2670. 1400.1310.1495.16 BRL528.7044.550.3529.97.4122.024280. 001N/A1.1371.0440. 2960.2440.2517.17 BRL629.1045.290.2130.67.9622.524340. 0010.6171.3241.5900. 0220.0200.0485.40 BRL729.2045.320.5330.17.3421.884560. 0010.0501.9331.2540. 3350.3240.3497.32 BRL829.6046.100.5429.67.6523.214550. 0010.5171.5011.5140. 2530.2300.2227.96

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106 Southern Study Area, Rainy Season, Water Column StationSalinityCond.OxygenTemp.pHSO4ClNO3NH4TSNTNSRPTSPTPSiO2(ppt)(mS/cm ) (mg/L)(oC)(mM)(mM)(mg/L)(mg/L)(mg/ L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L) IRL29WC29.5045.308.1828.68.4024.40478 0.0040.0150.4380.467 0.0310.0520.0592.21 IRL30WC29.2045.007.4029.08.2424.65485 0.0010.0170.4430.496 0.0200.0390.0512.21 IRL31WC28.9044.507.0929.08.2024.01474 0.0010.0210.4580.489 0.0160.0340.0442.63 IRL32WC29.6045.508.3028.68.3325.21490 0.0010.0150.4090.439 0.0340.0520.0672.01 IRL33WC29.8045.806.1929.18.0725.25489 0.0010.0530.4790.485 0.0500.0650.0792.24 IRL34WC29.8045.807.9129.18.1525.18493 0.0020.0240.4200.424 0.0490.0660.0821.74 IRL35WC28.6044.007.4629.38.1323.90469 0.0020.0180.3160.352 0.0600.0740.0832.01 IRL36WC28.5044.006.0429.38.0224.01473 0.0020.0560.3130.349 0.0640.0750.0842.15 IRL37WC28.7044.106.1729.37.9924.43474 0.0020.0530.3500.364 0.0660.0750.0822.26 IRL38WC28.2043.6029.106.68.0623.42459 0.0030.0540.3370.330 0.0640.0750.0772.34 IRL39WC26.6041.406.2628.58.1322.22439 0.0010.0130.3030.348 0.0550.0700.0831.99 IRL40WC26.5041.305.6829.08.0821.91431 0.0010.0430.3250.345 0.0490.0600.0692.38 IRL41WC26.2040.905.7628.18.0221.31424 0.0440.0080.4160.329 0.0410.0550.0662.38 IRL42WC25.8040.306.5227.28.1121.44422 0.0020.0130.3130.363 0.0300.0450.0642.02 BRL1WC28.6044.474.1927.38.4822.59444 0.0010.0250.6350.723 0.0080.0250.0403.04 BRL2WC29.0045.056.6629.08.6322.80452 0.0010.0290.5370.594 0.0120.0310.0362.74 BRL3WC28.4044.195.4028.58.3921.59429 0.0020.0420.6100.688 0.0080.0240.0443.51 BRL4WC28.5044.236.7628.98.6122.29441 0.0020.0290.5750.611 0.0110.0310.0352.72 BRL5WC28.6044.516.9029.18.6421.86432 0.0010.0240.5420.616 0.0070.0270.0483.25 BRL6WC29.8046.165.8727.98.5723.09454 0.0000.0160.5010.515 0.0040.0190.0262.19 BRL7WC29.5045.675.2528.58.6323.13454 0.0010.0190.5140.584 0.0110.0320.0452.74 BRL8WC29.5045.604.3927.38.4323.07456 0.0010.0140.4740.551 0.0100.0340.0612.70

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107 Southern Study Area, Rainy Season, Groundwater and Surface water StationSalinityCond.OxygenTemp.pHSO4ClNH4NO3TSNTNSRPTSPTPSiO2(ppt)(mS/cm ) (mg/L)(oC)(mM)(mM)(mg/L)(mg/L)(mg/L)(mg/L ) (mg/L ) (mg/L ) (mg/L ) (mg/L) Groundwater Wells BHSpring1.803.511.8126.67.552.05310 .1820.0020.4300.444 0.0020.0040.00115.32 (F)GW3311.202.540.5027.17.521.10220 .3970.0000.6030.605 0.0030.0030.00016.20 (S)GW9211.603.322.0827.67.751.613 0N/A0.0040.6740.689 0.0030.0050.00415.93 (F)GW14730.000.600.2725.76.730.006 0.5910.0021.3281.339 0.7420.6190.71011.75 GW15610.902.071.5625.77.551.46190 .3500.0020.5700.625 0.0030.0020.00016.35 (F)GW16470.902.062.1332.47.651.12200 .3970.0160.5470.543 0.0030.0030.00018.17 Surface WaterHorse Creek26.9041.703.9232.47.51 17.003380.0390.0160.3900. 5220.0630.0830.1052.99Eau Gallie River26.1040.508.2630.88.13 21.854340.0270.0010.3630. 5130.0540.0690.0901.97Crane Creek23.0036.306.4830.37.93 19.063820.0310.0010.4570. 5380.0890.0890.1142.35Turkey Creek0.200.888.1630.27.730.57110.081 0.0661.0000.9880. 0200.0310.04212.76St. Sebastian River21.6034.107.7031.18.14 17.473550.0210.0020.2820. 3820.0520.0630.0854.64Sebastian Inlet33.7051.008.5929.58.22 29.625700.0140.0110.0700. 1240.0110.0200.0240.44

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108 Northern Study Area, December, 1999, Pore Water StationPortDepthSalinityCond.OxygenTemp. Cl-SO4NO3NH4TSNTNSRPTSPTPSiO2#(cm)(ppt)(mS/cm ) (mg/L)(oC)(mM)(mM)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L) IRL 616922.4025.800.6921.538021.370.0040.7771.1091.0990.0390.0380.0354.13 21424.8039.205.6621.140720.050.0140.1320.8100.8750.0010.0150.0452.37 3-4724.5038.801.1121.539821.330.0010.5941.0151.0180.0360.0360.0383.64 IRL 513024.8039.106.3821.540522.000.0060.0980.6321.0110.0010.0060.0602.18 2-124.8039.105.5021.740322.140.0060.1100.6990.9520.0040.0090.0532.18 3-3124.8039.106.2421.740022.170.0210.1200.6620.9930.0010.0090.0572.18 4-6024.1038.201.0121.939221.640.0051.2181.5571.5870.1210.1030.1195.30 5-8929.3045.400.9822.047526.380.0041.4381.8041.7280.0640.0560.0597.73 IRL 2212927.4042.704.4523.044323.400.0180.4100.8200.9500.0390.0420.0732.29 2-427.5042.901.5922.544223.530.0020.7410.9530.9650.0360.0330.0352.97 3-3227.9043.600.7822.245124.120.0361.0711.2901.3290.0640.0580.0524.01 4-12328.7046.200.5022.149627.440.1511.8782.0011.9260.1310.0151.0559.09 IRL 41-3922.3035.601.0221.836419.330.0002.6852.6782.8320.2410.1760.22112.96 2-6430.2046.400.7422.546626.040.0025.1433.8643.8650.1780.1260.12013.67 3-9533.3051.000.9822.453228.660.0045.6572.1504.2030.1810.1740.15916.40 4-12433.4051.001.0522.653930.620.0013.5293.1263.0730.0800.0720.08111.35 5-15633.8051.600.8022.954430.950.0112.9792.0932.4680.0770.0890.08511.00 6-18533.3051.000.8023.353930.710.0142.2081.9712.0350.0610.0670.09410.13

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109 Southern Study Area, Dry Season, Pore Water StationPortDepthSalinityCond.OxygenTemp.pH Cl-SO4NO3NH4TSNTNSRPTSPTP SiO2#(cm)(ppt)(mS/cm)(mg/L)(oC)(mM)(mM)(mg/L)(m g/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L) IRL317-15722.4035.600.8124.87.4937019.260.0030.0622.2252.8010.2170.0810.06414.54 8-19722.6036.804.5027.27.5937418.620.0050.2960.0002.5500.2470.1290.11711.30 IRL326-3319.4032.700.5728.07.6032215.670.0040.7241.1280.9550.1330.0410.0264.81 7-7320.9034.705.5227.27.6831315.030.0040.7230.9161.0080.1270.1420.1429.46 8-11318.6030.801.2926.67.5531315.260.0070.5880.6080.6590.1640.1580.30910.70 BRL13-3019.6031.303.4028.08.0831915.330.0080.8810.5200.1560.1460.1570.1864.89 5-11019.7031.401.8329.27.6332216.300.0110.4060.6020.6720.1930.0770.0899.42 6-15021.8034.601.6127.57.6435818.840.0100.9231.3801.4620.3790.2180.2459.54 8-19019.6031.402.2728.57.7632315.760.0090.9450.4472.2500.0350.1191.1765.67 BRL21-1019.2030.901.3026.77.6131614.870.0010.1900.5700.2950.0030.0000.0152.51 2-3018.1030.101.3726.97.6930815.150.0020.5630.8870.8610.0110.0050.0483.39 3-5018.1029.200.4726.57.7229814.380.0030.5221.0370.8610.0950.0000.0584.50 5-11022.0034.900.4525.77.5736418.820.0040.4151.0600.2930.2430.0610.1057.81 6-15024.7038.800.5825.87.5540321.920.0050.5961.0401.0720.2130.0450.0806.60 7-19025.3039.900.5525.57.3942923.300.0070.5891.1501.0010.2490.0940.1166.47 8-23027.1042.300.7024.87.4744323.210.0050.7541.1651.3020.3070.1540.1526.78 BRL55-5019.1030.600.6627.07.6131214.900.0041.1251.3140.7070.1780.0550.0225.73 8-7031.2047.901.2025.97.5240226.240.0061.2022.3333.0250.1490.0320.00017.54 BRL64-1420.9034.301.2526.57.4531715.470.0050.5500.8490.8650.0820.0000.0733.26 5-4420.1033.401.5527.27.8630314.440.0030.6090.9761.0390.0740.0000.0803.56 6-8419.5032.903.5028.07.8928913.800.0040.8891.3470.8980.0330.0000.0455.39 8-16420.6032.901.2427.07.6733317.110.0050.8561.0261.0780.0850.0000.08710.27 BRL73-1421.6036.303.1028.57.7332015.690.0070.9381.0180.9260.1160.1170.1693.89 4-4420.7034.604.5527.57.9030714.980.0181.1950.1890.2270.0960.1040.1746.64 5-7419.8032.401.7826.37.7628713.860.0071.1490.0001.4510.2560.1130.1758.96 6-11421.4034.702.0525.77.7531715.060.0141.4401.5151.4790.5800.3720.4588.34 7-15425.0039.900.6426.17.7736419.520.0051.5501.3961.4521.0640.7920.8975.93

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110 Southern Study Area, Rainy Season, Pore Water StationPortDepthSalinityCond.OxygenTemp.pH Cl-SO4NO3NH4TSNTNSRPTSPTP SiO2#(cm)(ppt)(mS/cm)(mg/L)(oC)(mM)(mM)(mg/L)(m g/L)(mg/L)(mg/L)(mg/ L)(mg/L)(mg/L)(mg/L) IRL294-8020.6035.501.1430.107.3832415.960.0021.4401.1631.4400.1980.1340.17417.82 5-11020.7035.601.8629.807.5834717.300.0000.5881.4411.1930.0950.0960.09411.45 6-150N/AN/AN/AN/AN/A47724.450.0000.0300.4660.4750.0140.0380.0372.29 BRL11-1026.7034.901.0429.907.6244922.420.0000.0470.6330.6160.0360.0690.0755.65 5-11020.6035.100.7529.107.3734917.720.0001.3651.7091.3160.2400.2220.25113.26 6-15022.1037.700.6629.707.2436520.340.0021.7360.9871.7380.5090.4470.53811.53 BRL21-1026.7044.500.5529.407.9144822.760.0000.1320.6690.6570.0200.0450.0373.86 2-3025.1042.200.7829.307.8342521.310.0000.3400.8940.7870.0650.0760.0703.83 3-5023.1039.000.2229.407.5538519.190.0000.6181.3091.0880.0940.1080.1084.84 4-8019.9034.000.2429.107.5632916.300.0020.8181.0951.1500.1250.1070.1027.85 5-11027.5036.300.1828.907.37369N/A0.0010.2471.0141.1210.3500.3040.34010.35 6-15023.9040.000.3728.807.3239420.950.0010.4571.2540.9710.4000.3550.37710.63 7-19026.0042.600.2728.207.2243022.990.0010.5731.4001.3480.3640.3060.3109.86 8-23026.5044.00N/A28.907.4744023.660.0020.7511.3411.2410.4950.3920.3267.36 BRL52-2026.4043.800.4129.107.9743721.800.0010.2500.8560.8220.1240.1130.1127.17 3-4024.9041.700.3029.107.4742121.580.0010.5381.4491.3360.1180.1160.1296.01 4-7024.2040.800.3429.307.5240920.930.0010.0982.0051.5610.0750.0810.0806.85 5-10027.5045.700.5529.307.43458N/A0.0020.6661.3291.8060.1160.1060.09810.03 BRL61-1026.9045.802.1131.108.0545222.990.0020.2640.7840.8310.0230.0460.0464.46 2-3026.0043.900.3129.907.7442921.380.0020.4231.2611.1740.1110.1000.0914.48 3-5021.6037.600.4631.007.6236317.290.0020.7541.1951.2050.0840.0830.0954.93 4-8020.9036.501.3831.107.6435516.910.0000.7511.2901.1060.0760.0590.0665.74 6-15021.3036.700.3930.107.5634917.510.0010.6231.0231.1040.0880.0790.0789.60 BRL73-14.526.9037.301.0530.207.7644622.960.0020.2720.8090.8330.1150.1130.1284.16 4-44.527.6044.802.2329.407.69N/AN/AN/AN/AN/AN/AN/AN/AN/AN/A 7-154.527.2045.403.9429.708.58N/AN/AN/AN/AN/AN/AN/AN/AN/AN/A

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111 LIST OF REFERENCES Adamus, C., Bergman, M., 1993. Development of a nonpoint source pollution load screening model. Draft Report. St. Johns River Water Management District. Behnke, J. 1975. A summary of the biogeochemistry of nitrogen compounds in groundwater. Journal of Hydrology, Vol. 27; 155-167. Belanger, T.V., Mikutel, D.F., 1985. On the use of seepage meters to estimate groundwater nutrient loading to lakes. Water Resources Bulletin, Vol. 21 (2); 265-272. Belanger, T.V., Walker, R.B., 1990. Ground water seepage in the Indian River Lagoon, Florida, p. 367-375. In Tropical Hydrology and Caribean Water Resources. Proceedings on the International Symposium of the American Water Resources Association. Belanger, T.V., Montgomery, M.T., 1992. Seepage meter errors. Limnology and Oceanography, Vol. 37; 1787-1795. Bokuniewicz, H., 1980. Groundwater seepage into Great South Bay, New York. Estuarine and Coastal Marine Science. Vol.10; 437-444. Bokuniewicz, H., 1992. Analytical descriptions of subaqueous groundwater seepage. Estuaries. Vol. 15; 458-464. Brown, D.W., Kenner, W.E., Crooks, J.W., Foster, J.B., 1962. Water Resources of Brevard County, Florida. Florida Geological Survey, Report of Investigations No. 28. Tallahassee. Bradner, L.A., Knowles, L., 1999. Potentiometric surface of the upper Floridan Aquifer in the St. Johns River Water Management District and vicinity, Florida. USGS, Open file Report 99-0608 & 99-100. Bradner, L.A., Knowles, L., 2000. Potentiometric surface of the upper Floridan Aquifer in the St. Johns River Water Management District and vicinity, Florida. USGS, Open file Report unpublished.

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112 Bugna, G.C., Chanton, J.P., Cable, J.E., Burnett, W.C., Cable, P.H., 1996. The importance of groundwater discharge to the methane budgets of nearshore and continental shelf waters of the northeastern Gulf of Mexico. Geochimica et Cosmochimica Acta, Vol. 23: 4735-4746. Cable, J.E., Bugna, G.C., Burnett, W.C., Chanton, J.P., 1996a. Application of 222Rn and CH4 for assessment of groundwater discharge to the coastal ocean. Limnology and Oceanography, Vol. 41(6); 1347-1353. Cable, J.E., Burnett, W.C., Jeffrey P.C., Weatherly, G.L., 1996b. Estimating groundwater discharge into the northeastern Gulf of Mexico using radon-222. Earth and Planetary Science Letters, Vol. 144; 591-604. Cable, J.E., Burnett, W.C., Chanton, J.P, 1997a. Magnetude and variations of groundwater seepage along a Florida marine shoreline. Biogeochemistry, Vol. 38; 189-205. Cable, J.E., Burnett, W.C., Chanton, J.P., Corbett, D.R., Cable, P.H., 1997b. Field evaluation of seepage meters in the coastal marine environment. Estuarine, Coastal and Shelf Science, Vol. 45; 367-375. Capone, D.G., Bautista, M.F., 1985. A groundwater source of nitrate in nearshore marine sediments. Nature, Vol. 313; 214-216. Cherkauer, D.S., Nader, D.C., 1989. Distribution of groundwater seepage to large surface-water bodies: the effect of hydraulic heterogeneities. Journal of Hydrology, Vol. 109; 151-165. Church, T. M., 1996. An underground route for the water cycle. Nature, Vol. 380; 579580. Connor, J.N., Belanger, T.M., 1981. Ground water seepage in Lake Washington and the Upper St. Johns River Basin, Florida. Water Resources Bulletin, Vol. 17 (5); 779-805. Conover, C.C., Geraghty, J.J., Parker, G.G., 1984. Chapter 4; Groundwater. In (Eds.) Fernald, E.A., Patton, D.J.; Water Resources Atlas of Florida. Florida State University, Tallahassee. Corbett, D.R., Chanton, J., Burnett, W., Dillon, K., Rutkowski, C., 1999. Patterns of groundwater discharge into Florida Bay. Limnology and Oceanography, Vol. 44; 1045-1055. Day, J.W., Hall, C.A., Kemp, W.M., Yanez-Arancibia, A., 1989. Estuarine Ecology. John Wiley & Sons, New York.

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114 Johannes, R.E., 1980. The ecological significance of the submarine discharge of groundwater. Marine Ecology, Vol. 3; 365-373. Lapointe, B.E., Clark, M.W., 1992. Nutrient inputs from the watershed and coastal eutrophication in the Florida Keys. Estuaries, Vol. 15 (4); 465-476. Lee, D.R., 1977. A device for measuring seepage flux in lakes and estuaries. Limnology and Oceanography, Vol. 22 (1); 140-147. Lewis, J.B., 1987. Measurements of groundwater seepage flux onto a coral reef; Spatial and temporal variations. Limnology and Oceanography, Vol. 32 (5); 1165-1169. Li, L., Barry, D.A., 1999. Submarine groundwater discharge and associated chemical input to a coastal sea. Water Resources Research, Vol. 35; 3253-3259. Miller, J.A., 1997. Hydrogeology of Florida. In The geology of Florida. (Eds.) Randazzo, A.F., Jones, D.S.; University Press of Florida, Gainesville. Moore, W.S., 1996. Large groundwater inputs to coastal waters revealed by 226Ra enrichments. Nature, Vol. 30; 612-614. Motz, L.H., Gordu, F., 2001. Estimates of groundwater discharge and nutrient loading to the Indian River Lagoon. St. Johns River Water Management District, Final Report; Contract Number 99G245, Palatka, Florida. Pandit, A., El-Khazen, C.C., 1999. Groundwater seepage into the Indian River Lagoon at Port St. Lucie. Florida Scientist, Vol. 53; 169-179. Pickens, J.F., Cherry, J.A., Coupland, R.M., Grisak, G.E., Merritt, W.F., Risto, B.A., 1981. A multilevel device for ground-water sampling. Ground Water Monitoring & Remediation. Vol. 2; 48-51. Pin, C., Bassin, C., 1992. Evaluation of Sr-specific extraction chromatographic method for isotopic analysis in geologic materials. Anal. Chim. Acta., Vol. 269; 249-255. Rao, D., 1987. Surface Water Hydrology. In Indian River Lagoon Joint Reconnaissance Report. (Eds.) J. S. Steward, J. A., VanArman. St Johns River Water Management District and the South Florida Water Management District, Contract CM-137 and CM-138. Reay, W.G., Gallagher, D.L., Simmons, G.M., 1992. Groundwater discharge and its impact on surface water quality in a Chesapeake Bay Inlet. Water Resources Bulletin, Vol. 28; 1121-1134.

