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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 2, sulfur and nutrient contamination, biogeochemical cycling, and effects > project summary

Project Summary Sheet

U.S. Geological Survey, Greater Everglades Priority Ecosystems Science (PES) Initiative

Fiscal Year 2004 Study Summary Report

Study Title: Integrated Biogeochemical Studies in the Everglades: Task 1 - Nutrients, Sulfur, and Organics
Study Start Date: 10/01/2000 Study End Date: 9/30/2007
Web Sites:; (now
Location (Subregions, Counties, Park or Refuge): Total Everglades Ecosystem
Funding Source: USGS Priority Ecosystems Science (PES) Initiative
Principal Investigator(s): William H. Orem (, 703.648.6273)
Study Personnel: H.E. Lerch (, 703.648.6278); A.L. Bates, (; 703.648.6279); M. Corum (, 703.648.6488); R.A. Zielinski (, 303.236.4719); K. Simmons (, 303.236.7321); B. McPherson (, 813.975.8620)
Supporting Organizations: SFWMD, FLDEP, ENP, USFWS, USEPA
Associated / Linked Studies: (1) Integrated Biogeochemical Studies in the Everglades: Task 2 - Mercury Cycling and Bioaccumulation (David Krabbenhoft,, (2) Interactions of Mercury with Dissolved Organic Carbon in the Everglades (George Aiken,, (3) Development and Stability of Everglades Tree Islands, Ridge and Slough, and Marl Prairies (Debra Willard,, (4) The Effects of Water Flow on the Transport of Suspended Particles and Particle-Associated Nutrients in the Everglades (Judson Harvey,, (5) Ecological Risk Assessment of Toxic Substances in the South Florida Ecosystem: Wildlife Effects and Exposure Assessment (Tim Gross,, (6) Historical Changes in Salinity, Water Quality and Vegetation in Biscayne Bay (G. Lynn Wingard,, (7) Ecosystem History of the Southwest Coast-Shark River Slough Outflow Area (G. Lynn Wingard,

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 (described here), focuses on nutrients, sulfur, and organics, and in collaboration with Task 2 also examines the complex interactions of these substances (especially sulfur) with mercury (synergistic and antagonistic). 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/sulfur/mercury/organics), and provide CERP and GEER management with quantitative information for critical decisions, such as estimates of the maximum sulfur, nutrient, and mercury loads producing permissible levels of methylmercury in the ecosystem, the toxic effects of sulfur 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, sulfur, organics, and mercury 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 sulfur contamination of the Everglades originating from EAA canal discharge, and links between sulfur contamination and methylmercury production and bioaccumulation in the ecosystem (Goldilocks Hypothesis). Sulfur contamination has arguably a 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 sulfur (sulfate and sulfide) producing specific levels of methylmercury production and bioaccumulation in the Everglades. This data will be useful for managers in determining what levels of sulfur contamination produce acceptable levels of methylmercury in Everglades' biota. Sulfur contamination may also represent a threat to macrophytes in the ecosystem through buildup of toxic sulfide in sediments. Mesocosm studies are currently underway 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 sulfur remobilization from organic soils, and methylmercury production and bioaccumulation. Limiting dry/rewet cycles in critical areas can be used as a management tool to reduce levels of methylmercury in biota. Work is also underway to work with modelers for incorporation of a sulfur 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 sulfur loads to the ecosystem) on methylmercury production and bioaccumulation, especially in Everglades National Park.

Recent Products: (1) Louda, Orem et al., 2004, Potential sources of hydrogel stabilization of Florida Bay lime mud sediments and implications for organic matter preservation. 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, Introduction to mercury special issue: Environmental Geology 43, 245-246. (4) 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 Geological Society of America Meeting, March 2004, Tysons Corner, VA, Program and Abstracts. (5) Bates, Orem, et al., 2004, Everglades water quality issues: II. Sulfur contamination and links to methylmercury production. NE/SE Regional Geological Society of America Meeting, March 2004, Tysons Corner, VA, Program and Abstracts. (6) Orem, et al., 2004, Everglades water quality issues: I. Phosphorus contamination. NE/SE Regional Geological Society of America Meeting, March 2004, Tysons Corner, VA, Program and Abstracts. (7) 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, Program and Abstracts.

Planned Products: (1) Synopsis Report: Sulfur Contamination in the Everglades and Sulfur Controls on Methylmercury Production, (2) Phosphorus on Everglades' Tree Islands Paper, (3) One presentation and One Poster at Restoration Science Meeting (Orlando, December 2004), (4) paper on Sulfur and Mercury in Big Cypress National Preserve, (5) Fact Sheet on Big Cypress Water Quality, (6) Joint papers (with Krabbenhoft and Gilmour) on (a) Mercury Mesocosm Studies, and (b) Dry/Rewet Studies of Sulfur Remobilization and Methylmercury Production, (7) Biscayne Bay Nutrient History 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:]:

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 (sulfur, 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 methylmercury formation in STA's. The study supports the Arthur R. Marshall Loxahatchee NWR Internal Canal Structure Project by addressing the impacts of water quality (sulfur/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 sulfur) and its ecological impact, p. 71.

Key Findings:

  1. Sulfur originating from EAA canal discharge contaminates about one third of the remaining Everglades at levels up to 100x background, and plays a key role in mediating methylmercury production and bioaccumulation in the ecosystem (the “Goldilocks Hypothesis”). Achieving acceptable levels of toxic methylmercury in Everglades' fish and wildlife will require reduction of both mercury and sulfur contamination to the Everglades, including limits on sulfur use in the EAA, and other mitigation strategies.
  2. Dry/rewet cycles in the Everglades play a major role in remobilizing sulfur from organic sediments and stimulating methylmercury production and bioaccumulation. Effective management of dry/rewet cycles is important for minimizing methylmercury levels in Everglades fish and wildlife.
  3. Phosphorus is not an effective control agent for the Everglades methylmercury problem, and maintaining high phosphorus discharges from the EAA to the Everglades to reduce the mercury problem will not be effective.
  4. Planned diversions of canal water contaminated with sulfate into Big Cypress National Preserve may have the unwanted effect of increasing methylmercury production and bioaccumulation.

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