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projects > linking land, air and water management in the southern everglades and coastal zone to water quality and ecosystem restoration: task 1, mercury cycling, fate and bioaccumulation
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Project Work Plan
Greater Everglades Science Program: Place-Based Studies
Project Work Plan FY 2003
A. GENERAL INFORMATION:
Project Title: Integrated Biogeochemical Studies in the Everglades
Project Summary: Over the past half century, the south Florida ecosystem has seen dramatic change due to explosive population growth and needs of these people (for example, water and energy use, transportation, and land development for residential, agricultural and commercial uses). It is estimated that over 35 percent of the original natural landscape has been converted to agricultural or urban use. And, most of the remaining portions have been altered significantly from their original characteristics through the establishment of over 2,250 km of canals have resulted in what is now ostensibly a series of contiguous water-control impoundments (McPherson et al., 1976). This project represents an integration of a number of individual but interrelated tasks that address environmental impacts in the south Florida ecosystem using biogeochemical approaches. The overall programmatic goal of this project is to examine the complex interactions of mercury, sulfur and nutrient contamination (synergistic and antagonistic) among the major sub-ecosystems present in south Florida to provide direct feedback to aid the Everglades Restoration Plan development and implementation. This information is needed at many levels, from those who are concerned with the potential for water treatment wetlands (STAs) to yield unsafe loads of methylmercury, to those responsible for possible implementation and enforcement of mercury air emission reduction laws, to those who are concerned over the possible ecological effects of the ASR program.
Currently, a great number of biological, hydrological, chemical, and societal issues are confronting not only those people responsible for designing and implementing the Everglades Restoration Plan, but also the citizens of south Florida and millions of people who frequent this area to enjoy the many pleasing aspects of this unique environmental setting. In order to address any of these issues, however, multi-disciplinary, integrated science approaches need to be developed and applied to derive the most complete scientific information possible upon which the most responsible decisions or action plans can be implemented. For example, the Aquifer Storage and Recovery (ASR) program is largely a result of current water shortages in south Florida and the anticipated significant population growth in the coming decades. However, a great deal of uncertainty surrounds what possible effects may result from the release of sub-surface stored water in terms of potential for the generation of toxic chemicals during storage (including methylmercury) and their effects on indigenous organisms of the Everglades, as well as hydraulic fracturing or bio-fouling of the aquifer itself. Of the issues of chemical concern in the south Florida ecosystem, the intersection of mercury, nutrient and sulfate contamination in the various sub-ecosystems presents an extremely challenging problem to investigate, but one that has enormously important repercussions for the resident wildlife, the public who make use of this region for recreational purposes or for subsistence fishing, and the south Florida agricultural industry that provides for a significant component of our Countrys need for a reliable vegetable source. Possibly more importantly, the previous and ongoing work conducted by the USGS on mercury cycling and methylmercury production in the Everglades has had national international impact, and presently is viewed as the best research upon which proposed federally mandated mercury emission standards would be based. The importance and impact of our research in south Florida can be demonstrated by the appointment of one of the project members (David Krabbenhoft) to a White House Interagency Working Group (IWG) to develop the current Administrations policy on mercury and methylmercury, and to identify the research and development needs to improve environmental conditions of mercury contamination and potential toxic threats to humans and wildlife. During the initial meeting of this IWG, the Chair specifically quoted findings from the Aquatic Cycling of Mercury in the Everglades (ACME) project as fundamentally important for evaluating the best pathways for evaluating how to proceed on this complex issue.