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115 Robinson, M.A., Gallagher, D.L., Reay, W.G., 1998. Field observations of tidal and seasonal variations in ground water discharge to tidal estuaring surface water. Ground Water Monitoring & Remediation, Vol. 18; 83-92. Robinson, M.A., Gallagher, D.L., 1999. A model of ground water discharge from an unconfined coastal aquifer. Journal of Ground Water, Vol. 37; 80-87. Rutkowski, C.M., Burnett, W.C., Iverson, R.L., Chanton, J.P., 1999. The effect of groundwater seepage on nutrient delivery and seagrass distribution in the northeastern Gulf of Mexico. Estuaries, Vol. 22; 1033-1044. Schelske, C.L., Aldridge, F.J., Kenney, W.F., 1999. Assessing nutrient limitation in trophic state in Florida lakes. In Phosphorus Biogeochemistry in subtropical ecosystems. Florida as a case example. (Eds.) K.R. Reddy, G.A., OConnor, C.L. Schelske; CRC/Lewis Publishers, pp. 321-330. Scott, T.M., 1990. The lithostratigraphy of the Hawthorn Group of peninsular, Florida. Florida Geological Survey, Open File Report. Tallahassee, FL. Shaw, R.D., Prepas, E.E., 1989. Anomalous, short-term influx of water into seepage meters. Limnology and Oceanography, Vol. 34 (7); 1343-1351. Sigua, G.C., Steward, J.S., Tweedale, W.A., 2000. Water-quality monitoring and biological integrity assessment in the Indian River Lagoon, Florida: Status, trends and loadings (1988-1994). Environmental Mangement, Vol. 25; 199-209. Simmons, G.M., 1992. Importance of submarine groundwater discharge (SGWD) and seawater cycling to material flux across sediment/ water interfaces in marine environments. Marine Ecology, Vol. 84; 173-184. Smith, N.P., 1987. An introduction to the tides of Floridas Indian River Lagoon. Florida Scientist, Vol. 50; 49-61. Smith, N.P., 1993. Tidal and nontidal flushing of Floridas Indian River Lagoon. Estuaries, Vol. 16; 739-746. Stickney, R.R. 1984. Estuarine ecology of the Southeastern United States and Gulf of Mexico. Texas A&M University Press, College Station. Strickland, J.D., Parsons, T.R., 1972. A practical handbook of seawater analysis. Fish. Res. Bd., Canada, Bulletin; 167-311. Tibbals, C.H., 1990. Hydrology of the Floridan Aquifer system in east-central Florida. U.S. Geological Survey Professional Paper 1403-E. Washington, D.C.

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116 Toth, D.J., 1988. Salt water intrusion in coastal areas of Volusia, Brevard and Indian River Counties. Technical Publication SJ 88-1, St Johns River Water Management District, Palatka, Florida. Trefry, J.H., Feng, H., Trocine, R.P., Metz, S., Grguric, G., Vereecke, R., Cleveland, S., 1992. Concentrations and benthic fluxes of nutrients from sediments in the Indian River Lagoon, Florida (Project Muck, Phase II), Final Report to the St. Johns River Water Management District. Trochine, R.P., Trefry, J.H., 1996. Metal concentrations in sediment, water and clams from the Indian River Lagoon, Florida. Marine Pollution Bulletin, Vol. 32 (10); 754-759. Valiela, I., Teal, J.M., Volkman, S., Shafer, D., Carpenter, E.J., 1978. Nutrient and particulate fluxes in a salt marsh ecosystem: Tidal exchanges and inputs by precipitation and groundwater. Limnology and Oceanography, Vol. 23 (4), 798812. Valiela, I., Peckol, P., DeMeo-Anderson, B., DAvanzo, C., Sham, C., Lajtha, K., 1992. Coupling of watersheds and coastal waters: sources and consequences of nutrient enrichment in Waquoit Bay, Massachusetts. Estuaries, Vol. 15 (4); 443-457. Wetzel, R.G, Likens, G.E., 1991. Limnological Analysis. Springer-Verby, New York. Williams, S.A., 1995. Regional ground water flow model of the Surficial Aquifer system in the Titusville/Mims area, Brevard County, Florida. St. Johns River Water Management District Technical Publication SJ95-5. Palatka, Florida Windsor, J.G., Steward, J., 1987. Water and sediment quality. In Indian River Lagoon Joint Reconnaissance Report. (Eds.) J. S. Steward, J. A., VanArman. St Johns River Water Management District and the South Florida Water Management District, Contract CM-137 and CM-138. Woodward-Clyde, 1994. Physical features of the Indian River Lagoon. Indian River Lagoon National Estuary Program, Final Technical Report. Project# 92F274C Zimmerman, C.F., Montgomery, J.R., Carlson, P.R., 1985. Variability of dissolved, reactive phosphate flux rates in nearshore estuarine sediments: Effects of groundwater flow. Estuaries, Vol. 8; 228-236.

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117 BIOGRAPHICAL SKETCH Mary K. Lindenberg was born on May 20, 1974, in St. Croix, Virgin Islands. She graduated from Florida International University in Miami, FL, with a Bachelor of Science degree in geology in 1998. From there, she continued her education at the University of Florida in the Geological Sciences Department, where she received a Master of Science degree in December, 2001.


Permanent Link: http://ufdc.ufl.edu/UFE0000328/00001

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Title: The quantity, characteristics, source and nutrient input of groundwater seepage into the Indian River Lagoon, FL
Physical Description: Mixed Material
Copyright Date: 2008

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Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
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Permanent Link: http://ufdc.ufl.edu/UFE0000328/00001

Material Information

Title: The quantity, characteristics, source and nutrient input of groundwater seepage into the Indian River Lagoon, FL
Physical Description: Mixed Material
Copyright Date: 2008

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
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THE QUANTITY, CHARACTERISTICS, SOURCE AND NUTRIENT INPUT OF
GROUNDWATER SEEPAGE INTO THE INDIAN RIVER LAGOON, FL

















By

MARY K. LINDENBERG


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

UNIVERSITY OF FLORIDA


2001




























Copyright 2001

by

Mary K. Lindenberg



























To my family















ACKNOWLEDGMENTS

I wish to express my appreciation to Dr. Jonathan Martin for giving me the

opportunity to share in the research of this project and for his guidance and editorial

assistance with my thesis writing. I also wish to express my gratitude to the other

members of my committee, Dr. Elizabeth Screaton and Dr. Louis Motz, for their time and

advice. I wish to thank the St. Johns River Water Management District for its financial

support. A special thank you goes to the two other principal investigators on this project,

Dr. Jaye Cable and Dr. Pete Swarzenski, who made working in the field fun, as well as a

major learning experience.

Others have contributed their time and, most of all, their patience. I would like to

thank William Kenney and Dr. C. Schelske for their hospitality and guidance at the

Fisheries Department; Jason Curtis for his unending assistance in the stable isotope lab;

Kevin Hartl for design and construction of many devices used in the field including the

seepage meters and the multisamplers (beautiful job!). I would also like to thank those

who supported me through their friendship.

Lastly, the greatest thank you goes to Kevin Caster, for without his support I

would have given up a long time ago.
















TABLE OF CONTENTS

page

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

LIST OF TABLES ........................................................ ............ ............. vii

LIST OF FIGU RES ......... ............................. .. .......... ........ ........... ix

ABSTRACT .............. .................. .......... .............. xi

CHAPTERS

1 IN TR O D U C TIO N ....................... .... ................ .... .. ........ ..............

Significance of Submarine Groundwater Seepage ................................. .................. 1
Importance of Groundwater Seepage and Nutrient Loading into Estuaries ................. 1
Indian R iver L agoon ............ ............................................. ........ .. ............ 2
P reviou s Studies......................................... ......... ..... 5
P u rp o se ........................................................................................................ . ..... ..... 8


2 R E G IO N A L SE TTIN G .................................................................. ........................ 9

L o c atio n ............................................................................. .................................. . 9
Physiographic Features ....................................................... .. .......... .. 12
Regional Hydrostratigraphy.......... .. .......... ........... ..................... .............. 13
Clim ate and H ydrologic Com ponents................................................. ... ................. 21


3 M E T H O D S .............................................................................24

Seepage Measurements Methods Review and Background Theory........................... 24
F field Sam pling ......................................... ........................ ....... ... ...... 25
Seepage Meter Construction, Deployment and Seepage Measurements.................. 25
Multisamplers ........................................... 30
Water Sample Collection .............. ..... .................................... 31
Analytical Techniques ............................................... .. 32
Field M measurements ...... ............ .......... .............. ... ....... 32
L laboratory M easurem ents ........................................................................................ 33




v












4 R E SU L T S ....................................................... 3 5

P recipitation and R charge ........................................................................................... 35
S eep ag e R ates ................................................................... 3 9
N north ern Stu dy A rea .................................................... ....................................... 39
Southern Study A rea ................................................... ..... ............ 41
Tracers................................. .............. 44
N utrients.............................. .............. ...... 4 8


5 D ISC U S SIO N ............................................................... 52

S eep ag e R ates ..................................................................... 52
Seasonal Relationship of Seepage Rates........................................ 52
Spatial Heterogeneity of Seepage Rates .................................. 54
Chloride............................................ ........ 57
Seasonal V ariation ........................ .... .......... .................... 58
Fraction of Fresh Groundwater in Seepage Water .................................................. 61
Effects of Seepage Water on Water Column Chemistry ........................................ 67
Evidence of Mixing Pore Water Chemistry .......................................................... 70
Evaporation and Surficial Runoff.................................................. .......... .... 75
N utrients.............................. .............. ...... 79
N itro g e n .................................................................................................................... 8 1
Phosphorus ................................. .......................... .... ..... ......... 83
Nutrient Loading ................................. ............................ .... ........ 83
L im iting N nutrients ..................................................... 86


6 CON CLU SION S ............................................. 88

APPENDICES

A STATION LOCATIONS ............................................. ......... ....... 91

B SEEPA GE RA TE S.....................................................................................94

C WATER CHEMISTRY DATA ................................................96

LIST OF REFEREN CES ........................................ ............... .... ................ 111

B IO G R A PH IC A L SK E T C H ..................................................................................... 117
















LIST OF TABLES


Table Page

1-1. Previous studies measuring groundwater discharge into marine environments............6

2-1. Sampling, times, measurements and locations. ........................... ..... ........ ....... 11

2-2. Lithologic and hydrogeologic information taken from wells in the coastal areas of
Volusia, Brevard and Indian River Counties, FL ............................................. 15

3-1. Blank and duplicate seepage flux values ............................................ ............... 29

4-1. Average, median, minimum, maximum and standard deviation of seepage flux rates
for the northern study area. ............................................................................. 40

4-2. The minimum and maximum seepage rates and the corresponding % change
between the dry and rainy seasons of the northern study area.............................40

4-3. Average, median, minimum, maximum and standard deviation of seepage flux rates
for the southern study area ....................................... ............... ............... 42

4-4. The minimum and maximum seepage rates and the corresponding % change
between the dry and rainy seasons of the southern study area. .........................42

4-5. The average, minimum, maximum and standard deviation of tracer concentrations
of the water column, seepage water and groundwater measured during the dry
season in the northern study area. .............................................. ............... 44

4-6. The average, minimum, maximum and standard deviation of tracer concentrations in
the water column, seepage water and groundwater measured during the rainy
season in the northern study area. .............................................. ............... 45

4-7. The average, maximum, minimum and standard deviation of tracer concentrations in
the water column, seepage water, groundwater, surface water and pore water
measured during the dry season in the southern study area.............................47

4-8. The average, minimum, maximum and standard deviation of tracer concentrations in
the water column, seepage water, groundwater, surface water and pore water
measured during the rainy season in the southern study area............................48









4-9. Average, minimum, maximum and standard deviation of nutrient concentrations in
seepage water, water column and groundwater during the dry season in the
northern study area .................................................. ....... .. ............ 49

4-10. Average, minimum, maximum and standard deviation of nutrient concentrations in
seepage water, water column and groundwater during the rainy season in the
northern study area ........... .......... .... ....... 50

4-11. Average, minimum, maximum and standard deviation of nutrient concentrations of
seepage water, water column, groundwater, surface water and pore water
during the dry season in the southern study area. ............. .............................. 50

4-12. Average, minimum, maximum and standard deviation of nutrient concentrations of
seepage water, water column, groundwater, surface water and pore water
during the dry season in the southern study area. .........................................51

5-1. Normal average monthly recharge values for the entire Indian River Lagoon. ............60

5-2. Average monthly recharge for the northern study area. ..........................................60

5-3. Average monthly recharge for the southern study area..........................................61

5-4. The chloride concentrations of seepage water, water column and groundwater used
to calculate the percentage groundwater found in the seepage water ................63

5-5. Time of water column circulation through sediments of the entire lagoon ................70

5-6. The minimum chloride concentration in pore water and depth in multisamplers from
the southern study area............... ...... .... .... .... ........ .... ......... ... 71

5-7. The percent of pore water with low chloride concentrations in seepage water in the
southern study area. ...................... .. .................... .............. .... .... ............73

5-8. Chloride concentrations of surface water measurements of dry and rainy season in
b oth stu dy areas ...................................................................76

5-9. Mean monthly streamflow of four major surficial discharges in the southern study
area. ............................................................................... 7 7

5-10. The average percent of inorganic and organic nutrient concentrations in total
soluble nitrogen and phosphorus concentrations for the dry and rainy seasons
of the northern and southern study areas. ................................. .................82

5-11. The average nutrient concentration, nutrient flux and nutrient loading of total
nitrogen and total phosphorus in the northern and southern study areas.............85

5-12. Nutrient concentrations and flux in each study area and nutrient loading quantity to
the Indian River Lagoon. ............................................ ............................. 87
















LIST OF FIGURES


Figure Page

2-1. The Indian River Lagoon System (including the Indian River Lagoon, the Banana
River Lagoon and the Mosquito lagoon) located in east Central Florida ..........10

2-2. Map and stations of the (a) northern study area and of the (b) southern study area...... 11

2-3. A hydrostratigraphic cross-section below the IRL from the Volusia/ Brevard County
line in the north to Sebastian Inlet in the south ......... ......... ........... ............... 14

2-4. Contours of the potentiometric surface of the Upper Floridan Aquifer during (a)
May 1999, (b) September 1999, (c) May 2000, (d) September 2000 ................17

2-5. Average monthly precipitation for the Indian River Lagoon region. The
precipitation values are based on the monthly mean of 17 stations in and
around the IRL from 1951 to 1980............................... ...................... 22

2-6. Average monthly potential evaporation for the Indian River Lagoon region. The
potential evaporation values are based on the monthly mean of 17 stations in
and around the IRL from 1951 to 1980. ................................... ............... 23

2-7. Average monthly recharge for the Indian River Lagoon region. The recharge values
are based on the monthly mean of 17 stations in and around the IRL from
19 5 1 to 19 80 .................................................... ................ 2 3

3-1. A depiction of a seepage meter placed in the sediment under the water column. .......26

3-2. A time series experiment showing 5 seepage rates from station IRL 6. .......................27

3-3. An example of a multisampling device. ............................................. ............... 30

4-1. The total monthly precipitation and potential evaporation values for the northern
IRL from M ay, 1998 to December, 1999. ................................... ..................... 36

4-2. Recharge values between May 1998 and December 1999 for the northern study area
study area (grey bars) and average recharge values taken from average data
over 30 years from 17 stations (black bars). .................. ................ ....... 36









4-3. The location of climate stations (squares) and surficial discharge stations (triangles)
in both the northern and southern study areas. ............. .................................... 37

4-4. The total monthly precipitation and potential evaporation values for the southern
study area between May, 1999 to July, 2000 FL. .......................................38

4-5. Recharge values between May 1999 and August 2000 for the southern study area
(grey bars) and average recharge values taken from average data of 30 years
and 17 stations (black bars)........................................... ........................... 38

4-6. Histogram of seepage flux for the dry season in the northern study area. ..................40

4-7. Histogram of seepage flux for the rainy season in the northern study area .................41

4-8. Histogram of seepage flux for dry season in the southern study area .........................43

4-9. Histogram of seepage flux for rainy season in the southern study area ......................43

4-10. The profile of chloride concentrations for 3 multisamplers measured during
December, 1999 in the northern study area. .............................. ......... ...... .46

5-1. The changes in salinity and temperature with depth in the water column for station
IRL16 during the rainy season in the northern study area. Sampled on August
1 6 1 9 9 9 ...................................................................... 6 4

5-2. Plot of seepage water chloride concentrations against the corresponding water
column chloride concentrations for the northern study area dry and rainy
season s. ...........................................................................68

5-3. Plot of seepage water chloride concentrations against the corresponding water
column chloride concentrations for the southern study area dry and rainy
season s. ...........................................................................69

5-4. The multisample profiles of chloride concentrations for the (A) dry and (B) rainy
seasons of the southern study area. ............................... .. ....................... 72

5-5. The average chloride concentrations of seepage water (italics) and the water column
(mM) for each transect during the dry season (A) and rainy season (B) in the
Indian River Lagoon compared with chloride concentrations of surficial
disch arg e. ....................................................... ................ 7 8

5-6. The constituents of total nitrogen. ............................................................................ 80

5-7. The constituents of total phosphorus. ........................................ ......................... 81















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

THE QUANTITY, CHARACTERISTICS, SOURCE AND NUTRIENT INPUT OF
GROUNDWATER SEEPAGE INTO THE INDIAN RIVER LAGOON, FL

By

Mary K. Lindenberg

December 2001


Chairman: Dr. Jonathan Martin
Major Department: Geological Sciences

The importance of groundwater seepage into estuaries is poorly understood, but it

may be a significant part of nutrient cycling. Groundwater seepage also can add nutrient

pollutants to an estuary, thereby changing the ecosystem to a state of eutrophic

conditions. One estuary where groundwater seepage may be important is the Indian

River Lagoon, located on the east coast of Florida. The Indian River Lagoon is home to

40 rare or endangered species, has great potential for economic resources and is rapidly

being developed increasing the potential threat of pollution from groundwater seepage.

Groundwater seepage was measured in two separate study areas of the lagoon; the

northern study area is located between N28f50i and N28f40i, and the southern study area

is located between N28f25i and N28f00i. Each study area was sampled at the end of the

dry season (May) and near the end of the rainy season (August). Using seepage meters to

measure seepage flux, average groundwater seepage into the Indian River Lagoon was

found to be 40 ml/m2/min and 63 ml/m2/min during the dry and rainy season,









respectively, in the northern study area and 28 ml/m2/min and 39 ml/m2/min during the

dry and rainy season, respectively, in the southern study area. Seepage rates increased

between the dry and rainy seasons in the northern study area by 58% and in the southern

study area by 41%. This seasonal increase in seepage rates may be related to the increase

in precipitation between the dry and rainy seasons. The chloride concentrations in

seepage water are very similar to the chloride concentration in lagoon water, indicating

that lagoon water cycles through the sediments possibly because of a density dependent

fluid flow. Using a mass balance equation of chloride concentrations, the percentage of

groundwater constitutes only 1%- 4% of seepage water discharged into the lagoon. The

chloride concentrations in pore water profiles reflect this mixing of lagoon water into the

pore water. Assuming that nutrients in groundwater seepage can be differentiated from

recycled lagoon water, nutrient loading of total nitrogen and total phosphorus in seepage

water was 11 to 17 times the total nitrogen and 14 to 23 times the total phosphorus of

surface water discharge from drainage areas surrounding the lagoon. Nutrient loading

from seepage water may also affect the limiting nutrient for primary production in each

study area. This implies that seepage water may provide an important control on nutrient

distribution to the Indian River Lagoon.














