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Chemical tracing and analytical and mass-balance modes of pore water circulation in the Banana River Lagoon, Florida

University of Florida Institutional Repository

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CHEMICAL TRACING AND ANALYTICAL AND MASS-BALANCE MODES OF PORE WATER CIRCULATION IN TH E BANANA RIVER LAGOON, FLORIDA By JEHANGIR H. BHADHA A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2003

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Copyright 2003 by Jehangir H. Bhadha

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iii ACKNOWLEDGMENTS I would like to thank the St Johns River Water Management District for having funded my research. I would like to thank my advisor, Dr. Jonathan Martin, for his constant support and guidance throughout my research. I would also like to thank my committee members, Dr. John Jaeger and Dr. Clay Montague, for their assistance and resourceful suggestions towards my thesis. I would like to thank Dr. Jason Curtis and William Kenny for letting me use the labs and assisting me with my physical and chemical analyses. I would like to thank Maryle a Hart in helping me use the core logger and sectioning my cores. I would like to thank my good friend and ex-colleague Melroy Borges for his many valuable comments a nd suggestions, and in assisting me with graphic imaging. I would like to thank the faculty, staff, and all of my colleagues here at the Department of Geological Sciences (Univers ity of Florida) for their help and support throughout my time in Gainesville. Last but not the least, I woul d like to thank my parents back home in India for their support, blessings and patience; especially for not having complained how much they have missed me in the past three years.

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iv TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iii LIST OF TABLES.............................................................................................................vi LIST OF FIGURES..........................................................................................................vii ABSTRACT....................................................................................................................... ix CHAPTER 1 INTRODUCTION........................................................................................................1 1.1 Statement of Problem.............................................................................................1 1.2 Hypotheses..............................................................................................................6 1.3 Goals and Objectives..............................................................................................6 1.4 Study Area..............................................................................................................7 1.4.1 Geology and Hydrology of the Indian River Lagoon System......................9 1.4.2 Regional Climate........................................................................................10 2 METHODS.................................................................................................................13 2.1 Water Samples......................................................................................................13 2.1.1 Pore Water Samples...................................................................................13 2.1.2 Lagoon and Seep Water Samples...............................................................16 2.1.3 Analyses.....................................................................................................17 2.2 Sediment Cores.....................................................................................................18 2.2.1 Sampling.....................................................................................................18 2.2.2 Analyses.....................................................................................................20 3 RESULTS...................................................................................................................23 3.1 Physical Analyses.................................................................................................23 3.1.1 Description of Cores...................................................................................23 3.1.2 Porosity.......................................................................................................27 3.1.3 Density........................................................................................................28 3.2 Chemical Analyses...............................................................................................29 3.2.1 Total Phosphorus (TP) and Total Nitrogen (TN).......................................29 3.2.2 Total Organic Matter (OM)........................................................................30 3.2.3 Total Carbon (TC)......................................................................................30

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v 3.2.4 Biogenic Silica (SiO2)................................................................................31 3.2.5 210Pb and Sedimentation Rates...................................................................31 4 DISCUSSION.............................................................................................................39 4.1 Introduction...........................................................................................................39 4.1.1 Conceptual Model......................................................................................40 4.2 Sediment Profiles..................................................................................................43 4.2.1 Correlation Between Physical Pr operties and Ground Water Discharge Rates.................................................................................................................43 4.2.2 Density........................................................................................................44 4.2.3 Total Organic Matter as a Source of Nutrients...........................................45 4.2.4 Comparison of Total Phosphorus (TP) and Total Nitrogen (TN) with Nutrient Fluxes.................................................................................................46 4.2.5 Redfield Ratios and their Signifi cance to the Banana River Lagoon.........47 4.3 Emerson’s SiO2 Mixing Model............................................................................51 4.3.1 Introduction................................................................................................51 4.3.2 The Model..................................................................................................52 4.3.3 Model Solution and Results........................................................................55 4.4 Mass Balance Calculation.....................................................................................59 4.4.1 Introduction................................................................................................59 4.4.2 Calculations................................................................................................63 5 CONCLUSIONS........................................................................................................66 5.1 Summary...............................................................................................................66 5.2 Future Work..........................................................................................................69 APPENDIX A PHYSICAL AND CHEMICAL ANALYT ICAL DATA FROM CORE BRL2........70 B PHYSICAL AND CHEMICAL ANALYT ICAL DATA FROM CORE BRL6........73 LIST OF REFERENCES...................................................................................................76 BIOGRAPHICAL SKETCH.............................................................................................82

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vi LIST OF TABLES Table page 1-1. Various techniques used to measure ground water discharge in the Indian River Lagoon (from Martin et al. 2000)...............................................................................3 1-2. Summary of measured and 30-year aver age rainfall for the sampling sites (from Martin et al. 2000)....................................................................................................11 2-1. Estimated precision of various solutes for water samples..........................................18 2-2. Estimated precision of vari ous sediment sample analyses.........................................22 3-1. Estimation of sedimentation rates at BRL2 and BRL6 using gamma detectors........31 4-1. Description and values of parameters used in the model for BRL2...........................55 4-2. Average concentration of TP, TN and SiO2 up to 80 cm within the sediment at BRL2 and BRL6......................................................................................................63 4-3. Average pore water concentrations up to 80 cm (from Lindenberg 2001)................64 4-4. Comparing input fluxes to the sediment versus output fluxes to the lagoon water of TP, TN and SiO2 at BRL2 and BRL6.................................................................64

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vii LIST OF FIGURES Figure page 1-1. Location map of study area..........................................................................................8 1-2. Average monthly precipitation for the year 2000 (from Mart in et al 2000)...............12 2-1. Design of a multi-sampler (from Martin et al. 2000).................................................15 2-2. Vibracoring technique being used to collect the sediment core.................................19 3-1. Sediment Core from BRL2. Images to the right are real photographic images of short sections of the core representing the five zones.............................................25 3-2. Sediment Core from BRL6. Images to the right are real photographic images of short sections of the core representing the eight zones...........................................26 3-3. Porosity of sediment (a) BRL2, (b) BRL6.................................................................27 3-4. Bulk Density of sediments (a) BRL2, (b) BRL6........................................................28 3-5. Total phosphorus concentrations in sediment (a) BRL2, (b) BRL6...........................33 3-6. Total nitrogen concentrations in sediment (a) BRL2, (b) BRL6................................34 3-8. Total carbon concentrations in sediment (a) BRL2, (b) BRL6..................................36 3-9. Concentration of total organic and total inorganic carbon present in the sediment at (a) BRL2 (b) BRL6.............................................................................................37 3-10. SiO2 concentrations in sediment (a) BRL2, (b) BRL6.............................................38 4-1. Clprofile concentration suggesting mixing in shallow sediments in the Banana River Lagoon (BRL). C.Z = Coastal zone, FW = Fresh water, U.A = Unconfined aquifer, C.A = Confined aqui fer, AT = Aquitard (Inset of the Clprofile taken from Martin et al. 2000)......................................................................41 4-2. A conceptual model showing mixing at the sediment-water interface due to bioturbation or wave action. L.W.= Lagoon Water, S.W.= Seep Water, P.W. = Pore Water. B = Worms bu rrowing into sediment and ingesting sediment particles....................................................................................................42

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viii 4-3. Redfield ratios of organic C:P:N within sediments at BRL2.....................................49 4-4. Redfield ratios of organic C:P:N within sediments at BRL6.....................................50 4-5. Model solutions for the depth distri bution of silicate fo r enhanced mixing (K = 10-3 cm2 s-1) with no non-local transport ( = 0), and molecular diffusion (K = 10-5 cm2 s-1) and non-local transport ( = 4 10-7 s-1): May 2000.................57 4-6. Model solutions for the depth distri bution of silicate fo r enhanced mixing (K = 10-3 cm2 s-1) with no non-local transport ( = 0), and molecular diffusion (K = 10-5 cm2 s-1) and non-local transport ( = 4 10-7 s-1): August 2000.............58 4-7. Model solutions for the depth distri bution of silicate fo r enhanced mixing (K = 10-3 cm2 s-1) with no non-local transport ( = 0), and molecular diffusion (K = 10-5 cm2 s-1) and non-local transport ( = 4 10-7 s-1): December 2000........59 4-8. Cross section of the seep meter show ing organic matter remineralization at the sediment-water interface enclosed within the seep meter. P.W.= pore water, L.W.= lagoon water, S.W.= seep water..................................................................62

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ix Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science CHEMICAL TRACING AND ANALYTICAL AND MASS-BALANCE MODES OF PORE WATER CIRCULATION IN TH E BANANA RIVER LAGOON, FLORIDA By JEHANGIR H. BHADHA May 2003 Chair: Dr. Jonathan Martin Major Department: Geological Sciences The determination of nutrient fluxes is an important calculation in coastal and estuarine settings. Investigation of physical properties and chemical composition of the sediments in the Banana River Lagoon sugge sts that shallow sediments could be an important source of nutrients to the lagoon. Th is nutrient flux depends on (i) the rate of ground water discharge and (ii) th e concentration of the nutrien t in the discharged water. Mixing between the lagoon and pore water can alter the composition of shallow marine sediments, which are a source of nutrients to the lagoon through ground water discharge. Two sites previously studied for water chemistry viz. BRL2 and BRL6 were selected for collecting cores. Average por osity of sediments from BRL2 was ~31 %, compared to BRL6 which was 39 %. Nutrient fluxes cannot be measured with seep meters because of a number of possible arti facts, including induced flow effects and enhanced organic matter remineralization, due to limited availability of dissolved oxygen within the seep meter.

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x Mass balance calculations using pore water c oncentrations in BRL2 suggest that TP discharge may be ~ 20%, and TN discharge ~ 100 % greater than th e input of P and N through detrital OM. These high output fl uxes are a result of organic matter remineralization at shallow depths below th e sediment-water interface, due to mixing between lagoon and shallow pore waters. De termining the exact mixing depth, and the depth to which OM remineralization may be influenced by this mixing may prove to be vital for mass balance calculations. Mathematically, the transport mechanis m that describes this mixing can be formulated using a one-dimen sional diffusion coefficient ( K ), a non-local term () and a reaction term ( R ). Profiles of SiO2 pore water concentrati on at BRL2 suggest that molecular diffusion ( K = 10-5 cm2 s-1) does not dominate the random transport mechanism to 110 cm below the sediment-water interface. For to approach the desired SiO2 concentration, it requires a diffusion coeffi cient that is two orders of magnitude faster ( K = 10-3 cm2 s-1) than molecular diffusion, suggesting an enhanced mixing process induced probably by bioturbation, wave act ion, and tidal pumping. A slightly slower mixing regime ( K = 10-4 cm2 s-1) below 110 cm may correspond to the maximum depth up to which wave action and tid al pumping may affect mixing.

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1 CHAPTER 1 INTRODUCTION 1.1 Statement of Problem Submarine ground water discharge is define d as any flow out across the seabed, regardless of composition or driving force. The discharge of ground water to coastal marine environments such as bays, estuar ies, and lagoons may represent an important transportation process for pollutants includi ng excess nutrients, from shallow sediments to overlying surface waters. The importance of such a phenomenon has gained increased recognition in recent years because studies have shown that submarine discharge of water transports nutrients from agricultural lands (Simmons 1992, Galla gher et al. 1996) and residential septic tanks (Weisk el and Howes 1992) to coastal ma rine waters. This nutrient flux has lead to poor water quality and eutr ophication of near s hore ecosystems (Nixon 1986, Corbett et al. 2000). The movement of water represents one of th e primary controls of the distribution of pollutants in estuaries (Galla gher 1996, Martin et al. 2000) Water budgets of estuaries are routinely determined by measuring the volumes of surface water runoff, atmospheric deposition, and evapotranspirati on in the area. One important variable in the budget, the ground water discharge, is poorly constrained because of the difficu lties associated with locating and measuring the flow (e.g. Moor e 1996, Cable et al. 1996a,b, Martin et al. 2000). Ground water discharge has previously been assumed to occur through seepage from aquifers, where confining layers are missi ng. In this case, wate r would originate on continents as meteoric water and flow latera lly through aquifers from the continents to

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2 coastal areas. However, the assumption that all ground water discharg e originates from the continents as they flow though major aqui fers may be erroneous. For example, recent modeling by Li et al. (1999) has shown th at only 4 % of ground water discharge to the Atlantic continenta l shelf recognized by Moore (1996) using 226Ra isotopes originates from the underlying Floridan aquifer. Martin et al. (2000) reached similar conclusions by comparing the chemical and isotopic compos itions of shallow pore water, discharging ground water, and surface lagoon water in the Indian River Lagoon, Florida. These observations have led to the suggestion th at lagoon water may be circulating through shallow marine sediments. This circulation may occur by pumping mechanisms, such as wave action and bio-irrigati on (e.g. Emerson et al. 1984, Shum 1992, Li et al. 1999). The need to identify and understand this additional source of wate r is critical in order to accurately assess the hydrologic an d nutrient budgets of the lagoon. Methods used to quantify ground wate r discharge include direct flow measurements using devices such as seep meters (Lee 1977, Martin et al. 2000), chemical tracers (Cable et al. 1996 a ., Bunga et al. 1996, Martin et al 2000), and numerical ground water flow models (Pandit and El-Khazeen 1990, Li et al. 1999, Robinson and Gallagher 1999). Seep meter and tracer techniques have yielded similar discharge rates, but the values can be greater by several orders of magnitude than th ose calculated using numerical modeling for identical areas (Table 1-1). Seep meters provide a simple and an inexpensive approach to assess ground water di scharge. Besides, they have been used widely, and thus can be compared with prev ious studies from other areas. Seep meters measure the total flux of water from the sediment regardless of its source, unlike numerical flow models, which are restricted to flow from the particular aquifer being

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3 modeled. This total flux could include additiona l sources such as re-circulated seawater or lagoon water that enters th e subsurface through tidal or wave pumping. However, their deployment is laborious and numerous deploymen ts are required in order to provide an integrated value from even a small region. Al so, there are a number of possible artifacts associated with using this technique. One such example is current/topography-induced flow, which suggests that the positive profile of seep meters creates an airfoil effect similar to the lift created by an airplane wing (Shinn et al 2002). Table 1-1. Various techniques used to meas ure ground water discharge in the Indian River Lagoon (from Martin et al. 2000). Reference, Year Location Technique Flux (ml/m2/min) Martin et al., 2000 Indian Rive r Lagoon, FL Tracer (Rn, Ra) 11 66 Martin et al., 2000 Indian River Lagoon, FL Seep meter 40 65 Pandit & El-Khazen, 1990 Indian River Lagoon, FL Numerical modeling 0.002 Ground water discharge may be particular ly important for Florida’s estuaries because of the occurrence of large and productive aquifer systems, a long coastline and extensive precipitation across the region. Wherev er an aquifer with a positive head is connected to overlying surface waters thr ough permeable bottom sediments, submarine ground water discharge may occur (Johannes 1980, Rutkowski et al. 1999). Such a situation occurs along the east coast of Florida in the In dian River Lagoon, where the Floridan or Surficial aquifers are semi-confined, suggesting th at water may flow from the aquifer to the overlying lagoon waters. It has been suggested that only ~ 2.5 % of ground water discharge to the Indian River Lagoon originates from the underlying Floridan aquifer (Martin et al. 2000, Lindenberg 2001) while the remaining discharged water could be the result of circulation through shallow marine sediments. Further, the Clconcentrations of regional por e water also suggest that th ere is signific ant amount of

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4 mixing between the shallow pore water and th e overlying lagoon wa ter (Martin et al. 2000). This mixing is shown by changes th rough time in the concentration of Clbetween 0-70 cm depths below the sediment-water inte rface, with little change through time in their concentration at depths below 70 cm. Activities of benthic organisms and the bi ogenic structures they produce influence the physical and chemical properties of ma rine sediment deposits (Aller 1980, Boudreau and Marinelli 1994, Sandnes 2000). Benthic acti vities such as feeding, burrowing, and irrigation result in particle and fluid tran sport near and across the sediment-water interface, a critical boundary zone for diagen ic reactions (Aller 1980). Effects of these activities on sediment properties may influe nce redox conditions of sediment and pore water, organic matter and contaminant-degr adation rates, dissolution of biogenic compounds (CaCO3 and SiO2), nutrient fluxes and pore water profiles. The need to account quantitatively for these e ffects has resulted in the de velopment of different types of one-dimensional numerical models that can predict vertical mixing of particulate sediment and diagenetic reactions (Ber ner 1980, Wheatcroft et al. 1990), and to characterize the geochemistry of ventilat ed sediments (Boudrea u 1984, Emerson et al. 1984, Sandnes et al. 2000). Emerson et al. (1984) sugge sted that pore water prof iles in shallow estuarine sediments of Puget Sound show characteristic s of enhanced pore water transport by animal activity. According to this study the fluxes of alka linity, ammonia and silicate across the sediment-water interface due to biol ogical processes are greater than that by molecular diffusion. Using an in situ 3H experiment and dissol ved silicate profiles he evaluated the transport parameter due to animal activity in th e uppermost 20 cm of

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5 sediments to be 1 5 x 10-7 s-1, which is in the range of similar parameters determined in other near shore environments in the U.S. such as, Long Island Sound (Goldhaber et al. 1977) and the Hudson River Estu ary (Hammond et al. 1977). Ground water flux rates have been the focu s of several studies in the past (e.g. Gallagher et al. 1996, Cable et al. 1996 b., Li et al. 1999), but the associated nutrient fluxes have rarely been measured. Quantifyi ng nutrient fluxes requires knowing nutrient concentrations within the wa ter column, shallow sediments, and the discharging ground water. While there is a stea dy input of nutrients entering the lagoon through deposition of sediments, they are constantly being released to the pore water from the sediment through remineralization of organic matter, and transp orted via diffusive and advective processes. Hence, the discharging ground water should be enriched in nutrients. This enrichment suggests that diagenetic reacti ons and flow rates in shallo w sediments are critical for determining nutrient fluxes. An interesting approach to understanding nutrient fluxes at the sediment-water interface could be by determining a mass bala nce calculation between detrital nutrient fluxes to the sediment, versus the flux of nut rients to the water column from ground water discharge. The bio-availability of dissolve d phosphorus and nitrogen is thought to control biological productivity (Tyrrell 1999, Schenau and Delange 2001). Only a small fraction of particulate phosphorus and nitrogen produ ced in the photic zone (depth to which sunlight can penetrate) is ultimately buried in the sediment, while the remainder is remobilized and reutilized by the marine eco system. Up to 99 % of the total nutrient fluxes out across the sediment wa ter-interface is a result of microbial oxidation within the upper 1-5 cm of the sediment, where most algae and benthic organisms live (Berner

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6 1980, Tyrrell 1999). These nutrient fluxes brought about by advective transport mechanisms, represents a far greater source of nutrient transporta tion than diffusive processes from shallow pore waters to th e overlying lagoon. However, if some of the seep water (i.e. all water that flows to the lagoon from underlying sediments and rocks) is re-circulated lagoon water, then only the exce ss nutrients in the seep water (i.e. seep water – lagoon water) will represent a new source of nutrient loading to the lagoon generated as a result of or ganic matter remineralization. 1.2 Hypotheses Through detailed field sampling and meas urements, laboratory analyses, and mathematical modeling I plan to test the following hypotheses: Ground water discharge includes all sour ces of water that flows across the sediment-water interface, including la goon water re-circulation through shallow marine sediments. The circulation of lagoon water through shallow marine sediments corresponds to a greater flux of water and associated nutrients from the sediments through advective rather than diffusive processes. The concentration of nutrient fluxes acro ss the sediment-water interface depends on the availability and magnitude of organic matter remineralization within shallow sediments. The Banana River Lagoon along the east coast of Fl orida is an ideal site to test the above hypotheses, because of the presence of highl y permeable and shallow aquifers, a long coastline and extensive but seasonal precipitation. 1.3 Goals and Objectives The goal of this research is to determin e the sources of ground water discharge, its nutrient load, and trace the m ovement of pore water at two sites in the Banana River Lagoon ( viz. BRL2 and BRL6). This goal will be met through successful completion of the following 3 objectives:

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7 1. To use visual evidences and physical properties of sediments in making correlations between sediment type and ground water discharge rate. 2. Using mathematical modeling to test the possibility of a non-local transport mechanism (enhanced mixing), which may af fect sediment-water dissolved fluxes in near shore marine environments. 3. To determine realistic nutrient fluxes acr oss the sediment-water interface within the lagoon, using mass bala nce calculations. Results from this project will provide a better scientific understanding of a fundamental process in estuaries, viz. the re-circulation of lagoon water within shallow sediments. If however, advective fluxes of nut rients are as large as those from surface runoff and atmospheric deposition, it is critical to determine the source(s) of these fluxes in order to estimate the magnitude of nutrient loading from natural in ternal process, such as bioturbation, tidal pumping, and wave ac tion. While internal nutrient loading may exceed the magnitude of external loading fr om surface water runoff, it is the external loading that ultimately drives this cycle. 1.4 Study Area The Indian River Lagoon system estuar y extends 250 km along Florida’s central Atlantic coast, from north of Cape Canavera l in Brevard County to as far south as St. Lucie inlet in Martin County. Three estuaries make up the system including the Indian River Lagoon, Banana River Lagoon and th e Mosquito Lagoon. The Mosquito Lagoon extends to New Smyrna Beach, approximately 30 km north of the northern end of the Indian River Lagoon, and the Banana River Lag oon is separated from the northern Indian River Lagoon by Merritt Island, marking the eastern edge of the Indian River Lagoon (Figure 1-1).

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8 Figure 1-1. Location map of study area.

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9 1.4.1 Geology and Hydrology of the Indian River Lagoon System The hydrostratigraphy of Florida can be broa dly divided into th ree principle units including from deepest to shallowest, the Fl oridan, Intermediate, and Surficial aquifers (Miller 1986, Scott 1992, Groszos et al. 1992). The Floridan a quifer consists of Miocene and older carbonate rocks. These rocks have be en extensively dissolved in the subsurface, and consequently are characterized by heterogeneous hydraulic conductivity and extensive subsurface drainage. The Floridan aquifer represents one of the most productive aquifer in the worl d, and provides the primary sour ce of water to the northern half of Florida. The Floridan aquifer is loca lly divided into the Upper and Lower Floridan aquifer depending on the presence of a confini ng unit. The Intermediate aquifer consists of carbonate lenses contained within the Miocene Hawthorne Group, which is composed of siliciclastic clay and phos phorite-rich rocks (Scott 1988). To the south of the Indian River Lagoon, the Intermediate aquifer is thin and relatively nonproductive (Toth 1988). The Surficial aquifer has been subdivided in to separate units informally named the Shallow Rock aquifer and Shallow Clastic a quifer (Toth 1988). These aquifers consist largely of mixtures of sand, coquina and clay layers, with the clay layers providing the confining layers between the aquifers. The Hawthorn Group acts as the primary confin ing layer to the Flor idan aquifer. In general, the Floridan aquifer is consider ed to be confined where the Hawthorn Group reaches a thickness of more than 33 m and semi -confined where it is less than 33 m thick. The boundary between confined and semi-conf ined Floridan aquifer cuts across the northern portion of the Indi an River Lagoon north of Mel bourne, and this boundary is missing in the northernmost reaches of the Indian River Lagoon and the Mosquito Lagoon (Scott 1988, Toth 1988). The shallow rock a quifer unit of the Surficial aquifer is

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10 Pliocene in age and equivalent to the Ta miami Formation. It overlies the Hawthorn Group and varies in thickness. It is approximately 30 m thick to the south of the Indian River Lagoon and is missing from the Lagoon to the north of approximately Cocoa. Four informally defined clastic aquifers border the Indian River Lagoon, including Terrace Island, Atlantic Coastal Ridge, Ten-mile Ridge and Inter-ridge aquifer. Terrace Island aquifer occurs on the barrier islands separa ting Indian River Lagoon from the Atlantic Ocean, and supplies potable and irrigation water to communities on the islands. The aquifer depends on local rainfall for replenis hment. The Atlantic Coastal Ridge aquifer occurs on the western bank of Indian River Lagoon and in the northern reaches of the lagoon is composed of the Pliestocene Anasta sia Formation. This aquifer provides most of the water supply for towns on the western edge of the northern Indian River Lagoon. 1.4.2 Regional Climate The subtropical climate for this region typi cally demonstrates a dry season (January to May), a rainy season (June to Septembe r), and a winter storm season (October to December). Three separate sampling trips were made to the lagoon in 2000 in the months of May, August, and December when samp les of lagoon, seep and pore water were collected (Martin et al. 2000, Lindenber g 2001). Climatic conditions during field sampling, and their comparisons with averag e conditions are important in order to determine how representative the data is fr om discrete field trips over relatively short periods, and thus, if the data can be extrap olated over longer time scales. Results from this study could represent a sing le point in time, however se veral such points would be required to make generalizations on a larg er time scale. The cumulative monthly precipitation data for Titusville and Melbourne for the year 2000 are presented in Table 1-2, along with values for the 30-year averag e precipitation for these sites. During 2000,

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11 the annual precipitation at Me lbourne, Florida, was 17 % be low the 30-year average at Vero Beach. Monthly precipitation was lower than the 30-year average by 10.03 cm (91 %) in May, by 6.70 cm (43 %) in August, and by 4.87 cm (88 %) in December 2000 (Figure 1-2). Rainfall in May was low overa ll, but sampling was done during a time when 80 % of the total monthly rainfall was de posited. The August wet season sampling trip encompassed a rainfall of 2.69 cm, which wa s 31 % of the total m onthly precipitation. A small amount of rain fell during the samp ling trip in December (0.051 cm), representing only 8 % of the total monthly quota. Although the sampling trips made in 2000 could be considered as those made during a drought-year for the study area, th e precision and comprehensiveness with which samples were collected and data repo rted proved very useful for my study, which was conducted in November 2002, under similar drought conditions. Table 1-2. Summary of measured and 30-year average rainfall for the sampling sites (from Martin et al. 2000). Month 2000 Precipitation, Melbournea (cm) 30-year Precipitation, Vero BeachB (cm) January 5.94 5.44 February 0.86 7.39 March 5.54 7.85 April 6.71 4.83 May 1.04 11.07 June 17.86 16.41 July 24.82 15.47 August 8.79 15.49 September 21.36 18.16 October 13.23 14.02 November 0.91 8.31 December 0.64 5.51 Annual 107.70 129.95 aSource: NOAA Monthly Station Normals, 1961-1990. bSource: NOAA, 2001 (http://www.srh.noaa.gov/ml/mlbclimat.html#2000).

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12 0 5 10 15 20 25 30Jan-00 Feb-00 Mar-00 Apr-00 May-00 Jun-00 Jul-00 Aug-00 Sep-00 Oct-00 Nov-00 Dec-00 Monthly Precipitation (cm) Total monthly Precp. (Melbourne) 30-yr normal (Vero Beach) Figure 1-2. Average monthly pr ecipitation for the year 2000 (from Martin et al 2000).

