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projects > integrated biogeochemical studies in the everglades: nutrients and sulfur > work plan
Project Work PlanGreater Everglades Science Program: Place-Based Studies Project Work Plan FY 2003 A. GENERAL INFORMATION:Project Title: Integrated Biogeochemical Studies in the Everglades Project start date: 10/1/00 Project end date: 9/30/05
Other Investigator(s): George R. Aiken
Project Summary: This project is an integration of a number of individual but interrelated tasks that address environmental impacts in the south Florida ecosystem using geochemical approaches. Externally derived nutrients, mercury and sulfur are three of the most important contaminants currently affecting this ecosystem. Other contaminants of concern include anthropogenically produced organic substances (pesticides, herbicides, polycyclic aromatic and aliphatic hydrocarbons) and other metals. The scientific focus of this project is to examine the complex interactions of these contaminants (synergistic and antagonistic), ecosystem responses to variations in contaminant loading (time and space dimensions), and how imminent ecosystem restoration steps may affect existing contaminant pools. The Everglades restoration program is prescribing ecosystem-wide changes to some of the physical, hydrological and chemical components of this ecosystem. However, it remains uncertain what overall effects will occur as these components react to the perturbations (especially the biological and chemical components) and toward what type of "new ecosystem" the Everglades will evolve. The approaches used will be extensions of previous efforts by the lead investigators, whereby we will enhance our abilities to address land management and ecosystem restoration questions. Major changes implemented in this project will include the use of environmental chambers (controlled enclosures or mesocosums) and isotopic tracers to provide a more definitive means addressing specific management questions, such as "What reductions in toxicity (methylation and bioaccumulation) would be realized if atmospheric mercury emissions were reduced by 75%?" or, "Over what time scales could we expect to see improvements to the ecosystem if nutrient and sulfur loading were reduced by implementation of agricultural best management practices and the storm water treatment areas (STA)?" Results of these geochemical 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). The south Florida ecosystem, including the Everglades, has been greatly impacted by many disturbances. Over 35 percent of the original natural ecosystem has been converted to agricultural or urban use, and most of the remaining portions are threatened by altered (unnatural) hydroperiods, over 2,250 km of canals that dissect what was once continuum of wetlands, water pollution, fires, and a steady loss of wildlife habitat (McPherson et al., 1976). The tasks described in this proposal focus on several of the major water chemistry changes that have occurred in this ecosystem (phosphorus, nitrogen, sulfur, and mercury loading) and the impacts on the biological systems that have been realized. In addition, through collaborations with other USGS programs (risk-assessment screening studies by T. Gross) we will help to facilitate the investigations of other contaminants of concern (organic chemicals, other toxic trace metals), which also likely enter the ecosystem from point and non-point sources in the urbanized and agricultural areas surrounding the Everglades. Costs to provide the field and analytical support for these collaborative efforts are not presently included in the budget of this proposal. Previous work by this team has shown that excess nutrients and sulfur enter the Everglades from canal discharge originating in Lake Okeechobee and the Everglades Agricultural Area (Zielinski et al., 1999; Orem et al., 1999a; Bates et al., in review). The increased nutrient load has altered biotic assemblages within parts of the ecosystem, especially in areas where eutrophic-adapted cattails (Typha domingensis) have replaced the native, oligotrophic-adapted sawgrass (Cladium jamaicense). It is also likely, though less clear, that increased nutrient load has exacerbated seagrass dieoff and extensive microalgal blooms in Florida Bay (Orem et al., 1999b). The extent of sulfur contamination in the Everglades was first documented by Bates et al. (1998) and Orem et al. (1999c). Unnaturally high levels of sulfate entering the Everglades have stimulated sulfate reduction and greatly increased concentrations of toxic and reactive hydrogen sulfide, and play a key role in controlling mercury toxicity (see below). Mercury contamination of the Everglades ecosystem is one of the most severe cases in the published literature (Ware et al. 1990). Currently, no human consumption of any Everglades' sport fish is recommended, and mercury has been identified as a principal factor in the death of at least one Florida panther which had a liver mercury concentration of 110 µg g-1 (Jordan 1990), and is strongly implicated in the deaths of two other panthers (Roelke et al. 1991). Previous work by the Aquatic Cycling of Mercury in the Everglades (ACME) project has revealed that mercury (Hg) and methylmercury (MeHg) distributions in water, sediment and biota show complex seasonal and spatial trends (Hurley et al. 1998; Cleckner et al. 1998), and that the cycling rates of Hg and MeHg are so rapid that many measurements need to be conducted on a diel basis (Krabbenhoft et al. 1998). In addition, ecosystem wide MeHg levels are controlled by in situ microbial processes (Gilmour et al. 1998; Marvin-Dipasquale and Oremland, 1998) and photochemical processes (Krabbenhoft et al. 1999a; Krabbenhoft et al. 1999b). Mercury loads to the Everglades are dominantly derived from atmospheric sources, but toxicity