Mercury contamination of the Everglades ecosystem is one of the most severe cases in the published literature and was identified as a principal factor in the death of at least one Florida panther which had a liver mercury concentration of 110 µ g g-1, and is strongly implicated in the deaths of two other panthers. Currently, no human consumption of any Everglades' sport fish is recommended. Previous work by the Aquatic Cycling of Mercury in the Everglades (ACME) project has revealed that mercury and methylmercury (MeHg) distributions in water, sediment and biota show complex seasonal and spatial trends, and that the cycling rates of Hg and MeHg are so rapid that many measurements need to be conducted on a diel basis. From 1995 to 1999, the ACME team studied the biogeochemical cycling of Hg in detail at a suite of sites across the Everglades. These studies revealed relations between biogeochemical factors and the production rate of MeHg, the most toxic and bioaccumulative form of mercury, which is central to understanding the mercury problem in the Everglades and elsewhere. We showed that there are clear, but very complex, ties between MeHg production and atmospheric Hg loading and sulfate (and possibly phosphate) loading from EAA runoff. However, because all of the primary driving factors of MeHg production co vary across the Everglades, a more "controlled" experimental approach was developed and implemented in 2000 that makes use of in situ mesocosms, stable isotopes of Hg, sulfur, and specific fractions of dissolved organic carbon to reveal their individual controlling influence on methylmercury production an bioaccumulation. To date, we have successfully conducted dosing experiments with the mercury isotopes and for the first time anywhere have revealed that there is an "aging effect" for new mercury added to the ecosystem. Specifically, we observed that more recent doses of mercury isotopes are more likely to be bioaccumulated than older mercury. These results have significant implications for how this problem should or can be managed in the Everglades and elsewhere. More recently, mesocosms dosed with gradients in mercury isotopes, sulfate, dissolved organic carbon (DOC), and combinations of these constituents, have revealed many new findings, including: (1) the additions of sulfate alone can substantially increase the level of MeHg production from the existing pools of inorganic Hg(II) residing in sediments; (2) the addition of sulfate and mercury together have a non-linear additive effect such that much higher levels of MeHg are produced from the combined addition as compared to the MeHg production response measured from the individual does responses; (3) DOC additions were probably the most surprising of all, and resulted in an immediate mobilization of existing MeHg in sediment, and also greatly increased (about 70x) the production of new MeHg from the mixed addition of mercury isotope and DOC; and (4) very minimal MeHg production response was observed from the additions of phosphate (note, in this case we sample the SFWMD P-dosing mesocosms that had been previously established to measure biological response to P loading).
Project Objectives and Strategy: This proposal identifies work elements that are logical extensions, and which build off, our previous work. Our overall scientific objective is to provide a complete understanding of the external factors (such as atmospheric mercury and sulfate runoff loads) and internal factors (such as hydroperiod maintenance and water chemistry) that result in the formation and bioaccumulation of MeHg in south Florida ecosystems, and to conduct this research is such a way that it will be directly useable by land and water resource managers. Overall, we will continue to apply technologies, sampling strategies and experimental designs that extend from the centimeter scale (incubation experiments), to the meso scale (in-field mesocosms), to the ecosystem scale. More specifically, we will seek to achieve the following sub-objectives (1) Extend our mesocosms studies to provide a more comprehensive examination of the newly discovered "new versus old" mercury effect by conducting studies under differing hydrologic conditions and sub-ecosystem settings so that our experimental results will be more generally applicable to the greater south Florida ecosystem including the STAs that have been recently constructed and are yielding very high levels of methylmercury but the cause is currently unknown; (2) Seek to further identify the mechanisms that result in extremely high levels of MeHg after natural drying and rewetting cycles in the Everglades and which have major implications for the Restoration Plan; (3) Follow up our initial evaluations (FY2002) of methylmercury production in Florida Bay sediments that showed surprisingly high levels of in situ methylation and maybe an important cause of high levels of mercury in commercial and sport fish in Florida Bay; (4) increase the level of collaboration with the TIME (Schffranek) and SICS (Swain) projects to facilitate the extended use of these models for mass transport estimates of nutrients contaminants in the Everglades National Park, Conservation Areas and estuarine environments; and, (5) conduct a series of synoptic sampling efforts in the Big Cypress National Preserve where Orem and McPherson have show anomalously high levels of nutrients (including sulfate) that would likely stimulate mercury methylation. In addition, results of all these investigations will provide critical elements for building ecosystem models and screening-level risk assessment for contaminants in the ecosystem, and this project will be closely linked with projects addressing ecosystem modeling (Reed Harris, Everglades and TMDL mercury modeling) and risk assessments (Tim Gross, USGS, Gainesville, FL).