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13 CHAPTER 2 METHODS 2.1 Water Samples In 2000 three separate sampling trips were made to the Indian River and Banana River Lagoons (May 2000, August 2000 and December 2000) to collect pore water, lagoon water and seep water samples from twen ty-one separate sta tions (Martin et al. 2000, Lindenberg 2001). Eight sites were sample d in the Banana River Lagoon, (BRL1 to BRL8), and thirteen sites were sampled from the Indian River Lagoon, (IRL29 to IRL42). In all, 70 bottom water samples and 90 pore water samples were collected. In addition, ground water wells, a spring, and numerous rivers and inlets were also sampled. All of the water chemistry data used here ha s been taken from Lindenberg (2001). 2.1.1 Pore Water Samples Pore water sampling was done using a devi ce called the “multi-sampler” (Martin et al. 2003). It consists of a multilevel piezometer that is used along with a peristaltic pump to extract water from the sediment pore spaces at various depths. The design of the multisampler consists of 2” ID schedule 80 PVC pipe with ” OD (3/8” ID) PVC tubing fed through the interior of the pipe (Figure 2-1). The PVC tubing is glued to ports in the pipes and each port is screened with a 250 M screen ing material (Nytex). The ports exit the 2” pipe in a spiral fashion with each one locate d 90 offset from the ports above and below. The tubing is lead outside the PVC pipe thr ough a T-joint. Multi-sampl ers were driven as far as possible into the sediment using a ha mmer. The distribution of ports is variable along the length of the multi-sample r, with the ports more closely spaced at the top than

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14 at the bottom. This distribu tion allows higher resolution sa mpling of the pore water near the sediment-water interface wh ere concentration gradients are likely to change more rapidly with depth because of diagenetic r eactions (Martin et al. 2000). Some ports did not yield water when pumped, and presumably were located within sedimentary layers with low permeability. Once the multi-samplers were installed, they were left to equilibrate for about 24 hours before extracting water. Water was pumped at a rate of approximately 1 ml/s into a small plastic bucket and the dissolved oxygen concentration, conductivity and temperature were monitored, until the values remained constant. Once the values remained constant, their values as well as t hose of pH and salinity were recorded and water samples were collected. After sufficient water was available for chemical analyses, water was drawn from the bucket into a 60 ml syringe and filtered through a 0.45 m filter into two 125 ml HDPE Na lgene bottles that were prelabeled with the station and the date. One bottle was acidified with 50 l of 16 N optima grade HCl. The samples were collected for a variety of analyses including conservative chemical tracers and nutrients. This study focuses mainly on stations BRL 2 and BRL6. These stations were chosen because at BRL2 the multi-sampler penetrated to its maximum depth of 230 cm, with all ports yielding water when pumped, thus providing a good resolution to the pore water profiles.

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15 Figure 2-1. Design of a multi-sampler (from Martin et al. 2000).

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16 2.1.2 Lagoon and Seep Water Samples Seep water refers to all water that fl ows to the lagoon from sediments and rocks that underlie the lagoon, and is collected at the sediment-wat er interface. Seep water was collected using a device cal led “seepage meters” (Lee 1977). Seepage meters are constructed from the ends of 55-gallon drums. The ends of the drums are cut from the sides so that 15 cm of the drum wall remained attached to the ends. Half inch holes are drilled into the flat top in order to insta ll connectors for the seepage bags (4 L plastic bag). The seep meters channel the water flow ing from the sediment into the seepage bag for a known amount of time. The volume of water collected in the bag, divided by the length of time of the collec tion and the surface area covered by the seepage meter yields a seepage flux rate in units of volume of wate r per surface area per time (ml/m2/min). The method used to collect seep water was sim ilar to the method used to measure seepage rate. The single difference between measuri ng seepage rate and co llecting seep water samples is that the seepage bags were clean and dry prior to attach ing them to the seep meters. The bags were left on the seep meter until at least 1 L of water had flowed into the bags. After sufficient water was available for chemical analyses, the bag was removed from the seepage meter. Water was drawn from the bags into a 60 ml syringe and filtered through a 0.45 m filter into two 125 ml HDP E Nalgene bottles that were pre-labeled with the station and the date. One bottle was acidified with 50 l of 16 N optima grade HCl, while a third bottle was used to store unfiltered and non-acidifie d water samples. All samples were kept refriger ated until analyzed.

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17 Lagoon water samples were collected by submerging a 2 L plastic bucket approximately 25 cm below the water surface. Samples were preserved in the same way as water from the seep meters at BRL2 and BRL6. 2.1.3 Analyses Analyses of` pore water, seep water a nd lagoon water were conducted and reported by Mary Lindenberg (2001). Measurements were done in the Land Use and Environmental Change Institute (LUECI) La boratory, at the Department of Geological Sciences, University of Florida. Concentrations of PO4 and SiO2 were measured on the non-acidified filtered water samples, and NH4 were measured on acidified filtered water samples using spectrophotometric techniques following procedures described in Clesceri et al. (1989). Nitrogen and phos phorus concentrations were measured following Kjeldahl digestion measurement on a Technicon Autoan alyzer II for both f iltered and non-filtered samples. The concentrations of these samples were reported as tota l nitrogen (TN) and total phosphorus (TP) concentrations for the non-filtered samples. Filtered samples were used to measure total solubl e nitrogen (TSN), total soluble phosphorus (TSP), and NO3 concentrations, prior to Kjeldahl digestion of the sample. Precision1 of PO4 and NH4 analyses was checked by analyzing a check st andard every fourth sample, and calculating the coefficient of variation (standard deviat ion divided by mean) of the values measured for the check standard. Precisions of the TSN, TN, TSP, TP and NO3 concentrations were checked by analyzing duplicates every tenth sample. Precision of the various solutes is reported in Table 2-1. 1 Precision is the coeffici ent of variation, COV = 1 /mean

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18 Table 2-1. Estimated precision of va rious solutes for water samples. Solute Precision (%) PO4 2.6 NH4 2.5 TSN 1.5 TN 1.7 TSP 4.1 TP 2.2 SiO2 0.5 2.2 Sediment Cores Two separate cores were taken, one fr om BRL2 and one from BRL6 respectively during a sampling trip to the Banana River Lagoon in November 2001. The cores were collected using vibracoring t echnique, which allows retrieval of long (up to 10 m), continuous, sections from unconsolidated sa turated sediments. Vibracoring works on the principle of liquefaction in fine-grained sediments by displacing sediment to allow passage of the pipe (Smith 1984). The effec tiveness of the vibracore in relation to penetration and recovery is di rectly related to the physical properties of the material being sampled. The technique works best in saturated organic sedi ments, clays, silty clays, silts and fine sands, but is inefficient in firm clay s and medium to coarse sands (USGS, 1998). 2.2.1 Sampling At BRL2 and BRL6 coring was accomplished using a 2 m long section of aluminum pipe as the core barrel, with an internal diameter of ~ 7.5 cm. The pipes were cut to a point and sharpened at one end to allow easy penetration (Figure 2-2). Once the pipes had been driven to a depth of ~1.9 m, the open end was capped to provide a slight vacuum as the pipes were retrieved. The pipes were then pulled out of the sediment using a winch and steel cable. Compaction for the co res was about 16 %. This was measured by

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19 calculating how much of the core had slumped within the pipe, prior to sectioning. Excess water was removed from the upper portion of the pipes, and the pipes were trimmed at both ends, without disturbing th e core. Top and bottom were marked on the pipe ends along with the core name and length of the section. The ends of the pipes were sealed with rubber caps and el ectrical tape. Compacted core lengths retrieved were 1.57 m and 1.62 m sediment from BRL2 and BRL6 re spectively. Both cores were transported to the Florida Institute of Paleoenvironmen tal Research (FLIPER) Laboratory, at the Department of Geological Sciences, University of Florida, while remaining vertical in order to minimize mixing. Figure 2-2. Vibracoring techni que being used to colle ct the sediment core. In the laboratory, the cores were split lengthwise, describe d, photographed and sampled two days after coring was completed. One section was used to measure sediment bulk density, and take high-resolution digital images (40 pixels/cm) of the entire core lengthwise, using the Geotek Multi-sensor Core Logger (MSCL). The accuracy of the

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20 bulk density was determined using a standard aluminum density calibration piece (Weber et al. 1997). The other section was used to take samples for measuring porosity, total carbon (TC), total nitrogen (TN), total phosphor us (TP), total organic matter (OM), and biogenic silica (SiO2). Samples were collected at 2 cm intervals. Before sample material was removed from the core barrels, the split surfaces were prepared by scrapping off the top few millimeters of the core to remove any contaminated material that may have originated during splitting. Sectioning was accomplished using a serrated knife, washing and drying the knife after each section. Each s ection was removed carefully and stored in a labeled, pre-weighed 25 ml Fisher brand plastic bottle. Each sample (bottle + wet sediment) was weighed, and then freeze-dried. 2.2.2 Analyses After freeze-drying, the samples were gen tly crushed to break up large lumps of sediment, shells and any other debris. Crushing was done by hand, using a ceramic mortar and pestle. Crushed sample material was well mixed and transferred back into their bottles. Percent porosity was calcul ated by using the formula: 100 Porosity % WS DS WSM M M where MWS = mass of wet bulk sediment, and MDS = mass of dried sediment. TC and TN were analyzed using a Carl o Erba NA 1500 analyzer, in the Stable Isotope Laboratory, at the De partment of Geological Scienc es, University of Florida. Approximately 60-100 g of sample was placed in tin c ups and dried under a heat lamp. TC and TN were determined following combus tion at 1000 C. Precision of the analyses

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21 was checked by analyzing duplicates every tenth sample, and calculating the relative percent difference (RPD), which is the absolu te difference between the duplicates divided by the mean of the duplicates (Table 2-2.). For BRL2 and BRL6 the average RPD for TC was 4.4 %, (largest difference 5.7 %), wh ereas the average RPD for TN was 4.1 % (largest difference 7.1 %). Total phosphorus was analyzed using a Br an-Luebbe Autoanalyzer, in the LUECI Laboratory, at the Department of Geological Sciences, University of Florida. To 0.05 g of dry mass sample 20 ml of 0.53 M sulfuric acid and 10 ml of 0.062 M potassium persulfate was added. The batch was sonicated for ten minutes. It was then placed in an autoclave for thirty-five minut es at about 100 C. Finally, 1 ml of the solution was added to 10 ml of 0.1325 N NaOH. All samples were centrifuged at 1500 rpm before analysis. Precision2 of the analyses was checked by analyz ing duplicates every tenth sample, and calculating the RPD. For BRL2 the average RPD was 2.5 %, and for BRL6 the average RPD was 2.2 % (largest difference 3.6 %). Biogenic SiO2 was also analyzed using the Bran-Luebbe Autoanalyzer, in the LUECI Laboratory, at the Department of Geol ogical Sciences, University of Florida. To 0.05 g of dry mass sample 40 ml of 5 % Na2CO3 solution was added. The batch was sonicated for ten minutes, and then placed in an autoclave for thirty-five minutes at 100 C. Finally, 1 ml of the solution was added to 9 ml of 0.105 N HCl. All samples were centrifuged at 1500 rpm before analysis. Pr ecision of the analyses was checked by analyzing duplicates every tenth sample, a nd calculating the RPD. For BRL2 the RPD was 1.4 %, and for BRL6 the RPD was 0.8 % (largest difference 1.9 %). 2 Precision is the Relative Percent Difference, RPD = (|x1-x2|)/xmean.

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22 Loss on ignition is a common and widely us ed method to estimate the total organic matter content of sediments (Dean 1974, Be ngtsson and Enell 1986). Approximately 2.0 g of dry mass sample was oxidized at 550 C in a muffle furnace for two hours. The weight loss during the process was measured by weighing the samples before and after heating. The difference in weight represente d the total organic matter content of the samples. An attempt was made to estimate sediment ation rates using measurements of the activity of naturally occurring radioisotopes in sediments. The method used is based on determining the activity of 210Pb (half-life 22.3 years), a decay product of 226Ra (half-life 1622 years) in the 238U decay series. Age at depth in sediments is determined from stratigraphic profiles of unsupported 210Pb (daughter product of 226Ra present in the sediment). Total 210Pb activities were measured by subtracting the supported 210Pb in equilibrium with 226Ra. Radiometric measurements were made using low background gamma counting systems with germanium det ectors (Schelske et al.1994). Activities for each radionuclide were calculated using empi rically derived factor s of variation in counting efficiency with sample mass and height (Schelske et al. 1994). Samples were prepared by packing plastic test tubes up to 3 cm with dry sediment. The amount of sediment packed was weighed, and the tubes we re then sealed with a mix of epoxy resin. They were set aside to equilibrate for three weeks before analysis. Table 2-2. Estimated precision of various sediment sample analyses Analyses Precision (%) BRL2 Precision (%) BRL6 TC 4.4 4.4 TN 4.1 4.1 TP 2.5 2.2 SiO2 1.4 0.8

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23 CHAPTER 3 RESULTS 3.1 Physical Analyses Physical analysis of cores such as type of sediments, color, texture, grain size, etc. can provide information that may be useful to compare with chemical analyses. For example, clay or dark muddy sediment is us ually rich in organic matter, compared to light siliceous sand. Sediments that have not been buried ap preciably, say less than about one meter, are subject to mixing by benthic or ganisms due to activities such as feeding and burrowing (Aller 1980, Berner 1 980, Sandnes et al. 2000, Boudreau 2000). Organisms such as crabs, snails and worms, mix surface sediments simply by crawling or plowing through it. Hence, the presence of burrow formations within sediments could correspond to mixing zones. 3.1.1 Description of Cores The core recovered from BRL2 is approximately 157 cm in length. Images taken from BRL2 allow the core to be categorized into five diffe rent zones (Figure 3-1). The upper 20 cm of BRL2 is composed of fine-gra ined, light siliceous sand, interspersed with large (~ 1.5 cm) calcareous shells. The sh ells are mostly molluscs (bivalves and gastropods), and most of them appear well preserved and intact. Between 20-30 cm depth the sediment composition and texture changes. At this depth the sediments are composed of dark muddy sand inter-layer ed with greenish clay lenses. Between 40-50 cm depth the composition of the sediment remains muddy sand, void of any clay lenses. A gradual transition in the composition of the sedi ment appears around 50 cm, changing from

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24 muddy to a dark siliceous type of sand, composed primarily of quartz sand grains. The next 90 cm of the core, between 50-140 cm dept h is composed entirely of dark siliceous sand, which is interspersed with small (~ 0.4 cm) calcareous shell fragments. At this horizon numerous vertical burrows occur as dark striations along the section. X-ray imaging has also identified the presence of these borrows. The bottom 17 cm between 140-157 cm is composed of light fine-grained siliceous sand, totally de void of any shells. In general core BRL6 shows a greater variation in composition compared to BRL2, however fewer burrow formations. The core recovered from BRL6 is approximately 162 cm long. The core is divided into eight zones on the basis of its sediment color, texture and composition. Two zones may be considered as transition zones, because they show subtle variations within the sediment suite (Figure 3-2). The upper 10 cm of BRL6 is composed of light siliceous sand, shell fragme nts, and fresh plant debris, such as weeds and roots. The horizon between 10-30 cm dept h is composed of light siliceous sand, but devoid of plant debris. Small burrows are also preserved within this zone. A thin layer of about 5 cm thickness, between 30-35 cm depth, is composed largely of calcareous shell fragments. Between 30-55 cm depth the amount of shell fragments decreases and the fraction of muddy sand increases. The sedime nts between 55-80 cm depth are almost entirely composed of dark muddy sand, with only few scattered frag ments of calcareous shell. The next 30 cm, between 80-110 cm depth, is completely composed of a dark clay layer, possibly reflecting a change in deposit ional environment. A horizon of dark muddy sand, devoid of any shell fragments occu rs between 110-135 cm depth. The bottom 27 cm, between 135-162 cm depth, shows a gradua l transition from dark muddy sand, to light siliceous sand.

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25 Figure 3-1. Sediment Core from BRL2. Images to the right are real photographic images of short sections of the core representing the five zones. 22 cm 2 cm 5 cm 5 cm 5 cm Real Ima g e Diagram Descri p tion

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26 Figure 3-2. Sediment Core from BRL6. Images to the right are real photographic images of short sections of the core representing the eight zones. 5 cm 5 cm 6 cm 5 cm 4 cm 1 cm 4 cm 2 cm Real Ima g e Diagram Descri p tion

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27 3.1.2 Porosity At BRL2, porosity ranges between 20-42 %, with an average of ~ 31 % (Figure 3-3 a). Two zones exhibit higher poros ity than the rest of the core the first at a depth between 20-30 cm, and the other between 110-120 cm depth. Both these zones of low porosity correspond to layers containing cl ay. Since clays are a lot more porous than sands it is not surprising that we observe these peaks. In ge neral, porosity of the sediments at BRL6 is slightly greater than at BRL2. Porosity valu es at BRL6 range between 35-58 %, with an average of ~ 39 % (Figure 3-3 b). A zone of hi gh porosity than the rest of the core occurs between 80-120 cm depth, similar to BRL 2 corresponding to a thick clay horizon. (a) (b) Figure 3-3. Porosity of sediment (a) BRL2, (b) BRL6.

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28 3.1.3 Density The bulk density of the sediment was m easured using the Geotek Multi-censor Core Logger, at every 1 cm section through out the entire core. These values occasionally reflect the type of sediment, for example, shelly zones show higher bulk density as compared to soft sandy or clayey ones. At BRL2 the bulk density values ranged between 1.70-2.15 gm/cc (Figure 3-4 a). A high density at depth of ~18 cm probably reflects the high concentration of large calcareous shells seen within that zone. At BRL6 (Figure 3-4 b) the bulk density values are fairly cons istent, ranging between 1.80-1.90 gm/cc, except between the depths of 80-110 cm where the va lues drop to as low as 1.58 gm/cc. This sudden drop in bulk density corresponds to th e clay horizon that ex ists at that depth. (a) (b) Figure 3-4. Bulk Density of sediments (a) BRL2, (b) BRL6.

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29 3.2 Chemical Analyses Regeneration and release of nutrients fr om estuarine sediments are controlled by the concentrations and burial rates of organic carbon, nitrogen and phosphorus. Thus, concentrations for organic C, N and P in sediment may provide information on the potential flux of nutrients from sediments to the overlying water. The information of nutrient concentration in the pore waters from previous work (Martin et al. 2000, Lindenberg 2001), coupled with the concentratio n in the sediment column from the two sites under study, can provide a better unders tanding of nutrients and organic matter content up to ~ 2 m below the sediment-water interface. At both sites the sediments are relatively low in organic C, N and P, although concentrations of TC, TN and TP within the sediments are greater at BRL6 than at BRL2. Sediments from BRL2 represent a typical open lagoon sandy environment (deeper water and further away from shore than BRL6), w ith low organic matter content. Thus the two sites provide a useful variety of sedi mentary environments within the lagoon. 3.2.1 Total Phosphorus (TP) and Total Nitrogen (TN) Sediments from BRL6 tend to have sli ghtly higher TP and TN concentrations relative to BRL2. Total P concentrations for BRL2 range between 0.0010.1 mg/g (Figure 3-5 a). Two distinct peaks occur between depths 22-38 cm, and 116-138 cm respectively. The TP concen tration at BRL6 ranges betw een 0.001-0.19 mg/g (Figure 3-5 b). A large peak in the co ncentration can be seen between 80-110 cm, corresponding to the distinct organic rich clay layer. Tota l P concentrations below 120 cm at BRL6 are below the methods detecti on limit of 0.001 mg/g TP. Total N concentrations at both sites are slightly higher than TP. The TN concentration at BRL2 ranges between 0.001-0.2 5 mg/g (Figure 3-6 a). Concentrations

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30 increase steadily to a depth of 30 cm fo llowed by a gradual drop. The TN concentration at BRL6 ranges between 0.1-0.28 mg/g (Figure 3-6 b), with a sudden peak (~ 0.75 mg/g) observed at a depth of 38 cm. 3.2.2 Total Organic Matter (OM) The concentration of total organic ma tter represents a sum of all organic constituents within the sediment column (e.g. organic carbon, nitrogen and phosphorus). While values less than 5 mg/g OM occur th rough much of the sedi ment column at BRL2, sharp deviations (peaks) up to 28 mg/g OM ar e seen at 20 cm depth (Figure 3-7 a). At BRL6, OM concentrations are as high as 44 mg/g, with numerous peaks seen between 35-80 cm (Figure 3-7 b). By subtracting th e TP and TN fraction from OM we can calculate the total organic car bon (TOC) present in the sedime nts. Since the concentration of TP and TN is almost an order of magn itude lower than OM, the emerging profile of TOC is not very different from OM. 3.2.3 Total Carbon (TC) The total carbon content within the sediment represents both the organic and the inorganic/carbonate fraction. Con centrations of TC in the sediments from both BRL2 and BRL6 show some variability with depth. At BRL2, TC concentrations range between 1-4 % through out the sediment column (Figure 3-8 a). A zone of high concentration is observed between 20-30 cm corresponding to the cl ay lenses that exist within that zone. BRL6 on the other hand shows slightly high er concentrations of TC matter, ranging between 1-8 % (Figure 3-8 b). A significant peak within the clay zone is observed between 80-110 cm.

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31 By subtracting the TOC fraction from TC we can calculate the total inorganic carbon (TIC) that is present in the sediment s. Figure 3-9 a, b compares the TOC-TIC fraction of the total carbon present in the sediments at BRL2 and BRL6 respectively. 3.2.4 Biogenic Silica (SiO2) At BRL2 the SiO2 concentrations are fairly co nstant throughout the sediment column, ranging between 2-11 mg/g (Figure 3-10 a). A gradual increas e in concentration is observed between 80-120 cm depth. While at BRL6 the SiO2 concentration ranges between 1-15 mg/g, except for a sharp p eak (~ 15 mg/g) between 80-110 cm depth corresponding to the clay zone (Figure 3-10 b). 3.2.5 210Pb and Sedimentation Rates Both cores were extremely difficult to date because of the nature of the sediments within the upper 20 cm. Since they contained very little organic matter and are mostly composed of sand (Figure 3-1 and 3-2), very low Pb-activity was measured. This is because sand particles have small surface area per unit volume, which makes it difficult for metal ions to get adsorbed on it, unlike cl ays. However, within the upper 6 cm in the sediment some unsupported 210Pb was present, and by usi ng only one data point we managed to calculate the sedimentation rate s for BRL2 and BRL6 to be 0.6 cm/yr and 0.8 cm/yr respectively (Table 3-1). Sediments below 6 cm contained no unsupported 210Pb, hence could not be dated. Table 3-1. Estimation of sedimentation rates at BRL2 and BRL6 using gamma detectors. Depth (cm) Excess 210Pb inventory (dpm/cm2) Age at depth (yr) Mass accumulation rate (mg/cm2/yr) Sedimentation rate (cm/yr) BRL2 0-2 2.362 31.0 125.7 0.6 BRL6 4-6 1.378 20.0 153.0 0.8

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32 However, in trying to estimate sedimentati on rates using this technique we violated a number of assumptions. Hence we estimated sedimentation rates for Banana River Lagoon by comparing it with sea-level rise along the east coast of Florida in the past 100 years. It has been estimated that within the past 100 years sea-level rise is ~ 1-2 mm/yr (Jaeger et al. 2002, unpublished). Hence, by us ing average particle density of 2.0 g/cm3 we calculated sedimentation accumulation rate to the Banana River Lagoon to be ~ 200 mg/cm2/yr.

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33 (a) (b) Figure 3-5. Total phosphorus concentra tions in sediment (a) BRL2, (b) BRL6.

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34 (a) (b) Figure 3-6. Total nitrogen concentrati ons in sediment (a) BRL2, (b) BRL6.

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35 (a) (b) Figure 3-7. Total organic matter in sediment (a) BRL2, (b) BRL6.

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36 (a) (b) Figure 3-8. Total carbon concentrati ons in sediment (a) BRL2, (b) BRL6.

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37 (a) (b) Figure 3-9. Concentration of total organic and total inorganic carbon present in the sediment at (a) BRL2 (b) BRL6.

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38 (a) (b) Figure 3-10. SiO2 concentrations in se diment (a) BRL2, (b) BRL6.

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39 CHAPTER 4 DISCUSSION 4.1 Introduction One of the most important consequences of early diagenesis is the control it exerts upon the chemical composition of shallow pore wa ters. If diagenetic chemical reactions occur close to the sediment-water interface, sharp concentration gradients may result within shallow pore waters. These changes in concentration of dissolved species in the pore waters will be important to fluxes of t hose species if discharged to the overlying lagoon through diffusive, and possibly advectiv e processes. For example, bacterially mediated chemical reactions in sediments and sediment pore water release dissolved ammonia and phosphate from decomposing or ganic matter. When concentrations of dissolved ammonia and phosphate build to elev ated levels in surficial sediments, an excess nutrient flux passes into the overlyi ng water column. This could be possible if there are unnaturally high con centrations of solid phase P and N present in the sediments to begin with. Shallow lagoon waters ar e typically higher in dissolved oxygen concentration than the underl ying pore waters. However, if there is re-circulation of lagoon water through the sediments, then th e cycling of oxygenated water through the sediments could control organic matter re generation at depths greater than a few centimeters below the sediment-water interface. Part of this study was designed to dete rmine the magnitude of the nutrient flux from the sediment to the overlying lagoon wate r at the sediment-wat er interface from two selected sites in the Banana River Lagoon, and compare it with the input flux brought

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40 about by surface runoff and sedimentation. The ca lculations of these fluxes are described later in the chapter. 4.1.1 Conceptual Model The concept of mixing in shallow marine sediments has been the focus of discussion for over two decades. A number of theories have been proposed that may cause this mixing, for example, bioirrigati on and bioturbation (Korosec 1979, Emerson et al.1984), wave action and tidal pumping (S hum 1992, 1993, Li et al. 2000), and fluiddensity fluctuations (Rasmussen et al. 2003). Re gardless of the process or processes that may cause this mixing, each one may be an important transport mechanism that can carry substantial amount of dissolved solutes fr om the sediments to the overlying water column. Mathematical modeling of these sorts of mixing processes is difficult because of the variety, irregularity, and complexity of each mechanism. The magnitude of these mixing processes should be important for nutri ent fluxes because of the increased organic matter regeneration that would occur in shallo w sediments as a result of diagenesis or metabolic activities of plants and micr oorganisms. Mixing of lagoon and pore water would also be important in estimating fluxes of other dissolved constituents because of the volume of water associated with advection. Pore water profiles of conser vative solutes, such as Clsuggest that there is significant amount of mixing be tween the shallow pore wate r and the overlying lagoon water in the Banana River Lagoon (Martin et al. 2000, 2001). This mixing is shown by changes through time in the concen trations of conservative so lutes at depths up to 70 cm within the sediment column, with little cha nge through time in thei r concentrations at depths below 70 cm (Figure 4-1).