is largely controlled by the relative rates of conversion to methylmercury, which in turn appears to be intimately associated with the sulfate/sulfide biogeochemical cycle (Benoit et al. 1999). Project Objectives and Strategy: We propose to carry out work in the following areas: (1) Water quality studies, (2) Field-scale and laboratory-scale experimental studies; and (3) Coordinating input of geochemical results into ecosystem models and risk assessment studies being conducted by others. Our work tasks in these areas will be framed within the context of the Everglades restoration effort, and needs of ecosystem land and water managers to understand how the restoration may affect water chemistry, biology, and contaminant toxicity. The overall question we are addressing with this effort is, "Near term changes to the Everglades are certain, but what will be the ecosystem-level result of these changes and over what time scales can we expect these changes to occur?" Our previous work (Phase I studies) has answered many key questions regarding mercury, sulfur, and nutrient cycling in the Everglades, and redefined several previously existing paradigms about the general environmental chemistry of mercury. At the same time, however, our work has revealed several critical information gaps that we propose to address with this proposal (Phase II studies). The proposed work will employ a variety of investigative approaches to achieve these objectives, including: field studies, controlled experiments (both field and lab scale), and modeling. Contaminants of concern will include nutrients, sulfur, mercury, organic compounds, and other metals. Protocols for the collection of samples and chemical analysis developed during Phase I studies will be employed in these Phase II efforts. Integration of the individual tasks within the project will be achieved by co-location of field sampling sites, and cooperative planning and contemporaneous execution of laboratory and field-enclosure experiments. Results from all tasks within the project will be archived within a single database, which will be made available through a Decision Support System (Web enabled) in a GIS framework to facilitate its use by ecosystem managers. This project is specifically designed to meet the needs of state and federal natural resource managers who need information on environmental pollutants in the Everglades, and what can be done to mitigate the problem. We will interact with resource managers on three major levels of decision making in South Florida (see figure 1). First, many actions related to the Everglades Restoration project could potentially affect the expression of mercury loading in terms of its toxicity, including water levels, flushing rates, STA implementation for sulfur and nutrient reductions and the use of periphyton-based treatment cells, DOC releases, etc… We will be designing our field and lab experiments to address many of the questions that surround how restoration plans may affect mercury toxicity. Second, mercury emissions reduction is a enforcement decision facing not only the State of Florida, but our Nation. Currently, we cannot say with great confidence whether the mercury levels observed in the Everglades are limited by the amount of mercury continually entering the system, or some other substrate. Although the existing data from ACME suggest that seasonal Hg loading from the atmosphere is concomitant with higher observed methylmercury levels, there are many other co-factors that could be causing this apparent correlation. Studies proposed herein will address this critical management decision. Third, although much of the previous efforts by the PI's are directly applicable risk analyses, a thorough attempt at a multi-contaminant risk assessment has not been addressed. Tim Gross of the USGS in Gainesville, Florida has proposed to perform a mutiple-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 his efforts and provide analytical and data support as funding is available.  Potential Impacts and Major Products: This project addresses the major water chemistry issues currently affecting the Everglades: (1) eutrophication from excess nutrients entering the ecosystem, (2) sulfur contamination of the Everglades and its relation to mercury methylation, (3) mercury loading and bioaccumulation in the Everglades food web, and (4) other contaminants of concern, including organic substances and metals. Major products include USGS Open-File Reports, articles in international science journals, USGS Fact Sheets, abstracts and presentations at national and international scientific meetings and at client agencies, contributions to USGS and interagency synopsis reports, databases, and the posting of reports and databases on the WWW. Input of geochemical data into ecosystem models and risk assessment studies will also be a principal product of this project. Nutrient studies are focused on using isotope methods (uranium/uranium isotopes, 15N, and 13C) to examine the sources of nutrients to the ecosystem, and on using sediment and porewater geochemical studies to determine the rates of nutrient recycling and nutrient sinks within the sediments. A nutrient sediment budget will be developed for incorporation in a nutrient model of the ecosystem. Results will assist managers in determining the fate of excess nutrients (especially phosphorus) stored in contaminated sediments (e.g. will the excess nutrients be buried, or recycled for movement further south into protected areas). The sediment studies will also provide managers with information relevant to the effectiveness of planned remediation methods. For example, will the type of sediments deposited in the STA's (e.g. mostly cattail peat) be effective for long-term storage of nutrients removed from agricultural runoff water? Also, what will be the effect of increased hydrologic