Project Summary Sheet

Overview & Objective(s): This study addresses the major water quality issues in the greater Everglades (nutrients, sulfur, mercury, organics), by investigating the sources, cycling, and sinks of these contaminants, and their effects on the natural resources within the ecosystem. Understanding the sources, sinks, cycling, and effects of contaminants is the first step in developing mitigation or resource management strategies to minimize the impacts of these contaminants on natural resources, while balancing other restoration priorities. Task 1 of this study focuses on nutrients, sulfur (S), and organics, and in collaboration with Task 2 also examines the complex interactions of these substances (especially S) with mercury (Hg). Emphasis is placed on ecosystem responses to variations in contaminant loading (changes in external and internal loading over time and space dimensions), and how imminent ecosystem restoration may affect existing contaminant pools and their impacts on natural resources in the ecosystem. The major objectives are to determine: (1) anthropogenic-induced changes in the water chemistry of the Everglades ecosystem, (2) biogeochemical processes within the ecosystem affecting water chemistry, (3) the predicted impacts of restoration efforts on water chemistry, and (4) the impacts of contaminants on natural resources in the ecosystem. The approach used includes a combination of field surveys, contaminant monitoring at key sites, experimental studies in the ecosystem using experimental chambers (mesocosms), and laboratory experiments using microcosms. The experimental field and laboratory studies are utilized to confirm conceptual models and hypotheses developed from field surveys. Study results will provide critical elements for building ecosystem models and screening-level risk assessment for the principal contaminants impacting water quality in the ecosystem (nutrients/S/Hg/organics), and provide CERP and GEER management with quantitative information for critical decisions, such as estimates of the maximum S, nutrient, and Hg loads producing permissible levels of methylmercury (MeHg) in the ecosystem, the toxic effects of S on macrophytes and other biota, estimates of the time required for ecosystem recovery from chemical contamination, and the effects of restoration on contaminant loads and impacts of contaminants. Results are incorporated into conceptual, mathematical, and risk assessment models of the Everglades ecosystem.

Status: Research conducted during phase 1 of this study focused primarily on field surveys to establish: (1) the natural, background levels of nutrients, S, organics, and Hg in the ecosystem, (2) the extent of contamination from these substances in the environment, (3) sources of these contaminants, (4) major sinks of these contaminants, and (5) biogeochemical processes in the ecosystem affecting contaminants. A major finding from phase 1 studies was the discovery of extensive S contamination of the Everglades originating from EAA canal discharge, and links between S contamination and MeHg production and bioaccumulation in the ecosystem (Goldilocks Hypothesis). Sulfur contamination has an arguably greater impact on the ecosystem than phosphorus. Phase 2 studies, beginning in 2001, took a more experimental approach using environmental chambers (mesocosms) and laboratory studies to establish the impacts of contaminants on biota, and to quantify the concentrations of S (sulfate and sulfide) producing specific levels of MeHg production and bioaccumulation in the Everglades. This data will be useful for managers in determining what levels of S contamination produce acceptable levels of MeHg in Everglades' biota. Sulfur contamination may also represent a threat to macrophytes and other organisms in the ecosystem through buildup of toxic sulfide in sediments. Mesocosm studies are currently underway (FY04-FY07) to evaluate the impact of sulfide on sawgrass and cattail growth. Laboratory studies have been used to show the effects of dry/rewet cycles on S remobilization from organic soils, and MeHg production and bioaccumulation. Limiting dry/rewet cycles in critical areas can be used as a management tool to reduce levels of MeHg in biota. Work is also underway to work with modelers for incorporation of a S module in the mercury cycling model. This will be critical for assessing the impacts of restoration efforts to restore sheet flow to the Everglades (with resulting higher S loads to the ecosystem) on MeHg production and bioaccumulation, especially in Everglades National Park (ENP). Work in FY05 will begin to examine the biogeochemical processes important in MeHg production in the coastal marine zone of Florida Bay and the Gulf coast, including the role of S.