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41 Figure 4-1. Clprofile concentration suggesting mi xing in shallow sediments in the Banana River Lagoon (BRL). C.Z = Coastal zone, FW = Fresh water, U.A = Unconfined aquifer, C.A = Confined aqui fer, AT = Aquitard (Inset of the Clprofile taken from Martin et al. 2000). If there is significant amount of mixing betw een lagoon and pore waters, then not all of the nutrients in the s eep water can be considered a new flux to the lagoon. Some nutrients dissolved in the seep water could be brought into the shallow se diments along with the lagoon water prior to flow through the sediment Nutrients could also originate from the upward flow of ground water. New sources of nutrients from ground water would be small, because nutrient concentrations in ground water are lower than in pore water and because ground water appears to be < 5 % of the seep water (Martin et al. 2000). This

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42 would suggest, that the re-circulation of lagoon water within shallow sediments could provide a mixing mechanism that could drive a large nutrient load to the lagoon, as well as remove a certain amount from the lagoon (Fig ure 4-2). This part of the nutrient cycle could be important and needs to be included in future estimates of nutrient reservoirs and budgets, even though it would represent a natural flux. The physical mechanism that drives this mixing is unknown, but must be consid ered as an important source of nutrients to the lagoon; because if excess nutrients are carried to the la goon from anthropogenic sources such as agricultural runoff or from septic tanks, the remediation of such a problem requires good information on the co mplete nutrient cycle in the lagoon. Figure 4-2. A conceptual model showing mixing at the sediment-water interface due to bioturbation or wave action. L.W.= Lagoon Water, S.W.= Seep Water, P.W. = Pore Water. B = Worms burrowing into sediment and ingesting sediment particles. Lagoon water recirculation due to wave action and tidal pumping Pore water circulation due to bioturbation cm 1 2 3 4 5

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43 4.2 Sediment Profiles An important factor that c ontrols the nature of the nut rient fluxes to the lagoon is the chemical composition of the bottom sediments. For example, sediments with high organic matter concentrations could provide a major source of the nutrient load. Physical properties of sediments, such as permeability, could also affect the nature of these fluxes by controlling the discharge rate of water through the sedime nts. Variations in both the concentration of various constituents in the sediments and their physical properties suggest that a very complex hydrodynami c system exists at BRL2 and BRL6. 4.2.1 Correlation Between Physical Propert ies and Ground Water Discharge Rates The porosity of the sediment is importan t because it controls the volume of water being exchanged. However, the rate of ground water discharge depends on the permeability of the sediments. One of the factors affecting porosity of sediments is bioturbation. Construction of burrows, and cons tant irrigation of thes e burrows result in a higher water content of sediments than w ould result in the absence of bioturbation (Berner 1980, Sandnes et al. 2000). The sediments from BRL2 show a uniform distribution of porosity through out the entire core, with the exception of the uppe r 30 cm where the porosity increases from 2040 % (Figure 3-3 a). This gradual peak in porosit y could be a result of the clay lenses that exist at this depth. The low porosity values within the upper 20 cm ma y be an artifact of losing some moisture at the time of transportation. The porosity shown by the sediment types found at BRL2 may also be a result of composition within the sands. While the small range in porosity reflects uniform gr ain size, sediment compaction with depth, could decrease the porosity. Visual observat ions of the sediments may provide a crude correlation between type of sediment and gr ound water discharge rate s. The presence of a

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44 shell hash layer in the upper 20 cm may provi de greater permeability for the discharging water, and hence, a slightly higher ground water discharg e rate of 44.5 ml/m2/min compared to BRL6 (Martin et al. 2000, Lindenberg 2001). At BRL6 the porosity of the sediments ranges between 35-58 %. Although the values are uniform up to 80 cm depth, a sharp pe ak in the porosity from 40-58 % is seen at depths between 80-120 cm (Figure 3-3 b). This sudden increase in porosity may have been a result of the thick clay layer that exists at that dept h (Figure 3-2). The presence of these clay horizons may act as aquitard s and obstruct the flow of water though the sediments. Hence, probably the reason w hy we observed slightly lower ground water discharge rates at BRL6 of 18.7 ml/m2/min, compared to BRL2 (Martin et al 2000, Lindenberg 2001). Using these observations to generalize for the entire lagoon should be done with caution since these observations consider ~ 160 cm cores from just two locations. Besides, a number of factors othe r than variations in permeability may be responsible for the differences in ground wa ter discharge rates between BRL2 and BRL6. These factors could include heterogeneous distribution of underlying confining layers, and variability in compaction and permeability of bottom sediments. 4.2.2 Density The bulk density of the sediment tends to reflect the type of sediment under study. For example, calcareous shelly zones t ypically correspond to higher bulk density compared to soft sands or clays. The bulk density of sediments at BRL2 ranges between 1.70-2.15 g/cc (Figure 3-4 a). A prominent peak of 2.15 g/cc occurs at a depth of 18 cm and corresponds with the layer of shell ha sh that exists at that depth (Figure 3-1). At BRL6 the bulk density of the sediments range between 1.6-2.0 g/cc (Figure 3-4 b). While a small peak of 2.0 g/cc corresponds with the thin veneer of fragmented calcareous

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45 shells observed at a depth of 35 cm, a sudden drop in bulk density to 1.6 g/cc between 80110 cm corresponds to the soft clay zone that exists at that depth (Figure 3-2). One reason why we observe a decrease in bulk density in the clays is because they may contain lowdensity, hydrated silicate minerals such as kaolinite, montmor illonite and opal. 4.2.3 Total Organic Matter as a Source of Nutrients High organic matter content in sediment s is usually associated with high sedimentation rates in environments ranging from the upper continental slope and outer shelf to near-shore deltas, bays and estu aries (Berner 1980). High OM is important because most of the early diagenetic change s exhibited by the sedi ments relate to the microbial decomposition of organic matter. Tw o factors are responsible for the high OM in the sediment. The first is the extent of biological productivity in the overlying water, which depends on the input of nutrients from surface runoff. The second is sedimentation rate, because rapidly deposited sediments are buried past the zone where redox reactions may regenerate the OM. The low concentration of OM content m easured in the sediment at BRL2 and BRL6 occur because the sediments are almost entirely composed of sand, and typically sandy sediments do not contain as much organics as clays. The reason for this is that coarser materials such as sand grains have lower surface area per unit of mass or volume compared to clays. Most chemical reacti ons in the sediments occur at the mineralsolution interface. Consequentl y, the lower the surface area, th e less chemically active the sediment may be, particularly with respect to weathering reactions, adsorption of solutes, and adsorption of organic matter. One reas on why sediments from BRL6 are slightly enriched in OM compared to BRL2 is proba bly because of its location. Site BRL2 is located in deeper waters out in the open lagoon, hence sedi ments from site BRL2 may be

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46 slightly older than BRL6, as a result may ha ve lost greater amount of OM through time. Even though the sediments from BRL2 and BRL 6 are almost entirely composed of sand, the clay horizons suggest that they may have retained some of the organic matter that escaped the destruction by organisms prior to burial. An important question is whether low concentrations of OM in the sediments are sufficient enough to provide a source of nutrients that can support the measured nutrien t fluxes to the lagoon (Martin et al. 2002). 4.2.4 Comparison of Total Phosphorus (TP) and Total Nitrogen (TN) with Nutrient Fluxes There are several sources of nutrients to the Banana River Lagoon. One such source is from surface water runoff, including anthr opogenic sources as a result of urbanization around the lagoon. Atmospheric deposition provides other sources of nitrogen. Remineralization of organic matter in the sedi ments provides another source of nutrients to the lagoon (Reddy et al. 1999). Inversely, the precipitation of apatite within the sediments through authigenic mineralization processes could remove some of the phosphorus from the sediment pore waters th at may be available for organic matter remineralization. Besides, the slow sediment ation rate (1-2 mm/yr) provides sufficient time for almost all of the P and N in the sediment to be remineralized and flushed back into the lagoon prior to burial. Finally, the circulation of la goon water through the sediments could further oxidize some of the P and N from the sediments. Previous estimates of nutr ient fluxes from sedimentar y sources have considered only diffusion as a transport mechanism (e .g. Trefry et al. 1992, Reddy et al.1999). The effect of remineralized nutrients to th e total nutrient budget of the lagoon would be greater than those pr ovided by diffusion alone (Marti n et al. 2000). However, low concentration of TP and TN in the sediments compared to seep water concentrations at

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47 BRL2 and BRL6, suggest that the sediment s alone could not have supported the high nutrient fluxes measured by the seep meters. Th e elevated concentrations of nutrients in the seep water are similar to the concentrations in the pore waters less than a couple of meters below the sediment-water interface (Martin et al. 2000). Although this may suggest that much of the nutrients in the s eep water are derived from the remineralization of organic matter within shallo w lagoon sediments, the rate and extent of mineralization depends on the availability of dissolved oxyge n (Froelich et al. 1979). If so, then the concentration of nutrients in the seep water measured using a seep meter does not provide a realistic estimate of the nutrient concentrati on and its associated fl uxes, because of the limited availability of oxygenated water trappe d inside the seep meter. Extrapolating these fluxes to the entire lagoon could provide an erroneous estimate of the potential magnitude of the flux of nutrients from sediments. 4.2.5 Redfield Ratios and their Signif icance to the Banana River Lagoon The two major sources of organic matter are terrestrial and marine plants and animals, and each have distinct C:P:N ratio s. Marine phytoplankton have a mean molar organic C:P ratio of 106:1, mean molar C:N ratio of 6.6:1, a nd mean molar N:P ratio of 16:1 (Redfield et al. 1963). In contrast, terre strial plants are im poverished in P and N relative to C, with characteristic C:P ra tios ranging up to or exceeding 800, and C:N ratios ranging up to or exceeding 1000 (Likens et al. 1981, Ruttenberg and Berner 1993). However, the presence of certain type of marine sea-grass ( Halodule wrightii ), algae ( Gracilaria sp.) and epiphytes could raise the Redf ield ratios consider ably. For example, average C:N:P in Halodule wrightii is 174:8:1, in Gracilaria it is 897:56:1 and in epiphytes it is 392:158:1 (Mont ague and Henley 2003, unpublishe d). If we assume that most of the organic matter in near-shore marine sediments such as the Banana River

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48 Lagoon is derived from marine phytodetritus, th en zones within the sediments that show higher C:P, C:N ratios suggest an abundance in growth of Halodule wrightii and Gracilaria sp. The importance of making such an observation lies not only in understanding the sources of organic matter to ma rine sediments, but also in assessing the overall influence it may have on the lagoon. The presence of these of marine planktons such as Halodule wrightii and Gracilaria sp. has been reported in the past (Montague and Henley 2003, unpublished). Halodule wrightii dominate in the northern region of the Indian River Lagoon, while Gracilaria sp. are drifting algae which are highly producti ve, abundant throughout the entire lagoon. The relatively high Redfield ratios at BRL 2 and BRL6 suggest that the sediments have been influenced by these spec ies of phytoplanktons th at are enriched in C, N and P (Figure 4-3 and 4-4). The C:P Redfield ratios between observed at BRL6 between 80-110 cm depth are almost five times lower than the expected Redfield values of 106:1 for marine sediments. One possible ex planation for that could be the authigenic mineralization of apatite that may account for the excess organic P present in that horizon. This precipitation of organic P to fo rm apatite is favored by the presence of CaCO3 in the form of shell fragments (Figure 3-2) whose surfaces act as a nucleating agent for apatite crystallization (Morse 1978, Berner 1980). Similar observations within carbonate sediments of Bermuda and Florida Bay, whose pore waters are saturated with respect to apatite has been demons trated in the pa st (Berner 1974).

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49 Figure 4-3. Redfield ratios of organi c C:P:N within sediments at BRL2.

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50 Figure 4-4. Redfield ratios of organi c C:P:N within sediments at BRL6.

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51 4.3 Emerson’s SiO2 Mixing Model Planktonic diatoms (plants) a nd radiolaria (animals) living in the surface waters of oceans and lagoons secrete skeletons consisti ng of opaline (amorphous) silica. Once they die, their siliceous remains settle to th e bottom and undergo dissolution. However, most of the dissolution occurs dur ing settling, but some may also occur at the bottom (sediment-water interface). Evidence for dissolu tion in shallow pore waters in the Banana River Lagoon is provided by concentrations of dissolved SiO2 in sediment pore water at BRL2, which are always higher than those in the overlying lagoon wa ter (Martin et al. 2000). Several models for the early diagenesis of SiO2 have been proposed (e.g. Hurd 1973, Wollast 1974, Schink 1975). The most comple te model treated di ssolution in terms of “reactive” or soluble silica to differentiate it from other less reactive forms such as crystalline silicate minerals (Berner 1980). Reactive SiO2 is presumed to be the opaline fraction of biogenic SiO2, and hence more soluble than th e crystalline fraction. However, the rate of dissolution of freshly deposited si liceous plankton may vary, and as a result of incomplete dissolution some opaline silica may accumulate in the sediments. 4.3.1 Introduction Emerson et al. (1984) proposed that the ulti mate fate of most reactive inorganic and organic matter introduced to Puget Sound depends on the chemical and physical processes that occur at the estuarine sedi ment-water interface. He suggested that mechanisms other than sedimentation and mo lecular diffusion were necessary to explain chemical or isotopic distribut ions in the sediments and pore waters. Benthic animal feeding and respiratory activities are impor tant processes near the sediment-water interface in all oxic aquatic environments. Wherever there is significant amount of biological activity, transport mechanisms may be increased. In near-shore, high-energy,

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52 environments such as estuaries these proce sses are rapid enough to influence transport within the sediment pore waters. Since anim al respiratory activities (and sometimes physical actions such as tides and waves) aid in the ventilation of the sediments, it is important to determine the feas ibility of generalizing these exchange mechanisms so that meaningful predictions for pollutants, such as excess nutrients, can be made. The transport mechanisms were evaluated using a one-dimensional model with a “non-local” (Imboden, 1981) source term to describe the distribution of silicates within the pore water. 4.3.2 The Model The movement of pore water within sediments can be cat egorized into two means of transport based on the characteristics of the pore water chemistry (Emerson et al. 1984). The first transport mechanism is char acterized as random motion and formulated as a diffusion process. The second transport mechanism is analogous to pumping models. The process is represented as a “non-local” source or sink term ( ) with dimensions of time-1. This term was coined by Imboden (1981), and simply means any mode of transport that is capable of exchanging material between nonadjacent points in the sediment, or between the overlying water and points in the sediment removed from the sediment-water interface (Imboden 1 981, Emerson et al., 1984, Sandes 2000). Mathematically the problem is formulated as one-dimensional diffusion with a non-local term and reaction: R C C z C K t C ) / (0 2 2 (4.1) (Emerson et al. 1984).

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53 Where is the rate parameter used to evaluate the non-local source. C is the concentration of a reactive solute in the bulk sediment (in this case SiO2 concentration) at depth z C0 is the concentration of dissolved SiO2 in the overlying water. R is the reaction term, that includes the rate of reaction, and K is the sediment diffusion coefficient, that includes the correction to the diffusion coeffi cient D at infinite dilution necessary for tortuosity ( ), i.e. K = D / 2 (Berner 1980). Since porosity () varies little with depth in se diments from BRL2 (Figure 3.3 a), K is also assumed to be constant with depth in the sediment in order to use the analytical solution. Tortuosity is a difficult parameter to measure directly, and thus a variety of empirical relationships between tortuosity and porosity have been developed. The best fit to available data takes the form 2 = 1 – ln(2) (Boudreau 1996). The boundary conditions required for the so lution of equation (4.1) depends on the physical characteristics of the particular setting. In order to describe silicate profiles in the sediments we assume (i) steady state, i.e. SiO2 concentration at a given depth re mains constant with time so that, C/t = 0, and (ii) that the rate of dissolution of diatoms is a first order. Using k as the first order rate constant (i.e. the dissolution rate of opal), equation (4.1) becomes: ]) Si [ ] Si ([ ) / ] Si [ ] Si ([ ] Si [ 00 2 2 ak dz d K Rearranging,

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54 / ] Si [ ] Si [ ] Si )[ ( ] Si [ 00 2 2 ak k dz d K (4.2) where [Si]0 = local concentration of por e water at depth 0, and [Si]a = asymptotic concentration of pore water (i.e. co ncentration value below which SiO2 concentration remains unchanged). The boundary conditions used are / [Si] [Si] 0, at 0 z G z Z zz 1[Si] at 1 (4.3) where Z1 is the bottom boundary depth in the sediment, and G is the gradient in [SiO2] at z = Z1. Using the above boundary conditions the solutio n to equation (4.2) was assumed to be / [Si] / [Si] [Si] ) cosh( ) cosh( ) sinh( ) / ] Si ([ ) 1 ( / ] Si [ ] Si [ ) ]( Si [0 0 1 ) ( ) ( 1 0 01 1a Z z Z z z z ak Z e e Z z G e e k z (4.4) (Emerson et al. 1984). where = ( / K )1/2 and = ( k + ).

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55 Table 4-1. Description and values of parame ters used in the model for BRL2. Parameter Description Value Reference k (s-1) Opal dissolution rate 5 10-7 (at 10 C) 23 10-7 (at 29 C) Emerson et al. 1984 K (cm2 s-1) Molecular diffusion coefficient 10-5 (at 30 C) Wollast et al. 1971 Emerson et al. 1984 Diffusion coefficient representing enhance mixing 10-3 (fast regime) 10-4 (slow regime) [Si]0 (M) Bottom water silica concentration 16 10-6 (May 2000) 45 10-6 (Aug. 2000) 22 10-6 (Dec. 2000) Martin et al. 2000 [Si]a (M) “Asymptotic” pore water concentration 130 10-6 (May 2000) 172 10-6 (Aug. 2000) 122 10-6 (Dec. 2000) Martin et al. 2000 Porosity 0.31 This study Z1 (cm) Bottom boundary (sediment) 110 Asymptotic depth G Slope of [Si] profile beyond the asymptotic depth 0 Assumption (s-1) “non-local” source parameter 0 (molecular diffusion) 4 10-7 (enhanced mixing) Emerson et al. 1984 Sandes et al. 2000. 4.3.3 Model Solution and Results Using the parameters described in Table 4-1 three separate SiO2 profiles were calculated from equation (4.4) for different values of K and each following a different trend. The first trend line repr esents molecular diffusion using K = 10-5 cm2 s-1, and = 0. The other two trend lines repr esents “enhanced mixing”, with K = 10-4 cm2 s-1, and = 4 10-7 s-1 as one, and K = 10-3 cm2 s-1, and = 4 10-7 s-1 as the other one. The reason for generating two separate trend lines to re present enhance mixing was only to represent one slightly faster diffusion coefficient rate than the other by using two separate values for K

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56 The model was tested on pore water samples collected from three separate sampling trips made to the Banana River La goon in May, August, and December of 2000 (Figure 4-5, 4-6 and 4-7). These results indicate that for all three seasons SiO2 profiles of the pore waters are reproduced by using enhanced diffusion rates of K = 10-3 cm2 s-1, and that molecular diffusion ( K = 10-5 cm2 s-1) does not dominate as a transport mechanism from the sediment-water interf ace, to a depth of 110 cm. A nonlocal term is required to account for the observed SiO2 profiles. For the non-lo cal transport parameter to approach the measured SiO2 concentration at depths of 110 cm requires enhanced mixing, using a diffusion coefficient ( K = 10-3 cm2 s-1) that are two orders of magnitude greater than simple molecular diffusion. This e nhanced mixing of sediments brought about collectively by biologi cal activity, tidal pumping or wave action could affect the distribution of certain solid and dissolved phases. For example the remobilization of metals such as Fe, Mn and Ni by the rem oval of sulfide from the pore waters, via ventilation of sediments with oxic overlying water, allowing the enrichment of dissolved metal (Emerson et al. 1984). In addition th e exchange mechanism between shallow pore waters and the bottom waters could alter th e redox chemistry of certain species. For example, high concentrations of Fe(II) and Mn(II) observed in the surface few centimeters and gradually decrease downward, indicate that benthic animal activity and physical pumping mechanisms are a domina nt process in shaping the chemical distribution of pore waters (Emerson et al. 1984). For all three seasons SiO2 concentrations tend to follow a slightly slower diffusive rate between 10-3 cm2 s-1 and 10-4 cm2 s-1 at depths greater th an 110 cm, up to 230 cm depth. This may mean that a different re gime exists between 110-230 cm depth, one

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57 which may still cause mixing, but not as e nhanced as the type seen between 0-110 cm depth. This could probably be due to the f act that wave action a nd tidal pumping do not influence mixing processes at depths great er than 110 cm below the sediment-water interface (Shum 1992). Molecular Vs. Enhanced Mixing at BRL2. MAY20000 40 80 120 160 200 240 050100150 [SiO2] MDepth (cm) Molecular Diffussion K=10.0 E-06 Enhanced Mixing K=10.0 E-05 Enhanced Mixing K=10.0 E-04 Pore Water [SiO2], BRL2 Figure 4-5. Model solutions for the depth dist ribution of silicate for enhanced mixing (K = 10-3 cm2 s-1) with no non-local transport ( = 0), and molecular diffusion (K = 10-5 cm2 s-1) and non-local transport ( = 4 10-7 s-1): May 2000.

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58 Molecular Vs. Enhanced Mixing at BRL2. AUG-20000 40 80 120 160 200 240 050100150200 [SiO2] MDepth (cm) Molecular Diffussion K=10.0 E-06 Enhanced Mixing K=10.0 E-05 Enhanced Mixing K=10.0 E-04 Pore Water [SiO2], BRL2 Figure 4-6. Model solutions for the depth dist ribution of silicate for enhanced mixing (K = 10-3 cm2 s-1) with no non-local transport ( = 0), and molecular diffusion (K = 10-5 cm2 s-1) and non-local transport ( = 4 10-7 s-1): August 2000.

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59 Molecular Vs. Enhanced Mixing at BRL2. DEC-20000 40 80 120 160 200 240 050100150[SiO2] MDepth (cm) Molecular Diffussion K=10.0 E-06 Enhanced Mixing K=10.0 E-05 Enhanced Mixing K=10.0 E-04 Pore Water [SiO2], BRL2 Figure 4-7. Model solutions for the depth distri bution of silicate for enhanced mixing (K = 10-3 cm2 s-1) with no non-local transport ( = 0), and molecular diffusion (K = 10-5 cm2 s-1) and non-local transport ( = 4 10-7 s-1): December 2000. 4.4 Mass Balance Calculation 4.4.1 Introduction De Baar and Suess (1993) estimated that 90 % of annual organic primary production is recycled within coastal surface waters. Only about 1 % of the remaining 10 % of organic matter which escapes to the deep ocean, is buried in marine sediments. The link between burial of organi c matter and primary production in surface waters depends on the efficiency of diagenetic reacti ons at the sediment-water interface. The quantification of nutrient fluxes from the sediment to the overlying water column has been measured in the past using seep meters (Gallagher et al. 1996, Martin et

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60 al. 2000). The procedure relied on sampling concen trations of various nutrient species in the seep water and converting th ese concentrations to fluxes on the basis of the seepage rates measured using seep meters. These wate r fluxes were several orders of magnitude greater than those measured using gr ound water flux rates by numerical modeling techniques (Pandit and El-Khazen 1990). If mixing is common in the shallow sediments (Chapter 4.1.1), then not all of the nutrients in the seep wate r can be considered as a new flux to the lagoon. Some of the dissolved nutri ents in the seep water would have been brought into the shallow sedime nt along with the circulati ng lagoon water. Some of the nutrients may have also originated from the upward flow of ground water, although a new source of nutrients from ground water would be small because the nutrient concentrations in ground water are lower th an in seep water a nd because ground water represents at most ~5 % of the seep wa ter (Martin et al. 2002 ). These observations suggest that most of the newly generated nutrients in the seep water, and subsequently the output nutrient flux to the lagoon originate from the remineralization of organic matter within shallow sediment pore water during mi xing. However, this could only be possible if there is enough organic P a nd N present in the sediment to support such high nutrient fluxes. One possible explanation for having obser ved these high seepage fluxes may have to do with the deployment of the seep-meter itself. The remineralization of organic matter within shallow sediments is a process that fo llows a definite successi on, and is primarily controlled by the availability of dissolved oxygen and othe r species in the sediments (Froelich et al. 1979). Once dissolved oxygen beco mes sufficiently depleted due to burial or restricted renewal of oxygenated wate r, further organic matter decomposition

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61 continues by the oxidatio n of nitrate present in the wate r. The overall reaction is known as denitrification. At BRL2 and BRL6 dissolved oxygen and NO3 are nearly depleted in the pore waters (Martin et al. 2002) suggesting that almo st all the oxygen has been utilized by microbial oxidation of organi c matter at the sediment-water interface. Although SO4/Cl ratios do not indicate that sulf ate reduction has begun (Martin et al 2000), there appears to be sulfide present in the water suggesting some sulfate reduction. The deployment of a seep meter at the sedi ment-water interface may expedite the process of organic matter remineralization, providi ng only a limited amount of dissolved oxygen exposed to a large unit area of sediment, w ithout any means of re-oxygenating the water trapped in the seep meter for over 24 hours. As a result, most of the P and N is being oxidized in the upper 1-2 cm at the sediment s-water interface within 24 hours, and gets collected in the seepage bags by diffusive a nd advective ground wate r discharge, and the remaining fraction of the TP and TN is preser ved in the sediment (F igure 4-8). This could also explain why concentrations of dissolved oxygen in the seep meters (0.2 mg/L) are depleted compared to the surrounding lagoon water (6.7 mg /L) within 24 hours after deploying the seep meter (Martin et al. 2000).

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62 Figure 4-8. Cross section of the seep meter showing organi c matter remineralization at the sediment-water interface enclosed within the seep meter. P.W.= pore water, L.W.= lagoon water, S.W.= seep water. Therefore, in order to make a realisti c nutrient mass balance calculation in the Banana River Lagoon, one needs to develop a mass balance calculation that compares input rate of nutrient fluxes to the lagoon in the form of surface runoff and sedimentation versus the output nutrient fluxes in the form of ground water discharge at the sediments water interface. A realistic estimate of the output fluxes could be cal culated using nutrient concentrations within shallow pore waters. If the nutrient fluxes to the sediment (input) are in excess with respect to the ground water discharge (output), then the excess OM present in the sediment column can be consid ered as a source of nutrients to the lagoon.