CHAPTER 1
INTRODUCTION


Significance of Submarine Groundwater Seepage

Submarine groundwater seepage refers to the diffuse discharge of groundwater to

a marine water body. Seepage water may include both seawater that circulates through

shallow sediments and groundwater discharging from aquifers (Bokuniewicz, 1980;

Cable et al., 1996 a, b; Church, 1996). Consequently, groundwater seepage is a collective

mixing of salt water from recirculated seawater and fresh water from aquifer

groundwater. Submarine groundwater seepage is also referred to as groundwater

discharge in the literature. Compared to runoff, precipitation and evaporation, however,

little is known of the magnitude of groundwater seepage to estuaries and the coastal

ocean (Johannes, 1980; Bokuniewicz, 1980; Connor and Belanger, 1981; Capone and

Bautista, 1985; Simmons, 1992; Bugna et al., 1996; Cable et al., 1996a, b; Church, 1996).

Groundwater seepage is important because it may represent a significant portion of the

hydrologic cycle in estuaries.


Importance of Groundwater Seepage and Nutrient Loading into Estuaries

Fresh water concentrations define estuaries. The fresh water concentration of

estuaries is determined by the amount of fresh water inflow and the extent of evaporation.

Fresh water inflow controls circulation, mixing and flushing in estuaries. These

processes help to remove pollutants, as well as mix, distribute and recycle nutrients









(Stickney, 1984). Groundwater may be a large component of the total fresh water input

to estuaries, although this component of the estuarine hydrologic budget is poorly known.

The potential for groundwater to add nutrients to aquatic habitats is particularly

important for ecological reasons (Belanger and Mikutel, 1985). For example, submarine

spring discharge was found to produce excess nitrogen to a coral reef system in

Discovery Bay, Jamaica (DiElia et al., 1981). More importantly, Valiela et al. (1978)

noted that groundwater contributes 20 times or more the amount of nutrients brought in

by precipitation to the Great Sippewissett Marsh, Massachusetts. Just as pristine

groundwater represents a significant, but natural, contribution of nutrients to a healthy

habitat, it may bring excessive nutrients if polluted. Excess nutrients cause

eutrophication, excess algal growth and destructive changes in community structure (Day

et al., 1989). For example, this problem was identified in Waquoit Bay, Massachusetts,

and the Florida Keys, Florida, where anthroprogenically derived nutrients in the

groundwater were shown to cause eutrophication of the aquatic systems (Lapointe and

Clark, 1992; Valiela et al., 1992).


Indian River Lagoon

The Indian River Lagoon is an important place to study groundwater discharge

because of the diverse range of animal species living in and around the lagoon, its

potential economic resources and rapid human development in the area surrounding the

lagoon.

The Indian River Lagoon is the most biodiverse estuary in North America, with

2,200 plant and 2,100 animal species living within its ecosystem (IFASHabitat). Forty of

the animal species are rare or endangered. The decline in animal and plant species,









seagrass and habitat loss in the Indian River Lagoon is the foci of the National Estuary

Program (Indian River Lagoon Program[IRLP], 1999). Pollution, sedimentation from

surface water and sediment runoff as well as discharge of agricultural and industrial

wastewater into the lagoon cause species decline in the Indian River Lagoon. In a

conference held on September 1, 1998, the Indian River Lagoon Program (IRLP) formed

an outline for restoration of the lagoon. On the top of the list for the restoration plan is

reduction of fresh water and storm water discharges into the lagoon (IRLP, 1999). This

restoration plan neglected groundwater seepage as another possible source of pollution,

and consequently this potentially important source of nutrients was not included in the

restoration plan for the lagoon. It is important to correctly quantify the seepage water

source that contributes to a polluted area by measuring nutrient loading and pollutants

from groundwater seepage.

In addition to the wide biodiversity, the Indian River Lagoon is critical to the

local economy. The coastal waters and the lagoon warm the surrounding farmland during

the winter, allowing a more predictable harvest for the citrus growing industry

(Woodward-Clyde, 1994). Throughout the lagoon, 21 species of finfish and 4 species of

shellfish support local commercial fisheries (Woodward-Clyde, 1994; IRLNEP, 1998).

The Indian River Lagoon is also used for recreational and tourist activities such as fishing

and boating. Boat access facilities, marinas, fishing supplies, bait, and marine stores

support a thriving tourist industry by providing recreational activities. Restaurants and

hotels also profit from aesthetic features of the lagoon. Consequently, the Indian River

Lagoon supports the sustenance and growth of industry and population in the region.









Protection of the lagoon and its link to the local economy requires identifying the

extent that nutrients and possible pollutants are added to the lagoon through groundwater

seepage. Eutrophic conditions resulting from excess nutrients could cause mass algal

blooms that block sunlight or phytoplankton blooms that deplete bottom waters of

dissolved oxygen. These eutrophic scenarios would diminish seagrass beds, which

aquatic animals use for food and habitat. Without such environments, levels of those

species would no longer support the fishing and tourist industries.

Pressures from urban and commercial development have detrimental effects on

the habitat of the lagoon. The human population around the lagoon has increased by

almost 124% from 1970 to 1990. By the year 2010, the human population is projected to

increase another 60% (IRLNEP, 1995). This population growth raises the concern for

contaminant input into the lagoon (Trochine and Trefry, 1996). In addition, population

growth could cause excessive groundwater withdrawal, because in Brevard County

groundwater is the largest source of potable water. Excessive groundwater withdrawal

may reduce groundwater flow into the lagoon or cause salt water intrusion in coastal

aquifers. If groundwater is a natural pathway for nutrients to flow into the lagoon, a

reduction of groundwater flow into the lagoon may reduce important nutrient input. Salt

water intrusion will degrade the quality of local potable water. Understanding the

impacts on the lagoon caused by changes in the water budget as population grows will

depend on a correct quantification of all the parts of the hydrologic budget, including

groundwater seepage.









Previous Studies

There have been many attempts worldwide to measure groundwater seepage into

surface water environments (Table 1-1). Seepage meters have been used to quantify

submarine groundwater seepage flux into estuaries, bays, oceans and coral reef systems

(Bokuniewicz, 1980; Lewis, 1987; Belanger and Walker, 1990; Belanger and

Montgomery, 1992; Reay et al., 1992; Simmons, 1992; Gallagher et al., 1996; Cable et

al., 1997a, b; Rutkowski et al., 1999). Seepage meters are limited to measuring only pore

water flow across the sediment-water interface and cannot be used to determine the

source of groundwater, for example fresh groundwater or recirculated water, because

without the additional measurement of natural chemical or isotopic tracers, the fresh

groundwater component cannot be differentiated from the recycled seawater component

of seepage water. Bokuniewicz (1980) found typical seepage rates of 27.8 ml/m2/min

within 30 m of shore in the Great South Bay, New York. Although streamflow is the

principle source of fresh water in the Bay, groundwater seepage accounts for 10 fi 20 %

of the total fresh water inflow. Bokuniewicz (1980) did not differentiate the components

of the seepage water. Without differentiating the components of the seepage water,

Bokuniewicz (1980) assumed the seepage water was fresh groundwater.

Other studies have used isotopic and chemical tracers such as Rn and Ra

radioisotopes and CH4 concentrations to measure fresh groundwater seepage into

nearshore marine environments (Bugna et al., 1996; Cable et al. 1996a, b; Moore, 1996;

Corbett et al., 1999). With the use of these tracers, groundwater was found to flow into

marine environments such as Florida Bay (Corbett et al., 1999), northeastern Gulf of

Mexico (Bugna et al., 1996; Cable et al., 1996a, b) and the South Atlantic Bight (Moore,










1996). These studies measure only the discharge of fresh groundwater and do not include

important seepage components such as circulated seawater.


Table 1-1. Previous studies measuring groundwater discharge into marine environments.
SEEPAGE FLUX
METHOD OF
LOCATION RANGEIAVERAGE ET REFERENCE
2/in MEASUREMENT
mlum /min2_______
Indian River Lagoon; -/83 S e Belanger and
'- -2.17 n 920 /83 Seepage Meter
Jensen Beach, FL Walker, 1990
Indian River Lagoon; Net GW*: 0.29 h 5.90 Finite Element Pandit and El-
Port St. Lucie, FL Model Khazen, 1990
Great South Bay, NY 6.9 h 27.8 Seepage Meter Bokuniewicz, 1980

Florida Keys 3.75 h 6.1 Seepage Meter Simmons, 1992

Onslowand Long 4.1 n 13.89 Seepage Meter Simmons, 1992
Bays, NC
Chesapeake Bay
Chesapeake Bay 0.3 h 61.5 Seepage Meter Reay et al., 1992
Inlet, VA
Gallagher et al.,
Chesapeake Bay 0 h 50.0/ 10.5 Seepage Meter g e
1996
Seepage Robinson et al.,
Chesapeake Bay Net GW*: 2 Meter/Calculation 19
Meter/Calculation 1998
Robinson et al.,
Chesapeake Bay Net GW*: 1 Calculation
1998
Robinson and
Chesapeake Bay 0 h 35 Numerical Model 1
Gallagher, 1999
NE Gulf of Mexico -6.9 h 166 /80 Seepage Meter CH4 Bugna et al., 1997
Concentrations
NE Gulf of Mexico 8.0 h 55.0 Seepage Meter Cable et al., 1997
Rutkowski et al.,
NE Gulf of Mexico 10 h 100 Seepage Meter 1
1999
oral reef; Barbados, 0.85 h 1.22 Seepage Meter Lewis, 1987
West Indies
South Atlantic Bight 65.1 226Ra Moore, 1996
Calculation based
South Atlantic Bight Net GW*: 48.0 Calculation ba Li and Barry, 1999
on Moore, 1996
*Net GW values only measure discharge of fresh groundwater.



Recently, numerical modeling and calculation were used to calculate groundwater

seepage and, in some cases, fresh or net groundwater seepage. Based on Mooreis (1996)









study, Li and Barry (1999) calculated that approximately 92% of total groundwater

seepage was produced from wave setup and tidal pumping and 8% resulted from fresh

groundwater. Robinson and Gallagher (1999) modeled the groundwater seepage process

based on density dependent fluid flow, the water table and changing tidal boundary

conditions in the Chesapeake Bay. They found that the fresh groundwater comprised

6.2% of the total groundwater seepage. Although calculations and groundwater modeling

can help to quantify the fresh groundwater component of seepage, these methods require

assumptions of hydrologic and geologic characteristics, such as hydraulic conductivity,

uniform sediment type and hydraulic head gradients (Belanger and Walker, 1990).

Previously, two groundwater seepage studies were completed in areas of the

Indian River Lagoon: Port St. Lucie, Florida (Pandit and El-Khazen, 1990), and Jensen

Beach, Florida (Belanger and Walker, 1990; Belanger and Montgomery, 1992). Belanger

and Walker found total seepage flux varied by a factor of two (-2.17 fi 920 ml/m2/min)

across a seepage meter transect traversing the 3.084 km width of the lagoon near Jensen

Beach, FL. Pandit and El-Khazen (1990) calculated that fresh groundwater seepage rates

ranged between 0.29 fi 5.90 ml/m2/min, using a unsteady groundwater flow, finite

element numerical model. The finite element numerical model was used to calculate

seepage rates based on a 2D idealized cross-section of the lagoon between the water table

divide on the mainland and the ocean, assuming the Hawthorn Formation is impermeable

and the groundwater source is from the Surficial Aquifer. Pandit and El-Khazen (1990)

assumed the hydraulic conductivity (Kx = 381 cm/day, Kzz = .762 cm/day) is the same

the entire width of their defined transect. The difference between the two studies shows

the range in fresh groundwater seepage rates from Pandit and El-Khazenis (1990) study









was 6.5% of the range in seepage rates found by Belanger and Walker (1990). This

difference may result from a conservative estimate of hydraulic conductivity values in

groundwater seepage rates modeled by Pandit and El-Khazen (1990). The average

groundwater seepage rate (3.80 ml/m2/min) calculated by Pandit and El-Khazen (1990)

was 4.5 % of the average seepage rate (83 ml/m2/min) measured by Belanger and Walker

(1990). The low flow rate measured by Pandit and El-Khazen (1990) takes into account

only fresh or net groundwater, whereas the larger flow rates measured by Belanger and

Walker (1990) include all of the water components in seepage water.


Purpose

There were three main objectives to this study. The first was to measure the

groundwater seepage to the Indian River Lagoon using seepage meters (Lee, 1977).

Ancillary objectives included determining how seepage rate fluctuations were caused by

seasonality of precipitation and if spatial variability of seepage rates is controlled by

aquifer composition and hydraulic properties. The second objective was to find the

source of the seepage water (e.g., the proportions of lagoon and groundwater) using

natural and environmental tracers such as chloride concentrations. The final objective

was to estimate the extent of nutrient loading to the estuaries from groundwater seepage.














CHAPTER 2
REGIONAL SETTING


Location

Located on the eastern margin of Florida, the Indian River Lagoon spans 251

kilometers from its northern end near Ponce De Leon Inlet to Jupiter Inlet in the south

(Figure 2-1) totaling 922 km2 in surface area (Woodward-Clyde, 1994; IRLNEP, 1998).

The water depth ranges between 1 and 3 m, and the average depth is 1.7 m (Smith, 1993).

The Indian River Lagoon System is made up of three interconnected water bodies, i.e.,

the Mosquito Lagoon, the Banana River Lagoon and the Indian River Lagoon proper

(Figure 2-1). The system is classified as a lagoonal estuary. The Indian River Lagoon

does not depend on one single river, but on many rivers for its source of fresh water. In

addition, its source of ocean water is from four small inlets, Sebastian, Ft. Pierce, St.

Lucie and Jupiter Inlets, that are located in the southern half of the lagoon. The ocean

connects to the Mosquito Lagoon through the Ponce De Leon Inlet and to Banana River

Lagoon through a system of locks in the Port Canaveral Inlet (Woodward-Clyde, 1994).

During this project, two separate areas of the Indian River Lagoon system were

studied (Figure 2-2a,b). The northern 16 km of the Indian River Lagoon was sampled

during 1999. To the south of the first site, between Cocoa and Melbourne, FL, the Indian

River Lagoon and Banana River Lagoon were sampled during 2000. Table 2-1 shows the

dates and the type of measurements recorded. The northern study site is predominantly

surrounded by citrus agriculture and government reserve lands of the Canaveral National









Seashore and the National Wildlife Refuge, while the southern study area is surrounded

by urban and commercial development. The northern Indian River Lagoon, including

both study areas, has small diurnal tides of 4 cm, and consequently wind-driven currents

are responsible for much of the water movement.


SNorthern Study Area

S" Mosquito Lagoon




Indian River Lagoon


Banana River Lagoon


Southern
Study Area


Figure 2-1. The Indian River Lagoon System (including the Indian River Lagoon, the
Banana River Lagoon and the Mosquito lagoon) located in east Central Florida. Boxes
show the 1999/northern (figure 2-2a) and 2000/southern (figure 2-2b) study sites.







11


Table 2-1. Sampling, times, measurements and locations.

Northern Study Area (1999)

May (Dry Season) August (Rainy Season) December (Dry Season)

Seepage meter, water Seepage meter, water Multisample ports and
column, surface water and column, surface water and water column
water column
groundwater groundwater

Southern Study Area (2000)

May (Dry Season) August (Rainy Season)
Seepage meter, water Seepage meter, water
column, surface water, column, surface water,
groundwater and groundwater and
multisample ports multisample ports _


rnCl iuiuhuulCrrppk]




IRLl0 9. f t :'



OIL4 1S9 rIp
'into-.
IR I~ jp


- H Is 12

I .


II-,
*ItP r I Ln


WIR 1i- t
CW. I


_Y.




S P ~'


,J.;1
I ~ -


0 .-


' 8 Kilometers


I I I

Figure 2-2. Map and stations of the (a) northern study area and of the (b) southern study
area. Seepage meter, surface water and groundwater well samples are denoted with
squares, circles and triangles, respectively.


N


A
"'i. .?


A MW 5


I "-r







12



b


N GV921 ,I
j iBHy l1 He'll ,lum'.
IRL 29-31.. -. 'IBRKl .
G:W 1472 141-,' -
STRI.3 ."fl" TRl 6


ITSC 0TnrPCirPki J. 1J 3.

GW164Q7 G\.ll.l
E.GR ,Tan Gallie Ritefr"", I 41
CNC iC'rnr C'rrckg -/
JJ
I Physiograhiy 'rrekj F







r d b t S r ll thlr .ebast I ian Inlet)
SSR iSL brbUaslitn Ri\cr'i, ''

4 0 4 8 12 16 Kilometers





Figure 2-2. Continued.

Physiographic Features

The Indian River Lagoon is part of a drainage basin (5795 km2 in area) bordered

by barrier islands to the east and the Atlantic Coastal Ridge on the west (Woodward-

Clyde, 1994). The Atlantic Coastal Ridge was formed from sand dune-type topography

and ranges in elevation to 55 feet above sea level. The Atlantic Coastal Ridge acts as a

drainage divide between the St. Johns River Valley and the Indian River Lagoon basin.

The barrier islands are a series of troughs and ridges that formed from paleobeach

environments (Brown et al., 1962). Paleobeach ridges on the barrier islands reach 3

meters above sea level (Brown et al., 1962).









Regional Hydrostratigraphy

More groundwater is available in Florida than any other state (Conover et al.,

1984). Five aquifers occur in the state of Florida. Two aquifers, the Sand and Gravel and

the Biscayne, occur only in the western panhandle and in the southeastern region of

Florida, respectively. The other three aquifers from bottom to top include the Floridan,

the Intermediate and the Surficial. These aquifers contain most of Floridais groundwater

because of their large aerial extent. The largest of the three is the Floridan Aquifer. The

Floridan Aquifer covers 128,748 km2 including the entire state of Florida and extending

into the coastal plains of Alabama, Georgia and South Carolina. The Floridan Aquifer is

an assemblage of permeable limestones and dolostones with small amounts of clay, sand

and marl (Conover et al., 1984). Above the Floridan Aquifer lies the Intermediate

Aquifer or the intermediate confining unit. This unit retards the exchange of water

between the overlying Surficial Aquifer and the underlying Floridan Aquifer (Scott,

1990). The confining unit is comprised of siliciclastic deposits interlayered with

carbonates (Scott, 1990). Above the Intermediate Aquifer is the Surficial Aquifer. As a

water table aquifer, the Surficial Aquifer system is composed of limestone beds,

unconsolidated sands, shells, shelly sands and occasional clay beds (Miller, 1997).

Figure 2-3 and table 2-2 describe the hydrostratigraphy of the region (Toth, 1988).

In northern study area, the lithology of the Surficial Aquifer is composed of two units: a

marl which ranges from 15.24 to 45.72 m thick and an overlying sand which ranges from

0 to 15.24 m thick. The marl unit is Pleistocene in age and consists of sands, shells, clays

and sandy clays. The lower marl formed in environments such as beach, lagoonal, tidal

flat and channels systems. The upper sand unit was formed as dunes, and it is clean with

some shell fragments (Williams, 1995). In the southern study area the lower Surficial







14


Aquifer system is composed of Pliocene and Miocene-aged Tamiami Limestone, also

known as the shallow rock aquifer. These bioclastic coquiniod lenses and beds are


Dept (f) Sebastian Inlet
Volusia/ Brevard Co. Titusville Cocoa Melbourne 1\
S/ ,Lagoon Surface,

n Surficial Aquifer System










--. Flori dan. Aquifer Srstem








1o lmIlen
S 10 2.kilomete


Figure 2-3. A hydrostratigraphic cross-section below the IRL from the Volusia/ Brevard
County line in the north to Sebastian Inlet in the south.




overlain in some areas by the Caloosahatchee Formation, which is composed of

undifferentiated sediments of clay sand and coquina. These sediments are overlain by the

Anastasia Formation, which contains Pleistocene-aged sandy coquina held together

loosely with calcareous cement. The Surficial undifferentiated sediments and the

Anastasia Formation compose the shallow sand and the shallow water table aquifer

(Toth, 1988). The Surficial Aquifer is a water-table aquifer where water tables can

fluctuate rapidly with rainfall, evapotranspiration and local streamflow. The Surfical
.. .r.0







Figure............ostratigraphic cross-section ..................revar
Anastasia ......i. .. e w sd an te s w we .. if
. . . . . . n













Anastasa Form tion c mpose te s..................................aquife
.... .... .... ..... .............................. .............................. s c a
flu tu tera i...... ...... ...... ......n lca sre mflw. Th S rfca










Aquifer holds significant amounts of fresh water in the Atlantic Coastal Ridge, which

supplies many homes with potable water (Williams, 1995).