Potential Impacts and Major Products: This project is purposefully designed, and has as one of its major goals, to provide integrated science for state and federal natural resource managers and decision makers who need relevant scientific information to aid in three critical areas of resource management: Restoration Plan Design, Environmental Regulations and Action Plans, and Risk Assessments (see Figure 1). Several major questions are looming related to Everglades Restoration, and several of which are directly related to our research efforts, including: Will the altered hydrology of the "New Everglades" promote, have no effect, or reduce the level of mercury methylation and bioaccumulation? The original test STA showed very depressed levels of methylmercury production, however, more recently constructed treatment wetlands have yielded some of the highest methylmercury levels ever observed in the Everglades, but what is the underlying cause and long-term consequences of this effect? Sulfate loading from agricultural runoff is directly linked to mercury methylation it the Everglades, but what is would be the long-term benefit of reduced sulfate loads if the existing pools of sulfur that now exist in the peat are capable of maintaining elevated levels of methylmercury production? Florida Bay is currently under a mercury advisory of contaminated fisheries, but is the source of the methylmercury from marsh runoff or in situ production in the Bay? Will increases in freshwater discharge to Florida Bay, one of the probably out comes of the Restoration effort, have an effect on methylmercury production in Florida Bay? Currently, plans for the Aquifer Storage and Recovery (ASR) project are to discharge recovered water to the marshes that has sulfate levels about the same as current Lake Okeechobee conditions (about 30-60 ppm). Will methylation occur in the aquifer or will the recovered stimulate mercury methylation upon discharge to the marshes? The ACME project has shown that "new mercury" inputs are more available to methylating microbes than "old mercury" already existing in the peat and sediments, precisely how quickly and to what new baseline conditions would the ecosystem would adjust to if absolute mercury emissions reductions were emplaced? Lastly, although the ACME project has provided a great deal to our overall understanding of mercury methylation and bioaccumulation, a logical extension of our research by tying to thorough risk assessment has not been conducted. Tim Gross and Beverly Arnold of the USGS in Gainesville, Florida has proposed to perform a multiple-contaminant risk assessment of critical endpoints (alligators, bass, brown-bullhead, ibises, mussels and apple snails), with emphasis placed on endocrine disruption and other reproductive effects. This project will coordinate with their efforts and provide analytical and data support as funding is available. We will solicit direct input from relevant management agencies (e.g., SFWMD, FDEP, USEPA, F&WS, NPS) as to what they feel should be examined through the use of controlled field enclosures and laboratory tests. We will continue to be closely aligned with the Everglades Mercury Model development (EPA, SFWMD, and FDEP funded) to assure our field and laboratory studies are in concert with the model construction, coding, and the predictive questions being asked of the model.
The scientific understanding by the ACME project for the general topic of mercury contamination of aquatic ecosystems has had many far-reaching impacts as well. Many "paradigm shifting discoveries" have been made by the ACME effort that have altered the way we view mercury cycling in the environment generally, or the overall understanding of the biogeochemistry of the Everglades. For example, our studies have demonstrated for the first time that dissolved organic carbon plays a direct role in the mercury methylation process, whereas before it was only perceived to be a transport, or stabilization ligand for mercury and methylmercury in solution. In the Everglades, we have discovered that dramatic changes in mercury and methylmercury concentrations occur on a diel basis and other investigators have followed our lead and shown this to be the case in other systems. In addition, before our work, the existence of the sulfate contamination plume originating from the Everglades Agricultural Area, and its impact on methylmercury formation was a direct outcome of ACME. Finally, the notoriety of the ACME project has resulted in David Krabbenhoft being appointed to a White House committee to develop a national policy for the current Administration on mercury and methylmercury.