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63 4.4.2 Calculations A simple mass balance model was computed to estimate the input versus the output fluxes of three chemical constituents viz. total phosphorus (TP), to tal nitrogen (TN) and biogenic silica (SiO2) at the sediment-water interface, at BRL2 and BRL6 respectively. In order to calculate input rates two parameters were required, the average concentration of the chemical constituents within the sediment column (up to 80 cm), and the rate of accumulation of sediments (Table 4-2). The accumulation rates were calculated by making an assumption that sedi mentation rates in the Banana River Lagoon corresponds to 1-2 1 mm/yr of sea-level rise within the past 100 years (Jaeger et al. 2001 unpublished). From this, the average sediment accumulation rate was calculated to be 200 mg/cm2/yr at BRL2 and BRL6. By multiplying the average concentration of the three constituents in the sediments by the sediment accumulation rate we computed the input flux rates to the sediment. The output ra te of the various so lutes to the lagoon was calculated by multiplying the concentration of the sediment pore water by ground water discharge rate. The ground water discharg e rates measured for BRL2 and BRL6 were 44.5 ml/m2/min ( 12 ml/m2/min), and 18.7 ml/m2/min ( 12.6 ml/m2/min) respectively. Both the values of pore water concentration (Table 4-3), and ground water discharge rates were taken from Lindenberg (2001). Results from the mass balance calculations for BRL2 and BRL6 are tabulated in Table 4-4. Table 4-2. Average concentration of TP, TN and SiO2 up to 80 cm within the sediment at BRL2 and BRL6. Location TP (mg/g) TN (mg/g) SiO2 (mg/g) BRL2 0.020 0.094 5.096 BRL6 0.033 0.208 2.848

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64 Table 4-3. Average pore water concentr ations up to 80 cm (from Lindenberg 2001). Location TP (mg/L) TN (mg/L) SiO2 (mg/L) BRL2 0.06 0.45 4.1 BRL6 0.08 0.92 4.0 Table 4-4. Comparing input fluxes to the sediment versus output fluxes to the lagoon water of TP, TN and SiO2 at BRL2 and BRL6. BRL2 BRL6 Input Flux Output Flux Input Flux Output Flux ( g/cm2/yr) ( g/cm2/yr) ( g/cm2/yr) ( g/cm2/yr) TP 4 50 % 5 25 % 7 50 % 3 30 % TN 19 50 % 38 25 % 42 50 % 33 30 % SiO2 1019 50 % 347 25 % 570 50 % 142 30 % Results from the mass balance calculations at BRL2 suggest that there is an over all 25 % increase in the output flux of TP, and tw ice as much of TN being released to the lagoon water than the input fl uxes to the lagoon sediments (however, within limits of error the fluxes seem to be well balanced). Although, a possible expl anation as to why we observe a slightly higher output flux may be because much of the N and P contained in the detrital OM is reminerali zed at depths shallower than 80 cm. In contrast, the output fluxes of SiO2 are almost three times lower than the input rates possibly because SiO2 remineralizes slower than P or N, hence does not have a similar artifact. In other words, SiO2 remains deposited in the sediments a lot longer than P and N. At BRL6, the output fluxes of TP and TN are slower than the rate at which it is deposited into the lagoon. Ther e are at least two possible re asons for this. Firstly, the input fluxes to the sediment are higher co mpared to BRL2, and secondly, although there is sufficient P and N present in the sediment to support higher output fluxes to the lagoon, the slower ground water discharg e rate prevents it from happening. However, within limits of error the input versus the output fl uxes of TP and TN at BRL6 seem to balance

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65 well. This would then suggest, that even t hough the concentration of OM in the sediments are low, they can provide the required amount to balance the output fluxes of TP and TN to the lagoon. Differentiating the mixing depth from th e depth of reaction requires utmost clarification while making similar mass bala nce calculations. An important observation that can be made from our mass balance cal culation is that averaging the N and P pore water concentrations over the mixing dept h does not represent the average depth of reaction. Hence, even though mixing may enha nce organic matter remineralization within the sediments, its influence is limited to sh allower depths than the mixing itself. By averaging pore water concentrations with dept hs that represent mixing zones, instead of zones of N and P remineralization reactions may result erroneous while calculating nutrient fluxes. Results from Table 4-4 show that although th e net input versus output fluxes of TP, TN and SiO2 are well balanced within calculated lim its of error. These output fluxes to the lagoon represents both the diffusive as we ll as advective fluxes. Estimates of nutrient fluxes to the Banana River Lagoon such as those made above using pore water concentrations, are more realistic than those calculated using seep water concentrations, however trying to estimate the exact depth of reaction may prove to be a difficult task. Although there may be errors re sulting from the extrapolation of the data from a small study area such as the Banana River Lagoon; differences between the measurements of individual nutrient fluxes obs erved at BRL2 and BRL6, indicat e the importance of P and N cycling to the lagoon with respect to ground water discharge, along with its effect on the chemical fate of the sediments.

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66 CHAPTER 5 CONCLUSIONS 5.1 Summary The determination of ground water discharge is important, but an elusive process. Ground water discharge rate can be a valuab le, if not a necessary addition to any quantitative nutrient or hydr ographic modeling effort in the Banana River Lagoon. Measurements of ground water discharge, and its associated nutrient flux using seep meters reflect rates that are greater than those calculated using numerical modeling and tracer techniques. These elev ated nutrient fluxes measured using seep meters suggest, that while diagenetic reactions such as or ganic matter remineralization at the sedimentwater interface can control the concentrations of these fluxes, it is the additional sources of water being discharged from the sedime nts to the lagoon through advective processes, such as bioturbation, wave action, and tidal pumping, that ultimately control the flux rate. Therefore, it is critical to estimate the magn itude of organic matter remineralization at the sediment-water interface, and also be able to identify the additional sources of ground water discharge within shallow sediments, to accurately access the hydrologic and nutrient budgets of the lagoon. Previous studies using conser vative tracers such as Cl-, have shown that much of the seep water at BRL2 originated from the lagoon. In other words, the lagoon water is being re-circulated through the sediments. There is also evidence suggesting that the lagoon water mixes with the pore water to ~70 cm depth below the sediment-water interface. This sort of mixi ng between the lagoon and pore wa ter is important for nutrient

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67 fluxes because of the greater volumes of wate r, and associated nutrients discharged from the sediments by advective rather than diffusi ve processes. By undertaking this research project I was able to provide some prelim inary information about the physical and chemical composition of the sediments that ma y control the source of the nutrients to the Banana River Lagoon; and by using math ematical modeling and mass balance calculations, was able to identify some of the processes controlli ng the discharge rates required to drive the associated nutrient fluxes to the lagoon. Both the sediment cores recovered from BRL2 and BRL6, showed variability in chemical composition as well as its physical properties, suggesting a rather complex hydrodynamic lagoon system. The sediments are sandy, inter-layered with calcareous shell fragments and an occasional clay horiz on. The high average porosity corresponded to high porosity. However, the low organi c matter (OM) content reflected the sandy nature of the sediments. By making mass bala nce calculations we were able to compare fluxes of TP, TN and SiO2, and see if there was sufficient OM in the sediments to support the output fluxes. Measuring fluxes using s eep meters may expedite the process by limiting the amount of dissolved oxygen availa ble to the sediments undergoing diagenetic reactions within only a few centimeters below the sediment water interface. If so, then almost all of the organic matter undergoes re mineralization at the sediment-water and only a small fraction ultimately gets buried in the sediments. This process could explain the high nutrient concentrations measured in the seep water. Therefore, in order to make mass balance calculations between input versus output nutrient fluxe s to the lagoon it is far more realistic to use pore water concentrations rather than seep water.

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68 Another factor that can control th e high nutrient fluxes is the ground water discharge rate. At BRL2, SiO2 pore water profiles suggest th at simple molecular diffusion cannot support the transport mechanism at th e sediment-water interface, up to 110 cm depth. The SiO2 profiles of the pore waters can only be reproduced by using enhanced diffusion rates of K = 10-3 cm2 s-1 which are two orders of magnitude faster than molecular diffusion. This process of enhan ced diffusion could only exist if there was substantial amount of mixing ta king place within sediment pore water, brought about by benthic animal activities, tidal pumping, and wave action. However, the SiO2 pore water profiles between 110-230 cm represents a sligh tly slower mixing regime, that could be explained by the fact that wave action and tid al pumping does not aff ect diffusion rates at depths greater than 110 cm. Finally, by correlating physical and chemical properties of the sediments, coupled with visual observations we were able to get a fairly good insight into some of the physiological processes in the Banana River Lagoon. For example, the small range in porosity corresponds to uniform grain-size and compaction of sediments with depth. The increase in porosity corresponded to the clay horizons, which act as aquitards within the sediments, limiting the flow of ground wate r discharge. This could be the reason why ground water discharge rates at BRL 2 are slightly higher (44.5 ml/m2/min) than those measured at BRL6 (18.7 ml/m2/min). Although ground water disc harge appears to have a major impact on nutrient cycling, trying to qua ntify the flux may be difficult, because of mixing brought about by the re-circulati on of lagoon water through the shallow sediments. The mechanisms driving mixing are unknown, but could involve physical and biological processes caused by bioturbation, tidal pumping, and wave action. The

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69 magnitude of these mixing processes should be important for nutrient fluxes because of the increased organic matter regeneration that occurs within shallow sediments from cycling of oxygenated lagoon water through the sediments. 5.2 Future Work This research work has provided us with some preliminary information about the Banana River Lagoon, such as the physical and chemical properties of the sediments, nutrient fluxes to the lagoon using shallow pore water con centrations, and using a SiO2 diagenetic model to describe enhanced mi xing within shallow sediment pore waters. However, many additional ques tions are raised by the results, and answers to these questions will be important in order to ga in a complete understa nding of the nutrient fluxes to the Banana River Lagoon. Some of the questions include: How do shallow sediment pore water concentr ations compare with measured nutrient fluxes within other areas of the lagoon th at have not been previously sampled? What is the magnitude and extent of mixi ng processes such as bioturbation, wave action or tidal pumping individually, be low the sediment-water interface? While answering these questions in the future emphasis should be laid on collecting pore water samples using smaller depth resoluti on, and higher frequenc y sampling trips in order to evaluate the time required for mixi ng between lagoon and pore waters to take place. In addition, future work should al so focus on developing other mathematical diagenietic models in evalua ting ground water discharge ra tes using conservative/nonconservative species, so as to better understand lagoon water ci rculation, and extent of organic matter rimineralization that may result from such a circulation.

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70 APPENDIX A PHYSICAL AND CHEMICAL ANALYTICAL DATA FROM CORE BRL2 Depth Porosity Density TP TN OM SiO2 TC (cm) (%) (g/cc) (mg/g) (mg/g) (mg/g) (mg/g) (%) 2 21.5 1.57 0.018 0.085 3.477 4.373 1.2 4 21.0 1.76 0.015 0.167 3.352 3.110 1.6 6 21.8 1.79 0.014 0.113 3.039 4.001 1.3 8 24.0 1.85 0.014 0.075 2.137 3.591 1.7 10 28.1 1.92 0.011 0.058 1.492 3.546 1.5 12 29.1 1.94 0.018 0.062 7.217 3.235 1.2 14 28.5 2.00 0.023 0.092 10.097 3.197 1.7 16 29.6 2.01 0.020 0.083 10.096 2.859 1.8 18 29.2 2.10 0.023 0.107 24.585 4.158 1.6 20 31.2 2.01 0.051 0.111 27.218 6.651 3.6 22 36.2 1.95 0.094 0.214 9.875 6.561 3.2 24 38.5 1.96 0.067 0.214 7.347 4.120 3.5 26 36.1 1.93 0.039 0.162 6.890 4.628 3.3 28 37.9 1.92 0.038 0.242 6.216 6.221 3.6 30 36.3 1.88 0.030 0.150 6.619 8.198 2.4 32 36.3 1.92 0.036 0.193 4.987 3.543 2.9 34 33.6 1.95 0.097 0.179 2.922 4.044 1.7 36 32.7 1.95 0.021 0.065 1.964 4.350 1.8 38 32.4 1.97 0.015 0.103 2.694 7.627 2.2 40 31.7 2.00 0.011 0.083 2.891 5.158 1.5 42 30.7 2.00 0.007 0.070 1.501 4.917 2.2 44 31.2 1.99 0.011 0.103 1.195 6.315 1.2 46 31.0 1.98 0.008 0.039 0.695 5.017 1.0 48 31.7 1.98 0.006 0.034 0.552 4.907 1.0 50 32.3 1.98 0.004 0.042 0.668 3.899 1.6 52 31.7 1.94 0.008 0.051 0.937 7.165 1.4 54 36.7 1.94 0.030 0.193 3.212 6.966 2.1 56 33.0 1.97 0.014 0.065 1.452 8.818 0.8 58 31.6 1.98 0.010 0.032 0.606 5.912 1.0 60 31.9 1.97 0.005 0.051 1.021 3.999 1.4 62 31.4 1.98 0.003 0.060 1.279 3.545 1.7 64 31.3 2.00 0.001 0.061 1.003 5.188 1.5 66 31.0 1.99 0.004 0.068 1.054 4.771 0.7 68 30.0 2.00 0.000 0.045 0.781 8.276 1.1

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71 Depth Porosity Density TP TN OM SiO2 TC (cm) (%) (g/cc) (mg/g) (mg/g) (mg/g) (mg/g) (%) 70 30.2 1.98 0.004 0.042 0.761 9.713 0.9 72 31.0 1.98 0.000 0.049 0.933 3.557 1.6 74 30.9 1.96 0.000 0.049 0.757 4.172 0.8 76 33.1 2.00 0.010 0.056 1.081 4.687 1.3 78 30.7 2.04 0.003 0.054 0.926 4.687 0.7 80 30.1 2.03 0.001 0.040 0.766 4.121 0.9 82 31.4 2.02 0.000 0.035 0.616 3.494 0.9 84 30.4 2.01 0.000 0.027 0.531 3.136 0.2 86 30.8 2.02 0.000 0.040 0.810 3.649 0.7 88 30.6 2.02 0.005 0.037 0.971 5.812 1.5 90 30.2 2.02 0.006 0.035 0.994 4.272 1.6 92 30.0 2.01 0.013 0.055 1.110 4.960 0.6 94 31.1 2.00 0.020 0.034 1.146 5.792 1.1 96 30.6 2.01 0.023 0.042 1.438 6.618 1.1 98 30.9 2.00 0.021 0.033 1.479 5.573 1.5 100 31.1 2.00 0.016 0.035 1.327 4.783 1.5 102 32.3 1.99 0.020 0.037 1.595 6.927 0.6 104 31.1 1.94 0.022 0.037 1.794 6.498 1.1 106 31.4 1.96 0.021 0.020 1.204 6.303 1.1 108 30.8 1.92 0.020 0.027 1.109 7.040 1.4 110 33.4 1.92 0.026 0.028 2.419 7.600 1.4 112 36.4 1.92 0.036 0.020 2.428 9.318 2.9 114 36.4 1.86 0.034 0.032 4.293 6.917 2.3 116 41.5 1.84 0.065 0.023 4.824 10.593 2.0 118 35.1 1.90 0.057 0.020 2.157 9.997 1.7 120 34.0 1.92 0.050 0.013 1.261 9.394 2.2 122 32.7 1.92 0.048 0.031 1.850 9.106 2.0 124 33.8 1.94 0.045 0.015 1.404 7.977 1.7 126 33.5 1.96 0.047 0.012 1.236 8.028 2.0 128 33.3 1.96 0.047 0.012 1.817 6.629 1.8 130 33.3 1.97 0.061 0.008 1.524 6.641 1.6 132 33.0 1.94 0.045 0.000 1.218 7.108 2.1 134 34.4 1.92 0.031 0.000 1.432 7.791 1.6 136 32.6 1.95 0.030 0.000 0.791 5.356 1.7 138 33.7 1.95 0.026 0.000 0.854 5.624 1.3 140 32.9 1.95 0.017 0.000 0.579 5.347 1.8 142 32.3 1.95 0.006 0.000 0.320 3.863 1.0 144 32.6 1.94 0.004 0.000 0.270 3.243 1.3 146 32.6 1.96 0.003 0.000 0.372 3.037 1.3 148 32.6 1.95 0.002 0.000 0.241 2.663 1.2 150 33.4 2.02 0.002 0.000 0.278 3.315 1.6

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72 Depth Porosity Density TP TN OM SiO2 TC (cm) (%) (g/cc) (mg/g) (mg/g) (mg/g) (mg/g) (%) 152 34.5 1.98 0.001 0.000 1.297 3.195 1.3 154 32.0 0.91 0.003 0.000 0.448 3.985 0.7 156 31.9 Nil Nil 0.000 0.657 3.195 Nil

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73 APPENDIX B PHYSICAL AND CHEMICAL ANALYTICAL DATA FROM CORE BRL6 Depth Porosity Density TP TN OM SiO2 TC (cm) (%) (g/cc) (mg/g) (mg/g) (mg/g) (mg/g) (%) 2 39.4 1.68 0.020 0.208 2.252 1.126 1.3 4 39.5 1.85 0.016 0.261 2.356 4.422 1.1 6 39.9 1.82 0.015 0.271 3.109 1.472 0.7 8 40.2 1.85 0.004 0.216 2.725 1.963 1.6 10 39.5 1.85 0.009 0.223 2.208 1.778 1.0 12 40.6 1.85 0.011 0.181 1.612 1.542 1.0 14 38.6 1.87 0.037 0.136 1.377 1.398 1.0 16 38.4 1.86 0.043 0.157 9.832 2.070 1.0 18 38.0 1.89 0.014 0.108 1.100 2.011 0.9 20 37.5 1.91 0.004 0.113 1.804 2.345 1.1 22 37.9 1.89 0.035 0.108 1.462 1.758 0.9 24 37.3 1.90 0.000 0.103 2.139 1.197 1.2 26 37.8 1.90 0.000 0.133 4.271 0.972 1.6 28 37.9 1.89 0.087 0.151 3.320 1.376 2.2 30 38.0 1.89 0.012 0.170 11.391 2.173 1.6 32 39.1 1.89 0.058 0.579 10.268 1.445 3.2 34 38.7 1.93 0.049 0.745 13.724 2.713 3.1 36 37.3 1.97 0.016 0.203 22.895 2.251 4.0 38 37.5 1.92 0.043 0.197 5.782 2.260 4.2 40 38.9 1.89 0.027 0.221 6.573 3.959 2.9 42 38.6 1.90 0.054 0.265 19.298 4.103 1.6 44 37.6 1.91 0.008 0.230 11.219 3.655 2.6 46 38.5 1.88 0.012 0.250 16.335 5.280 3.1 48 38.2 1.89 0.012 0.194 18.506 3.812 2.7 50 36.8 1.93 0.024 0.162 27.853 1.031 2.8 52 36.3 1.93 0.011 0.154 38.547 2.379 2.9 54 38.1 1.92 0.011 0.164 43.714 4.451 2.9 56 38.6 1.91 0.011 0.133 11.428 5.711 2.4 58 39.2 1.87 0.035 0.135 5.930 2.852 2.5 60 38.9 1.88 0.014 0.144 7.707 3.437 2.7 62 39.1 1.86 0.009 0.125 11.316 3.066 2.5 64 39.7 1.85 0.022 0.164 12.390 4.409 2.6 66 40.2 1.85 0.033 0.157 12.354 3.026 2.9 68 40.3 1.82 0.102 0.183 20.002 2.844 4.3

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74 Depth Porosity Density TP TN OM SiO2 TC (cm) (%) (g/cc) (mg/g) (mg/g) (mg/g) (mg/g) (%) 70 41.0 1.81 0.040 0.160 9.325 3.815 3.9 72 41.8 1.83 0.093 0.152 11.166 3.224 3.0 74 41.2 1.83 0.066 0.172 15.213 4.248 3.6 76 39.0 1.86 0.076 0.211 25.722 1.790 4.3 78 43.1 1.81 0.090 0.222 12.644 4.364 4.8 80 45.2 1.75 0.083 0.244 9.390 6.166 5.4 82 49.4 1.75 0.105 0.185 5.888 11.984 5.5 84 53.0 1.68 0.192 0.197 4.568 14.754 7.9 86 51.3 1.77 0.170 0.175 4.167 13.987 4.7 88 56.7 1.60 0.162 0.217 3.456 10.251 6.1 90 55.1 1.61 0.192 0.200 2.429 15.090 4.4 92 52.3 1.62 0.190 0.156 2.706 14.109 4.0 94 51.1 1.65 0.160 0.125 1.310 13.323 3.6 96 53.9 1.64 0.161 0.146 1.683 10.183 4.5 98 51.2 1.66 0.139 0.117 1.560 8.658 4.3 100 45.6 1.68 0.092 0.084 0.098 10.680 4.1 102 49.6 1.62 0.104 0.118 1.225 13.820 4.4 104 47.1 1.65 0.039 0.096 1.193 10.408 3.1 106 49.9 1.65 0.025 0.109 1.637 10.832 3.5 108 51.6 1.65 0.032 0.164 11.399 12.363 4.9 110 47.7 1.76 0.025 0.026 1.877 10.335 4.3 112 39.8 1.86 0.004 0.046 1.266 4.504 2.9 114 38.1 1.84 0.001 0.052 2.127 3.105 2.4 116 38.4 1.87 0.000 0.054 1.821 5.257 2.1 118 37.9 1.87 0.000 0.058 2.200 4.132 2.5 120 39.4 1.88 0.002 0.057 2.495 6.073 2.1 122 38.3 1.89 0.001 0.038 2.099 5.092 2.3 124 37.5 1.89 0.000 0.043 2.085 4.130 1.5 126 36.5 1.90 0.000 0.021 1.373 4.444 1.6 128 36.5 1.89 0.000 0.028 1.304 4.230 0.9 130 36.8 1.89 0.000 0.020 1.182 3.957 1.0 132 37.0 1.85 0.000 0.028 1.406 2.384 1.1 134 37.1 1.85 0.000 0.020 1.530 2.287 1.0 136 37.1 1.88 0.000 0.011 0.944 2.687 1.0 138 37.6 1.88 0.000 0.011 0.758 2.661 0.6 140 36.6 1.88 0.000 0.007 0.548 3.345 0.4 142 36.2 1.90 0.000 0.000 0.414 2.794 0.5 144 35.9 1.91 0.000 0.000 0.029 2.260 0.8 146 35.2 1.92 0.000 0.025 0.395 2.507 0.8 148 35.4 1.93 0.000 0.019 0.293 2.597 0.7 150 34.9 1.94 0.000 0.014 0.228 2.364 0.8

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75 Depth Porosity Density TP TN OM SiO2 TC (cm) (%) (g/cc) (mg/g) (mg/g) (mg/g) (mg/g) (%) 152 35.1 1.92 0.000 0.015 0.293 3.145 0.8 154 34.8 1.93 0.000 0.028 0.256 2.491 0.9 156 35.0 1.92 0.000 0.015 0.259 2.506 1.0 158 35.6 1.92 0.000 0.020 0.204 1.596 1.0 160 36.3 1.92 0.015 0.079 1.313 1.783 1.3 162 36.3 1.69 0.008 0.148 2.686 1.862 1.3

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79 Nixon S. W. (1986) Nutrient and the productivity of estu arine and coastal marine ecosystems. Journal of the Limnological Society of South Africa 12, 43-71. Pandit A., El-Khazen C.C. (1990) Ground water seepage into the Indian River lagoon at Port St. Lucie. Florid a Scientist 53, 169-179. Rasmussen L. L., Chanton J. P. Meacham S. P., Furbish D. J., Burnett W. C. (2003) Ground water flow, tidal mixing, and haline convection in coastal sediments: Field and modeling studies. Continental Shelf Research (Under review). Reddy K., Fisher M. M., Pant H., Inglett P. (1999) Indian River lagoon hydrodynamics and water quality model: Nutrient storage and transformations in sediments. St. Johns River Water Management District, Palatka, Fl. Redfield A. C., Ketchum B. H., Richards F. A. (1963) The influence of organisms on the composition of sea water. In Hill, N. M (Ed.) The Sea Wiley, 2, New York 26-77. Robinson M., Gallagher D. (1999) A mode l of ground water discharge from an unconfined coastal aquifer. Ground Water 37, 80-87. Rutkowski C. M., Burnett W. C., Iverson R. L., Chanton J. P. (1999) The effect of ground water seepage on nutri ent delivery and sea-grass distribution in the northeastern Gulf of Mexi co. Estuaries 22, 1033-1040. Ruttenberg K. C., Berner R. A. (1993) Au thigenic apatite formation and burial in sediments from non-upwelling, continen tal margin environments. Geochim. Cosmochim. Acta 57, 991-1007. Sandnes J., Forbes T., Hansen R., Sandnes B ., Rygg B. (2000) Bioturbation and irrigation in natural sediments, described by anim al-community parameters. Marine Ecology Progress Series 197, 169-179. Schelske C. L., Kenny W. F., Whitmore T. J. (2001) Sedimentation and nutrient deposition in Harris Chain-of-lakes. Sp ecial Publication SJ2001-SP7. St. John’s River Water Management District, Palatka. Schelske C. L., Peplow A., Mrenner M., Spencer C. N. (1994) Low-background gamma counting: applications for Pb210 dating of sediments. J ournal of Paleolimnology 10, 115-128. Schenau S. J., De Lange G. J. (2001) Phosphor us regeneration vs. bur ial in sediments of the Arabian Sea. Marine Chemistry 75, 201-217. Schink D. R., Guinasso N. L., Fanning K. A. (1975) Processes affecting the concentration of silica at the sediment-water interf ace of the Atlantic Ocean. Journal of Geophysics Research 80, 3013-3031.

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80 Scott T. M. (1988) The Lito starigraphy of the Hawthorn Gr oup (Miocene of Florida). Florida Geological Survey, 147. Scott T. M. (1992) A geological overview of Florida. Florida Geological Survey, 78. Shinn E. A., Reich C. D., Hickey T. D. (2002) Seepage meters and Bernoulli’s revenge. Estuaries 25 (1), 126-132. Shum K. T. (1992) Wave-induced Advective transport below a ri ppled water-sediment interface. Journal of Geophysical Research 97, 789-808. Shum K. T. (1993) The effects of wave induced pore water circulation on the transport of reactive solutes below a rippl ed sediment bed. Journal of Geophysical Research 98, 10,289-10,301. Shum K. T., Sundby B. (1996) Organic matter processing in continental shelf sedimentsthe sub-tidal pump revisited. Marine Chemistry 53, 81-87. Simmons G. M., Jr. (1992) Importance of submarine ground water discharge (SGWD) and seawater cycling to material flux acr oss sediment/water interfaces in marine environment. Marine Ecological Program Series 84, 173-184. Smith D. G. (1984) Vibracoring fluvial a nd deltaic sediments: Tips on improving penetration and recovery. Journal of Sedimentary Petroleum 54 (2), 660-663. Toth D. J. (1988) Salt water intrusion in coas tal areas of Volusia, Brevard, and Indian River Counties. Technical Publication SJ 88-1, 160. St. John’s River Water Management District, Palatka, Fl. Trefry J., Nai-Chi Chen, Trocine R. (1992) Impingement of organic-rich, contaminated sediments on Manatee Pocket, Florid a. Florida Scientist 55, 167-170. Tyrell T. (1999) The relative influences of nitrogen and phosphorus on oceanic primary production. Nature 400, 525-531. U.S.G.S. (1998) Detailed description for samp ling, sample preparation and analyses of cores from St. Bernard Parish, Louisiana. Open-File Report 98-429. Markewich H. W. Atlanta, Ga. Weber M. E., Niessen F., Kuhn G., Wiedicke M. (1997) Calibration and application of marine sedimentary physical properties us ing a multi-censor core logger. Marine Geology 136, 151-172. Weiskel P. K., Howes B. L. (1992) Differentia l transport of sewage-derived nitrogen and phosphorus through a coastal watershed. Environmental Science and Technology 26, 352-360.

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81 Wheatcroft R. A., Jumars P. A, Smith C. R ., Nowell A. M. (1990) A mechanistic view of the particulate diffusion coefficient: step length, rest periods and transport directions. Journal of Mari ne Research 48, 177-207. Wollast R. (1974) The silica problem. In The Sea Wiley, New York, 5, 359-354. Wollast R., Garrels R. M. (1971) Diffusion co efficient of silica in seawater. Nature Physical Science 229, 94. Zimmerman C. F., Montgomery J. R., Carls on P. R. (1985) Variability of dissolved reactive phosphate flux rates in near-shor e estuarine sediments: Effects of ground water flow. Estuaries 8, 228-236.