Table 2-2. Lithologic and hydrogeologic information taken from wells in the coastal
areas of Volusia, Brevard and Indian River Counties, FL (Toth, 1988).
Lithologic Unit
Epoch (loctin) Aquifer Unit Characteristics
(location)
Surficial Sands, coquina,
Sediments clay and organic
Holocene (north) Anastasia Shallow Sand and material Coquina with
Hoocene (north) sand, silt
Formation Shallow Water Table c
Pleistocene Ft. Thomson Fomatin Sr Sands, coquina limestone and
Formation (coastal) Aquifers limestone and organic material
(southwest) > organic material
Callosahatchee .
Formation
Undifferentiated Clay, sands and coquina
Pliocene Sediments
Mocene Gray Sand Tamiami Shallow 3 Sands with some Recrystallized
Zone Formation Gray and Rock coquina and mestonesand
Aquifer bioclastic
(southwest) (east) Aquifer some clay coquinoids
Intermediate
Secondary Ier Phosphatic dolosilts, sands, clays
Miocene Hawthorn Group Artesian Aquifer System and carbonate beds
or Confining Unit
Suwannee Limestone bioclastic, chalky or recrystallized
limestone
OligoceneLim bioclastic, recrystallized or dolmitic
Ocala Limestone
Floridan Aquifer System limestone
Avon Park Limestone dolostone; bioclastic or recrystallized
Eocene limestone
Lake City Limestone limestone or dolostone



The confining unit in east-central Florida consists ofinterbedded siliciclastic and

carbonate sediments of the Hawthorn Group (Scott, 1990). The intermediate confining

unit and Intermediate Aquifer system increase in thickness from less than 3 m to greater

than 150 m from the northern study area to the southern study area (Figure 2-3). The

Hawthorn Group sediments are missing in areas that include the northern study area

(Scott, 1990) resulting in unconfined or semi-confined (the Surficial Aquifer can act as a

confining unit) conditions for the Floridan Aquifer, which may hydraulically connect to

the Surficial Aquifer system (Toth, 1988; Scott, 1990; Williams, 1995). The Hawthorn









Group is composed of interbedded clay, silt, sand and carbonate beds of Miocene age.

These sediments make up two zones of the Hawthorn Group. The upper zone is

composed of green clays and silts, whereas clays and carbonate materials comprise the

lower zone.

The Floridan Aquifer system is composed of Eocene and Oligocene aged

limestone units. The lower Lake City Limestone unit, a white, fossiliferous, recrystalized

limestone with some dolostone, is overlain by the Avon Park Limestone unit. The two

zones of the Eocene aged Avon Park Limestone comprise a lower distinct lithology of

low porosity dolostone and an upper interbedded limestone and dolostone region.

Overlying the Avon Park limestone is the late Eocene aged Ocala Limestone. The Ocala

Limestone is a light colored, weak to hard cemented, recrystalized, foraminiferal,

coquiniod limestone. Between the Ocala Limestone and the Hawthorn Group lies the

Oligocene-aged bioclastic to chalky limestone of the Suwannee Limestone. The

Suwannee Limestone is generally thin to absent in the study area but is present in the

southern areas of Brevard County and increases in thickness to the south (Toth, 1988).

Where the Floridan Aquifer is confined in the Indian River Lagoon study area, its

potentiometric surface can reach heights ranging from 1.5 to 10 m above sea level

(Figure 2-4). Groundwater should thus flow from the Floridan into the Surficial Aquifer

and ultimately into the lagoon. The rate of upward flow will depend on the hydraulic

conductivity of the overlying confining unit as well as differences between the heads of

the two aquifers.







17



N a





IN


-W E














*0 10
24 7
18













3 -6
1*20
c2a4 each







34









31





0 10 20 30 40 50 Miles

0 10 20 30 40 50 Kilometers


Figure 2-4. Contours of the potentiometric surface of the Upper Floridan Aquifer during
(a) May 1999, (b) September 1999, (c) May 2000, (d) September 2000 (Bradner and
Knowles, 1999). Contour interval is 5 ft.







18










*9




























-o
17M oil -17







Beach















I I I Iand
10 20 30 40





38








043 39
S41 \35
341


10 20 3


10 20 30 40


'0 40 50 Miles

50 Kometers
50 Kilometers


Figure 2-4. Continued.





19





....2 7 -.


333
36 34 3

.,- "




30 .2
3;o.rA Aj






37> A i
39
>f 38 r\ Q ".i



37 n
3 -- -... .-. ...
: : : 7- : :" : : ::' :."3
3.9 ...., .. ,. 3 1 '


3 7 7 :: : : \ ... 34," .S-.





Figure 2-4. Continued.
Figure 2-4. Continued.








T .. \
" ', .' ", N d


: 7 : : : : "..", 2 .' E
7 -- .
14
/y, i
., 1. 2 9 "\ '. a t
Sr-
_1 1 .. .


3: 3 14

.. 1
S .
34 3.4 33:


38 37 36
*| -


38
.. .. .
37 3


39 38


41 .

42 .

43
S: .1


43
.. .-- ..

10 0 10 20 3


38

) 40 Kilometers


Figure 2-4. Continued.









Climate and Hydrologic Components

The Indian River Lagoon is located in a transition region between sub-tropic and

temperate climates, and consequently its climate is influenced by its latitude. Climate is

also influenced by the proximity of the Atlantic Ocean and the Gulf Stream, which passes

the full length of the lagoon approximately 50 to 100 km from the shore. From 1951 to

1980, the Indian River Lagoon basin received an annual average of 127 cm of rainfall.

Figure 2-5 shows the average monthly rainfall for a thirty-year period. The lows and

highs for annual rainfall amounts range from 113 cm to 144 cm (Woodward-Clyde,

1994). A Class A pan evaporation station in Vero Beach, FL supplied values since 1952.

Using a pan coefficient factor of 0.78, the calculated annual potential evaporation was

124.5 cm. Figure 2-6 shows the potential evaporation rates are greatest between the

months of March through September (Rao, 1987).

For a 30-year period the average annual temperature for the Indian River Lagoon

system was 23oC. Maximum temperatures were as high as 380C during the summer and

minimal temperatures were as low as -8oC during the winter (Woodward-Clyde, 1994).

Mean temperatures for the summer months do not vary significantly along the length of

the lagoon, but mean temperatures during the winter months can be 4 to 5 C warmer in

the south than the north (Rao, 1987).

Recharge to the Surficial Aquifer system is primarily from precipitation (Figure

2-7), minor amounts of irrigation water and upward leakage from the Upper Floridan

Aquifer (Williams, 1995). For east-central Florida, 50% of the precipitation occurs

during the summer months of June through September (the wet season), which means

recharge is relatively higher during the summer months (Williams, 1995). When the

water table is high during the wet season, the water table response to rainfall may occur









within minutes in low lying areas (Williams, 1995). Discharge from areas of the Surficial

Aquifer, which include seepage, springflow, well discharge, flow to drainage ditches and

evapotranspiration, will increase due to increased rainfall and recharge during the

summer months (Williams, 1995).


Figure 2-5. Average monthly precipitation for the Indian River Lagoon region. The
precipitation values are based on the monthly mean of 17 stations in and around the IRL
from 1951 to 1980 (Rao,1987).









16 Dry Season 4- Rainy Season N- Dry Season -o


I :
U










A' I
4.6


<> 2s


M monthh
Month :-'


x a-
C' C'


Figure 2-6. Average monthly potential evaporation for the Indian River Lagoon region.
The potential evaporation values are based on the monthly mean of 17 stations in and
around the IRL from 1951 to 1980 (Rao, 1987).


6


E

- 0


4 Dry Season 4 Rainy Season 1- Dry Season -
U


~=1


'~ '
4.-


I'll


'C' $'2
<> ,rs


Month
Month


'~ az x a
C~' C' ~ C
.7' .-


I I
Figure 2-7. Average monthly recharge for the Indian River Lagoon region. The recharge
values are based on the monthly mean of 17 stations in and around the IRL from 1951 to
1980 (Rao, 1987).


S


A .














CHAPTER 3
METHODS


Seepage Measurements Methods Review and Background Theory

The seepage meter (Figure 3-1) was first devised by Israelson and Reeve (1944)

to study seepage outflow from irrigation canals (Fellows and Brezonik, 1980). Since

then, seepage meters have been used to study groundwater discharge into lakes (Lee,

1977; Downing and Peterka, 1978; Fellows and Brezonik, 1980; Connor and Belanger,

1981; Belanger and Mikutel, 1985; Cherkauer and Nader, 1989; Hirsh, 1998) rivers/

canals, estuarine/coastal regions (Bokuniewicz, 1980; Capone and Bautista, 1985;

Simmons, 1992; Cable et. al, 1996a, b) and coral reef habitats (Lewis, 1987).

Several laboratory-scale tests experiments have been conducted to test the

accuracy of seepage meters. Lee (1977) tested seepage water by varying the hydraulic

gradient in a rectangular tank and measuring the flow. Leeis (1977) study showed a

linear correlation between changes in seepage rate and hydraulic gradient. The slopes of

the regression lines differed per location which was attributed to heterogeneity of

sediment type throughout the test tank (Lee, 1977). Belanger and Montgomery (1992)

also used a series of laboratory experiments to test the seepage meter device under known

conditions. Belanger and Montgomery (1992) found seepage rates varied per location

which they inferred to be a function of heterogeneous permeability. Shaw and Prepas

(1989) discovered that empty seepage bags would fill rapidly because of a difference in









hydraulic gradient between the water column and the bags. This result led to a

modification of the technique where seepage bags were pre-filled with 1000 ml of water.


Field Sampling

Seepage Meter Construction, Deployment and Seepage Measurements

Seepage meters were constructed from 55 gallon steel drums. The drums were

cut 15 cm from the ends to form a cup-like container. One half inch diameter ports were

drilled into the flat top, 6 cm from the edge of the meter. Two screw-sized holes were

drilled into one side of the meter to attach rubber handles. The meters were sanded and

painted with two coats of two-part marine epoxy paint. A male garden hose fitting was

inserted into the port and made watertight using rubber washers and silicon caulking.

Rubber handles were screwed into the side of the meter using washers and silicon

caulking.

Seepage meters were placed into the sediment like an upside-down cup (Figure 3-

1). The sides were pushed into the sediment to prevent water from flowing into the meter

under the rim. The side with the port was tilted slightly upward to prevent an

accumulation of gases, which could lead to backpressure and lift the meter free of the

sediment.

The arrangement of stations differed between the northern and southern study

areas. In the northern study area, seepage was measured over five short transects

containing 2 to 8 seepage stations and six individual seepage stations in deep water sites

(Figure 2-2a). In the southern study area, four transects extended in an east west

direction across the lagoon (Figure 2-2b). The northern two transects traverse both the






26

Indian River Lagoon and the Banana River Lagoon and the southern two transects were

confined to the Indian River Lagoon.




Water Column
Receptacle Bag





Ball Valve
Port

















through the port. Arrows indicate direction of groundwater discharge.


After installation, the meters were left to equilibrate for at least 24 hours, which

allowed enough time to eliminate any effects that may be caused by backpressure during
deployment of the meters (Figure 3-2). Polyethylene seepage bags were used to collect













water that flowed from the port. Two sizes of polyethylene bags were used; 5 liter bags

had wall thickness of 4 mm while 4 liter bags had wall thickness of 1.5 mm. The
0.28 m2 M15Ncm











different size wall thickness of each bag did not alter the measured seepage rates.

Seepage bags were attached to the male garden hose fitting using zip ties and electrical

tape. The male fitting was attached to a female garden hose fitting with a ball valve.


100

90 --

80
C
70

E 60-

x 50
U-m
w 40

w 30

20

10

0
30 -----------------------------------



8/17/99 8/17/99 8/17/99 8/17/99 8/17/99 8/17/99 8/17/99 8/17/99 8/17/99 8/17/99 8/17/99 8/17/99
7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00 19:12 20:24
Time


Figure 3-2. A time series experiment showing 5 seepage rates from station IRL 6. Error
bars show the length of time the bags were left on the meter. Stabilization of seepage
flux rates resolve around 90 ml/m2/min within 12 hours of placing the seepage meter into
the sediment.




Seepage rates were measured by adding 1000 ml of lagoon water to the bags prior

to deployment in order to prevent pressure anomalies (Shaw and Prepas, 1989). After the

1000 ml of water was added, the valve was closed, then connected to the port of the

seepage meter. Once installed on the meter, the valve was opened to allow flow of water

either into or out of the bag. After a sufficient amount of time (approximately 1 to 2

hours), the valve was closed, the bag was removed from the seepage meter and the

volume of water in the bag was measured using either a 1000 ml or a 2000 ml graduated









cylinder. This process was repeated sequentially for three measurements at each seepage

meter site. The seepage flux was calculated by dividing the volume of water that flowed

into the bag by the amount of time the bag was on the meter and by the area of the meter

(0.28 m2).

Control experiments, termed blank seepage measurements, were set up to measure

seepage in an environment where seepage was blocked from flowing from the sediments

below the lagoon floor. Blank seepage rates were measured in the simulated non-seepage

flow environment. A non seepage flow environment was made by placing a small, 2.5 m

diameter, plastic, children s wading pool on the floor of the lagoon and filling it with

sediment -0.5 m deep. The wading pool simulated a non seepage flow environment by

blocking seepage from flowing from sediments below the pool to the sediments in the

pool. Once 24 hours had passed after deploying a seepage meter in the pool, seepage

rates were measured in the same way seepage rates were measured from seepage meters

deployed on the floor of the lagoon.

The average, standard deviation, minimum and maximum blank seepage flux

were calculated for all measurements in both study areas (Table 3-1). The average blank

seepage flux was 10.9 ml/m2/min with 1 of 4.9 ml/m2/min. The minimum blank

seepage flux was 5.8 ml/m2/min, measured at station IRL3 during the rainy season in the

northern study area. The maximum blank seepage flux was 17.6 ml/m2/min, measured at

station IRL7 during the rainy season in the northern study area. Blank seepage flux

measurement were not conducted during the dry season in the northern study area.

Seepage meters were deployed in duplicate to find the relative difference of

seepage rates measured from closely spaced seepage meters. Duplicate seepage meters










were deployed within a few meters of each other at a station. The average, minimum and

maximum percent difference of seepage rates measured from duplicate seepage meters

were calculated for all duplicate stations in both study areas. The average percent

difference of duplicate seepage rates was 61.9% (Table 3-1). The minimum percent

difference between duplicate seepage rates was 7.4%, measured from station BRL1

during the dry season in the southern study area. The maximum percent difference

between duplicate seepage rates was 84.9%, measured from BRL1 during the rainy

season in the southern study area. Duplicate seepage measurements were not conducted

during the dry season in the northern study area.


Table 3-1. Blank and duplicate seepage flux values.
Blank Duplicate Duplicate
S Seepage Seepage Seepage
o Flux o Flux Fhux
_m 2/ n M ]/n 2fi in % Difference
Northern X IRL3 13.4 + 16.8 BRL6a 59.6 + 19.8 72.5
Study 5.8 + 52 BRL6c 102.8 + 13.9
Area IRL7 14.5 + 1.4
)n 17.6 + 5.1
0

Southern O BRL1 7.7 + 52 BRL1a 43.1 + 16.9 7.4
Study a BRL1b 40.1 + 8.7
Area BRL3a 13.1 + 5.4 75.3
o
M BRL3b 23.0 + 9.4

SBRL1 63 + 72 BRL1a 303 + 113 84.9
BRL1b 56.0 + 38.4
(C BRL3a 8.8 + 9.0 69.2
iO BRL3b 15.0 + 103

Average 10.9 + 6.8 61.9
Minimum 5.8 7.4
Maximum 17.6 84.9
St. Deviation 4.9









Multisamplers

Multiple level samplers (i multisamplersi) were used to sample pore waters at

depths up to 2 m below the lagoon floor (Pickens et al., 1981; Fetter, 1994).

Multisamplers are made of a PVC pipe with smaller PVC tubes that extend inside the

pipe from the top to screened ports at several depths (Figure 3-3). The bottom end of

each tube is screened with 250 [tm spectra mesh screening to prevent sediments from

clogging the tubes.


Figure 3-3. An example of a multisampling device. Modified from Fetter, 1994.


Opening









Two different types of multisamplers were used in the northern area and southern

study areas. Sampling tubes of multisamplers in the northern area extended along the

outside of the PVC pipe, while sampling tubes of multisamplers used in the southern area

were fed through the inside the PVC pipe. The way the multisamplers were deployed

also differed in the northern and southern areas. In the northern study area, a hole was

augured and the multisampler was inserted into it. In the southern study area, the

multisamplers were pounded into the sediment.

Water Sample Collection

Seepage water was collected using a technique similar to that used to measure

seepage rates, except that dry seepage bags were deployed on the seepage meters. The

bags were attached to the seepage meter until approximately 1 liter of water filled the

bags. The water was filtered through a 0.45 [tm filter while transferred from the bag into

two 125 ml HDPE Nalgene bottles using a 60 ml syringe. Except for the May 1999

sampling trip, another HDPE Nalgene sample bottle was used to collect unfiltered water.

The bottles were labeled with the station and date and wrapped with parafilm to protect

the notation. Throughout the day, the Nalgene bottles were stored on ice. At the end of

the day, 16 N optima grade HC1 was added to one of the filtered sample bottles and all

bottles were refrigerated. The samples were kept refrigerated until analyzed.

One water column sample was collected from each transect and from individual

sites in the northern study area. In contrast, water column samples were collected at

every station in the southern study area. Water column samples were either collected by

immersing a 1000 ml graduated cylinder just below the water surface of the lagoon or by

pumping water 50 cm above the lagoon floor. The sample from the water column were









stored and preserved in the same manner as samples of seepage water. An unfiltered

sample was not collected for the dry season (May) of the 1999 northern study area.

Groundwater samples were taken from wells surrounding the two lagoon field

areas. Water was pumped from the wells using 12 V powered electric pump and a garden

hose. While pumping the water, temperature and conductivity were monitored until they

stabilized, then the samples were stored and preserved the same way as samples of

seepage water and water column. An unfiltered sample was not collected for the dry

season (May) of the 1999 northern study area.

The ports on each multisampler were pumped using a peristaltic pump and flowed

through a liter sized container. Conductivity and dissolved oxygen were monitored until

stabilized, then afterwards water was collected and filtered using a syringe or stored

unfiltered in HPDE bottles in a manner similar to the seepage water sampling techniques.

Not all multisampler ports provided water, but those that did continually would pump

unlimited volumes of water. The volumes that were actually pumped were not

monitored, but were generally less than one liter.


Analytical Techniques

Field Measurements

While on site, conductivity, salinity, temperature, dissolved oxygen and pH were

measured on all samples with portable field meters. An Orion model #250A meter was

used to measure pH. Conductivity, temperature and salinity were measured with an

Orion model #130 conductivity meter. Dissolved oxygen was measured with a YSI

model #55 oxygen meter. At the beginning of each day, the dissolved oxygen and pH

meters were calibrated using manufacturer directions. The conductivity meter was









calibrated at the beginning of each sampling trip. To measure seepage water, the probes

were either placed directly into the seepage bags after they were cut open or the seepage

sample was first transferred to a 1 L graduated cylinder and then measured. Water

column measurements of conductivity, salinity, temperature and dissolved oxygen were

obtained by placing the probes into the water column in the immediate vicinity of the

seepage meter. Water column measurements of pH were made by measuring the water

column sample collected in a 1 L graduated cylinder for water analysis. Conductivity,

salinity, temperature and pH were measured on the groundwater as water was pumped

into a 1 liter plastic bucket. Multisampler pore water from each port was collected in a 1

liter container, then measurements were taken inside the container.

Laboratory Measurements

Chloride. The C1- concentrations were measured by titrating with AgNO3 at the

University of Florida (Gieskes and Peretsman, 1986). Measurements of an internal

standard (St. Augustine Seawater or SAS) yields a reproducibility of less than 0.5%.

Sulfate. Sulfate concentrations were measured from the filtered samples using an

Automated Dionex model 500 Ion Chromatograph. Measurements of an internal

standard (St. Augustine Seawater or SAS) yields a reproducibility of less than 0.8%.