flow from the "replumbing" of the canal network in the Everglades on nutrient mobility and recycling in the wetlands? How will this "replumbing" affect nutrient flow to the mangrove areas and Florida Bay? Studies of nutrient (and sulfur) geochemistry in dated cores will provide information on historical changes in the chemical conditions existing in south Florida wetlands. This will provide wetland managers with baseline information on the water chemistry goals needed to achieve "restoration" of the ecosystem. It will also provide land managers with an estimate of the range of concentrations of chemical species and environmental conditions that have affected the south Florida ecosystem in the past. Geochemical history data in combination with information from paleontologic studies of the USGS paleoecology group will also provide insights on how organisms in the south Florida ecosystem have responded to environmental change in the past, and predict how these organisms will likely respond to changes in the ecosystem resulting from restoration efforts. Studies of sulfur contamination relate directly to the issue of methylmercury production and bioaccumulation within the ecosystem, a threat to wildlife and people in south Florida. Microbial sulfate reduction in anoxic wetland sediments is the principal mechanism for the methylation of mercury. Recent findings show that for south Florida wetlands methylmercury production and bioaccumulation is highly correlated with sulfide. Thus, sulfur geochemistry plays a central role in this methylation process. Our studies are focused on examining the sources of sulfur to the Everglades using stable isotope methods (34S and 18O of sulfate). Understanding the source of sulfate to the wetlands of south Florida may be a key to understanding why mercury methylation rates are so high in certain regions of the Everglades, and on how remediation efforts in the Everglades may impact mercury methylation rates. We are also examining the sulfur geochemistry of sediments on a regional scale, with emphasis on areas that are methyl mercury "hotspots". Apart from its role in methylation of mercury, sulfur is a contaminant of concern in the freshwater Everglades because of its reactivity and toxicity in the form of sulfide. Accumulation of sulfide in sediments of the Everglades can greatly alter redox conditions, metal speciation, and organic matter composition. All of the scientific efforts related to mercury will be directly related to management questions surrounding how mercury toxicity will be affected by the restoration efforts. Efforts during the first phase of mercury investigations were necessarily more exploratory in nature, because there was essentially no previous information on mercury in the Everglades for the ACME project to form a starting point. With a good base of knowledge now in place, we can focus our studies on more specific management related questions such as those stated above in the Project Objectives and Strategy. We will continue to be active participants in the multi-agency South Florida Mercury Science Program, and will provide our findings to the relevant management agencies in verbal and written formats. We intend to continue the production of scientific journal papers, and USGS Fact Sheets to disseminate the description of our project and our findings. 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. We will also coordinate our studies with the risk assessment studies related to mercury proposed by Gross and others. Finally, we intend to integrate all the information from this project into one consistent data base, and be in a Management Decision Support System that will be enabled with a GIS driver (ARC View). Collaborators: Cindy Gilmour (Academy of Natural Sciences, Estuarine Research Center, St. Leonard, MD)
B. WORK PLANTitle of Task 1: Integrated Biogeochemical Studies in the Everglades: Nutrients, Sulfur, and Organics
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 in methylmercury production and bioaccumulation. A major focus is on ecosystem responses to variations in contaminant loading (changes in external and internal loading in time and space), and how imminent ecosystem restoration may affect existing contaminant pools. Phase I studies showed that large portions of the northern Everglades are contaminated with sulfur and nutrients. Isotope tracer studies demonstrated that the sulfur and phosphorus originates from canals draining the Everglades Agricultural Area, and is consistent with a source from fertilizer. Sulfur entering the ecosystem from contaminated canal water plays a key role in regulating the amount and distribution of methylmercury production, a major contaminant issue in the Everglades. Other findings were: (1) Taylor Slough is not a major source of nutrients to eastern Florida Bay. (2) Phosphorus and nitrogen are enriched in post 1980's sediments from Florida Bay, about the same time as the first observations of seagrass dieoff. (3) Drought and fire play a key role in remobilizing sequestered contaminants from sediments (especially sulfur), and stimulate methylmercury production in drought/fire-affected areas. Phase II emphasizes experimental studies to amplify and expand on phase I field results. This includes the use of environmental chambers (mesocosms), and laboratory studies (microcosms) to examine the effects of changing environmental conditions (increased contaminant loading, changes in hydroperiod, drought/fire) on contaminant concentrations and methylmercury production. Phase II work also includes contaminant (nutrients, sulfur, and organics) source, loading, sequestration, and cycling studies in portions of the ecosystem not previously targeted, including Lake Okeechobee and the Kissimmee River Basin, 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 Methodology - Mesocosms are left open to the outside environment until experiments are to be run. During experiments, mesocosms are closed off 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). Results of mesocosm studies from FY01 and 02 show that: (1) introduced or "new" inorganic mercury is methylated by sulfate reducing bacteria at a much greater rate than mercury bound in the sediments (old mercury). (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, and may enhance bioaccumulation through "extraction" of methylmercury from sediment porewater. FY03 Work - Publication of results from the FY02 mesocosm studies as a series of papers in an international journal will be a high priority 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. 