The ACME project has been a major contributor to the peer-reviewed literature, and we intend to continue the production of scientific journal papers, and USGS Fact Sheets to disseminate the description of our project and our findings. The ACME Phase I synthesis document is currently in layout phase by the Publication Unit in the Wisconsin District Office and are targeting completing by the end of the 2002 calendar year.
Collaborators: George Aiken, USGS, Boulder, CO. Cindy Gilmour, Academy of Natural Sciences, Estuarine Research Center, St. Leonard, MD. Darren Rumbold, SFWMD, Ft. Meyers, FL. David Evans, NOAA, Raleigh, NC.
Clients: Florida Department of Environmental Protection (T. Atkeson, D. Axelrad), South Florida Water Management District (L. Fink); U.S. Fish and Wildlife Service, Arthur R. Marshall Loxahatchee National Wildlife Refuge (L. Brandt and B. Arrington); National Park Service, Everglades National Park (T. Armentano); Big Cypress National Preserve
B. WORK PLAN
Title of Task 2: Integrated Biogeochemical Studies in the Everglades: Mercury Cycling, Methylation and Bioaccumulation
Task Summary and Objectives: This project integrates a number of individual but interrelated tasks that use geochemical approaches to address contaminant and water quality issues in the south Florida ecosystem. Task 1 of this project focuses on biogeochemical processes and the sources and cycling of nutrients, sulfur, and organics in the ecosystem. It coordinates with other tasks to examine the complex involvement of nutrients, organics, and especially sulfur and ties intimately to Task 2, Mercury Cycling, Methylation and Bioaccumulation, through the complex intertwining of the sulfur and mercury cycles. The major focus is on ecosystem responses to variations in contaminant loading (e.g., mercury, sulfate, DOC), natural and anthropogenic perturbations (e.g., fire, water level maintenance), and how imminent ecosystem restoration may affect future levels of methylmercury contamination of this fragile ecosystem. Our Phase I studies reveal the ecosystem-wide trends of methylmercury contamination in the Everglades, and what were the controlling factors of these trends. Phase II studies will continue to build off our major findings and seek to provide a more meaning full and direct connection to CERP, and to expand our investigations to other parts of the ecosystem where time and staff limitations prohibited examinations in the past but that are now feasible. The sub tasks described here have a wide range of operating scales, from small scale lab tests to whole-ecosystem mass flux estimates, that will allow for a more expanded use of our data, as well as working in sub ecosystems not examined previously, including Florida Bay and the interfacing Mangroves, Big Cypress National Preserve, and Shark River Slough and the southwest coast.
Work to be undertaken during the proposal year and a description of the methods and procedures:
(1) Mesocosm Studies
Background/Objectives - We are currently using environmental enclosures placed in the ecosystem (mesocosms) to examine the effects of changing water quality variables on methylmercury production and bioaccumulation. These experiments are designed to examine the effects of individual variables and multivariable interaction effects on methylmercury production. Variables of interest with regard to methylmercury production include: inorganic mercury (added in isotopic form), sulfur, nutrients (especially phosphorus), DOC, and iron. All Tasks on the project cooperate on the mesocosm work: Task 1 focuses on the effects of sulfur and nutrients on methylmercury production, Task 2 focuses on mercury, and Task 3 on DOC
Methodology-Our experimental mesocosms have "breathing holes" that are left open to the outside environment during the intervening time between experiments so that the enclosed areas can equilibrate with the native environment. Our observations (direct measurements of pH, dissolved oxygen, temperature, and observations of general visual health) have shown that the leaving the mesocosms enclosed for 2-4 months does not produce an artificial "mesocosm effect" and bias our results. During experiments, the breathing holes are closed with silicone stoppers and chemical additions are made to sets of mesocosms to test the effects of the chemical additions on methylmercury production. Each chemical addition (variable) is tested at multiple concentration levels. In some sets of mesocosms, multiple chemical species are