Ammonium. Ammonium (N-H4) was analyzed for samples from the northern

study area using a Spectronic 401 Spectrophotometer by Milton Roy (Gieskes and

Peretsman, 1986). Samples from the southern study area were measured using the

oxidation method of determining ammonia with an Bran and Luebe auto analyzer

(Strickland and Parsons, 1972).









Nitrate and nitrite. Nitrate was measured using a copper-cadmium reducing

column with an Bran and Luebe auto analyzer (Strickland and Parsons, 1972). Nitrite

measurements were measured without the cadmium column.

Total nitrogen. Total soluble nitrogen and total nitrogen (a difference of filtered

and unfiltered samples, respectively) were measured on the Bran and Luebe autoanalyzer

using a persulfate digestion technique (DiElia et al.., 1976).

Phosphate. Phosphate or SRP (soluble reactive phosphorus) was measured using

a colorimetric method on the Spectronic 401 Spectrophotometer by Milton Roy (Gieskes

and Peretsman, 1986) for samples from the northern study area. The samples from the

southern study area were measured on the Bran and Luebe auto analyzer (Wetzel and

Likens, 1991).

Total phosphorus. Total soluble phosphorus and total phosphorus (a difference

of filtered and unfiltered samples, respectively) were measured by using a persulfate

digestion solution, then autoclaved before they were measured on the Bran and Luebe

auto analyzer (Wetzel and Likens, 1991).














CHAPTER 4
RESULTS


Precipitation and Recharge

Precipitation data for the northern study area was taken from Titusville and Big

Flounder rain stations in the northern study area (NOAA Southeastern Regional Climate

Center Columbia, SC,Tabitha White, pers. comm. St. Johns River Water Management

District) (Figure 4-1). Evaporation data was taken from either the Vero Beach or the Fort

Pierce stations (NOAA Southeastern Regional Climate Center Columbia, SC). The

potential recharge for the northern study area is calculated as the value of precipitation

minus potential evaporation that are shown in figure 4-1. The recharge for the northern

study area is shown along with the average monthly recharge for the IRL region for

comparison in figure 4-2 (Rao, 1987). The position of each climate station is located in

figure 4-3.

Precipitation data for the southern study area was taken from the Melbourne

station in the southern study area (NOAA Southeastern Regional Climate Center

Columbia, SC) (Figure 4-4). Evaporation data was taken from either the Vero Beach or

the Fort Pierce stations (NOAA Southeastern Regional Climate Center Columbia, SC).

The recharge for the southern study area is calculated as the value of precipitation minus

potential evaporation that are shown in figure 4-4. The recharge for the southern study

area is shown along with the average monthly recharge for the IRL region for comparison

in figure 4-5 (Rao, 1987).











I. 1I


40


U


lM Precipitation -- Evaporation

4- Wet Season ---- Dry Season -- Wet Season 4----


30

25

20

15

10- t I Ir1- 00-



0


Date


I 1

Figure 4-1. The total monthly precipitation and potential evaporation values for the
northern IRL from May, 1998 to December, 1999 (NOAA Southeastern Regional
Climate Center Columbia, SC, Tabitha White, pers. comm. St. Johns River Water
Management District).





H Northern Study Area Recharge 1Average IRL Recharge
0 1- Rainy Season n Dry Season 4 Rainy Season -0


Date


Figure 4-2. Recharge values between May 1998 and December 1999 for the northern
study area study area (grey bars) and average recharge values taken from average data
over 30 years from 17 stations (black bars) (Rao, 1987).













..'


usville .,












Eau Gallie River
)urne Int. Airport .
Crane Creek


Turkey Creek


Fellsmere





0 0 20


'-.
Canal .
*'4


Vero Beach

40 Kilometers

Fort Pierce
Fort Pierce .


Figure 4-3. The location of climate stations (squares) and surficial discharge stations
(triangles) in both the northern and southern study areas.


Titi


Melbc


.4 r'
,'-.







































Figure 4-4. The total monthly precipitation and potential evaporation values for the
southern study area between May, 1999 to July, 2000 FL (NOAA Southeastern Regional
Climate Center Columbia, SC).


Figure 4-5. Recharge values between May 1999 and August 2000 for the southern study
area (grey bars) and average recharge values taken from average data of 30 years and 17
stations (black bars) (Rao, 1987).


3I Precipitation -- Evaporation
50
Rainy Season 4 Dry Season 4 Rainy Season I
45

40

35

30

E25

20

15

10

5

0
May- Jun- Jul- Aug- Sep- Oct- Nov- Dec- Jan- Feb- Mar- Apr- May- Jun- Jul- Aug-
99 99 99 99 99 99 99 99 00 00 00 00 00 00 00 00
Date


HSouthern Study Area Recharge EAverage Monthly Recharge


20
E

2P 10-----
ero-

I WU O I*


May- Jun- Jul- Aug- Sep- Oct- Nov- Dec- Jan- Feb- Mar- Apr- May- Jun- Jul- Aug-
99 99 99 99 99 99 99 99 00 00 00 00 00 00 00 00
Date









Seepage Rates

Northern Study Area

In the northern area, the average, minimum and maximum seepage rate increased

between the dry and rainy seasons (Table 4-1). None of the reported seepage rate values

are corrected for the values of blank seepage flux measurements. The average of all

measured seepage fluxes was 39.91 ml/m2/min with l y of 21.66 ml/m2/min during the

dry season. The average of all measured seepage fluxes was 63.08 ml/m2/min with 1o of

30.99 ml/m2/min during the rainy season. The minimum seepage flux for the dry season

of 2.91 ml/m2/min occurred at station IRL25. The minimum seepage flux for the rainy

season of 22.00 ml/m2/min also occurred at station IRL25. The maximum seepage flux

for the dry season of 103.66 ml/m2/min occurred at station IRL23. The maximum

seepage flux for the rainy season of 144.40 ml/m2/min occurred at station IRL7.

Between dry and rainy season of the northern study area there was a 58% increase

in average seepage rates (Table 4-2). Minimum values for both the dry and rainy season

occurred at station IRL25 and increased by 652%, whereas the maximum increase in

seepage rates from May to August was 697% at IRL7. The station with the maximum

seepage rate during the dry season was IRL23 and during the rainy season was IRL7.

Out of the 28 stations, seven stations including IRL 5, 12, 15, 18, 23, 27 and 28,

decreased in seepage rates from dry to the rainy season. The average decrease in seepage

rate is -11%, where the greatest decrease was -19% at station IRL12.

Both the rainy and dry seasons exhibit a rightward skewness or positively skewed

frequency curve (Figure 4-6, 4-7).










Table 4-1. Average, median, minimum, maximum and standard deviation of seepage
flux rates for the northern study area.

APerage Medan Mn Value Staion IVbx Value Station St.Dev.*
Season nirni rrin ni/rn rrinl/ in irrin d__ ni/rrin _l/nirrin
Dy 39.91 37.64 2.93 IRL25 103.66 IRL23 21.66
Rainy 63.08 53.15 22.00 IRL25 144.40 IRL7 30.99
*Standard dedion of al rreasred seepage rates


Table 4-2. The minimum and maximum seepage rates and the corresponding % change
between the dry and rainy seasons of the northern study area.
Station Dry Season Rainy Season
ml/mzmin ml/mzmin % Increase
Average 39.91 63.08 58.1
IRL 7 18.1 144.4 697.0
IRL 25 2.9 22.0 652.0
% Decrease
IRL 12 92.1 74.3 -19.3
IRL 23 103.7 89.9 -13.3



Average value of 39.9 ml/m2/min


12


10

O


E 6
z

4 -





0
0-14.99 15-29.99 30-44.99 45-59.99 60-74.99 75-89.99 90-104.99
Seepage Flux (ml/m2/min)


Figure 4-6. Histogram of seepage flux for the dry season in the northern study area.











*Average Value of 63.1 ml/m2/min
14


0-14.99 15-29.99 30-44.99 45-59.99 60-74.99
Seepage Flux (ml/m2min)


75-89.99 90-104.99


Figure 4-7. Histogram of seepage flux for the rainy season in the northern study area.



Southern Study Area

In the southern study area, the average and maximum seepage rates increased

between the dry and rainy seasons, but the minimum seepage flux decreased (Table 4-3).

None of the reported seepage rate values are corrected for the values of blank seepage

flux measurements. The average of all measured seepage fluxes was 27.3 ml/m2/min

with 1 of 13.1 ml/m2/min during the dry season. The average of all measured seepage

fluxes was 39.5 ml/m2/min with la of 23.5 ml/m2/min during the rainy season. The

minimum seepage flux for the dry season of 10.1 ml/m2/min occurred at station IRL41.

The minimum seepage flux for the rainy season of 8.8 ml/m2/min occurred at station

BRL3. The maximum seepage flux for the dry season of 57.7 ml/m2/min occurred at


6


2









station IRL40. The maximum seepage flux for the rainy season of 94.3 ml/m2/min

occurred at station IRL39.

The increase in average seepage rate was 41% from the dry to the rainy season.

The largest increase at an individual station was 245% at IRL29 (Table 4-4). Out of 20

stations measured in the southern study area, seven stations including BRL 1, 3, 4, IRL

31, 36, 38, and 42 decreased in seepage rate from the dry to rainy season. The average

decrease for these stations was -19% and the largest decrease was -37%.

The dry and rainy season seepage rates produced a left and a rightwardly skewed

frequency curve, respectively (Figure 4-8 and 4-9).


Table 4-3. Average, median, minimum, maximum and standard deviation of seepage
flux rates for the southern study area.
Average IVbdan MnVlue SMiaion IVbxVaue Slaion SL v*
Season nl/n/rin nilr/nin nlr/nin nrril/niin nrl/ir/rin
Dy 27.69 24.57 10.11 IFL41 57.71 IF4RA 1286
ainy 39.11 35.92 885 IR3 95.97 IRL39 23.22
*3andad cctiaon dfl rreasufed seeage rides


Table 4-4. The minimum and maximum seepage rates and the corresponding % change
between the dry and rainy seasons of the southern study area.
Station Dry Season Rainy Season
mlm/m in ml/m2/min % Increase
Average 27.69 39.11 41.3
IRL41 10.11 16.62 64.0
IRL29 14.45 49.91 245.0
IRL39 30.37 94.31 210.5
% Decrease
BRL3 13.10 8.85 -32.5
BRL4 41.98 26.55 -36.8










Average value of 26.9 mllm2/min


0-1499 15-2999 30-4499 45-5999 60-7499 75-8999 90-10499
Seepage Flux (ml/m2/min)


Figure 4-8. Histogram of seepage flux for dry season in the southern study area.


I 1


Figure 4-9. Histogram of seepage flux for rainy season in the southern study area.


Average value of 39.1 mlm2/min


0-1499 15-29 99 30-44 99 45-5999 60-74 99
Seepage Velocity (ml/m/min)


......... ........


75-8999 90-10499









Tracers

All average, minimum, maximum and standard deviation for tracer concentrations

are posted in the following tables for the dry season of the northern study area (Table 4-

5), the rainy season for the northern study area (Table 4-6), the dry season for the

southern study area (Table 4-7) and the rainy season for the southern study area (Table 4-

8).

Northern study area. During the dry season, the average chloride concentration

in the seepage water and water column was 588 mM with la of 16.2 mM and 595 mM

with la of 11.4 mM, respectively (Table 4-5). Chloride concentrations of four

groundwater well samples that penetrate the Floridan Aquifer, range between 3 and 18

mM, however GW- 3 and GW-6 were 153 mM and 219 mM, respectively. The well that

provided GW-3 is in a different hydrologic basin (Figure 2-2a). The well that


Table 4-5. The average, minimum, maximum and standard deviation of tracer
concentrations of the water column, seepage water and groundwater measured during the
dry season in the northern study area.
Salinity Cond. Oxygen pH Cl SO4
_ppt) mS/cm (mg/L)_ (mM) (mM)
Ave Water Column 40.26 60.46 9.48 8.33 595 31.48
Max 41.40 63.10 10.75 8.43 610 32.48
Min 38.00 58.60 8.24 8.24 567 29.35
St. Deviation 0.93 1.31 0.86 0.08 11.4 0.91

Ave Seepage Water 39.83 60.12 4.38 7.45 588 31.15
Max 41.40 63.40 9.84 7.77 616 32.22
Min 37.50 47.70 1.16 7.22 560 29.04
St. Deviation 1.08 3.44 2.05 0.13 16.20 0.90

Ave Groundwater 6.3 5.6 0.5 7.1 67.1 3.02
Max 14.5 15.7 1.0 7.5 219.0 9.96
Min 0.4 0.1 0.3 6.8 3.2 0.00
St. Deviation 6.7 8.7 0.4 0.3 94.5 4.68









provided GW-6 penetrates the Surficial Aquifer on the coastal side of the lagoon.

Surface water samples from the Haulover Canal (HOC) were similar in concentration to

the water column. Turnbull Creek (TBC), with a value of 514 mM, had a lower chloride

concentration than average seepage water and average water column values.

During the rainy season, the average chloride concentration in the seepage water

and the water column was 565 mM with la of 20.6 mM and 554 mM with la of 14.9

mM, respectively (Table 4-6). The chloride concentrations of four groundwater samples

range between 5 mM and 21 mM, however, GW- 3 and GW-6 were 154 mM and 282

mM, respectively. The surface water samples, TBC and HOC, were similar to the

average water column samples.




Table 4-6. The average, minimum, maximum and standard deviation of tracer
concentrations in the water column, seepage water and groundwater measured during the
rainy season in the northern study area.
Salinity Cond. Oxygen pH CI SO4
(ppt) mS/cm) (mg/L) (mM) (mM)
Ave Water Column 37.70 62.30 5.41 8.13 554 29.43
Max 40.30 65.50 8.23 8.63 571 31.70
Min 35.50 60.60 1.34 8.01 528 27.40
St. Deviation 1.36 1.60 1.83 0.18 14.9 1.17

Ave Seepage Watei 37.95 62.91 2.18 7.40 565 29.39
Max 41.90 67.80 6.12 7.71 621 31.70
Min 35.60 60.40 0.22 6.95 533 25.60
St. Deviation 1.52 1.97 1.55 0.20 20.6 1.29

Ave Groundwater 5.66 13.50 N/A 7.55 80 1.53
Max 17.10 27.98 N/A 9.50 282 9.10
Min 0.40 0.87 N/A 6.74 5 0.00
St. Deviation 7.36 12.25 N/A 1.12 115 3.71

During the dry season, the water column chloride concentrations are greater than

the seepage water chloride concentrations, while during the rainy season the opposite is











true. Overall, the chloride concentrations of the dry season samples are greater than those


of the rainy season samples.


Multisamplers were sampled during December 1999 in the northern study area,


four months after the rainy season sampling trip. Profiles from the water column down


into the sediment water interface show chloride concentrations that were -100-200 mM


lower than the seepage water and water column concentration measured during the rainy


season (Figure 4-10).


Average Water Column
Chloride Concentrations
300 350 400 450 500 550 600
30 A
30----------A -------------- ,,,I\

I 0 Sediment
-- water
interface
-20 %,
0 Average Seepage Wa
E "-- Chloride Concentrations
-.. ODry Season
A Rainy Season
S -70 -..
70

c0
Io "

-120"-



-170

S-+- IRL4

-i-IIRL5
-220
Chloride (mM)



Figure 4-10. The profile of chloride concentrations for 3 multisamplers measured during
December, 1999 in the northern study area.




Southern study area. During the dry season, the average chloride concentration


in the seepage water and the water column was 341 mM with la of 26.4 mM and 348


mM with la of 33.6 mM, respectively (Table 4-7). The chloride concentration of six









groundwater samples range between 4 mM and 34 mM and surface waters samples

(including canals and streams) range from 228 mM to 531 mM during the dry season.


Table 4-7. The average, maximum, minimum and standard deviation of tracer
concentrations in the water column, seepage water, groundwater, surface water and pore
water measured during the dry season in the southern study area.
Salinity Cond. Oxygen Temp. pH CI SO4
(ppt) mS/cm (mg/L) (oC) (mM) (mM)
Ave Water Column 21.31 33.86 7.02 27.99 8.40 348 17.12
Min 19.00 30.70 5.47 26.90 8.06 313 15.01
Max 26.80 41.10 9.15 29.30 8.77 430 21.61
St. Deviation 2.18 3.09 0.77 0.70 0.18 34 1.93

Ave Seepage Wate 21.69 34.59 0.78 27.78 7.51 341 15.97
Min 19.00 30.60 0.13 26.40 7.19 314 13.16
Max 26.50 43.60 3.00 28.60 7.94 401 25.35
St. Deviation 2.45 4.49 0.93 0.62 0.23 26 2.96

Ave Groundwater 1.13 2.16 0.65 26.04 7.09 19 1.11
Min 0.10 0.20 0.11 24.50 4.33 4 0.00
Max 2.00 3.81 2.33 31.50 7.86 34 2.04
St. Deviation 0.73 1.36 0.77 2.46 1.26 12 0.73

Ave Surface Water 25.22 42.81 6.44 28.96 8.26 359 20.22
Min 18.00 32.57 5.52 26.60 8.11 228 11.10
Max 36.00 56.30 7.27 30.40 8.37 531 31.11
St. Deviation 7.05 9.48 0.79 1.45 0.11 113 8.45

During the rainy season, the average chloride concentration in the seepage water

and the water column was 449 mM with lo of 18.7 mM and 457 mM with lo of 22.6

mM, respectively, (Table 4-8). The chloride concentration of five groundwater samples

range between 6 mM and 31 mM and surface water samples (including canals and

streams) range from 228 mM to 531 mM during the rainy season. Chloride

concentrations in the seepage water and water column of the dry season are lower than

seepage water and water column of the rainy season.









Table 4-8. The average, minimum, maximum and standard deviation of tracer
concentrations in the water column, seepage water, groundwater, surface water and pore
water measured during the rainy season in the southern study area.
Salinity Cond. Oxygen Temp. pH Cl SO4
(ppt) (mS/cm (mg/L) (oC) (mM) (mM)
Ave Water Column 28.5 44.2 7.4 28 8.3 457 23.3
Min 25.8 40.3 4.2 7 8.0 422 21.3
Max 29.8 46.2 29.1 29 8.6 493 25.3
St. Deviation 1.2 1.7 5.0 5 0.2 22.6 1.3

Ave Seepage Water 28.9 45.6 1.3 30 7.4 449 23.0
Min 25.8 43.8 0.2 30 7.0 422 21.6
Max 38.5 47.7 4.0 32 8.2 483 25.3
St. Deviation 3.0 1.3 1.1 0 0.4 18.7 1.0

Ave Groundwater 1.1 2.3 1.4 28 7.5 21 1.2
Min 0.0 0.6 0.3 26 6.7 6 0.0
Max 1.8 3.5 2.1 32 7.8 31 2.1
St. Deviation 0.6 1.1 0.8 3 0.4 9.2 0.7

Ave Surface Water 21.9 34.1 7.2 31 7.9 348 17.6
Min 0.2 0.9 3.9 30 7.5 11 0.6
Max 33.7 51.0 8.6 32 8.2 570 29.6
St. Deviation 11.4 17.3 1.8 1 0.3 185.3 9.5


In the southern study area, multisamplers were measured during both the dry and

rainy seasons. The minimum chloride concentration in the pore water was 337 mM

during the dry season and 324 mM during the rainy season. The maximum chloride

concentration in the pore water was 443 mM during the dry season and 477 mM during

the rainy season.


Nutrients

All average, minima, maxima and standard deviations for nutrient concentrations

are posted in the following tables for the dry season of the northern study area (Table 4-

9), the rainy season for the northern study area (Table 4-10), the dry season for the

southern study area (Table 4-11) and the rainy season for the southern study area (Table

4-12). All posted concentrations of N3- include concentrations of both NO3- and NO2z.









Northern study area. The concentration of TSN in the water column, seepage

water and groundwater increased between the dry and rainy seasons. The concentrations

of TSP in the water column and groundwater decreased between the dry and rainy

seasons. However, TSP concentrations increased in the seepage water between the dry

and rainy seasons.

