Studies of sulfur within the ecosystem relate directly to the issue of methyl mercury production and bioaccumulation, a serious threat to both wildlife and to the human population. Microbial sulfate reduction in wetlands (an anaerobic process) is the primary driver of mercury methylation. Recent findings show that, for south Florida wetlands, methyl mercury 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 (S 34 and O 18 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, 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". We are emphasizing co-sampling with USGS mercury researchers (ACME team).
The geochemical history component of this project 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 quality goals needed to achieve "restoration" of the ecosystem. It will also provide land managers with an estimate of the range of water quality 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 and others 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. Geochemical history studies in the southern part of the south Florida ecosystem are focused on (1) historical nutrient, productivity, and salinity change in the Taylor Slough area, (2) the use of organic markers and stable isotopes to examine seagrass history in Florida Bay, and (3) historical patterns of nutrient and productivity change in Florida Bay. These topics are of interest to land and water managers in south Florida.
From the beginning, one goal of this project has been to remain flexible and responsive to the needs of land and water managers in south Florida. As a result, project goals, while remaining largely intact, have been altered to reflect management and regulatory needs. This will continue to be a priority through the anticipated end date of this project.
This project uses both field studies and laboratory experiments to examine the biogeochemical cycling of nutrients, carbon, and sulfur in sediments. Field studies involve the collection of surface water, vegetation, sediment cores, and sediment porewater for chemical analysis. Appropriate protocols are used for the collection of samples and for chemical analysis. Sampling areas were selected to cover as wide an area as possible in the initial reconnaissance stages of the project. The project database includes information from the Everglades Agricultural Area, Everglades Nutrient Removal Area, Water Conservation Areas 1A, 2A, 2B, 3A, and 3B, Big Cypress National Preserve, and Everglades National Park (Shark River Slough, Taylor Slough, mangrove fringe area, and Florida Bay). Areas selected for detailed process-oriented studies were chosen to reflect specific problems in the ecosystem. Thus, samples for examining sources of nutrients and sulfur to the Everglades have focused on canals draining the EAA. Biogeochemical cycling studies have focused on a comparison of eutrophied and pristine sites for nutrients, and on areas of high and low methyl mercury production for the sulfur studies. Sampling sites were also chosen based on recommendations and requests from land and water management agencies. Emphasis on Taylor Slough and ENR reflects the needs of managers to understand the effects of proposed remediation efforts on the ecosystem. Isotope studies provide information on the sources of nutrients, carbon, and sulfur to the ecosystem, and information on biogeochemical cycling. Studies of nutrient, carbon, and sulfur speciation in sediments provides information on the processes occurring in sediments and on the major sinks for these elements in the sediments. Porewater studies are particularly useful for determining the major biogeochemical processes in sediments and for geochemical modeling aimed at quantitative estimates of reaction and recycling rates, and fluxes of chemical species between sediments and surface waters. Organic geochemical studies of sediments are useful for examine differences in chemical reactions among various sediments types (e.g. cattail peat and sawgrass peat), and how this may affect the ecosystem. Laboratory studies are primarily aimed at validating and extending observations from field studies. Experiments include: (1) laboratory decomposition of cattail and sawgrass under different simulated environmental conditions, (2) estimation of diffusion coefficients for nutrients and sulfate using a diffusion cell approach, and (3) adsorption studies of nutrients on various organic substrates (i.e. cattail peat, sawgrass peat, marl peat). Geochemical history studies emphasize analysis of dated cores. Thus, co-sampling with the USGS dating team is essential. Core samples are typically shared with the USGS paleontology group. Sampling sites are chosen in areas of suspected recent environmental change (e.g. lower Taylor Slough saltwater intrusion), areas of continuous sediment accumulation (Florida Bay sites), and to reflect different regions of the ecosystem. Planned major products include: (1) a series of presentations at local and national meetings (both scientific and managers meetings), (2) a series of USGS Open-File reports which will contain all data generated from the project, (3) a series of papers in scientific journals incorporating key pieces of the data sets and focusing on specific aspects of the overall study, (4) a number of Fact Sheets designed for public information, (5) a synthesis report describing the overall project, and containing key data, and references to all published reports, (6) a database from the project in GIS format, (7) placement of reports and data from this project on a WEB site for public access.
Analytical procedures used for the solid phase samples include: (1) elemental analysis for C,H,N,O, and S, (2) oxidation, wet chemical extraction and colorimetry for P, (3) mass spectrometry for stable isotope analysis, (4) wet chemical analysis for sulfur speciation, (5) wet chemistry, gas chromatography, and gas chromatography/mass spectrometry for lignin phenol analysis.
Porewater, groundwater, and surface water were analyzed for various constituents by the following methods: pH (elctrochemistry), alkalinity (titration), sulfide (electrochemistry), sulfate, chloride, bromide, iodide, fluoride (ion chromatography), nutrients (colorimetric), metals (inductively coupled plasma mass spectrometry), salinity, conductivity, and total dissolved solids (electrochemistry), Eh (electrochemistry), dissolved oxygen (electrochemistry), and dissolved organic carbon (DOC analyzer, chemical oxidation and infrared detection). Redox sensitive chemical species were determined immediately in the field (pH, alkalinity, sulfide, Eh), metals were acidified for storage prior to analysis, nutrients and anions were frozen for storage prior to analysis.