PAGE 92

82 BIOGRAPHICAL SKETCH I started my education in 1980 when I jo ined St. Peter’s High School, Bombay, India. I studied there for twelve years, from kindergarten to X grade. In 1992 I joined St. Xavier’s College, a part of the University of Bombay. I completed the Junior College (high school equivalent) level in 1994, a nd then went on to Degree College in St. Xavier’s. I graduated in May 1997 having earn ed a Bachelor of Science (Honors) degree with geology as my major, and gemology as my minor. In 1997 I started my master’s degree program from St. Xavie r’s College and graduated in June 1999 with a Master of Science (Distinction) degree, majoring in geology. In Fall 2000 I joined the Department of Geological Sciences at the University of Fl orida (Go Gators!). I plan on graduating in Spring 2003 with a Master of Science degree, with a major in geology and a minor in environmental engineering scienc es. Apart from this I will al so receive a certificate in hydrologic sciences as part of the Hydrologi c Sciences Academic Cluster here at the University of Florida.


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Title: Chemical tracing and analytical and mass-balance modes of pore water circulation in the Banana River Lagoon, Florida
Physical Description: Mixed Material
Creator: Bhadha, Jehangir H. ( Author, Primary )
Publication Date: 2003
Copyright Date: 2003

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CHEMICAL TRACING AND ANALYTICAL AND MASS-BALANCE MODES OF
PORE WATER CIRCULATION IN THE BANANA RIVER LAGOON, FLORIDA













By

JEHANGIR H. BHADHA


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


2003

































Copyright 2003

by

Jehangir H. Bhadha















ACKNOWLEDGMENTS

I would like to thank the St. Johns River Water Management District for having

funded my research. I would like to thank my advisor, Dr. Jonathan Martin, for his

constant support and guidance throughout my research. I would also like to thank my

committee members, Dr. John Jaeger and Dr. Clay Montague, for their assistance and

resourceful suggestions towards my thesis. I would like to thank Dr. Jason Curtis and

William Kenny for letting me use the labs and assisting me with my physical and

chemical analyses. I would like to thank Marylea Hart in helping me use the core logger

and sectioning my cores. I would like to thank my good friend and ex-colleague Melroy

Borges for his many valuable comments and suggestions, and in assisting me with

graphic imaging. I would like to thank the faculty, staff, and all of my colleagues here at

the Department of Geological Sciences (University of Florida) for their help and support

throughout my time in Gainesville. Last but not the least, I would like to thank my

parents back home in India for their support, blessings and patience; especially for not

having complained how much they have missed me in the past three years.
















TABLE OF CONTENTS
page

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

LIST OF TABLES ....................................................... ............ ....... ....... vi

L IST O F FIG U R E S .... ...... ................................................ .. .. ..... .............. vii

ABSTRACT .............. .................. .......... .............. ix

CHAPTER

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

1.1 Statem ent of Problem ................. .... .......................... .. ......... ............ ..... 1
1.2 H ypotheses .............................................. 6
1.3 G oals and Objectives .............................................. .. ..... .. ........ .. ..
1 .4 S tu d y A rea .................................... ....... ... ............ .............. 7
1.4.1 Geology and Hydrology of the Indian River Lagoon System .......... ......
1.4.2 R regional Clim ate ....... ........ ...... ..... .. ........ .. ..................10

2 METHODS ...................... ............................. 13

2.1 W after Samples ........................................................................ .... ......... ................. 13
2.1.1 Pore W ater Sam ples ............................................................................13
2.1.2 Lagoon and Seep W ater Samples...................... ................... .......... 16
2.1.3 A analyses ..................................... ... ..... ........ ...... 17
2.2 Sediment Cores ........... ....................... ......... .. 18
2.2.1 Sampling ................................................................................................... 18
2 .2 .2 A n a ly se s ............................................................................................... 2 0

3 R E S U L T S .............................................................................2 3

3.1 Physical Analyses ............... ........................... ... ...... ...............23
3.1.1 Description of Cores .............................................. 23
3.1.2 P orosity ............... ............................................................ ... ............. 27
3 .1.3 D en sity ................................................................................ .............. 2 8
3.2 C hem ical A analyses ................................................ ................29
3.2.1 Total Phosphorus (TP) and Total Nitrogen (TN) ......................................29
3.2.2 Total O rganic M atter (OM ) ................................................................. 30
3.2.3 Total C arbon (TC) ............................................................ 30









3.2.4 B iogenic Silica (Si0 2) ........................................ .......................... 31
3.2.5 210Pb and Sedimentation Rates ........................................ ...............31

4 D IS C U S SIO N ..................................................................................... 39

4 .1 In tro d u ctio n ..................................................................................................... 3 9
4 .1.1 C on ceptu al M odel ........................................................... .....................4 0
4.2 Sedim ent Profiles ......................... .... ........ .. ...... .... ...... ................ ........ 43
4.2.1 Correlation Between Physical Properties and Ground Water Discharge
R a te s ................................................................................ 4 3
4.2.2 D density ..................................... ....................... ........ ............... 44
4.2.3 Total Organic Matter as a Source of Nutrients.........................................45
4.2.4 Comparison of Total Phosphorus (TP) and Total Nitrogen (TN) with
N utrient Fluxes ........................................................ .... ....... ......... 46
4.2.5 Redfield Ratios and their Significance to the Banana River Lagoon.........47
4.3 Em erson's Si02 M ixing M odel ........................................ ........................ 51
4 .3 .1 Introdu action .................................................................. 5 1
4 .3.2 T he M odel .................................................................... 52
4.3.3 M odel Solution and R esults.................................... ............................. 55
4.4 M ass B balance C alculation........................................................... ............... 59
4 .4 .1 Introdu action ............................................................59
4 .4 .2 C alcu nation s ............................................................63

5 C O N C L U SIO N S ................................................................66

5.1 Sum m ary ........... .... .............. .................................. ..........................66
5 .2 F u tu re W o rk .................................................................................................... 6 9

APPENDIX

A PHYSICAL AND CHEMICAL ANALYTICAL DATA FROM CORE BRL2 ........70

B PHYSICAL AND CHEMICAL ANALYTICAL DATA FROM CORE BRL6 ........73

L IST O F R EFE R EN C E S ............... ............... ......................................... 76

B IO G R A PH ICA L SK ETCH .......................................................................... ... 82














v
















LIST OF TABLES


Table page

1-1. Various techniques used to measure ground water discharge in the Indian River
Lagoon (from M artin et al. 2000).............. ........................ ............ ............... 3

1-2. Summary of measured and 30-year average rainfall for the sampling sites (from
M martin et al. 2000) ................. ............... .. .. .......... .. ........ .. ............ 11

2-1. Estimated precision of various solutes for water samples ..................... ................18

2-2. Estimated precision of various sediment sample analyses......................... ........ 22

3-1. Estimation of sedimentation rates at BRL2 and BRL6 using gamma detectors. .......31

4-1. Description and values of parameters used in the model for BRL2...............................55

4-2. Average concentration of TP, TN and Si02 up to 80 cm within the sediment at
BRL2 and BRL6. .............. ........... ... .... .. .......... .... .... .. ............. 63

4-3. Average pore water concentrations up to 80 cm (from Lindenberg 2001). ..............64

4-4. Comparing input fluxes to the sediment versus output fluxes to the lagoon water
of TP, TN and Si02 at BRL2 and BRL6. .......................... ............... 64
















LIST OF FIGURES


Figure page

1-1. Location m ap of study area. ............................................... .............................. 8

1-2. Average monthly precipitation for the year 2000 (from Martin et al 2000)..............12

2-1. Design of a multi-sampler (from Martin et al. 2000). ..............................................15

2-2. Vibracoring technique being used to collect the sediment core. ..............................19

3-1. Sediment Core from BRL2. Images to the right are real photographic images of
short sections of the core representing the five zones ................ ............... 25

3-2. Sediment Core from BRL6. Images to the right are real photographic images of
short sections of the core representing the eight zones. ....................... ....... 26

3-3. Porosity of sediment (a) BRL2, (b) BRL6. .......................... ............... 27

3-4. Bulk Density of sediments (a) BRL2, (b) BRL6 .............. ...................... ...........28

3-5. Total phosphorus concentrations in sediment (a) BRL2, (b) BRL6...............................33

3-6. Total nitrogen concentrations in sediment (a) BRL2, (b) BRL6..............................34

3-8. Total carbon concentrations in sediment (a) BRL2, (b) BRL6 ...............................36

3-9. Concentration of total organic and total inorganic carbon present in the sediment
at (a) B R L 2 (b) B R L 6. ................................... .......... ................ ............. 37

3-10. SiO2 concentrations in sediment (a) BRL2, (b) BRL6 ....................... ..................38

4-1. C1- profile concentration suggesting mixing in shallow sediments in the
Banana River Lagoon (BRL). C.Z = Coastal zone, FW = Fresh water, U.A =
Unconfined aquifer, C.A = Confined aquifer, AT = Aquitard (Inset of the C1
profile taken from M artin et al. 2000) ............... ..................... ........... ............... 41

4-2. A conceptual model showing mixing at the sediment-water interface due to
bioturbation or wave action. L.W.= Lagoon Water, S.W.= Seep Water,
P.W. = Pore Water. B = Worms burrowing into sediment and ingesting
sedim ent particles .............................. ...................... ... .. ...... .... .. .... ...... 42









4-3. Redfield ratios of organic C:P:N within sediments at BRL2. .................................49

4-4. Redfield ratios of organic C:P:N within sediments at BRL6. ...................................50


4-5. Model
(K=
(K=

4-6. Model
(K=
(K=

4-7. Model
(K=
(K=


solutions for the depth distribution of silicate for enhanced mixing
10-3 cm2 s-1) with no non-local transport (a = 0), and molecular diffusion
10-5 cm2 s-1) and non-local transport (a = 4 x 10-7 s-1): May 2000 ................57

solutions for the depth distribution of silicate for enhanced mixing
10-3 cm2 s-1) with no non-local transport (a = 0), and molecular diffusion
10-5 cm2 s-1) and non-local transport (a = 4 x 10-7 s-1): August 2000.............58

solutions for the depth distribution of silicate for enhanced mixing
10-3 cm2 s-1) with no non-local transport (a = 0), and molecular diffusion
10-5 cm2 s-1) and non-local transport (a = 4 x 10-7 s-1): December 2000........59


4-8. Cross section of the seep meter showing organic matter remineralization at the
sediment-water interface enclosed within the seep meter. P.W.= pore water,
L.W .= lagoon water, S.W .= seep water. ..................................... ............... 62















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

CHEMICAL TRACING AND ANALYTICAL AND MASS-BALANCE MODES OF
PORE WATER CIRCULATION IN THE BANANA RIVER LAGOON, FLORIDA

By

JEHANGIR H. BHADHA

May 2003

Chair: Dr. Jonathan Martin
Major Department: Geological Sciences

The determination of nutrient fluxes is an important calculation in coastal and

estuarine settings. Investigation of physical properties and chemical composition of the

sediments in the Banana River Lagoon suggests that shallow sediments could be an

important source of nutrients to the lagoon. This nutrient flux depends on (i) the rate of

ground water discharge and (ii) the concentration of the nutrient in the discharged water.

Mixing between the lagoon and pore water can alter the composition of shallow marine

sediments, which are a source of nutrients to the lagoon through ground water discharge.

Two sites previously studied for water chemistry viz. BRL2 and BRL6 were

selected for collecting cores. Average porosity of sediments from BRL2 was -31 %,

compared to BRL6 which was 39 %. Nutrient fluxes cannot be measured with seep

meters because of a number of possible artifacts, including induced flow effects and

enhanced organic matter remineralization, due to limited availability of dissolved oxygen

within the seep meter.









Mass balance calculations using pore water concentrations in BRL2 suggest that TP

discharge may be 20%, and TN discharge -100 % greater than the input of P and N

through detrital OM. These high output fluxes are a result of organic matter

remineralization at shallow depths below the sediment-water interface, due to mixing

between lagoon and shallow pore waters. Determining the exact mixing depth, and the

depth to which OM remineralization may be influenced by this mixing may prove to be

vital for mass balance calculations.

Mathematically, the transport mechanism that describes this mixing can be

formulated using a one-dimensional diffusion coefficient (K), a non-local term (a) and a

reaction term (R). Profiles of SiO2 pore water concentration at BRL2 suggest that

molecular diffusion (K = 10-5 cm2 s-1) does not dominate the random transport

mechanism to 110 cm below the sediment-water interface. For a to approach the desired

SiO2 concentration, it requires a diffusion coefficient that is two orders of magnitude

faster (K= 10-3 cm2 s-1) than molecular diffusion, suggesting an enhanced mixing process

induced probably by bioturbation, wave action, and tidal pumping. A slightly slower

mixing regime (K = 10-4 cm2 S-1) below 110 cm may correspond to the maximum depth

up to which wave action and tidal pumping may affect mixing.














CHAPTER 1
INTRODUCTION

1.1 Statement of Problem

Submarine ground water discharge is defined as any flow out across the seabed,

regardless of composition or driving force. The discharge of ground water to coastal

marine environments such as bays, estuaries, and lagoons may represent an important

transportation process for pollutants including excess nutrients, from shallow sediments

to overlying surface waters. The importance of such a phenomenon has gained increased

recognition in recent years because studies have shown that submarine discharge of water

transports nutrients from agricultural lands (Simmons 1992, Gallagher et al. 1996) and

residential septic tanks (Weiskel and Howes 1992) to coastal marine waters. This nutrient

flux has lead to poor water quality and eutrophication of near shore ecosystems (Nixon

1986, Corbett et al. 2000).

The movement of water represents one of the primary controls of the distribution of

pollutants in estuaries (Gallagher 1996, Martin et al. 2000). Water budgets of estuaries

are routinely determined by measuring the volumes of surface water runoff, atmospheric

deposition, and evapotranspiration in the area. One important variable in the budget, the

ground water discharge, is poorly constrained because of the difficulties associated with

locating and measuring the flow (e.g. Moore 1996, Cable et al. 1996a,b, Martin et al.

2000). Ground water discharge has previously been assumed to occur through seepage

from aquifers, where confining layers are missing. In this case, water would originate on

continents as meteoric water and flow laterally through aquifers from the continents to









coastal areas. However, the assumption that all ground water discharge originates from

the continents as they flow though major aquifers may be erroneous. For example, recent

modeling by Li et al. (1999) has shown that only 4 % of ground water discharge to the

Atlantic continental shelf recognized by Moore (1996) using 226Ra isotopes originates

from the underlying Floridan aquifer. Martin et al. (2000) reached similar conclusions by

comparing the chemical and isotopic compositions of shallow pore water, discharging

ground water, and surface lagoon water in the Indian River Lagoon, Florida. These

observations have led to the suggestion that lagoon water may be circulating through

shallow marine sediments. This circulation may occur by pumping mechanisms, such as

wave action and bio-irrigation (e.g. Emerson et al. 1984, Shum 1992, Li et al. 1999). The

need to identify and understand this additional source of water is critical in order to

accurately assess the hydrologic and nutrient budgets of the lagoon.

Methods used to quantify ground water discharge include direct flow

measurements using devices such as seep meters (Lee 1977, Martin et al. 2000), chemical

tracers (Cable et al. 1996 a., Bunga et al. 1996, Martin et al 2000), and numerical ground

water flow models (Pandit and El-Khazeen 1990, Li et al. 1999, Robinson and Gallagher

1999). Seep meter and tracer techniques have yielded similar discharge rates, but the

values can be greater by several orders of magnitude than those calculated using

numerical modeling for identical areas (Table 1-1). Seep meters provide a simple and an

inexpensive approach to assess ground water discharge. Besides, they have been used

widely, and thus can be compared with previous studies from other areas. Seep meters

measure the total flux of water from the sediment regardless of its source, unlike

numerical flow models, which are restricted to flow from the particular aquifer being









modeled. This total flux could include additional sources such as re-circulated seawater

or lagoon water that enters the subsurface through tidal or wave pumping. However, their

deployment is laborious and numerous deployments are required in order to provide an

integrated value from even a small region. Also, there are a number of possible artifacts

associated with using this technique. One such example is current/topography-induced

flow, which suggests that the positive profile of seep meters creates an airfoil effect

similar to the lift created by an airplane wing (Shinn et al 2002).

Table 1-1. Various techniques used to measure ground water discharge in the Indian
River Lagoon (from Martin et al. 2000).
Reference, Year Location Technique Flux
(ml/m2/min)
Martin et al., 2000 Indian River Lagoon, FL Tracer (Rn, Ra) 11 66
Martin et al., 2000 Indian River Lagoon, FL Seep meter 40 65
Pandit & El-Khazen, 1990 Indian River Lagoon, FL Numerical 0.002
__modeling

Ground water discharge may be particularly important for Florida's estuaries

because of the occurrence of large and productive aquifer systems, a long coastline and

extensive precipitation across the region. Wherever an aquifer with a positive head is

connected to overlying surface waters through permeable bottom sediments, submarine

ground water discharge may occur (Johannes 1980, Rutkowski et al. 1999). Such a

situation occurs along the east coast of Florida in the Indian River Lagoon, where the

Floridan or Surficial aquifers are semi-confined, suggesting that water may flow from the

aquifer to the overlying lagoon waters. It has been suggested that only 2.5 % of ground

water discharge to the Indian River Lagoon originates from the underlying Floridan

aquifer (Martin et al. 2000, Lindenberg 2001), while the remaining discharged water

could be the result of circulation through shallow marine sediments. Further, the Cf1

concentrations of regional pore water also suggest that there is significant amount of









mixing between the shallow pore water and the overlying lagoon water (Martin et al.

2000). This mixing is shown by changes through time in the concentration of C1 between

0-70 cm depths below the sediment-water interface, with little change through time in

their concentration at depths below 70 cm.

Activities of benthic organisms and the biogenic structures they produce influence

the physical and chemical properties of marine sediment deposits (Aller 1980, Boudreau

and Marinelli 1994, Sandnes 2000). Benthic activities such as feeding, burrowing, and

irrigation result in particle and fluid transport near and across the sediment-water

interface, a critical boundary zone for diagenic reactions (Aller 1980). Effects of these

activities on sediment properties may influence redox conditions of sediment and pore

water, organic matter and contaminant-degradation rates, dissolution of biogenic

compounds (CaCO3 and SiO2), nutrient fluxes and pore water profiles. The need to

account quantitatively for these effects has resulted in the development of different types

of one-dimensional numerical models that can predict vertical mixing of particulate

sediment and diagenetic reactions (Berner 1980, Wheatcroft et al. 1990), and to

characterize the geochemistry of ventilated sediments (Boudreau 1984, Emerson et al.

1984, Sandnes et al. 2000).

Emerson et al. (1984) suggested that pore water profiles in shallow estuarine

sediments of Puget Sound show characteristics of enhanced pore water transport by

animal activity. According to this study the fluxes of alkalinity, ammonia and silicate

across the sediment-water interface due to biological processes are greater than that by

molecular diffusion. Using an in situ 3H experiment and dissolved silicate profiles he

evaluated the transport parameter due to animal activity in the uppermost 20 cm of









sediments to be 1 5 x 107 s1, which is in the range of similar parameters determined in

other near shore environments in the U.S. such as, Long Island Sound (Goldhaber et al.

1977) and the Hudson River Estuary (Hammond et al. 1977).

Ground water flux rates have been the focus of several studies in the past (e.g.

Gallagher et al. 1996, Cable et al. 1996 b., Li et al. 1999), but the associated nutrient

fluxes have rarely been measured. Quantifying nutrient fluxes requires knowing nutrient

concentrations within the water column, shallow sediments, and the discharging ground

water. While there is a steady input of nutrients entering the lagoon through deposition of

sediments, they are constantly being released to the pore water from the sediment through

remineralization of organic matter, and transported via diffusive and advective processes.

Hence, the discharging ground water should be enriched in nutrients. This enrichment

suggests that diagenetic reactions and flow rates in shallow sediments are critical for

determining nutrient fluxes.

An interesting approach to understanding nutrient fluxes at the sediment-water

interface could be by determining a mass balance calculation between detrital nutrient

fluxes to the sediment, versus the flux of nutrients to the water column from ground water

discharge. The bio-availability of dissolved phosphorus and nitrogen is thought to control

biological productivity (Tyrrell 1999, Schenau and Delange 2001). Only a small fraction

of particulate phosphorus and nitrogen produced in the photic zone (depth to which

sunlight can penetrate) is ultimately buried in the sediment, while the remainder is

remobilized and reutilized by the marine ecosystem. Up to 99 % of the total nutrient

fluxes out across the sediment water-interface is a result of microbial oxidation within the

upper 1-5 cm of the sediment, where most algae and benthic organisms live (Berner









1980, Tyrrell 1999). These nutrient fluxes brought about by advective transport

mechanisms, represents a far greater source of nutrient transportation than diffusive

processes from shallow pore waters to the overlying lagoon. However, if some of the

seep water (i.e. all water that flows to the lagoon from underlying sediments and rocks) is

re-circulated lagoon water, then only the excess nutrients in the seep water (i.e. seep

water lagoon water) will represent a new source of nutrient loading to the lagoon

generated as a result of organic matter remineralization.

1.2 Hypotheses

Through detailed field sampling and measurements, laboratory analyses, and

mathematical modeling I plan to test the following hypotheses:

* Ground water discharge includes all sources of water that flows across the
sediment-water interface, including lagoon water re-circulation through shallow
marine sediments.

* The circulation of lagoon water through shallow marine sediments corresponds to
a greater flux of water and associated nutrients from the sediments through
advective rather than diffusive processes.

* The concentration of nutrient fluxes across the sediment-water interface depends on
the availability and magnitude of organic matter remineralization within shallow
sediments.

The Banana River Lagoon along the east coast of Florida is an ideal site to test the above

hypotheses, because of the presence of highly permeable and shallow aquifers, a long

coastline and extensive but seasonal precipitation.

1.3 Goals and Objectives

The goal of this research is to determine the sources of ground water discharge, its

nutrient load, and trace the movement of pore water at two sites in the Banana River

Lagoon (viz. BRL2 and BRL6). This goal will be met through successful completion of

the following 3 objectives:









1. To use visual evidences and physical properties of sediments in making
correlations between sediment type and ground water discharge rate.

2. Using mathematical modeling to test the possibility of a non-local transport
mechanism (enhanced mixing), which may affect sediment-water dissolved fluxes
in near shore marine environments.

3. To determine realistic nutrient fluxes across the sediment-water interface within the
lagoon, using mass balance calculations.

Results from this project will provide a better scientific understanding of a

fundamental process in estuaries, viz. the re-circulation of lagoon water within shallow

sediments. If however, advective fluxes of nutrients are as large as those from surface

runoff and atmospheric deposition, it is critical to determine the sources) of these fluxes

in order to estimate the magnitude of nutrient loading from natural internal process, such

as bioturbation, tidal pumping, and wave action. While internal nutrient loading may

exceed the magnitude of external loading from surface water runoff, it is the external

loading that ultimately drives this cycle.

1.4 Study Area

The Indian River Lagoon system estuary extends 250 km along Florida's central

Atlantic coast, from north of Cape Canaveral in Brevard County to as far south as St.

Lucie inlet in Martin County. Three estuaries make up the system including the Indian

River Lagoon, Banana River Lagoon and the Mosquito Lagoon. The Mosquito Lagoon

extends to New Smyrna Beach, approximately 30 km north of the northern end of the

Indian River Lagoon, and the Banana River Lagoon is separated from the northern Indian

River Lagoon by Merritt Island, marking the eastern edge of the Indian River Lagoon

(Figure 1-1).





















Atlantic Ocean


mm.m
0 1 2 34 5
km


80'30'


Mosquito
Lagoon


Banana
Lagoon


STUDY AREA


SVero
Beach


Ul1W


8045'


Figure 1-1. Location map of study area.


80'30









1.4.1 Geology and Hydrology of the Indian River Lagoon System

The hydrostratigraphy of Florida can be broadly divided into three principle units

including from deepest to shallowest, the Floridan, Intermediate, and Surficial aquifers

(Miller 1986, Scott 1992, Groszos et al. 1992). The Floridan aquifer consists of Miocene

and older carbonate rocks. These rocks have been extensively dissolved in the subsurface,

and consequently are characterized by heterogeneous hydraulic conductivity and

extensive subsurface drainage. The Floridan aquifer represents one of the most

productive aquifer in the world, and provides the primary source of water to the northern

half of Florida. The Floridan aquifer is locally divided into the Upper and Lower Floridan

aquifer depending on the presence of a confining unit. The Intermediate aquifer consists

of carbonate lenses contained within the Miocene Hawthorne Group, which is composed

of siliciclastic clay and phosphorite-rich rocks (Scott 1988). To the south of the Indian

River Lagoon, the Intermediate aquifer is thin and relatively non-productive (Toth 1988).

The Surficial aquifer has been subdivided into separate units informally named the

Shallow Rock aquifer and Shallow Clastic aquifer (Toth 1988). These aquifers consist

largely of mixtures of sand, coquina and clay layers, with the clay layers providing the

confining layers between the aquifers.

The Hawthorn Group acts as the primary confining layer to the Floridan aquifer. In

general, the Floridan aquifer is considered to be confined where the Hawthorn Group

reaches a thickness of more than 33 m and semi-confined where it is less than 33 m thick.

The boundary between confined and semi-confined Floridan aquifer cuts across the

northern portion of the Indian River Lagoon north of Melbourne, and this boundary is

missing in the northernmost reaches of the Indian River Lagoon and the Mosquito

Lagoon (Scott 1988, Toth 1988). The shallow rock aquifer unit of the Surficial aquifer is









Pliocene in age and equivalent to the Tamiami Formation. It overlies the Hawthorn

Group and varies in thickness. It is approximately 30 m thick to the south of the Indian

River Lagoon and is missing from the Lagoon to the north of approximately Cocoa. Four

informally defined plastic aquifers border the Indian River Lagoon, including Terrace

Island, Atlantic Coastal Ridge, Ten-mile Ridge and Inter-ridge aquifer. Terrace Island

aquifer occurs on the barrier islands separating Indian River Lagoon from the Atlantic

Ocean, and supplies potable and irrigation water to communities on the islands. The

aquifer depends on local rainfall for replenishment. The Atlantic Coastal Ridge aquifer

occurs on the western bank of Indian River Lagoon and in the northern reaches of the

lagoon is composed of the Pliestocene Anastasia Formation. This aquifer provides most

of the water supply for towns on the western edge of the northern Indian River Lagoon.

1.4.2 Regional Climate

The subtropical climate for this region typically demonstrates a dry season (January

to May), a rainy season (June to September), and a winter storm season (October to

December). Three separate sampling trips were made to the lagoon in 2000 in the months

of May, August, and December when samples of lagoon, seep and pore water were

collected (Martin et al. 2000, Lindenberg 2001). Climatic conditions during field

sampling, and their comparisons with average conditions are important in order to

determine how representative the data is from discrete field trips over relatively short

periods, and thus, if the data can be extrapolated over longer time scales. Results from

this study could represent a single point in time, however several such points would be

required to make generalizations on a larger time scale. The cumulative monthly

precipitation data for Titusville and Melbourne, for the year 2000 are presented in Table

1-2, along with values for the 30-year average precipitation for these sites. During 2000,









the annual precipitation at Melbourne, Florida, was 17 % below the 30-year average at

Vero Beach. Monthly precipitation was lower than the 30-year average by 10.03 cm (91

%) in May, by 6.70 cm (43 %) in August, and by 4.87 cm (88 %) in December 2000

(Figure 1-2). Rainfall in May was low overall, but sampling was done during a time when

80 % of the total monthly rainfall was deposited. The August wet season sampling trip

encompassed a rainfall of 2.69 cm, which was 31 % of the total monthly precipitation. A

small amount of rain fell during the sampling trip in December (0.051 cm), representing

only 8 % of the total monthly quota.