Southern study area. The concentrations of TSN increased in the water column,

seepage water, groundwater and surface water between the dry and rainy seasons. The

concentrations of TSP increased in the water column, seepage water, groundwater and

surface water between the dry and rainy seasons. However, TSP concentrations

decreased in the seepage water between the dry and rainy seasons.




Table 4-9. Average, minimum, maximum and standard deviation of nutrient
concentrations in seepage water, water column and groundwater during the dry season in
the northern study area.
NO3 NH4 TSN SRP TSP SiO2
(mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L)
Ave Water Column 0.006 0.099 0.919 0.006 0.017 0.47
Max 0.013 0.125 1.038 0.008 0.022 1.39
Min 0.001 0.069 0.790 0.006 0.015 0.15
St. Deviation 0.004 0.017 0.076 0.001 0.002 0.31

Ave Seepage Watel 0.006 2.563 2.625 0.069 0.108 5.11
Max 0.017 6.308 4.023 0.259 0.412 10.10
Min 0.001 0.689 1.375 0.000 0.017 2.72
St. Deviation 0.005 1.437 0.831 0.078 0.108 1.79

Ave Groundwater 0.002 0.632 0.893 0.090 0.148 0.02
Max 0.010 0.919 2.186 0.300 0.610 0.03
Min 0.000 0.459 0.300 0.014 0.014 0.01
St. Deviation 0.004 0.156 0.703 0.120 0.235 0.01










Table 4-10. Average, minimum, maximum and standard deviation of nutrient
concentrations in seepage water, water column and groundwater during the rainy season
in the northern study area.
NO3 NH4 TSN TN SRP TSP TP SiO2
(mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L)
Ave Water Column 0.055 0.135 1.089 1.324 0.000 0.016 0.037 1.71
Max 0.102 0.251 1.251 1.471 0.000 0.017 0.045 4.00
Min 0.027 0.042 0.930 1.232 0.000 0.014 0.031 0.66
St. Deviation 0.028 0.061 0.097 0.068 0.000 0.001 0.005 0.93

Ave Seepage Watel 0.048 3.858 2.698 3.008 0.093 0.153 0.234 5.05
Max 0.113 30.623 9.358 12.176 0.818 2.318 2.635 10.27
Min 0.008 0.344 1.160 1.716 0.000 0.015 0.040 1.67
St. Deviation 0.025 5.092 1.372 1.753 0.150 0.390 0.443 1.98

Ave Groundwater 0.024 1.026 1.006 1.074 0.076 0.125 0.129 0.02
Max 0.059 2.472 2.646 2.794 0.424 0.663 0.622 0.03
Min 0.001 0.479 0.352 0.346 0.000 0.001 0.000 0.01
St. Deviation 0.024 0.771 0.875 0.952 0.170 0.264 0.244 0.01


Table 4-11. Average, minimum, maximum and standard deviation of nutrient
concentrations of seepage water, water column, groundwater, surface water and pore
water during the dry season in the southern study area.
NO3 NH4 TSN TN SRP TSP TP SiO2
(mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L)
Ave WaterColumn 0.002 0.031 0.302 0.329 0.042 0.044 0.032 1.32
Min 0.000 0.007 0.081 0.250 0.001 0.002 0.001 0.00
Max 0.006 0.092 0.380 0.430 0.602 0.628 0.051 6.49
St. Deviation 0.002 0.022 0.062 0.049 0.126 0.131 0.011 1.28

Ave Seepage Wate 0.007 0.379 0.598 2.114 1.046 0.715 0.694 11.50
Min 0.001 0.001 0.003 0.020 0.036 0.000 0.000 0.00
Max 0.014 0.826 3.143 11.358 4.180 3.114 3.004 31.06
St. Deviation 0.003 0.227 0.705 2.913 1.222 0.940 0.843 9.21

Ave Groundwater 0.005 0.485 0.436 0.714 0.125 0.085 0.081 15.62
Min 0.000 0.386 0.000 0.141 0.001 0.000 0.000 12.15
Max 0.009 0.634 0.619 2.250 0.759 0.557 0.564 17.72
St. Deviation 0.004 0.089 0.247 0.695 0.281 0.209 0.213 1.74

Ave SurfaceWater 0.017 0.033 0.268 0.258 0.040 0.017 0.073 3.44
Min 0.003 0.017 0.122 0.061 0.001 0.000 0.021 0.43
Max 0.051 0.047 0.349 0.404 0.102 0.045 0.160 8.47
St. Deviation 0.020 0.013 0.093 0.129 0.037 0.019 0.056 3.11









Table 4-12. Average, minimum, maximum and standard deviation of nutrient
concentrations of seepage water, water column, groundwater, surface water and pore
water during the dry season in the southern study area.
NO3 NH4 TSN TN SRP TSP TP SiO2
(mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L)
Ave Water Column 0.003 0.027 0.441 0.475 0.032 0.048 0.060 2.43
Min 0.000 0.008 0.303 0.329 0.004 0.019 0.026 1.74
Max 0.044 0.056 0.635 0.723 0.066 0.075 0.084 3.51
St. Deviation 0.009 0.016 0.102 0.122 0.022 0.019 0.018 0.44

Ave Seepage Water 0.003 0.635 1.591 1.521 0.460 0.395 0.442 8.73
Min 0.001 0.050 0.582 0.518 0.022 0.020 0.029 2.28
Max 0.012 1.897 3.169 2.917 1.913 1.605 2.017 20.37
St. Deviation 0.003 0.528 0.643 0.623 0.471 0.395 0.484 5.44

Ave Groundwater 0.004 0.383 0.692 0.708 0.126 0.106 0.119 15.62
Min 0.000 0.182 0.430 0.444 0.002 0.002 0.000 11.75
Max 0.016 0.591 1.328 1.339 0.742 0.619 0.710 18.17
St. Deviation 0.006 0.146 0.322 0.320 0.302 0.251 0.289 2.12

Ave Surface Water 0.016 0.036 0.427 0.511 0.048 0.059 0.077 4.19
Min 0.001 0.014 0.070 0.124 0.011 0.020 0.024 0.44
Max 0.066 0.081 1.000 0.988 0.089 0.089 0.114 12.76
St. Deviation 0.025 0.024 0.311 0.281 0.029 0.028 0.036 4.41














CHAPTER 5
DISCUSSION


Seepage Rates

Groundwater seepage measured from seepage meters in the northern and southern

study areas reflect flow of water across the sediment water interface that was greater than

seepage rates measured from blank experiments. In both the northern and southern study

areas, seepage rates increased from the dry to the rainy seasons based on the average

seepage rate. In addition, seepage rates vary spatially across each study area during each

season. The following discussion of seepage rates will focus on two questions. The first

part of the discussion will focus on whether the seasonal increase in seepage rates was a

direct result of increased precipitation from the dry to the rainy season. The second part

of the discussion will focus on the cause of spatial variation of seepage rates.

Seasonal Relationship of Seepage Rates

Temporal variations in seepage rates measured using seepage meters have been

found in studies of coral reef, nearshore and estuarine environments (Lewis, 1987; Cable

et al., 1997b; Robinson et al., 1998). Along the Barbados coast, seepage rates were twice

as high during the rainy season than the dry season because the Barbados aquifer, a

highly permeable and transmissible aquifer, is recharged during the rainy season, thus

increasing the flow of groundwater (Lewis, 1987). Cable et al. (1997b) found that mean

monthly integrated seepage rates to decrease from 21.4 L/m/min to 3.6 L/m/min from

August 1992 to March of 1993 off shore of the panhandle of Florida. The decrease in









seepage rate corresponds to a decrease in monthly precipitation from -35 cm to -15 cm

from August 1992 to March 1993 in the study area.

Seepage rates increased from the dry to the rainy season in both study areas. On

average, seepage rates increased by 58% from the dry to rainy seasons of the northern

study area, although seven stations show decreasing seepage rates (Table 4-2). On

average, seepage rates increased by 41% from the dry to rainy seasons of the southern

study area, although eight stations show decreasing seepage rates (Table 4-4). All

seepage rates were compared using the Wilcoxon signed rank test. The Wilcoxon signed

rank test is a nonparametric test that compares probability distributions of sampled data

sets and can be used with skewed data similar to the sets of this study (Figure 4-5, 4-6, 4-

7, 4-8). The Wilcoxon signed rank was used to show that there is a significant difference

with 95% confidence in the distributions of the seepage rates between the two seasons of

both study areas.

One possible cause for the observed increased seepage is from an increase in

discharge from the Surficial Aquifer. Discharge from the Surficial Aquifer will increase

when precipitation recharge to the aquifer increases. The dry season average monthly

precipitation value (October, 1998 through April, 1999) was 3.96 cm, while the rainy

season average monthly precipitation value was 8.60 (May through August, 1999) for the

northern study area (Figure 4-1). The dry season average monthly precipitation value

(October, 1999 through April, 2000) was 5.24 cm, while the rainy season average

monthly precipitation value (May through August 2000) was 11.2 cm in the southern

study area (Figure 4-4). Precipitation recharge increased 2-fold between the dry and the









rainy seasons in both the northern and southern study areas. A two-fold increase may

provide enough recharge to aquifers, which is then discharged into the lagoon as seepage.

Spatial Heterogeneity of Seepage Rates

Seepage rates varied spatially throughout the northern and southern study areas.

In the northern study area, seepage rates ranged from 3 ml/m2/min to 104 ml/m2/min

during the dry season and from 22 ml/m2/min to 144 ml/m2/min during the rainy season

(Table 4-1). In the southern study area, seepage rates ranged from 10 ml/m2min to 58

ml/m2min during the dry season and from 9 ml/m2min to 96 ml/m2min during the rainy

season (Table 4-3). This range in seepage rate is not surprising considering the average

difference was 61% at stations with duplicate seepage measurements (Table 3-1).

Many factors may have caused these observed variations of seepage rates. These

factors include the spatial heterogeneity of hydraulic properties and composition of the

aquifers that lie below the Indian River Lagoon, the presence of benthic dwelling

organisms in sediments and the composition of sediments below each station.

The variability of hydraulic properties of the Floridan Aquifer may have caused

the spatial changes in measured seepage rates. The Upper Floridan Aquifer is a

cavernous limestone system known for its heterogeneous hydraulic properties (Tibbals,

1990). Assuming groundwater is the cause of the seepage, vertical conduits in the system

would allow increased upward groundwater flow. Increased upward groundwater flow

would produce faster seepage rates. However, the Floridan Aquifer is partially overlain

by a confining unit in the northern study area and fully overlain by the confining unit in

the southern study area. Consequently, the confining unit and the Surficial Aquifer may

control the spatial variation of seepage rates, rather than the Floridan Aquifer.









The presence of the Hawthorn Group confining layer is not well mapped

throughout the northern study area. Toth (1988), Tibbals (1990) and Scott (1990) suggest

that the Hawthorn Group is missing in northern Brevard County, although the location of

the boundary is not clearly defined because of limited well coverage. Pockets of the

confining unit could be scattered throughout the area. Where the confining units are

missing in the northern study area water flows upward from the Floridan Aquifer to the

Surficial Aquifer (Toth, 1988). In areas where the confining unit is breached, seepage

rates would be expected to increase due to increased groundwater flow from the Floridan

Aquifer, except where there is a confining layer in the Surficial Aquifer. The confining

unit thickens to the south and ranges between 30.5 m to 45.7 m in thickness in the

southern study area. The confining unit retards upward flow of groundwater from the

Floridan Aquifer to the Surficial Aquifer. Low upward flow from the Floridan Aquifer

may result in slower seepage flux in the southern study area than the northern study area.

Seepage rates may have decreased from the northern study area to the southern study area

due to the increased thickness of the confining unit in the southern study area, assuming

precipitation recharge remained constant. The average seepage rates decreased by 44%

between the dry season in the northern study area and the dry season in the southern

study area (Table 4-1, 4-3). The average seepage rates decreased by 61% between the

rainy season in the northern study area and the rainy season in the southern study area

(Table 4-1, 4-3). In addition, because the confining layer is uniformly distributed, it

would not have a significant effect on the variability of the seepage rates in the southern

study area. Where the confining unit is present, the Surficial Aquifer is likely to control

the spatial variation in seepage rates.









The hydraulic properties of the Surficial Aquifer, such as transmissivity and

hydraulic conductivity, vary throughout the study area. The transmissivities range from

2.5 L/d/m to 98.7 L/d/m in Brevard and Indian River Counties (Toth, 1988). The

hydraulic conductivity can range by two orders of magnitude in east-central Florida

(Toth, 1988). The Surficial Aquifer contains beds of fine-grained materials that act as

confining units and these beds may lead to changes in measured seepage rates (Toth,

1988). The presence of minor confining units would slow the rate of flow in the Surficial

Aquifer and the rate of seepage measured above the local confining unit.

The presence of benthic dwelling organisms in sediments may increase or

decrease seepage rates by altering sediment characteristics. Sediments are altered by

organisms through bioturbation, biodeposition and production of cementing by-products

such as shells and mucous (Day et al., 1989). Through bioturbation, organisms burrow

into sediments forming conduits. The presence of conduits alters the hydraulic properties

of sediments by increasing porosity and permeability. Elevated porosity and permeability

would increase seepage water flow rates. Biodeposition is the buildup of macroinfaunal

feces and the deposit of bacterial mucous in sediments. The mucous and feces act as

cementing agents and bind sediment particles together (Day et al., 1989). Cemented

particles reduce porosity and permeability in the sediments. Reduced porosity and

permeability would reduce seepage water flow rates.

The variation of composition in the sediments may effect the spatial distribution

of seepage rates. Sediments range from mud to sand sized particles in the northern and

southern study areas of the lagoon. Mud and clay sized particles may have low

permeabilities of 10-6 to 10-3 darcys while, sand sized particles may have increased









permeabilities of 10-2 to 102 darcys (Fetter, 1994). Increased permeability in sediments

will allow increased seepage rates compared to areas of low permeability.

Spatial variability of seepage rates was more likely controlled by changes in

hydraulic properties and composition of sediments and the upper stratigraphy of the

Surficial Aquifer, where seepage flow was locally defined beneath each seepage station.

The presence of the Hawthorn Group confining unit and the Floridan Aquifer more likely

control seepage rates on a regional scale between the northern and southern study areas.


Chloride

Chloride concentrations were measured to determine the source of seepage water

based on concentrations of groundwater, seepage water and the water column of the

lagoon. Chloride concentrations in seepage water and the water column decreased

between the dry and rainy seasons in the northern study area and increased between the

dry and rainy seasons in the southern study area. In addition, chloride concentrations in

the seepage water and water column were greater in the northern study area than the

southern study area. The following discussion of chloride concentrations will focus on

three questions. The first part of the discussion will focus on the cause of the variation in

chloride concentrations from the dry to the rainy season in each study area. The second

part of the discussion will focus on tracing the source of seepage water using chloride

concentrations. The third part of the discussion will focus on how evaporation and

surficial runoff directly effects chloride concentrations in the water column and indirectly

effects chloride concentrations in seepage water.









Seasonal Variation

Average chloride concentrations in the seepage water decreased from the dry to

rainy season in the northern study area and increased from the dry to rainy season

southern study area. In the northern study area, the percent decrease of the average

chloride concentration was 4% in seepage water from the dry to the rainy season. In the

southern study area the percent increase in average chloride concentration was 31% in the

water column and 32% in the seepage water from the dry to the rainy season.

The total normal average monthly recharge is fi9.67 cm during the dry season

(October through April) and 7.0 cm during the rainy season (May through August) (Table

5-1) (Rao, 1987). The total average monthly recharge was -26.1 cm during the dry

season (October 1998 through April 1999) and fi8.0 cm during the rainy season (May

1999 through August 1999) in the northern study area (Table 5-2). The total monthly

recharge was 7.5 cm during the dry season (October 1999 through April 2000) and 0.1

cm during the rainy season (May 2000 through August 2000) in the southern study area

(Table 5-3).

The changes in chloride concentrations may have been caused by precipitation

recharge to the lagoonal basin or a lack of normal precipitation leading to evaporation.

The total monthly recharge increased from the dry season to the rainy season in the

northern study area. An increase in recharge may have controlled the decrease in

chloride concentrations of the seepage water between the dry and rainy seasons of the

northern study area, by diluting the seepage water. In contrast, the total monthly recharge

decreased from the dry to rainy season of the southern study area. The decrease in

recharge from the dry to the rainy season may be attributed to increased precipitation

from a hurricane, which increased normal precipitation by a factor of two during the dry









season. Two hurricanes contributed excessive amounts of rain when they passed through

the study areas at the end of the rainy season and the beginning of the dry season in 1999.

Assuming the hurricane precipitation was so extensive that it caused a change in water

column chloride concentrations, the chloride concentrations of pore water profiles

measured in the northern study area during December, 1999, were 100 to 200 mM less

in the water column than the average chloride concentrations of the dry and rainy season

water column (Figure 4-10). The southern study area received 10 cm more rainfall than

the northern study area for September 1999. The extensive recharge during the dry

season was caused by significant precipitation during Hurricane Irene that passed through

in October 1999. The excessive precipitation increased the total recharge value for the

rainy season to over 2 times the normal average dry season. The southern study area may

have undergone the same dilution process as the northern study area. The chloride

concentrations in the water column measured during the dry season may not have been

indicative of natural conditions due to dilution of the lagoon from increased recharge.

Chloride concentrations may have increased between the dry and rainy seasons in the

southern study area as the lagoon returned to natural conditions after the hurricanes. In

addition, chloride concentrations may have increased due to a lack of normal recharge

from the dry to the rainy seasons. The total monthly recharge during the rainy season

was 7 cm less than the normal monthly recharge during the rainy season. The recharge

during the rainy season may have been insufficient to dilute chloride concentrations in

the water column; leading to evaporation as a factor that increased the chloride

concentrations measured during the rainy season.










Table 5-1. Normal average monthly recharge values for the entire Indian River Lagoon.
Normal Average Values for the Entire Lagoon
Precipitation* Potential* Recharge
Month (cm) Evaporation (cm) (cm)
January 5.5 5.7 -0.2
February 6.9 7.6 -0.7
March 7.4 10.8 -3.4
April 6.1 13.0 -6.9
May 11.0 14.4 -3.4
June 17.5 13.6 3.9
July 16.7 13.6 3.1
August 16.0 12.6 3.4
September 18.2 11.1 7.1
October 13.0 9.7 3.2
November 5.4 6.8 -1.4
December 5.1 5.4 -0.3
*Rao Report, 1987


Table 5-2. Average monthly recharge for the northern study area.

Northern Study Area
Precipitationa Potential Recharge
Month (cm) Evaporation (cm) (cm)
May-98 2.7 10.8 -8.0
Jun-98 2.1 9.9 -7.8
Jul-98 12.7 N/A N/A
Aug-98 18.0 16.0 2.0
Sep-98 22.1 5.8 16.3
Oct-98 2.8 7.0 -4.1
Nov-98 5.0 7.4 -2.4
Dec-98 5.1 7.9 -2.9
Jan-99 7.0 5.6 1.4
Feb-99 2.3 6.3 -4.0
Mar-99 1.9 9.5 -7.5
Apr-99 3.6 10.2 -6.6
May-99 6.6 11.1 -4.5
Jun-99 10.7 9.8 0.9
Jul-99 1.2 11.5 -10.2
Aug-99 15.9 10.1 5.8
Sep-99 33.9 6.3 27.6
aTitusville and Scotsmoor weather stns.(NOAA, SJRWMD)
bVero Beach and Ft.Pierce weather stns.(NOAA)










Table 5-3. Average monthly recharge for the southern study area.
Southern Study Area
Precipitationa Potentialb Recharge
Month (cm) Evaporation (cm) (cm)
May-99 16.5 11.1 5.4
Jun-99 14.4 9.8 4.6
Jul-99 3.0 11.5 -8.4
Aug-99 17.3 10.1 7.3
Sep-99 43.4 8.1 35.4
Oct-99 34.0 7.7 26.3
Nov-99 6.3 10.3 -4.0
Dec-99 6.1 7.2 -1.0
Jan-00 5.9 6.0 0.0
Feb-00 0.9 6.9 -6.1
Mar-00 5.5 9.4 -3.9
Apr-00 6.7 10.5 -3.8
May-00 1.0 12.6 -11.5
Jun-00 17.9 11.5 6.3
Jul-00 17.1 10.1 7.0
Aug-00 8.8 10.5 -1.7
aMelbourne weather stn. (NOAA)
bVero Beach and Ft.Pierce weather stns.(NOAA)


Fraction of Fresh Groundwater in Seepage Water

It is important to determine the percentage of groundwater in seepage water to

assess the hydrologic budget of the region in order to confirm numerical models of

groundwater seepage such as the one developed by Pandit and El-Khazen (1990). The

source of groundwater seepage is also an important control on its chemical composition.