Recent Products:
(1) Louda, Orem et al. (2004) J. Coastal Res. 20, 448-463.
(2) Orem (2004) Impacts of sulfate contamination on the Florida Everglades ecosystem. USGS Fact Sheet FS 109-03, 4 pp.
(3) Kolker, Orem, Lechler (2003) Environmental Geology 43, 245-246.
(4) Wingard G. Lynn, Orem William, and others (2004) U.S. Geological Survey Open File Report 2004-1312.
(5) Wingard, Orem et al. (2004) Paleoecological, biochemical, and geochemical analyses of estuarine sediment cores: pieces in the south Florida ecosystem restoration puzzle. NE/SE Regional GSA Meeting, March 2004, Tysons Corner, VA, Abstract.
(6) Bates, Orem, et al. (2004) Everglades water quality issues: II. Sulfur contamination and links to methylmercury production. NE/SE Regional GSA Meeting, March 2004, Tysons Corner, VA, Abstract.
(7) Orem, et al. (2004) Everglades water quality issues: I. Phosphorus contamination. NE/SE Regional GSA Meeting, March 2004, Tysons Corner, VA, Abstract.
(8) Gilmour, Krabbenhoft, Orem, and Aiken (2004) The influence of drying and rewetting on Hg and S cycling in Everglades soils. The 7th International Conference on Mercury as a Global Pollutant, September 2004, Lujubjina, Slovenia, Abstract.
(9) Wingard G.L., Orem W.H., and others (2004) Natural Variability versus Anthropogenic Change: A case study in Biscayne Bay, Florida. First National Conference on Ecosystem Restoration, Lake Buena Vista, FL, December 2004, Abstract, p. 479.
(10) Orem W., and others (2004) Sulfur Contamination in the Florida Everglades: Where Does it Come From, What is its Extent, What are Its Impacts, and What Can We do About it? First National Conference on Ecosystem Restoration, Lake Buena Vista, FL, December 2004, Abstract, p. 323.
(11) Orem W., and others (2004) Water Quality in Big Cypress National Preserve: Present Conditions and Potential Impacts of Restoration Plans. First National Conference on Ecosystem Restoration, Lake Buena Vista, FL, December 2004, Abstract, p. 324.
(12) Krabbenhoft D., Orem W., Aiken G., and Gilmour C. (2004) Mercury Contamination and Land-Management: The Convergence of Two Issues in the Everglades to Control Methylmercury Contamination at the Ecosystem Scale. Invited Keynote presentation at the 7th International Conference on Mercury as a Global Pollutant, September 2004, Lujubjina, Slovenia, Abstract.
(13) Krabbenhoft, D., Orem, W., Aiken, G., Gilmour, C., Olson, M., DeWild, J., and Olund, S. (2004) Mercury contamination of the Florida Everglades: a convergence of external forces and natural ecosystem sensitivity. First National Conference on Ecosystem Restoration, Lake Buena Vista, FL, December 2004, Abstract, p. 235.
(14) Swarzenski P., Orem W., McPherson B., and Baskaran M. (2005) Biogeochemical transport in the Loxahatchee River estuary, Florida: The role of submarine groundwater discharge. American Geophysical Union Meeting, New Orleans, LA, May 2005, Abstract.
(15) Zielinski R.A., Orem W.H., and others (2005) Fertilizer-derived uranium and sulfur in rangeland soil and runoff: a case study in central Florida. J. Air, Water and Soil Sci., submitted.
(16) Orem W.H., and others (2005) Assessment of groundwater input and water quality changes impacting natural vegetation in the Loxahatchee River and floodplain ecosystem, Florida.
(17) Orem W.H., and others (2005) Synopsis Report: Sulfur Contamination in the Everglades and Sulfur Controls on Methylmercury Production. In: Mercury Synopsis Report (Krabbenhoft D.P., Ed.), USGS Publication, in review.

Planned Products:
(1) Phosphorus on Everglades' Tree Islands Paper,
(2) Joint papers (with Krabbenhoft and Gilmour) on (a) Mercury Mesocosm Studies, and (b) Dry/Rewet Studies of Sulfur Remobilization and Methylmercury Production,
(3) Biscayne Bay Nutrient History paper.
(4) Big Cypress water quality paper.
(5) Sulfur geochemistry of the Everglades paper.

Specific Relevance to Information Needs Identified in DOI's Science Plan in Support of Ecosystem Restoration, Preservation, and Protection in South Florida (DOI's Everglades Science Plan) [See Plan on SOFIA's Web site: http://sofia.usgs.gov/publications/reports/doi-science-plan/]:

This study supports several of the projects listed in the DOI science plan. The study supports the Comprehensive Integrated Water Quality Feasibility Study in the Landscape Science needs of the DOI Science Plan (p. 85), by examining links between water quality and ecosystem structure and function, identifying degraded parts of the ecosystem and quantifying links to contaminants (nutrients, sulfur, organics, and mercury), and investigating the impacts of ASR on the ecosystem. It also addresses risks to wildlife from soil-borne contaminants (S, mercury, organics), through studies of the effects of dry/rewet cycles (Threats Associated with Rehydration of Agricultural Lands, p. 87; Predicting bioavailability of mercury (methylation) following inundation of dry land based on soil and water chemistry, p. 89) on MeHg formation in STA's. The study supports the Arthur R. Marshall Loxahatchee NWR Internal Canal Structure Project by addressing the impacts of water quality (S/nutrients/mercury) and water management practices on refuge resources, p. 40. The study addresses the Combined Structural and Operational Plan (CSOP) and the Water Conservation Area 3 Decompartmentalization and Sheetflow Enhancement by addressing the potential for increases in toxic contaminant loads (especially S) and its ecological impact, p. 71.

Key Findings:

1. Sulfur originating from EAA canal discharge contaminates about 1/3 of the remaining Everglades at levels up to 100x background, and plays a key role in mediating MeHg production and bioaccumulation in the ecosystem. Achieving acceptable levels of toxic MeHg in Everglades' fish and wildlife will require reduction of both mercury and S contamination to the Everglades, including limits on S use in the EAA, and other mitigation strategies.
2. Recent decreases in MeHg production in the central Everglades is closely linked to decreases in sulfate concentrations in this area. Decreases in Hg emissions may also be a factor. It is suspected that excess sulfate is now diverted to ENP as part of restoration efforts, and may trigger increased MeHg production and bioaccumulation in ENP.
3. Phosphorus is not an effective control agent for the Everglades MeHg problem, and maintaining high phosphorus discharges from the EAA to the Everglades to reduce the Hg problem will not be effective.
4. Dry/rewet cycles in the Everglades play a major role in remobilizing S from organic sediments and stimulating methylmercury production and bioaccumulation. Effective management of dry/rewet cycles is important for minimizing MeHg levels in Everglades fish and wildlife.
5. Planned diversions of canal water contaminated with sulfate into Big Cypress National Preserve may have the unwanted effect of increasing methylmercury production and bioaccumulation.