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 STA's will be designed to provide managers with information on how best to operate the STA's to minimize methylmercury production. (2) Drought/Burn and Rewet Experiments Methodology - The experimental approach involves: (1) collection of a series of small cores from two sites (WCA 3A-15, and STA-2), (2) drying of these cores for different times in a laboratory under controlled conditions, (3) rewetting of these cores with water collected at the two core collection sites, 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 - We will continue to analyze samples from the first drought/rewet experiment that will end in September 2002. Results from all experiment PI's will be combined in a database, and a series of publications on the results will be written up for publication. A follow-up experiment will be conducted in FY03 (continuing into FY04) using a larger core approach at two new sites (a high sulfur and low sulfur site in the northern Everglades). The larger cores will slow down the drying process in the lab, and more closely simulate conditions in the ecosystem. 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? GEER planners with information on how to limit the effects of drought and rewet cycles on methylmercury production. Results will be especially useful for managing STA's and northern WCA 3, areas that experience more frequent drought/rewet cycles. (3) Nutrient and Sulfur Sources in Big Cypress Methodology - Surface water, groundwater, porewater, and sediment cores 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. Groundwater will be obtained from existing wells in the Preserve. Samples will be analyzed for nutrients (carbon, nitrogen, and phosphorus), sulfur species, sulfur isotopic composition, uranium, and uranium activity ratio. The uranium and uranium activity ratio is used as a tracer for phosphorus sources. We (Orem/Zielinski/Simmons) have used this approach successfully to examine the sources of phosphorus to the northern Everglades, and to the rivers north of Lake Okeechobee. This approach can differentiate uranium (and phosphate) originating from agriculture, groundwater, and background. Similarly, sulfur isotopes will be used to trace the sources of sulfur entering Big Cypress. We (Orem/Bates/Lerch) previously used sulfur isotopes to trace the sources of excess sulfate entering the northern Everglades. 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 the source(s) and fate of the phosphorus entering the 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. (4) Aquifer Storage and Recovery (ASR) Water Quality Methodology - Sampling of ASR experimental sites would be done in collaboration with the ASR science team, and with other members of this project looking at mercury (Krabbenhoft) and DOC (Aiken) water quality issues related to ASR. Sulfur species would be collected using a standard sampling protocol and analytical scheme, similar to that used in our work on sulfur contamination from canal discharge. In addition to sulfur species (sulfate, sulfide, thiosulfate, sulfite, total S), we would also examine the isotopic composition of the sulfur in the ASR water. This could then potentially be used to examine the fate of sulfur released from ASR water into the ecosystem. Sulfur isotope analysis ( FY03 Work - Work on sulfur in ASR water in FY03 would involve collaborative sampling with Krabbenhoft, Aiken, and others at selected ASR test sites. A series of preliminary samples would examine the range of sulfur concentration and speciation in ASR water, and the isotopic composition of this water. A preliminary report on these results would be prepared. (5) Florida Bay Mercury Methylation and Sulfur Biogeochemistry Methodology - The ACME II group (Krabbenhoft/Orem/Aiken) will examine the biogeochemistry of mercury methylation in Florida Bay sediments using a multifaceted field approach. Task 1 (Orem et al.) would concentrate on evaluating the biogeochemistry of sulfur in Florida sediments and porewater. We would examine sulfur speciation and concentrations in sediments and sediment porewater. We have previously sampled in Florida Bay (1996-2001) and are familiar with the problems of coring and porewater extraction in the carbonate ooze underlying much of the bay. We would use an analytical scheme for sulfur speciation and quantification of sulfur species that we used previously in the Everglades and Florida Bay. FY03 Work - Preliminary coring and porewater sampling would be conducted at selected sites nearshore and offshore in Florida Bay. Sampling would be conducted in collaboration with Krabbenhoft (Task 2 - mercury), and Aiken (Task 3 - DOC). A preliminary report would be prepared, with plans for a journal paper to be prepared in FY04. Planned Outreach:
Related Work Plans:
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34S) would involve isolation of the sulfate or sulfide using a precipitation approach, and measurement of the isotopic composition of the sulfur using isotope ratio mass spectrometry. We have used this approach previously to trace the sources of sulfur entering the Everglades.