The concentration of chloride in the groundwater, seepage water and water

column was used to find the percentage of groundwater flowing into the seepage meters.

Groundwater has low chloride concentrations, ranging from 3 mM to 33 mM because of

its source from precipitation. In addition, there is no source of chloride in the upper

Floridan, Intermediate and Surficial aquifers, although in some coastal areas groundwater

may contain chloride that originates as seawater intrusion. Nonetheless, the low chloride

concentration of groundwater means that chloride should be a useful tracer of









groundwater in the seepage water. Assuming two-end member mixing, the fraction of

lagoon and aquifer water can be calculated from the following equation:

fgw = (C-Cm)/(C1-Cgw) Eq. (1)

Where fgw is the fraction of groundwater that enters the seepage meter, C1 is the value of

the tracer in the lagoon water, Cgw is the value of the tracer in the groundwater and Cm is

the value of the tracer in the seepage water.

The percentage of groundwater flowing into the lagoon was calculated for the dry

and rainy seasons in the northern and southern study areas using equation (1). Using

average values of chloride, the fraction of groundwater flowing into the lagoon during the

dry season in the northern study area was calculated to be 4.0 %, 0.0 %, 0.0 %, -0.2 %, -

1.4 % and 0.8 % for transect stations IRL1-8; IRL9,10,16; IRL17-20; IRL21-24; IRL11,

25-28, respectively (Table 5-4). Using average values of chloride, the fraction of

groundwater flowing into the lagoon during the rainy season in the northern study area

was calculated to be -0.2 %, -11.7 %, -3.7 %, -1.5 %, -1.3 % and 0.0 % for transect

stations IRL1-8; IRL9,10,16; IRL17-20; IRL21-24; IRL11, 25-28, respectively. Using

average values of chloride, the fraction of groundwater flowing into the lagoon during the

dry season in the southern study area was calculated to be fi2.5 %, -0.3 %, -1.3 %, 0.7 %,

2.6 % and 2.4 % for transect stations IRL29-31; BRL1-5; IRL32-34; BRL6-7; IRL35-38

and IRL39-42, respectively. Using average values of chloride, the fraction of

groundwater flowing into the lagoon during the rainy season in the southern study area

was calculated to be 3.7 %, 1.4 %, 1.9 %, 1.6 %, 2.9 % and 0.5 % for transect stations

IRL29-31; BRL1-5; IRL32-34; BRL6-7; IRL35-38 and IRL39-42, respectively. The

groundwater percentage calculated for transects IRL9, 10,16; IRL12-15 and IRL17-20










Table 5-4. The chloride concentrations of seepage water, water column and groundwater
used to calculate the percentage groundwater found in the seepage water.
Northern Study Area
Dry Season 1999 Average Chloride Concentrations (mM)
Transect Groundwater n Seepage water n Water column n % Groundwater
IRL1-8 7.75a 4 579 8 603 1 4.0
IRL9,10,16 7.757 4 591 3 591 2 0.0
IRL12-15 7.75a 4 602 4 602 2 0.0
IRL17-20 7.75a 4 568 4 567 1 -0.2
IRL21-24 7.75a 4 607 4 599 1 -1.4
IRL11,25-28 7.75a 4 591 5 596 5 0.8
Rainy Season 1999 Chloride Concentrations (mM)
Transect Groundwater n Seepage water n Water column n % Groundwater
IRL1-8 10.25a 4 572 8 571 1 -0.2
IRL9,10,16 10.25a 4 592 1 531 1 -11.7
IRL12-15 10.25a 4 592 4 571 1 -3.7
IRL17-20 10.25a 4 536 4 528 1 -1.5
IRL21-24 10.25a 4 544 4 537 1 -1.3
IRL11,25-28 10.25a 4 554 5 554 5 0.0
Southern Study Area
Dry Season 2000 Chloride Concentrations (mM
Transect Groundwater n Seepage water n Water column n % Groundwater
IRL29-31 19ab 7 342 2 334 2 -2.5
BRL1-5 19ab 7 320 5 319 5 -0.3
IRL32-34 19ab 7 336 3 332 3 -1.3
BRL6-8 19ab 7 324 3 326 3 0.7
IRL35-38 19a'b 7 354 2 363 2 2.6
IRL39-42 19a'b 7 392 3 401 3 2.4

Rainy Season 2000 Chloride Concentrations (mM)
Transect Groundwater n Seepage water n Water column n % Groundwater
IRL29-31 21a'b 6 462 3 479 3 3.7
BRL1-5 21ab 6 431 4 437 4 1.4
IRL32-34 21a,b 6 480 2 489 2 1.9
BRL6-8 21a'b 6 448 3 455 3 1.6
IRL35-38 21a,b 6 456 4 469 4 2.9
IRL39-42 21a,b 6 427 3 429 3 0.5
aWells sampled from the Floridan Aquifer
bWells sampled from the Surficial Aquifer
n = number of samples


during the rainy season in the northern study area produced lower negative values than

the dry season because of precipitation that diluted chloride concentrations of the lagoon

water to values lower than the seepage waters. An example of this dilution was observed

while sampling the water column on the 16th during the August sampling trip of 1999. A

gradient of temperature and salinity (Figure 5-1) was measured and indicated a cooler

and less saline surface of the water column caused by a passing storm earlier in the day.











Consequently, the seepage water, although possibly diluted by fresh groundwater, was

more saline than the overlying water column. In addition, negative values indicate that

the chloride concentrations in the sampled groundwater wells are not indicative of Cgw

endmember values. Therefore, in order to calculate the fraction of groundwater in the

seepage water, it is important to have high resolution measurements of the chloride

concentrations in the water column. It is also important to measure the vertical

distribution of chloride concentrations in the water column. In the northern study area,

the water column was sampled from -30 cm below the surface. While in the southern

study area, high resolution measurements and vertical distribution of chloride

concentrations in the water column were taken into account by sampling the water

column -50 cm above the sediment water interface and by measuring the gradient of

temperature and salinity in the water column at each station.


Salinity (ppt)
37 37.5 38 38.5 39 39.5 40 40.5 41
0 1
Salinity
a Temperature
0.5

0
0

0

0.




2
1.5 ----------------- -------




29.4 29.6 29.8 30 30.2 30.4 30.6 30.8
Temperature C



Figure 5-1. The changes in salinity and temperature with depth in the water column for
station IRL16 during the rainy season in the northern study area. Sampled on August 16,
1999.









Assuming groundwater samples from wells was the correct Cgw endmember value

of seepage water, then the 1 fi 4 % groundwater in seepage water may reflect the volume

of fresh water that seeps into the lagoon based on the Pandit and El-Khazen (1990) study.

Pandit and El-Khazen (1990) calculated 34 fi 38 million m3 of fresh groundwater from

the Surficial Aquifer flows into the lagoon annually. The annual groundwater seepage

into the lagoon calculated by Pandit and El-Khazen (1990) is 0.002 % the minimum and

0.0005 % the maximum annual seepage rates into the lagoon measured for this study.

Based on Pandit and El-Khazen (1990), the percent groundwater contribution in seepage

is much smaller than the percent of groundwater calculated with chloride concentrations.

The difference between the two calculations suggest that fresh groundwater inflow into

the lagoon from the Surficial Aquifer is smaller than total seepage flow measured with

seepage meters (Motz and Gordu, 2001).

The groundwater percentages calculated for this study indicate that only a small

fraction of fresh groundwater flows into the Indian River Lagoon. Low fresh

groundwater percentages may have resulted from at least two causes. First, the source of

seepage water might be from regions of the aquifers that have undergone salt-water

intrusion. If this is the case, then groundwater well chloride concentrations are not valid

for equation 1. Increased chloride concentrations in the Surficial and Floridan aquifers

result from lateral seawater intrusion which results from overpumping of fresh water and

subsequent infiltration of seawater (Toth, 1988; Tibbals, 1990). Alternatively, seawater

that remains in an aquifer because the aquifer was previously inundated with seawater

during times of higher stands of sealevel may upwell into the fresh water lens (Toth,

1988; Tibbals, 1990).









Second, lagoon water may have circulated into the sediment to become the

primary component of seepage water. Many studies have concluded that seawater

circulates through sediments. Seawater circulation is believed to be caused by fresh

groundwater hydraulic head (Simmons, 1992). As less dense fresh groundwater flows

upward, the more saline pore waters flow downward into the sediment to displace the

fresh groundwater. Bokuniewicz (1992) describes this physical phenomenon as density

driven salt fingering, after analyzing the salinity distribution of pore water in cores taken

from Great South Bay, New York. The salt-fingering results from an unstable density

gradient of saline pore waters that overlie fresh pore waters, resulting in narrow plumes

of salt water dipping into the fresh water region. The density inversion only accounts for

mixing when increased chloride concentrations in the water column overly lower chloride

concentrations in the sediment pore water. When lower chloride concentrations in the

water column overly increased chloride concentrations in the sediment pore water

another mechanism must control mixing between the two.

The concept that the circulating lagoon water constitutes the majority of seepage

water is inconsistent with the idea that the source of seepage water is directly from

aquifer groundwater. Therefore, seepage rate variations that were said to be caused by

increased precipitation to aquifer groundwater from the dry to rainy seasons is also

inconsistent with this finding because fresh aquifer groundwater was not the source of

seepage water. Changes in chloride concentrations in seepage water and the water

column from dry to rainy season may be controlled by direct recharge to the water

column based on the idea that seepage is primarily composed of lagoon water, which is









opposite of the idea that changes in recharge to aquifers will control changes is chloride

concentrations of seepage water and the water column.

Effects of Seepage Water on Water Column Chemistry

The chloride concentrations of the water column correlate directly to the seepage

water chloride concentrations for the dry and rainy seasons of the northern and the

southern study areas (Figures 5-2, 5-3). Although, there was one instance of known

density layering in the water column, in general, the density was uniform with depth.

The chloride concentration of seepage water may directly effect the concentration in the

water column by diluting or concentrating the chloride concentrations in the water

column. If chloride concentrations in the seepage water control the chloride

concentrations in the water column then the source of the seepage water would have to

derive from aquifers that have undergone salt-water intrusion and not from circulating

lagoon water. Assuming seepage water is largely composed of circulated lagoon water,

the relationship shown in figure 5-2 and 5-3 suggest that the water column chloride

concentrations may control seepage concentrations.

The regression lines of the dry and rainy seasons measured in both study areas are

offset from the line representing seepage water concentration equals water column

concentrations (Figures 5-2, 5-3). This offset may result from water column chloride

concentrations that were affected by other factors such as meteoric water or evaporation.

For example, the regression lines that offset to the left of the line indicating seepage

water concentrations equal water column concentrations suggest that water column

chloride concentrations increased compared to seepage water concentrations. The water

column chloride concentrations may have increased compared to seepage water

concentrations due to evaporation. Alternatively, the regression lines that offset to the












610

E 600

S590

580
U

0 570

2 560
c
U
c 550
E
O 540

) -x
530

520
520 540 560 580 600
Seepage Water Chloride Concentration (mM)
Y=X is the line representing seepage water concentrations equal water column


-Y=X







y = 0 527x + 282 94
R2 = 0 4824
Dry Season
Dry Season
Rainy Season
Linear (Dry Season)
-Linear (Rainy Season)
y = 0 623x + 204 3
R2 = 0 7183
Rainy Season


Figure 5-2. Plot of seepage water chloride concentrations against the corresponding
water column chloride concentrations for the northern study area dry and rainy seasons.




right of the line indicating seepage water concentrations equal water column


concentrations suggest that water column chloride concentrations decreased compared to


seepage water concentrations. The water column chloride concentrations may have


decreased because precipitation directly on the lagoon diluted the chloride concentrations


of the water column. The regression lines of the dry season in the northern study area


and both the dry and rainy seasons in the southern study area are offset to the left of the


line indicating seepage water concentrations equal water column concentrations. This


ofset suggests that the water column chloride concentrations increased compared to


seepage water concentrations due to evaporation. The regression line of the rainy season


in the northern study area is offset to the right of the line indicating seepage water


concentrations equal water column concentrations. This offset suggests that the water











column chloride concentrations decreased compared to seepage water concentrations due


to precipitation.


500
d Y-- =X
E 480
r_
2 460

440
440 y =1 1293x 42 9
SR2 = 0 9563
o 420 Dry Season
400 DrySeason
4 Rainy Season
,O --Linear(Rainy Season)
M 380 Linear (Dry Season)
E y =0 1 0547x 15 988
0R2 = 0 8029
"0 Rainy Season
U 340--

( 320

300
300 320 340 360 380 400 420 440 460 480 500
Seepage Water Chloride Concentration (mM)
Y=X is the line representing seepage water concentrations equal water column


Figure 5-3. Plot of seepage water chloride concentrations against the corresponding
water column chloride concentrations for the southern study area dry and rainy seasons.




Assuming that most of the seepage water is recirculated lagoon water, it is


possible to calculate the time it takes for entire volume of lagoon water column to


circulate through the sediments. This calculation can be made by dividing the volume of


lagoon water by the seepage rate (Table 5-5). This calculation indicates it would take


29.6 days during the dry season and 18.7 days during the rainy season for the lagoon


water to circulate through the sediments of the entire lagoon using seepage rates from the


northern study area. Using seepage rates from the southern study area this calculation


indicates it would take 42.6 days during the dry season and 30.2 days during the rainy


season for total volume of the water in the lagoon to circulate through the sediments.









Therefore, when the water column chemistry changes, it takes up to a month before the

same changes are reflected in the chemistry of the sediment pore water.




Table 5-5. Time of water column circulation through sediments of the entire lagoon.
Area 922 km2 For Entire Lagoon
Volume 1.57 km3
Northern Seepage Flux Flux for Total Lagoon Circulation
Study Area ml/m2/min Area (ml/min) Time (days)
Dry Season 39.91 3.68 x 1010 29.6
Rainy Season 63.08 5.82 x 1010 18.7
Southern Seepage Flux Flux for Total Lagoon Circulation
Study Area ml/m2/min Area (ml/min) Time (days)
Dry Season 27.69 2.55 x 1010 42.6
Rainy Season 39.11 3.61 x 1010 30.2

Evidence of Mixing Pore Water Chemistry

Chloride concentrations in pore waters at certain depths were lower than chloride

concentrations of seepage water and water column of the dry and rainy seasons of the

southern study area. Chloride concentrations decrease to a minimum of 287 mM to 313

mM at a depth of 50 cm to 84 cm in the multisampler profiles of stations BRL7, 6, 2 and

IRL32 during the dry season (Figure 5-4a, Table 5-6). The minimum values in each

profile are lower than the average chloride concentration of seepage water (341 mM) and

water column (348 mM) measured during the dry season (Figure 5-4B, Table 5-8).

Chloride concentrations decrease to a minimum of 324 mM to 409 mM at a depth of 80

cm to 150 cm in the multisampler profiles of station IRL29, BRL2, 1, 6 and 5 during the

rainy season (Figure 5-4b, Table 5-6). The minimum values in each profile were lower

than the average chloride concentration of seepage water (449 mM) and water column









(457 mM) measured during the rainy season. The low chloride concentrations in the pore

waters range between 70 cm and 150 cm depth into the sediment during the rainy season.




Table 5-6. The minimum chloride concentration in pore water and depth in
multisamplers from the southern study area.
Lowest Pore Water Chloride
Concentrations (Dry Season)
Depth into Concentration
Station Sediments (cm) (mM)
BRL7 74 287
BRL6 84 289
BRL2 50 298
IRL32 73 313
Average 297
Lowest Pore Water Chloride
Concentrations (Rainy Season)
Depth into Concentration
Station Sediments (cm) (mM)
IRL29 80 324
BRL2 80 329
BRL1 110 349
BRL6 150 349
BRL5 70 409
Average 352

Multisampler profiles may show mixing of chloride concentrations of lagoon

water that circulated into sediments to mix with pore water. The low chloride

concentrations in the pore water at the 50 cm to 150 cm horizon layer would have a lower

density than the water column at each station. This density inversion may drive water

upward, exchanging with the higher density lagoon water. The mixed pore waters and

lagoon waters would be sampled as seepage water.

The percent of pore water that contributed to the seepage water was calculated

using equation (1) for the dry and rainy season in the southern study area. The average

chloride concentration in the pore water (Cgw) was calculated by averaging the













A 280
50 -



0-



S-50-

E

S-100 -
C,
,c

S-150 -



-200 -



-250


B 280
50


Chloride (mM)


300 320 340 360 380 400 420 440 460 480


0
o ..... ---' = :' "- ---" ---' 'x-- y^



-50 *










K IRL29 1
E x *-









-- BRL2
-200 -4-BRL1
A- BRL5
BRL6
Average Water Column
-250 0 Average Seepage Water
Chloride (mM)



Figure 5-4. The multisample profiles of chloride concentrations for the (A) dry and (B)
rainy seasons of the southern study area. Values plotted at the sediment water interface
indicate seepage water collected from the same station. Values plotted 30 cm above
sediment water interface symbolizes water column collected from the same station.


300 320 340 360 380 400 420 440 460 480









lowest chloride concentration in each multisampler profile of the 50 cm to 150 cm layer.

The average chloride concentration in the seepage water and the water column of each

season was used to calculate the percent of pore water contribution to seepage water.

With these values, equation (1) indicates that seepage water was composed of 13.0% pore

water during the dry season and 7.6% pore water during the rainy season in the southern

study area (Table 5-5). Using low pore water concentrations as the Cgw endmember in

Eq. 1 suggests that pore water 50 to 150 cm below the sediment-water interface is not a

significant source of seepage water. This further suggests that the source of seepage

water is likely from the circulation of lagoon water into the sediments and not a

significant source from pore water below.

The change from the dry to the rainy season of the contribution of pore water to

seepage water implies that the source of the low chloride concentrations in the pore water

may be ephemeral without sufficient dilution of the circulating lagoon water, such as

when large storms drop heavy precipitation. The contribution of pore water, that

originated from lagoon water, to seepage water further supports the idea that seepage

water is largely composed of circulating lagoon water.




Table 5-7. The percent of pore water with low chloride concentrations in seepage water
in the southern study area.
Dry Season % Pore Water in Seepage Water
Pore Water n Seepage water n Water column n % Pore Water
297* 4 341 20 347 20 13.0

Rainy Season % Pore Water in Seepage Water
Pore Water n I Seepage water n Water column n % Pore Water
352* 5 449 20 457 20 7.6
*Average concentrations calculated from the lowest pore water chloride concentrations
measured in each multisampler profile from 50 cm to 150 cm depth









The sediment horizon layer retaining lower chloride concentrations than other

depths into the sediment may have resulted from dilution of the lagoon after two

hurricanes dropped extensive precipitation over the study area in September and October

of 1999 (Table 5-3). After the lagoon water was diluted from extensive rainfall, it

circulated into the sediments to provide the 50 cm to 150 cm horizon layer with lower

chloride concentrations. Over the extent of the dry season, chloride concentrations in the

water column increased due to evaporation. Assuming the water column circulates into

the sediments within 43 days (Table 5-7) after increasing in concentration, the chloride

concentrations in the 50 cm to 150 cm horizon layer should increase to values similar to

the water column within that time. The average low pore water chloride concentration

measured during the rainy season (352 mM) did increase from the dry to the rainy season

to values greater than the average water column chloride concentrations measured during

the dry season (347 mM). The increase in low pore water chloride concentration

suggests the water column circulated into the sediments within the time of sampling from

the dry to the rainy season (-90 days). If the lowest pore water chloride concentrations

increased to concentrations similar to the water column within 43 days from time the

water column was measured during the dry season, then the pore water chloride

concentrations would have increased by 1.16 mM/day. Using the same rate of increase,

lowest pore water chloride concentrations should have increased to an average of 401.7

mM for the rainy season, because the chloride concentrations in the water column

continued to increase from the dry to the rainy season by 1.22 mM/day. From the dry to

the rainy season, the lowest pore water chloride concentration did not increase by 1.16

mM/day because the 50 cm to 150 cm sediment horizon may be low in permeability or









circulating lagoon water may not recirculate as quickly into sediment depths greater than

50 cm than depths less than 50 cm.