Although the sampling trips made in 2000 could be considered as those made

during a drought-year for the study area, the precision and comprehensiveness with

which samples were collected and data reported proved very useful for my study, which

was conducted in November 2002, under similar drought conditions.

Table 1-2. Summary of measured and 30-year average rainfall for the sampling sites
(from Martin et al. 2000).
Month 2000 Precipitation, 30-year Precipitation,
Melbournea (cm) Vero BeachB (cm)
January 5.94 5.44
February 0.86 7.39
March 5.54 7.85
April 6.71 4.83
May 1.04 11.07
June 17.86 16.41
July 24.82 15.47
August 8.79 15.49
September 21.36 18.16
October 13.23 14.02
November 0.91 8.31
December 0.64 5.51
Annual 107.70 129.95
aSource: NOAA Monthly Station Normals, 1961-1990.
bSource: NOAA, 2001 (http://www.srh.noaa.gov/ml/mlbclimat.html#2000).






12



30

u 25

0
00 Total monthly Precp.
C". (Melbourne)
15
U 30-yr normal (Vero
a- 10 Beach)





000000000000
ooo000000000000
C L- 6) Q 0-
S u_ < 2 < U) Z r)


Figure 1-2. Average monthly precipitation for the year 2000 (from Martin et al 2000).














CHAPTER 2
METHODS

2.1 Water Samples

In 2000 three separate sampling trips were made to the Indian River and Banana

River Lagoons (May 2000, August 2000 and December 2000) to collect pore water,

lagoon water and seep water samples from twenty-one separate stations (Martin et al.

2000, Lindenberg 2001). Eight sites were sampled in the Banana River Lagoon, (BRL1 to

BRL8), and thirteen sites were sampled from the Indian River Lagoon, (IRL29 to IRL42).

In all, 70 bottom water samples and 90 pore water samples were collected. In addition,

ground water wells, a spring, and numerous rivers and inlets were also sampled. All of

the water chemistry data used here has been taken from Lindenberg (2001).

2.1.1 Pore Water Samples

Pore water sampling was done using a device called the "multi-sampler" (Martin et

al. 2003). It consists of a multilevel piezometer that is used along with a peristaltic pump

to extract water from the sediment pore spaces at various depths. The design of the multi-

sampler consists of 2" ID schedule 80 PVC pipe with /4" OD (3/8" ID) PVC tubing fed

through the interior of the pipe (Figure 2-1). The PVC tubing is glued to ports in the pipes

and each port is screened with a 250 [iM screening material (Nytex). The ports exit the 2"

pipe in a spiral fashion with each one located 900 offset from the ports above and below.

The tubing is lead outside the PVC pipe through a T-joint. Multi-samplers were driven as

far as possible into the sediment using a hammer. The distribution of ports is variable

along the length of the multi-sampler, with the ports more closely spaced at the top than









at the bottom. This distribution allows higher resolution sampling of the pore water near

the sediment-water interface where concentration gradients are likely to change more

rapidly with depth because of diagenetic reactions (Martin et al. 2000). Some ports did

not yield water when pumped, and presumably were located within sedimentary layers

with low permeability.

Once the multi-samplers were installed, they were left to equilibrate for about 24

hours before extracting water. Water was pumped at a rate of approximately 1 ml/s into a

small plastic bucket and the dissolved oxygen concentration, conductivity and

temperature were monitored, until the values remained constant. Once the values

remained constant, their values as well as those of pH and salinity were recorded and

water samples were collected. After sufficient water was available for chemical analyses,

water was drawn from the bucket into a 60 ml syringe and filtered through a 0.45 |tm

filter into two 125 ml HDPE Nalgene bottles that were pre-labeled with the station and

the date. One bottle was acidified with 50 [tl of 16 N optima grade HC1. The samples

were collected for a variety of analyses including conservative chemical tracers and

nutrients.

This study focuses mainly on stations BRL2 and BRL6. These stations were chosen

because at BRL2 the multi-sampler penetrated to its maximum depth of 230 cm, with all

ports yielding water when pumped, thus providing a good resolution to the pore water

profiles.










To water
surface


71 cm


Connectors


Sediment-Water
I nterface
10

30
cm) Port
50


80 'Length
5.7 cm


10 Screened
interval
13.3 cm2

50
Cross Section
Patch
90 4 s Screening
V e") Material

PVC tube
'30
PVC Pipe


Figure 2-1. Design of a multi-sampler (from Martin et al. 2000).


Cable


Depth (c


2









2.1.2 Lagoon and Seep Water Samples

Seep water refers to all water that flows to the lagoon from sediments and rocks

that underlie the lagoon, and is collected at the sediment-water interface. Seep water was

collected using a device called "seepage meters" (Lee 1977). Seepage meters are

constructed from the ends of 55-gallon drums. The ends of the drums are cut from the

sides so that 15 cm of the drum wall remained attached to the ends. Half inch holes are

drilled into the flat top in order to install connectors for the seepage bags (4 L plastic

bag). The seep meters channel the water flowing from the sediment into the seepage bag

for a known amount of time. The volume of water collected in the bag, divided by the

length of time of the collection and the surface area covered by the seepage meter yields a

seepage flux rate in units of volume of water per surface area per time (ml/m2/min). The

method used to collect seep water was similar to the method used to measure seepage

rate. The single difference between measuring seepage rate and collecting seep water

samples is that the seepage bags were clean and dry prior to attaching them to the seep

meters. The bags were left on the seep meter until at least 1 L of water had flowed into

the bags.

After sufficient water was available for chemical analyses, the bag was removed

from the seepage meter. Water was drawn from the bags into a 60 ml syringe and filtered

through a 0.45 [tm filter into two 125 ml HDPE Nalgene bottles that were pre-labeled

with the station and the date. One bottle was acidified with 50 [tl of 16 N optima grade

HC1, while a third bottle was used to store unfiltered and non-acidified water samples. All

samples were kept refrigerated until analyzed.









Lagoon water samples were collected by submerging a 2 L plastic bucket

approximately 25 cm below the water surface. Samples were preserved in the same way

as water from the seep meters at BRL2 and BRL6.

2.1.3 Analyses

Analyses of pore water, seep water and lagoon water were conducted and reported

by Mary Lindenberg (2001). Measurements were done in the Land Use and

Environmental Change Institute (LUECI) Laboratory, at the Department of Geological

Sciences, University of Florida. Concentrations of PO4 and Si02 were measured on the

non-acidified filtered water samples, and NH4 were measured on acidified filtered water

samples using spectrophotometric techniques following procedures described in Clesceri

et al. (1989). Nitrogen and phosphorus concentrations were measured following Kjeldahl

digestion measurement on a Technicon Autoanalyzer II for both filtered and non-filtered

samples. The concentrations of these samples were reported as total nitrogen (TN) and

total phosphorus (TP) concentrations for the non-filtered samples. Filtered samples were

used to measure total soluble nitrogen (TSN), total soluble phosphorus (TSP), and NO3

concentrations, prior to Kjeldahl digestion of the sample. Precision1 of PO4 and NH4

analyses was checked by analyzing a check standard every fourth sample, and calculating

the coefficient of variation (standard deviation divided by mean) of the values measured

for the check standard. Precisions of the TSN, TN, TSP, TP and NO3 concentrations were

checked by analyzing duplicates every tenth sample. Precision of the various solutes is

reported in Table 2-1.


1 Precision is the coefficient of variation, COV = 1c/mean









Table 2-1. Estimated precision of various solutes for water samples.
Solute Precision (%
PO4 2.6
NH4 2.5
TSN 1.5
TN 1.7
TSP 4.1
TP 2.2
SiO2 0.5


2.2 Sediment Cores

Two separate cores were taken, one from BRL2 and one from BRL6 respectively

during a sampling trip to the Banana River Lagoon in November 2001. The cores were

collected using vibracoring technique, which allows retrieval of long (up to 10 m),

continuous, sections from unconsolidated saturated sediments. Vibracoring works on the

principle of liquefaction in fine-grained sediments by displacing sediment to allow

passage of the pipe (Smith 1984). The effectiveness of the vibracore in relation to

penetration and recovery is directly related to the physical properties of the material

being sampled. The technique works best in saturated organic sediments, clays, silty

clays, silts and fine sands, but is inefficient in firm clays and medium to coarse sands

(USGS, 1998).

2.2.1 Sampling

At BRL2 and BRL6 coring was accomplished using a 2 m long section of

aluminum pipe as the core barrel, with an internal diameter of 7.5 cm. The pipes were

cut to a point and sharpened at one end to allow easy penetration (Figure 2-2). Once the

pipes had been driven to a depth of-1.9 m, the open end was capped to provide a slight

vacuum as the pipes were retrieved. The pipes were then pulled out of the sediment using

a winch and steel cable. Compaction for the cores was about 16 %. This was measured by









calculating how much of the core had slumped within the pipe, prior to sectioning.

Excess water was removed from the upper portion of the pipes, and the pipes were

trimmed at both ends, without disturbing the core. Top and bottom were marked on the

pipe ends along with the core name and length of the section. The ends of the pipes were

sealed with rubber caps and electrical tape. Compacted core lengths retrieved were 1.57

m and 1.62 m sediment from BRL2 and BRL6 respectively. Both cores were transported

to the Florida Institute of Paleoenvironmental Research (FLIPER) Laboratory, at the

Department of Geological Sciences, University of Florida, while remaining vertical in

order to minimize mixing.






















Figure 2-2. Vibracoring technique being used to collect the sediment core.

In the laboratory, the cores were split lengthwise, described, photographed and

sampled two days after coring was completed. One section was used to measure sediment

bulk density, and take high-resolution digital images (40 pixels/cm) of the entire core

lengthwise, using the Geotek Multi-sensor Core Logger (MSCL). The accuracy of the









bulk density was determined using a standard aluminum density calibration piece (Weber

et al. 1997). The other section was used to take samples for measuring porosity, total

carbon (TC), total nitrogen (TN), total phosphorus (TP), total organic matter (OM), and

biogenic silica (Si02). Samples were collected at 2 cm intervals. Before sample material

was removed from the core barrels, the split surfaces were prepared by scrapping off the

top few millimeters of the core to remove any contaminated material that may have

originated during splitting. Sectioning was accomplished using a serrated knife, washing

and drying the knife after each section. Each section was removed carefully and stored in

a labeled, pre-weighed 25 ml Fisher brand plastic bottle. Each sample (bottle + wet

sediment) was weighed, and then freeze-dried.

2.2.2 Analyses

After freeze-drying, the samples were gently crushed to break up large lumps of

sediment, shells and any other debris. Crushing was done by hand, using a ceramic

mortar and pestle. Crushed sample material was well mixed and transferred back into

their bottles.

Percent porosity was calculated by using the formula:


% Porosity = MWS -MDS x100
Mws

where Mws = mass of wet bulk sediment,

and MDS = mass of dried sediment.

TC and TN were analyzed using a Carlo Erba NA 1500 analyzer, in the Stable

Isotope Laboratory, at the Department of Geological Sciences, University of Florida.

Approximately 60-100 |tg of sample was placed in tin cups and dried under a heat lamp.

TC and TN were determined following combustion at 1000 oC. Precision of the analyses









was checked by analyzing duplicates every tenth sample, and calculating the relative

percent difference (RPD), which is the absolute difference between the duplicates divided

by the mean of the duplicates (Table 2-2.). For BRL2 and BRL6 the average RPD for TC

was 4.4 %, (largest difference 5.7 %), whereas the average RPD for TN was + 4.1 %

(largest difference 7.1 %).

Total phosphorus was analyzed using a Bran-Luebbe Autoanalyzer, in the LUECI

Laboratory, at the Department of Geological Sciences, University of Florida. To 0.05 g of

dry mass sample 20 ml of 0.53 M sulfuric acid and 10 ml of 0.062 M potassium

persulfate was added. The batch was sonicated for ten minutes. It was then placed in an

autoclave for thirty-five minutes at about 100 C. Finally, 1 ml of the solution was added

to 10 ml of 0.1325 N NaOH. All samples were centrifuged at 1500 rpm before analysis.

Precision2 of the analyses was checked by analyzing duplicates every tenth sample, and

calculating the RPD. For BRL2 the average RPD was 2.5 %, and for BRL6 the average

RPD was 2.2 % (largest difference 3.6 %).

Biogenic SiO2 was also analyzed using the Bran-Luebbe Autoanalyzer, in the

LUECI Laboratory, at the Department of Geological Sciences, University of Florida. To

0.05 g of dry mass sample 40 ml of 5 % Na2CO3 solution was added. The batch was

sonicated for ten minutes, and then placed in an autoclave for thirty-five minutes at

100 C. Finally, 1 ml of the solution was added to 9 ml of 0.105 N HC1. All samples were

centrifuged at 1500 rpm before analysis. Precision of the analyses was checked by

analyzing duplicates every tenth sample, and calculating the RPD. For BRL2 the RPD

was 1.4 %, and for BRL6 the RPD was 0.8 % (largest difference 1.9 %).


2 Precision is the Relative Percent Difference, RPD = (Ixi-x21)/Xmean.









Loss on ignition is a common and widely used method to estimate the total organic

matter content of sediments (Dean 1974, Bengtsson and Enell 1986). Approximately 2.0

g of dry mass sample was oxidized at 550 C in a muffle furnace for two hours. The

weight loss during the process was measured by weighing the samples before and after

heating. The difference in weight represented the total organic matter content of the

samples.

An attempt was made to estimate sedimentation rates using measurements of the

activity of naturally occurring radioisotopes in sediments. The method used is based on

determining the activity of 210Pb (half-life 22.3 years), a decay product of 226Ra (half-life

1622 years) in the 238U decay series. Age at depth in sediments is determined from

stratigraphic profiles of unsupported 210Pb (daughter product of 226Ra present in the

sediment). Total 210Pb activities were measured by subtracting the supported 210Pb in

equilibrium with 226Ra. Radiometric measurements were made using low background

gamma counting systems with germanium detectors (Schelske et al. 1994). Activities for

each radionuclide were calculated using empirically derived factors of variation in

counting efficiency with sample mass and height (Schelske et al. 1994). Samples were

prepared by packing plastic test tubes up to 3 cm with dry sediment. The amount of

sediment packed was weighed, and the tubes were then sealed with a mix of epoxy resin.

They were set aside to equilibrate for three weeks before analysis.

Table 2-2. Estimated precision of various sediment sample analyses
Analyses Precision (%) BRL2 Precision (%) BRL6
TC 4.4 4.4
TN 4.1 4.1
TP 2.5 2.2
SiO2 1.4 0.8














CHAPTER 3
RESULTS

3.1 Physical Analyses

Physical analysis of cores such as type of sediments, color, texture, grain size, etc.

can provide information that may be useful to compare with chemical analyses. For

example, clay or dark muddy sediment is usually rich in organic matter, compared to

light siliceous sand. Sediments that have not been buried appreciably, say less than about

one meter, are subject to mixing by benthic organisms due to activities such as feeding

and burrowing (Aller 1980, Berner 1980, Sandnes et al. 2000, Boudreau 2000).

Organisms such as crabs, snails and worms, mix surface sediments simply by crawling or

plowing through it. Hence, the presence of burrow formations within sediments could

correspond to mixing zones.

3.1.1 Description of Cores

The core recovered from BRL2 is approximately 157 cm in length. Images taken

from BRL2 allow the core to be categorized into five different zones (Figure 3-1). The

upper 20 cm of BRL2 is composed of fine-grained, light siliceous sand, interspersed with

large (- 1.5 cm) calcareous shells. The shells are mostly molluscs (bivalves and

gastropods), and most of them appear well preserved and intact. Between 20-30 cm depth

the sediment composition and texture changes. At this depth the sediments are composed

of dark muddy sand inter-layered with greenish clay lenses. Between 40-50 cm depth the

composition of the sediment remains muddy sand, void of any clay lenses. A gradual

transition in the composition of the sediment appears around 50 cm, changing from









muddy to a dark siliceous type of sand, composed primarily of quartz sand grains. The

next 90 cm of the core, between 50-140 cm depth is composed entirely of dark siliceous

sand, which is interspersed with small (- 0.4 cm) calcareous shell fragments. At this

horizon numerous vertical burrows occur as dark striations along the section. X-ray

imaging has also identified the presence of these borrows. The bottom 17 cm between

140-157 cm is composed of light fine-grained siliceous sand, totally devoid of any shells.

In general core BRL6 shows a greater variation in composition compared to BRL2,

however fewer burrow formations. The core recovered from BRL6 is approximately 162

cm long. The core is divided into eight zones on the basis of its sediment color, texture

and composition. Two zones may be considered as transition zones, because they show

subtle variations within the sediment suite (Figure 3-2). The upper 10 cm of BRL6 is

composed of light siliceous sand, shell fragments, and fresh plant debris, such as weeds

and roots. The horizon between 10-30 cm depth is composed of light siliceous sand, but

devoid of plant debris. Small burrows are also preserved within this zone. A thin layer of

about 5 cm thickness, between 30-35 cm depth, is composed largely of calcareous shell

fragments. Between 30-55 cm depth the amount of shell fragments decreases and the

fraction of muddy sand increases. The sediments between 55-80 cm depth are almost

entirely composed of dark muddy sand, with only few scattered fragments of calcareous

shell. The next 30 cm, between 80-110 cm depth, is completely composed of a dark clay

layer, possibly reflecting a change in depositional environment. A horizon of dark muddy

sand, devoid of any shell fragments occurs between 110-135 cm depth. The bottom 27

cm, between 135-162 cm depth, shows a gradual transition from dark muddy sand, to

light siliceous sand.









Real Image Description
Siliceous sand with
'" large (~1.5 cm)
' "- --- calcareous shells.


0

10

20

30

40

50O

60

70

80

90

100

110

120

130

14f


Muddy sand


Dark siliceous sand
interspersed with tiny
(-0.4 cm) calcareous
shells.
Vertical burrow
formations.


Light Siliceous sand


Figure 3-1. Sediment Core from BRL2. Images to the right are real photographic images
of short sections of the core representing the five zones.


Muddy sand
interlayered with
clayey lenses.


E--


150

157












Description
Light siliceous sand, shell
fragments and grass roots.
Light siliceous sand, tiny
burrow formations.


*-l_ II .' Calcareous shell fragments.
Fragmented shells
interspersed with dark
muddy sand


Dark muddy sand
interspersed with tiny
E fragmented calcareous
O ~Cshells



,111 IIlN .**&ut,;.w. Clay


Dark muddy sand


S Light Siliceous sand

... .


Figure 3-2. Sediment Core from BRL6. Images to the right are real photographic images
of short sections of the core representing the eight zones.


90

100

110

120

130

140

150

162









3.1.2 Porosity

At BRL2, porosity ranges between 20-42 %, with an average of- 31 % (Figure 3-3

a). Two zones exhibit higher porosity than the rest of the core, the first at a depth between

20-30 cm, and the other between 110-120 cm depth. Both these zones of low porosity

correspond to layers containing clay. Since clays are a lot more porous than sands it is not

surprising that we observe these peaks. In general, porosity of the sediments at BRL6 is

slightly greater than at BRL2. Porosity values at BRL6 range between 35-58 %, with an

average of 39 % (Figure 3-3 b). A zone of high porosity than the rest of the core occurs

between 80-120 cm depth, similar to BRL2 corresponding to a thick clay horizon.


% Porosity
10 20 30 40 50


(a)

Figure 3-3. Porosity of sediment (a) BRL2, (b) BRL6.


% Porosity
20 30 40 50 60









3.1.3 Density

The bulk density of the sediment was measured using the Geotek Multi-censor

Core Logger, at every 1 cm section through out the entire core. These values occasionally

reflect the type of sediment, for example, shelly zones show higher bulk density as

compared to soft sandy or clayey ones. At BRL2 the bulk density values ranged between

1.70-2.15 gm/cc (Figure 3-4 a). A high density at depth of-18 cm probably reflects the

high concentration of large calcareous shells seen within that zone. At BRL6 (Figure 3-4

b) the bulk density values are fairly consistent, ranging between 1.80-1.90 gm/cc, except

between the depths of 80-110 cm where the values drop to as low as 1.58 gm/cc. This

sudden drop in bulk density corresponds to the clay horizon that exists at that depth.


Density (gm/cc)
1.4 1.6 1.8 2.0


Density (gm/cc)
1.4 1.6 1.8 2.0


(a)

Figure 3-4. Bulk Density of sediments (a) BRL2, (b) BRL6.









3.2 Chemical Analyses

Regeneration and release of nutrients from estuarine sediments are controlled by

the concentrations and burial rates of organic carbon, nitrogen and phosphorus. Thus,

concentrations for organic C, N and P in sediment may provide information on the

potential flux of nutrients from sediments to the overlying water. The information of

nutrient concentration in the pore waters from previous work (Martin et al. 2000,

Lindenberg 2001), coupled with the concentration in the sediment column from the two

sites under study, can provide a better understanding of nutrients and organic matter

content up to 2 m below the sediment-water interface.

At both sites the sediments are relatively low in organic C, N and P, although

concentrations of TC, TN and TP within the sediments are greater at BRL6 than at BRL2.

Sediments from BRL2 represent a typical open lagoon sandy environment (deeper water

and further away from shore than BRL6), with low organic matter content. Thus the two

sites provide a useful variety of sedimentary environments within the lagoon.

3.2.1 Total Phosphorus (TP) and Total Nitrogen (TN)

Sediments from BRL6 tend to have slightly higher TP and TN concentrations

relative to BRL2. Total P concentrations for BRL2 range between 0.001- 0.1 mg/g

(Figure 3-5 a). Two distinct peaks occur between depths 22-38 cm, and 116-138 cm

respectively. The TP concentration at BRL6 ranges between 0.001-0.19 mg/g (Figure 3-5

b). A large peak in the concentration can be seen between 80-110 cm, corresponding to

the distinct organic rich clay layer. Total P concentrations below 120 cm at BRL6 are

below the methods detection limit of 0.001 mg/g TP.

Total N concentrations at both sites are slightly higher than TP. The TN

concentration at BRL2 ranges between 0.001-0.25 mg/g (Figure 3-6 a). Concentrations









increase steadily to a depth of 30 cm followed by a gradual drop. The TN concentration

at BRL6 ranges between 0.1-0.28 mg/g (Figure 3-6 b), with a sudden peak (- 0.75 mg/g)

observed at a depth of 38 cm.

3.2.2 Total Organic Matter (OM)

The concentration of total organic matter represents a sum of all organic

constituents within the sediment column (e.g. organic carbon, nitrogen and phosphorus).

While values less than 5 mg/g OM occur through much of the sediment column at BRL2,

sharp deviations (peaks) up to 28 mg/g OM are seen at 20 cm depth (Figure 3-7 a). At

BRL6, OM concentrations are as high as 44 mg/g, with numerous peaks seen between

35-80 cm (Figure 3-7 b). By subtracting the TP and TN fraction from OM we can

calculate the total organic carbon (TOC) present in the sediments. Since the concentration

of TP and TN is almost an order of magnitude lower than OM, the emerging profile of

TOC is not very different from OM.

3.2.3 Total Carbon (TC)

The total carbon content within the sediment represents both the organic and the

inorganic/carbonate fraction. Concentrations of TC in the sediments from both BRL2 and

BRL6 show some variability with depth. At BRL2, TC concentrations range between 1-4

% through out the sediment column (Figure 3-8 a). A zone of high concentration is

observed between 20-30 cm corresponding to the clay lenses that exist within that zone.

BRL6 on the other hand shows slightly higher concentrations of TC matter, ranging

between 1-8 % (Figure 3-8 b). A significant peak within the clay zone is observed

between 80-110 cm.









By subtracting the TOC fraction from TC, we can calculate the total inorganic

carbon (TIC) that is present in the sediments. Figure 3-9 a, b compares the TOC-TIC

fraction of the total carbon present in the sediments at BRL2 and BRL6 respectively.

3.2.4 Biogenic Silica (SiO2)

At BRL2 the SiO2 concentrations are fairly constant throughout the sediment

column, ranging between 2-11 mg/g (Figure 3-10 a). A gradual increase in concentration

is observed between 80-120 cm depth. While at BRL6 the SiO2 concentration ranges

between 1-15 mg/g, except for a sharp peak (- 15 mg/g) between 80-110 cm depth

corresponding to the clay zone (Figure 3-10 b).

3.2.5 21Pb and Sedimentation Rates

Both cores were extremely difficult to date because of the nature of the sediments

within the upper 20 cm. Since they contained very little organic matter and are mostly

composed of sand (Figure 3-1 and 3-2), very low Pb-activity was measured. This is

because sand particles have small surface area per unit volume, which makes it difficult

for metal ions to get adsorbed on it, unlike clays. However, within the upper 6 cm in the

sediment some unsupported 210Pb was present, and by using only one data point we

managed to calculate the sedimentation rates for BRL2 and BRL6 to be 0.6 cm/yr and 0.8

cm/yr respectively (Table 3-1). Sediments below 6 cm contained no unsupported 210Pb,

hence could not be dated.

Table 3-1. Estimation of sedimentation rates at BRL2 and BRL6 using gamma detectors.
Depth Excess 210Pb Age at Mass Sedimentation
(cm) inventory depth accumulation rate rate
(dpm/cm2) (yr) (mg/cm2/r) (cm/yr)

BRL2 0-2 2.362 31.0 125.7 0.6
BRL6 4-6 1.378 20.0 153.0 0.8






32


However, in trying to estimate sedimentation rates using this technique we violated

a number of assumptions. Hence we estimated sedimentation rates for Banana River

Lagoon by comparing it with sea-level rise along the east coast of Florida in the past 100

years. It has been estimated that within the past 100 years sea-level rise is 1-2 mm/yr

(Jaeger et al. 2002, unpublished). Hence, by using average particle density of 2.0 g/cm3

we calculated sedimentation accumulation rate to the Banana River Lagoon to be 200

mg/cm2/yr.












0.05


0.00
0

20

40

60

80

100

120

140

160





0.00
0 T-

20

40

60

80-

100

120

140

160


BRL2 Total Phosphorous (mg/g)
0.10


BRL6 Total Phosphorous (mg/g)
0.10


0.15


0.20


0.15


0.20


(b)

Figure 3-5. Total phosphorus concentrations in sediment (a) BRL2, (b) BRL6.


0.05









BRL2 Total Nitrogen (mg/g)
0.4


(a)

BRL6 Total Nitrogen (mg/g)
0.4


(b)

Figure 3-6. Total nitrogen concentrations in sediment (a) BRL2, (b) BRL6.










Total Organic matter (mg/g)
20 30


(a)
Total Organic matter (mg/g)
20 30


(b)

Figure 3-7. Total organic matter in sediment (a) BRL2, (b) BRL6.







36


% Total Carbon content

0 2 4 6 8
0

20

40

60 -
E
8 80

100

120 -

140

160

(a)
% Total Carbon content
0 2 4 6 8
0




40 -

60 -

o 80
Cd
100 -

120

140

160

(b)

Figure 3-8. Total carbon concentrations in sediment (a) BRL2, (b) BRL6.