added to examine interactive effects. For example, during FY02, mesocosm experiments were conducted at several sites in the Everglades to test the effects of sulfate addition (3 concentration levels), inorganic mercury (3 concentration levels), DOC (2 concentration levels), inorganic mercury plus sulfate (3 concentration levels), and inorganic mercury plus DOC. Following the additions, changes in chemical species (methylmercury and other mercury species, sulfur species, DOC, nutrients, anions, cations, Fe and Mn, redox, conductivity, pH) and microbial activity (sulfate reduction and mercury methylation rates) are determined in surface water, porewater, and sediments in the mesocosms over time (usually followed for several months following the start of the experiment). In addition, during each experiment we establish at least two control mesocosms to check for enclosure effects, and we take samples from the native environment near the mesocosms to assure that the mesocosms are tracking the overall season changes that are observed annually in the ecosystem. Results of mesocosm studies from FY01 and 02 show that: (1) introduced or "new" inorganic mercury is methylated preferentially over "old" mercury bound in the sediments, and this new mercury is bioaccumulated up to native fish preferentially as well; (2) Sulfate addition stimulates methylmercury production, but sulfate and inorganic mercury additions stimulate even higher methylmercury production; (3) Sulfide appears to inhibit methylmercury production to some extent. (4) DOC addition enhances methylmercury concentrations in surface water in two ways: first by enhancing availability of new mercury to methylating bacteria (directly or indirectly), and second, by increasing the net overall solubility of the produced methylmercury into the water column.
FY03 Work- We have already begun the process of drafting as series of papers for intended submission to high-visibility international journals. We expect that at least two manuscripts will be submitted by the end of FY02 and or early in FY03. We also propose to follow-up on our previous mesocosm studies on methylmercury production. Experiments will be repeated in order to verify and expand on results from FY02. A new feature in FY03 will be the use of isotopically labeled sulfate in the chemical additions to follow changes in sulfur geochemistry and its effects on methylmercury production. The Everglades Mercury Cycling Model has a major information gap in that it does not directly simulate sulfur cycling and linkages to methylation, primarily due to a lack of previous research on sulfur cycling rates, fate and speciation. Our previous mesocosm experiments were focused in the northern Everglades. In FY03 we propose to add another mesocosm site in an STA (probably STA-2). These constructed wetlands can behave as zones of low methymercury production (such as ENR), but also can produce very high levels of methylmercury (STA-2). The reasons for this are not fully understood, and mesocosm experiments in the STAs will be designed to provide managers with information on how best to operate the STAs to minimize methylmercury production.
(2) Drought/Burn and Rewet Experiments
Background/Objectives - Phase I ACME showed a very dramatic (about a 10-100X increase) effect of drying and rewetting cycles on methylmercury production bioaccumulation in fish in the Everglades. Detailed geochemical examinations showed that one reason for this pronounced effect is likely due to oxidation of reduced previously existing sulfur pools in the peat and sediment. However, it remains unresolved where the Hg in the MeHg is derived from, with likely sources from either the rainfall during the rewetting period or from liberation of previously bound mercury in sediment and peat. In FY02, we initiated a laboratory experiment to see if we could reproduce the drying and rewetting effect on mercury methylation in Everglades peat, and to provide more mechanistic information on the geochemical mechanisms. That experiment is currently ongoing and is expected to be completed by the end of FY02. It is likely follow-up experiments will be needed, given that we only used peat samples from one site, and the complexity of this phenomenon will likely need further evaluation. Given the intimate tie of this task to the Everglades Restoration Program (altered hydrologic regimes appear to be a certainty in the "new Everglades), a strong set of field and laboratory data would appear necessary.