Evaporation and Surficial Runoff

The difference in chloride concentrations of the water column was 520 fi 610 mM

and 310 fi 480 mM between the northern and southern study areas, respectively. The

high chloride concentrations in the northern study area when compared with the southern

study area may have resulted from extensive evaporation. Increased evaporation can

occur where the surface area to volume ratio of a water body increases. The surface area

to volume ratio is two times higher in the northern study area than the southern study area

because the average depth increases from the north to the south. The deepest water depth

in the northern study area is 2 m, while the average water depth is -1 m. In contrast, the

deepest water depth in the southern study area is 3.80 m and the average depth is -2.32

m. Consequently, the fraction of evaporation relative to the total volume of the lagoon is

less in the southern study area than the northern study area, because the southern study

area provides a lower surface area to volume. In areas of the lagoon where the surface

area to volume ratio increases, then the chloride concentrations of the water column will

increase, thus increasing the chloride concentrations in the seepage water after circulation

of the water column into the sediments.

Surface water runoff may reduce chloride concentrations directly in water column

and indirectly in seepage water in the southern study area. Surficial discharges are more

common in the southern study area than in the northern study area. There is little surface

water runoff to the northern study area except during major precipitation (Rao, 1987).

The chloride concentration in Turnbull Creek is similar to those of the water column

(Table 5-8), although the stream was never sampled following a rainstorm. The creeks









and rivers near the southern study area (EauGallie River, Crane Creek, Turkey Creek and

Sebastian River) contribute major discharges (Figure 4-3, Table 5-9) (Rao, 1987). The

chloride concentrations in the water column were higher in the northern study area

compared with the southern study area (Table 5-8). The surficial discharge in the

southern study area may reduce chloride concentrations through dilution of the lagoon

water. The surficial discharge in the northern study area may have been too small to

effect the chloride concentrations in the lagoon water, allowing evaporation to have a

greater effect on chloride concentrations.




Table 5-8. Chloride concentrations of surface water measurements of dry and rainy
season in both study areas.
Dry Season Rainy Season
Chloride Chloride
Concentration Concentration
(mM) (mM) /oDifference
Turnbull Creek 514 541 5.3
Northern Haulover Canal 601 582 -3.3
Study Area Average Water Column 595 554 -7.4

Eau Gallie River 295 434 47.4
Crane Creek 358 382 6.6
Southern Turkey Creek 228 11 -2021.0
Study Area Saint Sebastian River 531 355 -49.6
Sebastion Inlet 384 570 48.4
Average Water Column 348 457 31.3

Chloride concentrations would be expected to decrease during the rainy season

because rainfall would dilute chloride concentrations of the tributaries. Although Turkey

Creek and St Sebastian River decreased in chloride concentration by -2000% and -50%,

respectively, Crane Creek and EauGallie River increased in chloride concentrations, by

7% and 47% respectively, between the dry and rainy seasons. Furthermore, chloride

concentrations in the water column increased from the dry to the rainy season in the










southern study area. The chloride concentrations in the water column may have

increased due to lower than normal precipitation recharge and high evaporation (Table 5-

1, 5-3). The observed increase in chloride concentrations of EauGallie River and Crane

Creek may result from smaller drainage areas and discharge rates than those for Turkey

Creek and St. Sebastian River (Table 5-9). The drainage areas are larger because the C-l

Canal and the Fellsmere Canal drain the marshlands of the St. Johns River and

marshlands into the Turkey Creek and St. Sebastian River, respectively. The EauGallie

River and Crane Creek thus may not have collected enough precipitation to flush the river

of lagoon water near the sampling site, despite the increase in rainfall during the rainy

season.




Table 5-9. Mean monthly streamflow of four major surficial discharges in the southern
study area.
Drainage Area Mean Monthly Streamflow m3/s*
km2 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Eau Gallie River 98.4 0.27 0.26 0.31 0.22 0.21 0.35 0.40 0.57 0.63 0.50 0.34 0.22

Crane Creek 46.8 0.96 0.99 1.18 0.82 0.73 1.06 1.52 2.01 2.09 1.91 1.57 0.99
Turkey Creek/ C-1
253.8 3.65 2.82 4.08 2.74 2.30 3.91 5.44 5.61 7.56 7.62 5.10 1.86
Canal
St Sebastian Riverl/
203.1 1.81 1.72 2.26 1.74 1.35 2.72 2.50 3.54 4.13 3.37 3.03 1.82
Fellsmere Canal
*NWISWeb U.S. Geological Survey

During the dry season, the average chloride concentration of the water column of

each transect increased from the north to the south (Figure 5-5). In contrast, the average

chloride concentration in the water column of each transect decreased from the north to

the south during the rainy season. The chloride concentrations in the water column of the

southern transect increased slightly from dry season to rainy season compared to the

transects to the north. The low chloride concentration of the Turkey Creek discharge




































Figure 5-5. The average chloride concentrations of seepage water (italics) and the water
column (mM) for each transect during the dry season (A) and rainy season (B) in the
Indian River Lagoon compared with chloride concentrations of surficial discharge.


may have minimized the increase of chloride concentrations in the southern transect

between the dry and rainy seasons. The low chloride concentration of Turkey Creek

discharge may have reduced the change of chloride concentrations in the southern

transect by dilution of chloride concentrations in the water column. In addition, the

chloride concentrations in the water column circulated into the sediments, reducing the

change in chloride concentrations of seepage water of the southern transect.

Both evaporation and surficial runoff effect chloride concentrations in the water column.

By circulating into sediments, chloride concentrations in the water column control the









chloride concentrations in seepage water. Ultimately, evaporation and surficial runoff

indirectly effect the chloride concentrations in seepage water.


Nutrients

The contribution of nutrients from seepage water to the water column may be

very significant when compared to nutrient contribution from surficial input to the Indian

River Lagoon. The first part of the following discussion will focus on the importance of

inorganic and organic nitrogen and phosphorus species in seepage water and the water

column. The second part of the discussion will focus on the quantity of nutrient loading

from seepage water and relative comparison to nutrient loading from surface discharge.

The final part of the discussion will focus on the effects nutrient loading from seepage

water may have had on the limiting nutrient of primary production for each study area.

In marine environments, the concentration of organic nitrogen and phosphorus

species are usually higher than inorganic nitrogen and phosphorus species in the water

column, while the converse is true in the sediment pore water (Trefry et al., 1992;

Herbert, 1999). In the sediment pore water, bacteria mineralize organic nitrogen and

phosphorus, thereby leaving an increased concentration of inorganic nitrogen and

phosphorus (Trefry et al., 1992; Herbert, 1999). When seepage water flows into the

overlying water column, the inorganic species are assimilated into the food web,

increasing the concentration of organic species. Nutrients are recycled back down into

the sediment through the deposition and decay of organic matter and recirculation of

lagoon water (Trefry et al., 1992; Herbert, 1999).

Nitrogen occurs as dissolved inorganic, dissolved organic or particulate forms.

Dissolved inorganic nitrogen species include NO3-, NO2- and NH4+ (Figure 5-6).









Dissolved organic nitrogen species include amino acids, urea, proteins, purines and

pyrimidines etc. (Behnke, 1975; Herbert, 1999). The organic and inorganic species of

dissolved nitrogen comprise the total soluble nitrogen. Total soluble nitrogen and

particulate nitrogen combine to form the total nitrogen.



Inorganic Organic
& Total
S/Total Particulate Nitrogen
ie da w Soluble Nitrogen / (TN)
Dissoved Dssoved Nitrogen
Organic
Inorganic itrog (TSN)
Nitrogen (DON) DIN and
(DIN) (DON) DON
(DIN) Urea, Amino DON
N02- acids Proteins
N03O
O3-. Purines and
NH4 .
Pyrmidines


Figure 5-6. The constituents of total nitrogen.



Phosphorus also occurs as dissolved inorganic, dissolved organic or particulate

species (Figure 5-7). The dissolved inorganic species is P04-, which is also referred to as

soluble reactive phosphorus. Dissolved organic phosphorus species include proteins and

sugars etc. The organic and inorganic species of dissolved phosphorus comprise the total

soluble phosphorus. Total soluble phosphorus and particulate phosphorus combine to

form total phosphorus.

The nutrient data was interpreted based on the relative concentrations of nitrogen

and phosphorus in the water column and seepage waters. The summed concentrations of

the inorganic nitrogen species, NO2-, NO3-and NH4+, constitutes dissolved inorganic

nitrogen. The dissolved organic nitrogen was calculated as the difference between the









total soluble nitrogen and dissolved inorganic nitrogen. Dissolved organic phosphorus

was calculated as the difference between total soluble phosphorus and P043.



Inorganic Organic
& Total
Total Particulate Phosphorus
SSlublePhosphorus (TP)
issued Dissoved Phosphorus
Inorganic Organic (TSP)
Pihoshorus Phosphorus DIP and
(DIP) or (DOP) DOP
Soluble O
nProteins and
Reactiveng both dry and rainy seasons in the northern study area and the dry season in
Phosphorus sugars
(SRP)
PO4


Figure 5-7. The constituents of total phosphorus.



Nitrogen

During both dry and rainy seasons in the northern study area and the dry season in

the southern study area, the concentration of dissolved inorganic nitrogen was greater

than dissolved organic nitrogen concentrations in the seepage water, while in the water

column the dissolved organic nitrogen was greater than the dissolved inorganic nitrogen

concentrations (Table 5-10). This relationship was different during the rainy season in

the southern study area. The concentration of dissolved organic nitrogen was greater than

dissolved inorganic nitrogen in both the seepage water and the water column during the

rainy season. The dissolved organic nitrogen is usually greater than dissolved inorganic

nitrogen in the water column, although not in the seepage water. Dissolved organic

nitrogen was greater in the average seepage water (0.926 mg/L) than the average water

column (0.411 mg/L) during the rainy season. Dissolved organic nitrogen may have been










Table 5-10. The average percent of inorganic and organic nutrient concentrations in total
soluble nitrogen and phosphorus concentrations for the dry and rainy seasons of the
northern and southern study areas.
Northern Study Area
Dry Season 1999 Rainy Season 1999
DIN DIP DIN DIP
Water column 11% 35% Water column 17% 0%
Seepage water 98% 64% Seepage water 100% 59%
Groundwater 70% 61% Groundwater 100% 64%
DON DOP DON DOP
Water column 89% 65% Water column 83% 100%
Seepage water 2% 36% Seepage water 0% 41%
Groundwater 30% 39% Groundwater 0% 36%

Southern Study Area
Dry Season 2000 Rainy Season 2000
DIN DIP DIN DIP
Water column 11% 95% Water column 7% 67%
Seepage water 65% 100% Seepage water 40% 100%
Groundwater 100% 100% Groundwater 54% 100%
DON DOP DON DOP
Water column 89% 5% Water column 93% 33%
Seepage water 35% 0% Seepage water 60% 0%
Groundwater 0% 0% Groundwater 46% 0%


increased in the seepage water during the rainy season due to shallow lagoon water

circulation into the sediments or from the regeneration of dissolved organic nitrogen in

lagoon water trapped below the seepage meters. Based on the average seepage flux

measured during the rainy season (39.11 ml/m2/min), it would take 31.96 hours to flush

the seepage meter of lagoon water after deployment, although seepage meters over the

slowest seepage flux (8.85 ml/m2/min ) would take 5.9 days. Seepage water was sampled

from each seepage meter from 4 to 7 days after deployment. The seepage meters

measuring the slowest seepage rates may have retained some lagoon water that was

sampled as seepage water. Lagoon water measured as seepage water may have increased

the average concentration of dissolved organic nitrogen in seepage water to values greater

than natural conditions.









Phosphorus

During the dry and rainy seasons of the northern study area, the concentration of

dissolved inorganic phosphorus was greater than dissolved organic phosphorus in the

seepage water, while the concentration of dissolved organic phosphorus was greater than

the concentration of dissolved inorganic phosphorus in the water column (Table 5-10). In

contrast, during the dry and rainy seasons in the southern study area, dissolved inorganic

phosphorus was greater than dissolved organic phosphorus in both the water column and

the seepage water. Dissolved inorganic phosphorus may have been greater than

dissolved organic phosphorus in both the seepage water and the water column because

dissolved organic phosphorus concentrations in the seepage water was 0.0 mg/L in the

seepage water, thereby reducing its loading to the water column. Dissolved organic

phosphorus concentrations were low in the water column due to no seepage loading, thus

allowing dissolved inorganic phosphorus concentrations to be greater in the water

column.

Nutrient Loading

Seepage water may provide a considerable amount of additional nutrients to the

water column, because of the elevated dissolved inorganic nitrogen and phosphorus in the

seepage water. To calculate the contribution of newly generated nutrients to the water

column, the nutrient concentrations in lagoon water must be differentiated from the

nutrient concentrations in seepage water. The nutrient concentration in lagoon water may

be differentiated from the nutrient concentrations in the seepage water by subtracting all

forms of nutrient concentration in the water column from all forms of nutrient

concentrations in the seepage water. In order to make calculations, the average total

nitrogen and total phosphorus concentrations in the water column were subtracted from









the average total nitrogen and total phosphorus concentrations in the seepage water

(Table 5-11). The flux of nutrients was calculated using the corresponding seepage flux

measured during each season.

Nutrient loading was calculated for each study area and for the entire lagoon. The

annual nutrient flux value was calculated for the dry (212 days) and rainy (153 days)

seasons then added together to calculate the total annual nutrients added to the water

column from seepage flux. The annual nutrient loading of total nitrogen was 4.50 x 106

kg and total phosphorus was 4.59 x 105 kg in the northern study area. The annual

nutrient loading of total nitrogen was 6.03 x 106 kg and total phosphorus was 2.20 x 106

kg in the southern study area. A range of annual nutrient loading values to the entire

lagoon was calculated assuming nutrient fluxes of total nitrogen and total phosphorus was

uniform across the entire lagoon. The average annual load of total nitrogen ranged from

2.60 x 107 kg to 4.11 x 107 based on nutrient flux measured in the northern study area and

southern study area, respectively. The average annual load of total phosphorus ranged

from 4.52 x 106 kg to 7.89 x 106 based on nutrient flux measured in the northern study

area and southern study area, respectively.

Annual loads of total nitrogen and total phosphorus from seepage water are

greater than total annual loads of total nitrogen and total phosphorus from surficial

discharge into the Indian River Lagoon. The annual loads of total nitrogen and total

phosphorus from surficial discharge were 2.38 x 106 kg and 3.19 x 105 kg, respectively

based on the Pollution Load Screening Model (Adamus and Bergman, 1993; Woodward-

Clyde, 1994). On the basis of these calculations, the average total annual nutrient loads

from seepage water were thus greater than surficial discharge by factors of 10 to 17 for










total nitrogen and 14 to 25 for total phosphorus. Because the total annual loads from the

surficial discharge to the entire lagoon was calculated based on a pollution load model, it

may not be representative of surficial discharge nutrient loading made from physical

measurements. Assuming the pollution load model represents physical measurements of

surficial discharge into the lagoon, these calculations indicate that groundwater seepage

to the Indian River Lagoon may represent a previously unidentified, but important, source

of nutrients.


Table 5-11. The average nutrient concentration, nutrient flux and nutrient loading of total
nitrogen and total phosphorus in the northern and southern study areas.
Nutrient Concentration
TN TP
Northern Study Area mg/L mg/L
Dry Season# 1.706 0.091
Rainy Season 1.69 0.197
Southern Study Area
Dry Season 1.785 0.662
Rainy Season 1.064 0.382
Nutrient Loading
TN TP
kglyr kglyr
Sc Minimum* 8.96 x106 9.55 x105
SAverage* 4.11 x 10 4.52 x106

z j Maximum* 9.94 x 10 8.43 x106
E 2 Minimum* 6.99 x 106 2.57 x 106
Average* 2.60 x 107 7.89 x 106
cn Maximum* 4.97 x 107 1.82 x 107
#Nutrient concentrations measured as TSN and TSP
*Values based on average, min and max seepage flux









Limiting Nutrients

The atomic ratio of N:P can be used to determine the nutrient that limits primary

production (Schelske et al., 1999). The atomic ratio ofN:P, termed the Redfield Ratio, in

macroalgae is 16:1 (Day et al., 1989). Using the atomic ratio of DIN:DIP, values that are

less than 16 are considered nitrogen limiting and values greater than 16 are considered

phosphorus limiting to the growth of macroalgae (Schelske et al., 1999).

The limiting nutrient to the growth of macroalgae changes from phosphorus in the

northern study area to nitrogen in the southern study area. Phosphorus was limiting in the

seepage water and the water column of both seasons of the northern study area (Table 5-

12). In contrast, nitrogen was the limiting nutrient in seepage water and the water

column of both seasons in the southern study area. Similarly, Sigua et al. (2000) found

the ratio of N:P in the water column to decrease from the northern to the southern end of

the Indian River Lagoon, showing phosphorus as the limiting nutrient in the northern

study area and nitrogen as the limiting nutrient in the southern study area.

The limiting nutrient in the water column may be directly affected by nutrient

loading from seepage water. The average total annual loading of total nitrogen to the

entire lagoon was larger based on seepage flux and nutrient concentrations from the

northern study area than the southern study area (Table 5-12). The opposite was true for

total phosphorus, the average total annual loading to the entire lagoon was smaller based

on seepage flux and nutrient concentrations from the northern study area than the

southern study area. The shift from phosphorus limiting in the northern study area to

nitrogen limiting in the southern study area may be directly related to the shift in

increased loading of total phosphorus and decreased loading of total nitrogen in the










southern study area. The shift from phosphorus to nitrogen as the limiting nutrient will

affect primary production in each study area.




Table 5-12. Nutrient concentrations and flux in each study area and nutrient loading
quantity to the Indian River Lagoon.
Northern Study Area
Dry Season 1999 Rainy Season 1999
DIN DIP DIN/DIP DIN DIP DIN/DIP
(atoms/L) (atoms/L) ratio (atoms/L) (atoms/L) ratio
Water column 4.50E+18 1.17E+17 38 Watercolumn 7.95E+18 0.00E+00
Seepage water 1.10E+20 2.97E+18 37 Seepage water 1.68E+20 1.75E+18 96

Southern Study Area
Dry Season 2000 Rainy Season 2000
DIN DIP DIN/DIP DIN DIP DIN/DIP
(atoms/L) (atoms/L) ratio (atoms/L) (atoms/L) ratio
Water column 1.42E+18 8.17E+17 1.7 Watercolumn 1.29E+18 6.22E+17 2.1
Seepagewater 1.76E+19 2.03E+19 0.9 Seepage water 2.74E+19 8.95E+18 3.1
*DIP is limiting because concentrations are dose to zero.














CHAPTER 6
CONCLUSIONS

The results of this study show that seepage flow occurs in two study areas of the

Indian River Lagoon. The average seepage fluxes were 40 ml/m2/min and 63 ml/m2/min

during the dry and rainy season, respectively, in the northern study area and 28

ml/m2/min and 39 ml/m2/min during the dry and rainy season, respectively, in the

southern study area. The Wilcoxon signed rank test was used to show that there was a

significant difference of 95% confidence in the distributions of seepage flux between the

dry and rainy season of both study areas. The average seepage fluxes may differ

seasonally because of increased precipitation and recharge between dry and rainy

seasons. Seepage flux varied spatially and averaged 60% difference between duplicate

seepage measurements. The spatial heterogeneity in seepage flux may be controlled by

the spatial heterogeneity of hydraulic and compositional properties of sediments.

Detailed studies of hydraulic and compositional changes in sediments and aquifers could

be used to determine the controlling factor of spatial variability in seepage rates. Such

local studies can be achieved by using geophysical techniques, taking core samples and

performing hydraulic tests in wells placed in close proximity to each seepage station.

Geophysical techniques, such as seismic profiles, would show changes in thickness and

structure of sediments and rocks. An analysis of core profiles would show changes in

composition of sediments and aquifer rocks. Hydraulic tests, such as pump tests and slug

tests, would determine the transmissivity of sediments.