TOC-TIC (mg/g)
20


TOC-TIC (mg/g)
40


Figure 3-9. Concentration of total organic and total inorganic
sediment at (a) BRL2 (b) BRL6.


carbon present in the










Biogenic Silica (mg/g)
0 2 4 6 8


(a)

Biogenic Silica (mg/g)
0 2 4 6 8


10 12 14 16


10 12 14 16


(b)

Figure 3-10. SiO2 concentrations in sediment (a) BRL2, (b) BRL6.














CHAPTER 4
DISCUSSION

4.1 Introduction

One of the most important consequences of early diagenesis is the control it exerts

upon the chemical composition of shallow pore waters. If diagenetic chemical reactions

occur close to the sediment-water interface, sharp concentration gradients may result

within shallow pore waters. These changes in concentration of dissolved species in the

pore waters will be important to fluxes of those species if discharged to the overlying

lagoon through diffusive, and possibly advective processes. For example, bacterially

mediated chemical reactions in sediments and sediment pore water release dissolved

ammonia and phosphate from decomposing organic matter. When concentrations of

dissolved ammonia and phosphate build to elevated levels in surficial sediments, an

excess nutrient flux passes into the overlying water column. This could be possible if

there are unnaturally high concentrations of solid phase P and N present in the sediments

to begin with. Shallow lagoon waters are typically higher in dissolved oxygen

concentration than the underlying pore waters. However, if there is re-circulation of

lagoon water through the sediments, then the cycling of oxygenated water through the

sediments could control organic matter regeneration at depths greater than a few

centimeters below the sediment-water interface.

Part of this study was designed to determine the magnitude of the nutrient flux

from the sediment to the overlying lagoon water at the sediment-water interface from two

selected sites in the Banana River Lagoon, and compare it with the input flux brought









about by surface runoff and sedimentation. The calculations of these fluxes are described

later in the chapter.

4.1.1 Conceptual Model

The concept of mixing in shallow marine sediments has been the focus of

discussion for over two decades. A number of theories have been proposed that may

cause this mixing, for example, bioirrigation and bioturbation (Korosec 1979, Emerson et

al.1984), wave action and tidal pumping (Shum 1992, 1993, Li et al. 2000), and fluid-

density fluctuations (Rasmussen et al. 2003). Regardless of the process or processes that

may cause this mixing, each one may be an important transport mechanism that can carry

substantial amount of dissolved solutes from the sediments to the overlying water

column. Mathematical modeling of these sorts of mixing processes is difficult because of

the variety, irregularity, and complexity of each mechanism. The magnitude of these

mixing processes should be important for nutrient fluxes because of the increased organic

matter regeneration that would occur in shallow sediments as a result of diagenesis or

metabolic activities of plants and microorganisms. Mixing of lagoon and pore water

would also be important in estimating fluxes of other dissolved constituents because of

the volume of water associated with advection.

Pore water profiles of conservative solutes, such as Cf suggest that there is

significant amount of mixing between the shallow pore water and the overlying lagoon

water in the Banana River Lagoon (Martin et al. 2000, 2001). This mixing is shown by

changes through time in the concentrations of conservative solutes at depths up to 70 cm

within the sediment column, with little change through time in their concentrations at

depths below 70 cm (Figure 4-1).









































Figure 4-1. C1- profile concentration suggesting mixing in shallow sediments in the
Banana River Lagoon (BRL). C.Z = Coastal zone, FW = Fresh water, U.A =
Unconfined aquifer, C.A = Confined aquifer, AT = Aquitard (Inset of the C1-
profile taken from Martin et al. 2000).

If there is significant amount of mixing between lagoon and pore waters, then not all of

the nutrients in the seep water can be considered a new flux to the lagoon. Some nutrients

dissolved in the seep water could be brought into the shallow sediments along with the

lagoon water prior to flow through the sediment. Nutrients could also originate from the

upward flow of ground water. New sources of nutrients from ground water would be

small, because nutrient concentrations in ground water are lower than in pore water and

because ground water appears to be < 5 % of the seep water (Martin et al. 2000). This










would suggest, that the re-circulation of lagoon water within shallow sediments could

provide a mixing mechanism that could drive a large nutrient load to the lagoon, as well

as remove a certain amount from the lagoon (Figure 4-2). This part of the nutrient cycle

could be important and needs to be included in future estimates of nutrient reservoirs and

budgets, even though it would represent a natural flux. The physical mechanism that

drives this mixing is unknown, but must be considered as an important source of nutrients

to the lagoon; because if excess nutrients are carried to the lagoon from anthropogenic

sources such as agricultural runoff or from septic tanks, the remediation of such a

problem requires good information on the complete nutrient cycle in the lagoon.


Lagoon water
recirculation
due to wave
action and tidal
pumping


Pore water
circulation due
-to bioturbation


.. '. : ..



5

Figure 4-2. A conceptual model showing mixing at the sediment-water interface due to
bioturbation or wave action. L.W.= Lagoon Water, S.W.= Seep Water, P.W.
Pore Water. B = Worms burrowing into sediment and ingesting sediment
particles.









4.2 Sediment Profiles

An important factor that controls the nature of the nutrient fluxes to the lagoon is

the chemical composition of the bottom sediments. For example, sediments with high

organic matter concentrations could provide a major source of the nutrient load. Physical

properties of sediments, such as permeability, could also affect the nature of these fluxes

by controlling the discharge rate of water through the sediments. Variations in both the

concentration of various constituents in the sediments and their physical properties

suggest that a very complex hydrodynamic system exists at BRL2 and BRL6.

4.2.1 Correlation Between Physical Properties and Ground Water Discharge Rates

The porosity of the sediment is important because it controls the volume of water

being exchanged. However, the rate of ground water discharge depends on the

permeability of the sediments. One of the factors affecting porosity of sediments is

bioturbation. Construction of burrows, and constant irrigation of these burrows result in a

higher water content of sediments than would result in the absence of bioturbation

(Berner 1980, Sandnes et al. 2000).

The sediments from BRL2 show a uniform distribution of porosity through out the

entire core, with the exception of the upper 30 cm where the porosity increases from 20-

40 % (Figure 3-3 a). This gradual peak in porosity could be a result of the clay lenses that

exist at this depth. The low porosity values within the upper 20 cm may be an artifact of

losing some moisture at the time of transportation. The porosity shown by the sediment

types found at BRL2 may also be a result of composition within the sands. While the

small range in porosity reflects uniform grain size, sediment compaction with depth,

could decrease the porosity. Visual observations of the sediments may provide a crude

correlation between type of sediment and ground water discharge rates. The presence of a









shell hash layer in the upper 20 cm may provide greater permeability for the discharging

water, and hence, a slightly higher ground water discharge rate of 44.5 ml/m2/min

compared to BRL6 (Martin et al. 2000, Lindenberg 2001).

At BRL6 the porosity of the sediments ranges between 35-58 %. Although the

values are uniform up to 80 cm depth, a sharp peak in the porosity from 40-58 % is seen

at depths between 80-120 cm (Figure 3-3 b). This sudden increase in porosity may have

been a result of the thick clay layer that exists at that depth (Figure 3-2). The presence of

these clay horizons may act as aquitards and obstruct the flow of water though the

sediments. Hence, probably the reason why we observed slightly lower ground water

discharge rates at BRL6 of 18.7 ml/m2/min, compared to BRL2 (Martin et al 2000,

Lindenberg 2001). Using these observations to generalize for the entire lagoon should be

done with caution since these observations consider 160 cm cores from just two

locations. Besides, a number of factors other than variations in permeability may be

responsible for the differences in ground water discharge rates between BRL2 and BRL6.

These factors could include heterogeneous distribution of underlying confining layers,

and variability in compaction and permeability of bottom sediments.

4.2.2 Density

The bulk density of the sediment tends to reflect the type of sediment under study.

For example, calcareous shelly zones typically correspond to higher bulk density

compared to soft sands or clays. The bulk density of sediments at BRL2 ranges between

1.70-2.15 g/cc (Figure 3-4 a). A prominent peak of 2.15 g/cc occurs at a depth of

18 cm and corresponds with the layer of shell hash that exists at that depth (Figure 3-1).

At BRL6 the bulk density of the sediments range between 1.6-2.0 g/cc (Figure 3-4 b).

While a small peak of 2.0 g/cc corresponds with the thin veneer of fragmented calcareous









shells observed at a depth of 35 cm, a sudden drop in bulk density to 1.6 g/cc between 80-

110 cm corresponds to the soft clay zone that exists at that depth (Figure 3-2). One reason

why we observe a decrease in bulk density in the clays is because they may contain low-

density, hydrated silicate minerals such as kaolinite, montmorillonite and opal.

4.2.3 Total Organic Matter as a Source of Nutrients

High organic matter content in sediments is usually associated with high

sedimentation rates in environments ranging from the upper continental slope and outer

shelf to near-shore deltas, bays and estuaries (Berner 1980). High OM is important

because most of the early diagenetic changes exhibited by the sediments relate to the

microbial decomposition of organic matter. Two factors are responsible for the high OM

in the sediment. The first is the extent of biological productivity in the overlying water,

which depends on the input of nutrients from surface runoff. The second is sedimentation

rate, because rapidly deposited sediments are buried past the zone where redox reactions

may regenerate the OM.

The low concentration of OM content measured in the sediment at BRL2 and

BRL6 occur because the sediments are almost entirely composed of sand, and typically

sandy sediments do not contain as much organic as clays. The reason for this is that

coarser materials such as sand grains have lower surface area per unit of mass or volume

compared to clays. Most chemical reactions in the sediments occur at the mineral-

solution interface. Consequently, the lower the surface area, the less chemically active the

sediment may be, particularly with respect to weathering reactions, adsorption of solutes,

and adsorption of organic matter. One reason why sediments from BRL6 are slightly

enriched in OM compared to BRL2 is probably because of its location. Site BRL2 is

located in deeper waters out in the open lagoon, hence sediments from site BRL2 may be









slightly older than BRL6, as a result may have lost greater amount of OM through time.

Even though the sediments from BRL2 and BRL6 are almost entirely composed of sand,

the clay horizons suggest that they may have retained some of the organic matter that

escaped the destruction by organisms prior to burial. An important question is whether

low concentrations of OM in the sediments are sufficient enough to provide a source of

nutrients that can support the measured nutrient fluxes to the lagoon (Martin et al. 2002).

4.2.4 Comparison of Total Phosphorus (TP) and Total Nitrogen (TN) with Nutrient
Fluxes

There are several sources of nutrients to the Banana River Lagoon. One such source

is from surface water runoff, including anthropogenic sources as a result of urbanization

around the lagoon. Atmospheric deposition provides other sources of nitrogen.

Remineralization of organic matter in the sediments provides another source of nutrients

to the lagoon (Reddy et al. 1999). Inversely, the precipitation of apatite within the

sediments through authigenic mineralization processes could remove some of the

phosphorus from the sediment pore waters that may be available for organic matter

remineralization. Besides, the slow sedimentation rate (1-2 mm/yr) provides sufficient

time for almost all of the P and N in the sediment to be remineralized and flushed back

into the lagoon prior to burial. Finally, the circulation of lagoon water through the

sediments could further oxidize some of the P and N from the sediments.

Previous estimates of nutrient fluxes from sedimentary sources have considered

only diffusion as a transport mechanism (e.g. Trefry et al. 1992, Reddy et al.1999). The

effect of remineralized nutrients to the total nutrient budget of the lagoon would be

greater than those provided by diffusion alone (Martin et al. 2000). However, low

concentration of TP and TN in the sediments compared to seep water concentrations at









BRL2 and BRL6, suggest that the sediments alone could not have supported the high

nutrient fluxes measured by the seep meters. The elevated concentrations of nutrients in

the seep water are similar to the concentrations in the pore waters less than a couple of

meters below the sediment-water interface (Martin et al. 2000). Although this may

suggest that much of the nutrients in the seep water are derived from the remineralization

of organic matter within shallow lagoon sediments, the rate and extent of mineralization

depends on the availability of dissolved oxygen (Froelich et al. 1979). If so, then the

concentration of nutrients in the seep water measured using a seep meter does not provide

a realistic estimate of the nutrient concentration and its associated fluxes, because of the

limited availability of oxygenated water trapped inside the seep meter. Extrapolating

these fluxes to the entire lagoon could provide an erroneous estimate of the potential

magnitude of the flux of nutrients from sediments.

4.2.5 Redfield Ratios and their Significance to the Banana River Lagoon

The two major sources of organic matter are terrestrial and marine plants and

animals, and each have distinct C:P:N ratios. Marine phytoplankton have a mean molar

organic C:P ratio of 106:1, mean molar C:N ratio of 6.6:1, and mean molar N:P ratio of

16:1 (Redfield et al. 1963). In contrast, terrestrial plants are impoverished in P and N

relative to C, with characteristic C:P ratios ranging up to or exceeding 800, and C:N

ratios ranging up to or exceeding 1000 (Likens et al. 1981, Ruttenberg and Berner 1993).

However, the presence of certain type of marine sea-grass (Halodule wrightii), algae

(Gracilaria sp.) and epiphytes could raise the Redfield ratios considerably. For example,

average C:N:P in Halodule wrightii is 174:8:1, in Gracilaria it is 897:56:1 and in

epiphytes it is 392:158:1 (Montague and Henley 2003, unpublished). If we assume that

most of the organic matter in near-shore marine sediments such as the Banana River









Lagoon is derived from marine phytodetritus, then zones within the sediments that show

higher C:P, C:N ratios suggest an abundance in growth of Halodule wrightii and

Gracilaria sp. The importance of making such an observation lies not only in

understanding the sources of organic matter to marine sediments, but also in assessing the

overall influence it may have on the lagoon.

The presence of these of marine planktons such as Halodule wrightii and

Gracilaria sp. has been reported in the past (Montague and Henley 2003, unpublished).

Halodule wrightii dominate in the northern region of the Indian River Lagoon, while

Gracilaria sp. are drifting algae which are highly productive, abundant throughout the

entire lagoon. The relatively high Redfield ratios at BRL2 and BRL6 suggest that the

sediments have been influenced by these species of phytoplanktons that are enriched in

C, N and P (Figure 4-3 and 4-4). The C:P Redfield ratios between observed at BRL6

between 80-110 cm depth are almost five times lower than the expected Redfield values

of 106:1 for marine sediments. One possible explanation for that could be the authigenic

mineralization of apatite that may account for the excess organic P present in that

horizon. This precipitation of organic P to form apatite is favored by the presence of

CaCO3 in the form of shell fragments (Figure 3-2) whose surfaces act as a nucleating

agent for apatite crystallization (Morse 1978, Berner 1980). Similar observations within

carbonate sediments of Bermuda and Florida Bay, whose pore waters are saturated with

respect to apatite has been demonstrated in the past (Berner 1974).














C/P C/N N/P

0 100 200 300 400 0 10 20 30 40 50 0 5 10 15 20
0 I 1 0 1 1 .1 11 1 IiI I I I 0 I I 1 I i i i I i i i I

0* *



40 40 40-
I* *
.. -*
** *
60 60 60 -
0 I *I
i .... "
E E E I
S 80 80 80 -
"o -

100 100 100 -
3' I ~ ~. 100

120 120 -120


140 140 -140


160 1 2 16 0 1 1 1 1 1 1 60 1
0 100 200 300 400 0 10 20 30 40 50 0 5 10 15 20


Figure 4-3. Redfield ratios of organic C:P:N within sediments at BRL2.













C/P

0 100 200 300 400


C/N

0 50 100 150 200




" 1




I .
Is









I .
I "0


0 100 200 300 400 0 50 100 150 200


Figure 4-4. Redfield ratios of organic C:P:N within sediments at BRL6.


0 5 10 15 20


N/P

0 5 10


15 20









4.3 Emerson's SiO2 Mixing Model

Planktonic diatoms (plants) and radiolaria (animals) living in the surface waters of

oceans and lagoons secrete skeletons consisting of opaline (amorphous) silica. Once they

die, their siliceous remains settle to the bottom and undergo dissolution. However, most

of the dissolution occurs during settling, but some may also occur at the bottom

(sediment-water interface). Evidence for dissolution in shallow pore waters in the Banana

River Lagoon is provided by concentrations of dissolved Si02 in sediment pore water at

BRL2, which are always higher than those in the overlying lagoon water (Martin et al.

2000). Several models for the early diagenesis of Si02 have been proposed (e.g. Hurd

1973, Wollast 1974, Schink 1975). The most complete model treated dissolution in terms

of "reactive" or soluble silica to differentiate it from other less reactive forms such as

crystalline silicate minerals (Berner 1980). Reactive SiO2 is presumed to be the opaline

fraction of biogenic Si02, and hence more soluble than the crystalline fraction. However,

the rate of dissolution of freshly deposited siliceous plankton may vary, and as a result of

incomplete dissolution some opaline silica may accumulate in the sediments.

4.3.1 Introduction

Emerson et al. (1984) proposed that the ultimate fate of most reactive inorganic and

organic matter introduced to Puget Sound depends on the chemical and physical

processes that occur at the estuarine sediment-water interface. He suggested that

mechanisms other than sedimentation and molecular diffusion were necessary to explain

chemical or isotopic distributions in the sediments and pore waters. Benthic animal

feeding and respiratory activities are important processes near the sediment-water

interface in all oxic aquatic environments. Wherever there is significant amount of

biological activity, transport mechanisms may be increased. In near-shore, high-energy,









environments such as estuaries these processes are rapid enough to influence transport

within the sediment pore waters. Since animal respiratory activities (and sometimes

physical actions such as tides and waves) aid in the ventilation of the sediments, it is

important to determine the feasibility of generalizing these exchange mechanisms so that

meaningful predictions for pollutants, such as excess nutrients, can be made. The

transport mechanisms were evaluated using a one-dimensional model with a "non-local"

(Imboden, 1981) source term to describe the distribution of silicates within the pore

water.

4.3.2 The Model

The movement of pore water within sediments can be categorized into two means

of transport based on the characteristics of the pore water chemistry (Emerson et al.

1984). The first transport mechanism is characterized as random motion and formulated

as a diffusion process. The second transport mechanism is analogous to pumping models.

The process is represented as a "non-local" source or sink term (a) with dimensions of

time-1. This term was coined by Imboden (1981), and simply means any mode of

transport that is capable of exchanging material between nonadjacent points in the

sediment, or between the overlying water and points in the sediment removed from the

sediment-water interface (Imboden 1981, Emerson et al., 1984, Sandes 2000).

Mathematically the problem is formulated as one-dimensional diffusion with a non-local

term and reaction:

aC 02C
c=K a2 _a(C-C / ) + R (4.1)
at az

(Emerson et al. 1984).









Where a is the rate parameter used to evaluate the non-local source. C is the

concentration of a reactive solute in the bulk sediment (in this case SiO2 concentration) at

depth z. Co is the concentration of dissolved Si02 in the overlying water. R is the reaction

term, that includes the rate of reaction, and K is the sediment diffusion coefficient, that

includes the correction to the diffusion coefficient D at infinite dilution necessary for

tortuosity (0), i.e.

K=D/02

(Berner 1980).

Since porosity (q) varies little with depth in sediments from BRL2 (Figure 3.3 a), Kis

also assumed to be constant with depth in the sediment in order to use the analytical

solution. Tortuosity is a difficult parameter to measure directly, and thus a variety of

empirical relationships between tortuosity and porosity have been developed. The best fit

to available data takes the form

02 = 1 ln(2)

(Boudreau 1996).

The boundary conditions required for the solution of equation (4.1) depends on the

physical characteristics of the particular setting.

In order to describe silicate profiles in the sediments we assume (i) steady state, i.e.

SiO2 concentration at a given depth remains constant with time so that, cC/C = 0, and (ii)

that the rate of dissolution of diatoms is a first order. Using k as the first order rate

constant (i.e. the dissolution rate of opal), equation (4.1) becomes:

d2[Si]
0=K 2[Si] a([Si] -[Si]o/qS)+k([Si], -[Si])
dz2


Rearranging,









=K d2Si] (k+a)[Si]+k[Si], +a[Si]o/0 (4.2)
dz2

where [Si]o = local concentration of pore water at depth 0, and [Si]a = asymptotic

concentration of pore water (i.e. concentration value below which SiO2 concentration

remains unchanged).

The boundary conditions used are

atz = 0, [Si]= [Si]o /0


atz = Z, Si]= G (4.3)
Oz 1

where Z1 is the bottom boundary depth in the sediment, and G is the gradient in [SiO2] at

z = Z.

Using the above boundary conditions the solution to equation (4.2) was assumed to be

k[Si], +a[Si]o /# G sinh(vz)
[Si](z) [Si] +[Si] /(1 e) + ([Si]o / )e + G h(
P cosh(7Z,)
Sc(4.4)
ey(z+z,) i(zz,)[Si /
+e -e k[Si], + a[Si]o/ [Si]o /
cosh(yZ,)

(Emerson et al. 1984).

where y = (P / K)1/2 and P = (k + a).









Table 4-1. Description and values of parameters used in the model for BRL2.
Parameter Description Value Reference
k. (s-') Opal dissolution rate 5 x 10-7 (at 10 oC) Emerson et al. 1984
23 x 107 (at 29 OC)
K (cm2 s-1) Molecular diffusion 10-5 (at 30 OC) Wollast et al. 1971
coefficient Emerson et al. 1984
Diffusion coefficient 10-3 (fast regime)
representing enhance
mixing 10-4 (slow regime)
[Si]o (M) Bottom water silica 16 x 10-6 (May 2000) Martin et al. 2000
concentration 45 x 10-6 (Aug. 2000)
22 x 10-6 (Dec. 2000)
[Si]a(M) "Asymptotic" pore 130 x 10-6 (May 2000) Martin et al. 2000
water concentration 172 x 10-6 (Aug. 2000)
122 x 10-6 (Dec. 2000)
Porosity 0.31 This study
Z1 (cm) Bottom boundary 110 Asymptotic depth
(sediment)
G Slope of [Si] profile 0 Assumption
beyond the asymptotic
depth
a (s-1) "non-local" source 0 (molecular diffusion) Emerson et al. 1984
parameter 4 x 10-7 (enhanced Sandes et al. 2000.
mixing)

4.3.3 Model Solution and Results

Using the parameters described in Table 4-1 three separate SiO2 profiles were

calculated from equation (4.4) for different values of K and a, each following a different

trend. The first trend line represents molecular diffusion using K = 10-5 cm2 s-1, and a =

0. The other two trend lines represents "enhanced mixing", with K = 10-4 cm2 s-1, and a=

4 x 10-7 s-1 as one, and K= 10-3 cm2 s-1, and a= 4 x 10-7 s-1 as the other one. The reason

for generating two separate trend lines to represent enhance mixing was only to represent

one slightly faster diffusion coefficient rate than the other by using two separate values

for K.









The model was tested on pore water samples collected from three separate

sampling trips made to the Banana River Lagoon in May, August, and December of 2000

(Figure 4-5, 4-6 and 4-7). These results indicate that for all three seasons SiO2 profiles of

the pore waters are reproduced by using enhanced diffusion rates ofK = 10-3 cm2 s-1, and

that molecular diffusion (K= 10-5 cm2 s-1) does not dominate as a transport mechanism

from the sediment-water interface, to a depth of 110 cm. A non-local term is required to

account for the observed SiO2 profiles. For the non-local transport parameter a to

approach the measured SiO2 concentration at depths of 110 cm requires enhanced mixing,

using a diffusion coefficient (K= 10-3 cm2 s-1) that are two orders of magnitude greater

than simple molecular diffusion. This enhanced mixing of sediments brought about

collectively by biological activity, tidal pumping or wave action could affect the

distribution of certain solid and dissolved phases. For example the remobilization of

metals such as Fe, Mn and Ni by the removal of sulfide from the pore waters, via

ventilation of sediments with oxic overlying water, allowing the enrichment of dissolved

metal (Emerson et al. 1984). In addition the exchange mechanism between shallow pore

waters and the bottom waters could alter the redox chemistry of certain species. For

example, high concentrations of Fe(II) and Mn(II) observed in the surface few

centimeters and gradually decrease downward, indicate that benthic animal activity and

physical pumping mechanisms are a dominant process in shaping the chemical

distribution of pore waters (Emerson et al. 1984).

For all three seasons SiO2 concentrations tend to follow a slightly slower diffusive

rate between 10-3 cm2 s-1 and 10-4 cm2 S-1 at depths greater than 110 cm, up to 230 cm

depth. This may mean that a different regime exists between 110-230 cm depth, one









which may still cause mixing, but not as enhanced as the type seen between 0-110 cm

depth. This could probably be due to the fact that wave action and tidal pumping do not

influence mixing processes at depths greater than 110 cm below the sediment-water

interface (Shum 1992).


Molecular Vs. Enhanced Mixing at BRL2.
MAY- 2000


[SiO2] gM
50 100


0

40

80

120

160

200

240


150


-Molecular Diffussion
K=10.0 E-06
- Enhanced Mixing
K=10.0 E-05
- Enhanced Mixing
K=10.0 E-04
X Pore Water [SiO2],
BRL2


Figure 4-5. Model solutions for the depth distribution of silicate for enhanced mixing (K
=10-3 cm2 s1) with no non-local transport (a = 0), and molecular diffusion (K
= 105 cm2 s1) and non-local transport (a = 4 x 10-7 s-'): May 2000.


4 6

I




X
I I


X


X
_______










Molecular Vs. Enhanced Mixing at BRL2.
AUG-2000


[Si02] iM
0 50 100


150 200


S 80 '

c 120
Q.
SX Molecular Diffussion
O 160 K=10.0 E-06
Enhanced Mixing K=10.0
200 X E-05
-Enhanced Mixing K=10.0
0X E-04
240 X Pore Water [SiO2],
BRL2

Figure 4-6. Model solutions for the depth distribution of silicate for enhanced mixing (K
= 10-3 cm2 s-1) with no non-local transport (a = 0), and molecular diffusion (K
= 10-5 cm2 s-1) and non-local transport (a = 4 x 10-7 s-1): August 2000.











Molecular Vs. Enhanced Mixing at BRL2.
DEC-2000


[Si02] iM
0 50 100 150
0"



S 80

S120 -
0- Molecular Diffussion
O X K=10.0 E-06
o 160
Enhanced Mixing K=10.0
200 X E-05
-Enhanced Mixing K=10.0
X E-04
240 X Pore Water [SiO2], BRL2


Figure 4-7. Model solutions for the depth distribution of silicate for enhanced mixing (K
= 103 cm2 s-1) with no non-local transport (a = 0), and molecular diffusion (K
= 10-5 cm2 s-1) and non-local transport (a = 4 x 10-7 s-1): December 2000.



4.4 Mass Balance Calculation

4.4.1 Introduction

De Baar and Suess (1993) estimated that 90 % of annual organic primary

production is recycled within coastal surface waters. Only about 1 % of the remaining 10

% of organic matter which escapes to the deep ocean, is buried in marine sediments. The

link between burial of organic matter and primary production in surface waters depends

on the efficiency of diagenetic reactions at the sediment-water interface.