Methodology-The experimental approach involves: (1) collection of a series of small cores and transport to a controlled clean laboratory environment in Reston, Virginia, or St. Leonard, Maryland, (2) allowing the cores to dry completely for varying lengths of time under controlled conditions, (3) rewetting the cores with water collected from the original field sites, and is some cases spiked with stable mercury isotopes, and (4) analysis of surface water, porewater, and sediments in the rewetted cores at intervals of time following rewetting. Analytes measured in the samples included methylmercury and other mercury species, sulfur species, nutrients, anions, cations, DOC, and sediment parameters (organic carbon, total N, total P, total S, S species). Biological parameters measured included methylmercury production and sulfate reduction rates. The initial experiment was begun in March 2002 and is scheduled to end in September 2002.
FY03 Work-The experiment initiated will be completed in September 2002. The experiment results from each of the participating groups will be coalesced into a single database, and a series of manuscripts on the results will be drafted for publication. A follow-up experiment will be conducted in FY03 (continuing into FY04) using a larger core approach and additional sites (a high sulfur and low sulfur site in the northern Everglades). The larger cores will slow down the drying process in the lab, more closely simulate conditions in the ecosystem, and allow for larger sample sizes to ease the analysis step. Additional changes to the follow-up experiment will include shorter dry times and extended sampling times following rewet. Results will provide ecosystem managers, and CERP planners with information on how to limit the effects of drought and rewet cycles on methylmercury production. Results will be especially useful for managing STAs and northern WCA 3, areas that experience more frequent drought/rewet cycles.
(3) Florida Bay Mercury Methylation and Sulfur Biogeochemistry
Background/Objectives - In FY02 we collaborated with Darren Rumbold (SFWMD) and David Evans (NOAA) to execute a preliminary examination of mercury methylation rates in Florida Bay. The extremely scant literature currently available on mercury methylation in marine sediments (one published paper) suggested very low or now methylation) had persuaded us not to prioritize the Florida Bay ecosystem previously. However, our initial evaluations indicate that in fact moderate to high levels of methylation can occur in Florida Bay sediments, and my represent a primary source of methylmercury to commercial and sport fisheries. These results are were quite surprising, giving the very high levels of sulfide (100 ppm and higher) that are known to exist in Florida Bay sediments generally, and the previously identified inhibition effect of sulfide on mercury methylation. The objective of this task will be to determine a spatially complete assay of mercury methylation rates in Florida Bay, and to ascertain how the process proceeds in such sulfidic and carbon-poor sediments.
Methodology- We (Krabbenhoft/Orem/Aiken) will conduct a synoptic sampling of Florida Bay sub-ecosystems (mud flats, embayments, tidally influenced streams, etc ) to examine the biogeochemistry of mercury methylation in Florida Bay sediments. These investigations will include a complete examination of the biogeochemistry of sulfur, dissolved organic carbon, and mercury speciation and methylation rates in Florida sediments and porewater. Sediment and porewater samples will be take and analyzed for sulfur speciation and concentrations in sediments and sediment porewater. The same overall procedures used in the Everglades marshes will be employed in Florida Bay (with some modifications to account for the oozing sediments present there), which will allow for direct comparison of our results between these contrasting but effacing ecosystems.
FY03 Work- Preliminary efforts done in collaboration with Rumbold and Evans in Florida Bay during FY02 will greatly aid our site selection process and interpretation. Sites will be chosen to represent the majority of the east-to-west transitioning environments present in Florida Bay, as well and the near versus off shore variations. Sampling would be conducted in collaboration with Orem (Task 1 - sulfur and nutrient cycling), and Aiken (Task 3 - DOC). A preliminary report would be prepared, with plans for a journal paper to be prepared in FY04.