The quantification of nutrient fluxes from the sediment to the overlying water

column has been measured in the past using seep meters (Gallagher et al. 1996, Martin et









al. 2000). The procedure relied on sampling concentrations of various nutrient species in

the seep water and converting these concentrations to fluxes on the basis of the seepage

rates measured using seep meters. These water fluxes were several orders of magnitude

greater than those measured using ground water flux rates by numerical modeling

techniques (Pandit and El-Khazen 1990). If mixing is common in the shallow sediments

(Chapter 4.1.1), then not all of the nutrients in the seep water can be considered as a new

flux to the lagoon. Some of the dissolved nutrients in the seep water would have been

brought into the shallow sediment along with the circulating lagoon water. Some of the

nutrients may have also originated from the upward flow of ground water, although a

new source of nutrients from ground water would be small because the nutrient

concentrations in ground water are lower than in seep water and because ground water

represents at most -5 % of the seep water (Martin et al. 2002). These observations

suggest that most of the newly generated nutrients in the seep water, and subsequently the

output nutrient flux to the lagoon originate from the remineralization of organic matter

within shallow sediment pore water during mixing. However, this could only be possible

if there is enough organic P and N present in the sediment to support such high nutrient

fluxes.

One possible explanation for having observed these high seepage fluxes may have

to do with the deployment of the seep-meter itself. The remineralization of organic matter

within shallow sediments is a process that follows a definite succession, and is primarily

controlled by the availability of dissolved oxygen and other species in the sediments

(Froelich et al. 1979). Once dissolved oxygen becomes sufficiently depleted due to burial

or restricted renewal of oxygenated water, further organic matter decomposition









continues by the oxidation of nitrate present in the water. The overall reaction is known

as denitrification. At BRL2 and BRL6 dissolved oxygen and NO3 are nearly depleted in

the pore waters (Martin et al. 2002) suggesting that almost all the oxygen has been

utilized by microbial oxidation of organic matter at the sediment-water interface.

Although SO4/Cl ratios do not indicate that sulfate reduction has begun (Martin et al

2000), there appears to be sulfide present in the water suggesting some sulfate reduction.

The deployment of a seep meter at the sediment-water interface may expedite the process

of organic matter remineralization, providing only a limited amount of dissolved oxygen

exposed to a large unit area of sediment, without any means of re-oxygenating the water

trapped in the seep meter for over 24 hours. As a result, most of the P and N is being

oxidized in the upper 1-2 cm at the sediments-water interface within 24 hours, and gets

collected in the seepage bags by diffusive and advective ground water discharge, and the

remaining fraction of the TP and TN is preserved in the sediment (Figure 4-8). This could

also explain why concentrations of dissolved oxygen in the seep meters (0.2 mg/L) are

depleted compared to the surrounding lagoon water (6.7 mg/L) within 24 hours after

deploying the seep meter (Martin et al. 2000).











High nutrient
concentration
measured in \
I seepage bag


OM reminerali"tor
PW. at sediment ter
interfaoe


Figure 4-8. Cross section of the seep meter showing organic matter remineralization at
the sediment-water interface enclosed within the seep meter. P.W.= pore
water, L.W.= lagoon water, S.W.= seep water.

Therefore, in order to make a realistic nutrient mass balance calculation in the

Banana River Lagoon, one needs to develop a mass balance calculation that compares

input rate of nutrient fluxes to the lagoon in the form of surface runoff and sedimentation

versus the output nutrient fluxes in the form of ground water discharge at the sediments

water interface. A realistic estimate of the output fluxes could be calculated using nutrient

concentrations within shallow pore waters. If the nutrient fluxes to the sediment (input)

are in excess with respect to the ground water discharge (output), then the excess OM

present in the sediment column can be considered as a source of nutrients to the lagoon.









4.4.2 Calculations

A simple mass balance model was computed to estimate the input versus the output

fluxes of three chemical constituents viz. total phosphorus (TP), total nitrogen (TN) and

biogenic silica (SiO2) at the sediment-water interface, at BRL2 and BRL6 respectively.

In order to calculate input rates two parameters were required, the average

concentration of the chemical constituents within the sediment column (up to 80 cm), and

the rate of accumulation of sediments (Table 4-2). The accumulation rates were

calculated by making an assumption that sedimentation rates in the Banana River Lagoon

corresponds to 1-2 1 mm/yr of sea-level rise within the past 100 years (Jaeger et al.

2001 unpublished). From this, the average sediment accumulation rate was calculated to

be 200 mg/cm2/yr at BRL2 and BRL6. By multiplying the average concentration of the

three constituents in the sediments by the sediment accumulation rate we computed the

input flux rates to the sediment. The output rate of the various solutes to the lagoon was

calculated by multiplying the concentration of the sediment pore water by ground water

discharge rate. The ground water discharge rates measured for BRL2 and BRL6 were

44.5 ml/m2/min (+ 12 ml/m2/min), and 18.7 ml/m2/min ( 12.6 ml/m2/min) respectively.

Both the values of pore water concentration (Table 4-3), and ground water discharge rates

were taken from Lindenberg (2001). Results from the mass balance calculations for

BRL2 and BRL6 are tabulated in Table 4-4.

Table 4-2. Average concentration of TP, TN and SiO2 up to 80 cm within the sediment at
BRL2 and BRL6.
Location TP (mg/g) TN (mg/g) SiO2 (mg/g)

BRL2 0.020 0.094 5.096
BRL6 0.033 0.208 2.848









Table 4-3. Average pore water concentrations up to 80 cm (from Lindenberg 2001).
Location TP (mg/L) TN (mg/L) SiO2 (mg/L)

BRL2 0.06 0.45 4.1
BRL6 0.08 0.92 4.0

Table 4-4. Comparing input fluxes to the sediment versus output fluxes to the lagoon
water of TP, TN and SiO2 at BRL2 and BRL6.
BRL2 BRL6
Input Flux Output Flux Input Flux Output Flux
([Lg/cm2/yr) (Lg/cm2/yr) ([Lg/cm2/yr) ([g/cm2/yr)

TP 4 50 % 5 +25 % 7 50 % 3 +30 %
TN 19 50% 38 +25% 42 50% 33 +30%
SiO2 1019 +50% 347 25% 570 50 % 142 30 %

Results from the mass balance calculations at BRL2 suggest that there is an over all

25 % increase in the output flux of TP, and twice as much of TN being released to the

lagoon water than the input fluxes to the lagoon sediments (however, within limits of

error the fluxes seem to be well balanced). Although, a possible explanation as to why we

observe a slightly higher output flux may be because much of the N and P contained in

the detrital OM is remineralized at depths shallower than 80 cm. In contrast, the output

fluxes of SiO2 are almost three times lower than the input rates possibly because SiO2

remineralizes slower than P or N, hence does not have a similar artifact. In other words,

SiO2 remains deposited in the sediments a lot longer than P and N.

At BRL6, the output fluxes of TP and TN are slower than the rate at which it is

deposited into the lagoon. There are at least two possible reasons for this. Firstly, the

input fluxes to the sediment are higher compared to BRL2, and secondly, although there

is sufficient P and N present in the sediment to support higher output fluxes to the lagoon,

the slower ground water discharge rate prevents it from happening. However, within

limits of error the input versus the output fluxes of TP and TN at BRL6 seem to balance









well. This would then suggest, that even though the concentration of OM in the sediments

are low, they can provide the required amount to balance the output fluxes of TP and TN

to the lagoon.

Differentiating the mixing depth from the depth of reaction requires utmost

clarification while making similar mass balance calculations. An important observation

that can be made from our mass balance calculation is that averaging the N and P pore

water concentrations over the mixing depth does not represent the average depth of

reaction. Hence, even though mixing may enhance organic matter remineralization within

the sediments, its influence is limited to shallower depths than the mixing itself. By

averaging pore water concentrations with depths that represent mixing zones, instead of

zones of N and P remineralization reactions, may result erroneous while calculating

nutrient fluxes.

Results from Table 4-4 show that although the net input versus output fluxes of TP,

TN and SiO2 are well balanced within calculated limits of error. These output fluxes to

the lagoon represents both the diffusive as well as advective fluxes. Estimates of nutrient

fluxes to the Banana River Lagoon such as those made above using pore water

concentrations, are more realistic than those calculated using seep water concentrations,

however trying to estimate the exact depth of reaction may prove to be a difficult task.

Although there may be errors resulting from the extrapolation of the data from a small

study area such as the Banana River Lagoon; differences between the measurements of

individual nutrient fluxes observed at BRL2 and BRL6, indicate the importance of P and

N cycling to the lagoon with respect to ground water discharge, along with its effect on

the chemical fate of the sediments.














CHAPTER 5
CONCLUSIONS

5.1 Summary

The determination of ground water discharge is important, but an elusive process.

Ground water discharge rate can be a valuable, if not a necessary addition to any

quantitative nutrient or hydrographic modeling effort in the Banana River Lagoon.

Measurements of ground water discharge, and its associated nutrient flux using seep

meters reflect rates that are greater than those calculated using numerical modeling and

tracer techniques. These elevated nutrient fluxes measured using seep meters suggest,

that while diagenetic reactions such as organic matter remineralization at the sediment-

water interface can control the concentrations of these fluxes, it is the additional sources

of water being discharged from the sediments to the lagoon through advective processes,

such as bioturbation, wave action, and tidal pumping, that ultimately control the flux rate.

Therefore, it is critical to estimate the magnitude of organic matter remineralization at the

sediment-water interface, and also be able to identify the additional sources of ground

water discharge within shallow sediments, to accurately access the hydrologic and

nutrient budgets of the lagoon.

Previous studies using conservative tracers such as CI, have shown that much of

the seep water at BRL2 originated from the lagoon. In other words, the lagoon water is

being re-circulated through the sediments. There is also evidence suggesting that the

lagoon water mixes with the pore water to -70 cm depth below the sediment-water

interface. This sort of mixing between the lagoon and pore water is important for nutrient









fluxes because of the greater volumes of water, and associated nutrients discharged from

the sediments by advective rather than diffusive processes. By undertaking this research

project I was able to provide some preliminary information about the physical and

chemical composition of the sediments that may control the source of the nutrients to the

Banana River Lagoon; and by using mathematical modeling and mass balance

calculations, was able to identify some of the processes controlling the discharge rates

required to drive the associated nutrient fluxes to the lagoon.

Both the sediment cores recovered from BRL2 and BRL6, showed variability in

chemical composition as well as its physical properties, suggesting a rather complex

hydrodynamic lagoon system. The sediments are sandy, inter-layered with calcareous

shell fragments and an occasional clay horizon. The high average porosity corresponded

to high porosity. However, the low organic matter (OM) content reflected the sandy

nature of the sediments. By making mass balance calculations we were able to compare

fluxes of TP, TN and SiO2, and see if there was sufficient OM in the sediments to support

the output fluxes. Measuring fluxes using seep meters may expedite the process by

limiting the amount of dissolved oxygen available to the sediments undergoing diagenetic

reactions within only a few centimeters below the sediment water interface. If so, then

almost all of the organic matter undergoes remineralization at the sediment-water and

only a small fraction ultimately gets buried in the sediments. This process could explain

the high nutrient concentrations measured in the seep water. Therefore, in order to make

mass balance calculations between input versus output nutrient fluxes to the lagoon it is

far more realistic to use pore water concentrations rather than seep water.









Another factor that can control the high nutrient fluxes is the ground water

discharge rate. At BRL2, SiO2 pore water profiles suggest that simple molecular diffusion

cannot support the transport mechanism at the sediment-water interface, up to 110 cm

depth. The SiO2 profiles of the pore waters can only be reproduced by using enhanced

diffusion rates of K = 10-3 cm2 s-1 which are two orders of magnitude faster than

molecular diffusion. This process of enhanced diffusion could only exist if there was

substantial amount of mixing taking place within sediment pore water, brought about by

benthic animal activities, tidal pumping, and wave action. However, the SiO2 pore water

profiles between 110-230 cm represents a slightly slower mixing regime, that could be

explained by the fact that wave action and tidal pumping does not affect diffusion rates at

depths greater than 110 cm.

Finally, by correlating physical and chemical properties of the sediments, coupled

with visual observations we were able to get a fairly good insight into some of the

physiological processes in the Banana River Lagoon. For example, the small range in

porosity corresponds to uniform grain-size and compaction of sediments with depth. The

increase in porosity corresponded to the clay horizons, which act as aquitards within the

sediments, limiting the flow of ground water discharge. This could be the reason why

ground water discharge rates at BRL2 are slightly higher (44.5 ml/m2/min) than those

measured at BRL6 (18.7 ml/m2/min). Although ground water discharge appears to have a

major impact on nutrient cycling, trying to quantify the flux may be difficult, because of

mixing brought about by the re-circulation of lagoon water through the shallow

sediments. The mechanisms driving mixing are unknown, but could involve physical and

biological processes caused by bioturbation, tidal pumping, and wave action. The









magnitude of these mixing processes should be important for nutrient fluxes because of

the increased organic matter regeneration that occurs within shallow sediments from

cycling of oxygenated lagoon water through the sediments.

5.2 Future Work

This research work has provided us with some preliminary information about the

Banana River Lagoon, such as the physical and chemical properties of the sediments,

nutrient fluxes to the lagoon using shallow pore water concentrations, and using a SiO2

diagenetic model to describe enhanced mixing within shallow sediment pore waters.

However, many additional questions are raised by the results, and answers to these

questions will be important in order to gain a complete understanding of the nutrient

fluxes to the Banana River Lagoon. Some of the questions include:

* How do shallow sediment pore water concentrations compare with measured nutrient

fluxes within other areas of the lagoon that have not been previously sampled?

* What is the magnitude and extent of mixing processes such as bioturbation, wave

action or tidal pumping individually, below the sediment-water interface?

While answering these questions in the future, emphasis should be laid on collecting pore

water samples using smaller depth resolution, and higher frequency sampling trips in

order to evaluate the time required for mixing between lagoon and pore waters to take

place. In addition, future work should also focus on developing other mathematical

diagenietic models in evaluating ground water discharge rates using conservative/non-

conservative species, so as to better understand lagoon water circulation, and extent of

organic matter rimineralization that may result from such a circulation.
















PHYSICAL


APPENDIX A
AND CHEMICAL ANALYTICAL DATA FROM CORE BRL2


Depth Porosity Density TP TN OM SiO2 TC
(cm) (%) (g/cc) (mg/g) (mg/g) (mg/g) (mg/g) (%)
2 21.5 1.57 0.018 0.085 3.477 4.373 1.2
4 21.0 1.76 0.015 0.167 3.352 3.110 1.6
6 21.8 1.79 0.014 0.113 3.039 4.001 1.3
8 24.0 1.85 0.014 0.075 2.137 3.591 1.7
10 28.1 1.92 0.011 0.058 1.492 3.546 1.5
12 29.1 1.94 0.018 0.062 7.217 3.235 1.2
14 28.5 2.00 0.023 0.092 10.097 3.197 1.7
16 29.6 2.01 0.020 0.083 10.096 2.859 1.8
18 29.2 2.10 0.023 0.107 24.585 4.158 1.6
20 31.2 2.01 0.051 0.111 27.218 6.651 3.6
22 36.2 1.95 0.094 0.214 9.875 6.561 3.2
24 38.5 1.96 0.067 0.214 7.347 4.120 3.5
26 36.1 1.93 0.039 0.162 6.890 4.628 3.3
28 37.9 1.92 0.038 0.242 6.216 6.221 3.6
30 36.3 1.88 0.030 0.150 6.619 8.198 2.4
32 36.3 1.92 0.036 0.193 4.987 3.543 2.9
34 33.6 1.95 0.097 0.179 2.922 4.044 1.7
36 32.7 1.95 0.021 0.065 1.964 4.350 1.8
38 32.4 1.97 0.015 0.103 2.694 7.627 2.2
40 31.7 2.00 0.011 0.083 2.891 5.158 1.5
42 30.7 2.00 0.007 0.070 1.501 4.917 2.2
44 31.2 1.99 0.011 0.103 1.195 6.315 1.2
46 31.0 1.98 0.008 0.039 0.695 5.017 1.0
48 31.7 1.98 0.006 0.034 0.552 4.907 1.0
50 32.3 1.98 0.004 0.042 0.668 3.899 1.6
52 31.7 1.94 0.008 0.051 0.937 7.165 1.4
54 36.7 1.94 0.030 0.193 3.212 6.966 2.1
56 33.0 1.97 0.014 0.065 1.452 8.818 0.8
58 31.6 1.98 0.010 0.032 0.606 5.912 1.0
60 31.9 1.97 0.005 0.051 1.021 3.999 1.4
62 31.4 1.98 0.003 0.060 1.279 3.545 1.7
64 31.3 2.00 0.001 0.061 1.003 5.188 1.5
66 31.0 1.99 0.004 0.068 1.054 4.771 0.7
68 30.0 2.00 0.000 0.045 0.781 8.276 1.1










Depth Porosity Density TP TN OM SiO2 TC
(cm) (%) (g/cc) (mg/g) (mg/g) (mg/g) (mg/g) (%)
70 30.2 1.98 0.004 0.042 0.761 9.713 0.9
72 31.0 1.98 0.000 0.049 0.933 3.557 1.6
74 30.9 1.96 0.000 0.049 0.757 4.172 0.8
76 33.1 2.00 0.010 0.056 1.081 4.687 1.3
78 30.7 2.04 0.003 0.054 0.926 4.687 0.7
80 30.1 2.03 0.001 0.040 0.766 4.121 0.9
82 31.4 2.02 0.000 0.035 0.616 3.494 0.9
84 30.4 2.01 0.000 0.027 0.531 3.136 0.2
86 30.8 2.02 0.000 0.040 0.810 3.649 0.7
88 30.6 2.02 0.005 0.037 0.971 5.812 1.5
90 30.2 2.02 0.006 0.035 0.994 4.272 1.6
92 30.0 2.01 0.013 0.055 1.110 4.960 0.6
94 31.1 2.00 0.020 0.034 1.146 5.792 1.1
96 30.6 2.01 0.023 0.042 1.438 6.618 1.1
98 30.9 2.00 0.021 0.033 1.479 5.573 1.5
100 31.1 2.00 0.016 0.035 1.327 4.783 1.5
102 32.3 1.99 0.020 0.037 1.595 6.927 0.6
104 31.1 1.94 0.022 0.037 1.794 6.498 1.1
106 31.4 1.96 0.021 0.020 1.204 6.303 1.1
108 30.8 1.92 0.020 0.027 1.109 7.040 1.4
110 33.4 1.92 0.026 0.028 2.419 7.600 1.4
112 36.4 1.92 0.036 0.020 2.428 9.318 2.9
114 36.4 1.86 0.034 0.032 4.293 6.917 2.3
116 41.5 1.84 0.065 0.023 4.824 10.593 2.0
118 35.1 1.90 0.057 0.020 2.157 9.997 1.7
120 34.0 1.92 0.050 0.013 1.261 9.394 2.2
122 32.7 1.92 0.048 0.031 1.850 9.106 2.0
124 33.8 1.94 0.045 0.015 1.404 7.977 1.7
126 33.5 1.96 0.047 0.012 1.236 8.028 2.0
128 33.3 1.96 0.047 0.012 1.817 6.629 1.8
130 33.3 1.97 0.061 0.008 1.524 6.641 1.6
132 33.0 1.94 0.045 0.000 1.218 7.108 2.1
134 34.4 1.92 0.031 0.000 1.432 7.791 1.6
136 32.6 1.95 0.030 0.000 0.791 5.356 1.7
138 33.7 1.95 0.026 0.000 0.854 5.624 1.3
140 32.9 1.95 0.017 0.000 0.579 5.347 1.8
142 32.3 1.95 0.006 0.000 0.320 3.863 1.0
144 32.6 1.94 0.004 0.000 0.270 3.243 1.3
146 32.6 1.96 0.003 0.000 0.372 3.037 1.3
148 32.6 1.95 0.002 0.000 0.241 2.663 1.2
150 33.4 2.02 0.002 0.000 0.278 3.315 1.6









Depth Porosity Density TP TN OM SiO2 TC
(cm) (%) (g/cc) (mg/g) (mg/g) (mg/g) (mg/g) (%)
152 34.5 1.98 0.001 0.000 1.297 3.195 1.3
154 32.0 0.91 0.003 0.000 0.448 3.985 0.7
156 31.9 Nil Nil 0.000 0.657 3.195 Nil
















PHYSICAL


APPENDIX B
AND CHEMICAL ANALYTICAL DATA FROM CORE BRL6


Depth Porosity Density TP TN OM SiO2 TC
(cm) (%) (g/cc) (mg/g) (mg/g) (mg/g) (mg/g) (%)
2 39.4 1.68 0.020 0.208 2.252 1.126 1.3
4 39.5 1.85 0.016 0.261 2.356 4.422 1.1
6 39.9 1.82 0.015 0.271 3.109 1.472 0.7
8 40.2 1.85 0.004 0.216 2.725 1.963 1.6
10 39.5 1.85 0.009 0.223 2.208 1.778 1.0
12 40.6 1.85 0.011 0.181 1.612 1.542 1.0
14 38.6 1.87 0.037 0.136 1.377 1.398 1.0
16 38.4 1.86 0.043 0.157 9.832 2.070 1.0
18 38.0 1.89 0.014 0.108 1.100 2.011 0.9
20 37.5 1.91 0.004 0.113 1.804 2.345 1.1
22 37.9 1.89 0.035 0.108 1.462 1.758 0.9
24 37.3 1.90 0.000 0.103 2.139 1.197 1.2
26 37.8 1.90 0.000 0.133 4.271 0.972 1.6
28 37.9 1.89 0.087 0.151 3.320 1.376 2.2
30 38.0 1.89 0.012 0.170 11.391 2.173 1.6
32 39.1 1.89 0.058 0.579 10.268 1.445 3.2
34 38.7 1.93 0.049 0.745 13.724 2.713 3.1
36 37.3 1.97 0.016 0.203 22.895 2.251 4.0
38 37.5 1.92 0.043 0.197 5.782 2.260 4.2
40 38.9 1.89 0.027 0.221 6.573 3.959 2.9
42 38.6 1.90 0.054 0.265 19.298 4.103 1.6
44 37.6 1.91 0.008 0.230 11.219 3.655 2.6
46 38.5 1.88 0.012 0.250 16.335 5.280 3.1
48 38.2 1.89 0.012 0.194 18.506 3.812 2.7
50 36.8 1.93 0.024 0.162 27.853 1.031 2.8
52 36.3 1.93 0.011 0.154 38.547 2.379 2.9
54 38.1 1.92 0.011 0.164 43.714 4.451 2.9
56 38.6 1.91 0.011 0.133 11.428 5.711 2.4
58 39.2 1.87 0.035 0.135 5.930 2.852 2.5
60 38.9 1.88 0.014 0.144 7.707 3.437 2.7
62 39.1 1.86 0.009 0.125 11.316 3.066 2.5
64 39.7 1.85 0.022 0.164 12.390 4.409 2.6
66 40.2 1.85 0.033 0.157 12.354 3.026 2.9
68 40.3 1.82 0.102 0.183 20.002 2.844 4.3










Depth Porosity Density TP TN OM SiO2 TC
(cm) (%) (g/cc) (mg/g) (mg/g) (mg/g) (mg/g) (%)
70 41.0 1.81 0.040 0.160 9.325 3.815 3.9
72 41.8 1.83 0.093 0.152 11.166 3.224 3.0
74 41.2 1.83 0.066 0.172 15.213 4.248 3.6
76 39.0 1.86 0.076 0.211 25.722 1.790 4.3
78 43.1 1.81 0.090 0.222 12.644 4.364 4.8
80 45.2 1.75 0.083 0.244 9.390 6.166 5.4
82 49.4 1.75 0.105 0.185 5.888 11.984 5.5
84 53.0 1.68 0.192 0.197 4.568 14.754 7.9
86 51.3 1.77 0.170 0.175 4.167 13.987 4.7
88 56.7 1.60 0.162 0.217 3.456 10.251 6.1
90 55.1 1.61 0.192 0.200 2.429 15.090 4.4
92 52.3 1.62 0.190 0.156 2.706 14.109 4.0
94 51.1 1.65 0.160 0.125 1.310 13.323 3.6
96 53.9 1.64 0.161 0.146 1.683 10.183 4.5
98 51.2 1.66 0.139 0.117 1.560 8.658 4.3
100 45.6 1.68 0.092 0.084 0.098 10.680 4.1
102 49.6 1.62 0.104 0.118 1.225 13.820 4.4
104 47.1 1.65 0.039 0.096 1.193 10.408 3.1
106 49.9 1.65 0.025 0.109 1.637 10.832 3.5
108 51.6 1.65 0.032 0.164 11.399 12.363 4.9
110 47.7 1.76 0.025 0.026 1.877 10.335 4.3
112 39.8 1.86 0.004 0.046 1.266 4.504 2.9
114 38.1 1.84 0.001 0.052 2.127 3.105 2.4
116 38.4 1.87 0.000 0.054 1.821 5.257 2.1
118 37.9 1.87 0.000 0.058 2.200 4.132 2.5
120 39.4 1.88 0.002 0.057 2.495 6.073 2.1
122 38.3 1.89 0.001 0.038 2.099 5.092 2.3
124 37.5 1.89 0.000 0.043 2.085 4.130 1.5
126 36.5 1.90 0.000 0.021 1.373 4.444 1.6
128 36.5 1.89 0.000 0.028 1.304 4.230 0.9
130 36.8 1.89 0.000 0.020 1.182 3.957 1.0
132 37.0 1.85 0.000 0.028 1.406 2.384 1.1
134 37.1 1.85 0.000 0.020 1.530 2.287 1.0
136 37.1 1.88 0.000 0.011 0.944 2.687 1.0
138 37.6 1.88 0.000 0.011 0.758 2.661 0.6
140 36.6 1.88 0.000 0.007 0.548 3.345 0.4
142 36.2 1.90 0.000 0.000 0.414 2.794 0.5
144 35.9 1.91 0.000 0.000 0.029 2.260 0.8
146 35.2 1.92 0.000 0.025 0.395 2.507 0.8
148 35.4 1.93 0.000 0.019 0.293 2.597 0.7
150 34.9 1.94 0.000 0.014 0.228 2.364 0.8









Depth Porosity Density TP TN OM SiO2 TC
(cm) (%) (g/cc) (mg/g) (mg/g) (mg/g) (mg/g) (%)
152 35.1 1.92 0.000 0.015 0.293 3.145 0.8
154 34.8 1.93 0.000 0.028 0.256 2.491 0.9
156 35.0 1.92 0.000 0.015 0.259 2.506 1.0
158 35.6 1.92 0.000 0.020 0.204 1.596 1.0
160 36.3 1.92 0.015 0.079 1.313 1.783 1.3
162 36.3 1.69 0.008 0.148 2.686 1.862 1.3















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BIOGRAPHICAL SKETCH

I started my education in 1980 when I joined St. Peter's High School, Bombay,

India. I studied there for twelve years, from kindergarten to X grade. In 1992 I joined St.

Xavier's College, a part of the University of Bombay. I completed the Junior College

(high school equivalent) level in 1994, and then went on to Degree College in St.

Xavier's. I graduated in May 1997 having earned a Bachelor of Science (Honors) degree

with geology as my major, and gemology as my minor. In 1997 I started my master's

degree program from St. Xavier's College and graduated in June 1999 with a Master of

Science (Distinction) degree, majoring in geology. In Fall 2000 I joined the Department

of Geological Sciences at the University of Florida (Go Gators!). I plan on graduating in

Spring 2003 with a Master of Science degree, with a major in geology and a minor in

environmental engineering sciences. Apart from this I will also receive a certificate in

hydrologic sciences as part of the Hydrologic Sciences Academic Cluster here at the

University of Florida.