(4) Collaborations with the TIME (Schffranek) and SICS (Swain) projects
Background/Objectives - The Placed Based Studies program has supported the development of two major hydrologic investigations and model developments in south Florida: TIME and SICS. These efforts have lead to a greatly improved understanding of the hydrologic transport processes (spatially and temporally) within Everglades National Park and the Water Conservation Areas. However, the investigators of these projects have not explicitly interfaced with biogeochemical investigations to extend the use of these hydrologic models or the power of marrying the geochemistry databases to the water flow information to yield mass flux rates. These types of calculations are important because the Everglades are a dynamic ecosystem and current modeling exercises to predict the future Everglades have primarily focused on static water level estimates, and have not considered dynamic properties like water and constituent mass fluxes. During FY03, we initiate collaborations with the lead investigators of these two projects (Schffranek and Swain) to combine the strengths of the biogeochemistry and hydrologic research efforts to develop mass fluxes of nutrients, sulfur and mercury for the marshes.
Methodology - Lead investigators from the Biogeochemistry Tasks (Krabbenhoft, Orem and Aiken) will first conduct exploratory conversations with the TIME and SICS research teams to develop a strategy for marrying the two research efforts more closely. From these discussions, we will identify any data gaps that may currently exist between these studies (e.g., diffusion rate estimates) and formalize field plans to acquire the needed information. Members from each research team will participate in assembling the necessary databases to derive the mass flux estimates.
FY03 Work - This effort will be initiated in FY03, but will probably require additional follow up in FY04. Many of the ecosystem types where the TIME and SICS researchers are most active in Everglades National Park and near the coastal margins have not been evaluated at all by the ACME team. Therefore, some initial sampling of these environments will be necessary to support the completion of this sub task. Sampling efforts will be focused on those areas or specific locations where the TIME and SICS teams have monitoring instillations, which should expedite the mass flux calculations.
(5) Mercury Cycling and Bioaccumulation in Big Cypress National Preserve
Background/Objectives - The ACME Phase I researchers necessarily had to focus their intensive, process oriented research in fewer locations due to the extremely time intensive nature of this work. Because of this, many sub ecosystem types have remained largely uninvestigated with respect to mercury contamination and bioaccumulation. One notable example is Big Cypress National Preserve, where Orem and McPherson have recently showed the existence of unnaturally high levels of nutrients and sulfate (compared to southern WCA 3 and Shark River Slough). In other sub ecosystems where the ACME team has worked, slight to modest levels of nutrient and sulfate contamination have generally co-existed with the highest levels of methylmercury, such as central WCA-3A.
Methodology-Synoptic sampling efforts will be initiated in the fall/winter of FY03 to identify whether high levels of methylmercury exist in Big Cypress Preserve, and whether there are any spatial trends similar to what has been observed in other locations of the Everglades. Surface water, porewater, sediment and biological (e.g., periphyton, Gambusia, etc...) samples will be collected from sites throughout the Big Cypress Preserve. Although much of Big Cypress is a sandy soil, there are areas where peat or peaty muck is present and shallow cores and porewater can be obtained. Samples will be analyzed for total mercury, gaseous elemental mercury, and methylmercury species. Sampling efforts will be conducted in concert with Orem and Aiken to derive a complete geochemical data set to evaluate the similarities and/or differences between Big Cypress Preserve and the Conservation Areas. In the summer of FY03, and sampling trip will be conducted to make process specific measurements of methylation, demethylation, photo reduction, and gaseous mercury evasion.
FY03 Work-Work in FY03 will focus on sampling at selected sites throughout the Preserve, and chemical analysis of the samples. The study area will extend from the agricultural region north of the Big Cypress Preserve to the Ten Thousand Islands Area in the south. Sites will be primarily accessed by ground vehicle, but we will also explore possible helicopter support from the Big Cypress National Preserve for accessing more remote sites. Results from FY03 will be compiled and prepared for publication in various forms (Fact Sheet, journal publications, USGS publications) in FY04. The study will be the first to explore mercury speciation, cycling and bioaccumulation in Big Cypress Preserve, and to assess if sulfur and methylmercury production is an issue of concern. Results will assist managers in assessing potential threats to the Big Cypress Preserve and the Ten Thousand Islands Area from nutrient and sulfur inputs.
Related Work Plans:
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