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Project Summary Sheet

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

Fiscal Year 2004 Study Summary Report

Study Title: Interactions of Mercury with Dissolved Organic Carbon in the Everglades
Study Start Date: 10/1/00 Study End Date: 9/30/05
Web Sites:;;;
Location (Subregions, Counties, Park or Refuge): Central Everglades; Palm Beach, Broward and Miami-Dade County
Funding Source: USGS's Greater Everglades Science Initiative (PBS)
Principal Investigator(s): George Aiken,
Project Personnel: Jarrod Gasper,, Kenna Butler,
Supporting Organizations: Florida Department of Environmental Protection, South Florida Water Management District
Associated / Linked Projects: Projects by Krabbenhoft, Orem, and Kendall

Overview & Objective(s):
The objective of this project is to better define the roles of dissolved organic matter (DOM) in controlling the reactivity, bioavailability and transport of Hg in the Everglades. Our goal is to provide fundamental information on the nature and reactivity of DOM in the Everglades. Data and findings are published primarily in the form of journal articles that contribute to the basic understanding of how the Everglades system functions with regard to the nature and reactivity of DOM, and how the quality of the DOM controls the reactivity of Hg. The results of this research are critical for the design of effective management strategies for the ecological restoration of the Everglades and for mitigating mercury contamination of game fish in South Florida

The project is presently in the 4th year of a 5-year effort. Currently we are focusing on 5 major study elements important for future management strategies: 1) Hg-DOM binding studies designed to define the chemistry of DOM-Hg interactions and to improve geochemical models of the system; 2) Assessment of the effects of DOM on Hg methylation in field mesocosm studies; 3) Determination of the impacts of wet/dry cycling of the wetlands on Hg and DOM cycling; 4) Characterization of the geochemistry of new Storm Treatment Areas (STAs); and 5) Characterization and monitoring of changes in DOM and water quality throughout the Everglades system.

Recent & Planned Products:
Overall, this work has resulted in 1 PhD (1999), 3 Masters Theses (2000, 2001, and 2003) and 7 journal articles prior to FY02.

The following journal articles have been published since 2002:

Haitzer, M., Aiken, G.R., Ryan, J.N., 2003, Binding of Mercury to Aquatic Humic Substances, Environmental Science and Technology, vol. 37, 2436-2441.

Drexel, E.T., Haitzer, M., Ryan, J.N., Aiken, G.R., Nagy, K., 2002, Mercury Sorption to two Florida Everglades Peats: Evidence for Strong and Weak Binding and Competition by Dissolved Organic Matter Released from Peat, Environmental Science and Technology, vol. 36, 4058-4064.

Haitzer, M., Aiken, G.R., Ryan, J.N., 2002, Binding of Mercury to Dissolved Organic Matter, Environmental Science and Technology, vol. 36, 3564-3570.

Aiken, G., Haitzer, M., Ryan, J.N., and Nagy, K., 2003, Interactions between dissolved organic matter and mercury in the Florida Everglades, J. du Physique, vol. 107, 29-32.

Planned: 5 journal articles in preparation

Relevance to Greater Everglades Restoration Information [See DOI's Science Plan on SOFIA's Web site:]

This study supports the overarching goal, as outlined in the DOI science plan, of providing management information needs as they relate to water quality issues involving DOM, mercury and sulfur biogeochemistry. Specifically, our research supports several of the projects listed in the DOI science plan (Kissimmee-Okeechobee Watershed and Everglades Agricultural Area; Arthur R. Marshall Loxahatchee NWR Internal Canal Structures; Water Preservation Areas and Seepage Management; Everglades National Park, Biscayne Bay and Florida Keys; Landscape-Scale Science Needed to Support Multiple CERP Projects ) by (a) identifying factors controlling the concentration and reactivity of DOM, particularly in EAA, STAs, WCA-1, WCA-2 and WCA-3, (b) determining the effects of hydroperiod, hydrology and fire on DOM, (c) defining the interactions between DOM, sulfate and mercury on the bioavailability and transport of mercury.

The study supports the Kissimmee-Okeechobee Watershed and Everglades Agricultural Area project by providing data related to the quality waters, especially with regard to DOM, that may be injected as part of ASR (p 27) and providing data that will be useful in monitoring and assessing the effects EAA reservoirs on the natural system (p 29).

The study supports the Arthur R. Marshall Loxahatchee NWR Internal Canal Structures project by studying the factors controlling water quality, especially with regard to DOM in the STAs that will ultimately deliver water to Loxahatchee NWR (p 39-40). In a similar way, the study supports Water Preservation Areas and Seepage Management projects by providing baseline water quality data for the STA's (p 44).

The study supports Everglades National Park, Biscayne Bay and Florida Keys projects by providing the fundamental research needed to understand the linkages between geologic, hydrologic chemical and microbial processes that control the transport and fate of DOM, control DOM interactions with mercury and ultimately control the bioreactivity and bioaccumulation of mercury (p 68). In addition, the study supports the C-111 canal project (p 71) and the Additional Water for Everglades National Park and Biscayne Bay Feasibility Study (p 74) by studying the factors controlling DOM generation and transport from EAA and STAs. This information assists with the need for assessments of water quality contaminants.

The study supports Landscape-Scale Science Needed to Support Multiple CERP Projects by studying the influences of STAs on water quality and the generation and transport of DOM in the STAs (p 85), by addressing the need to identify linkages between water quality and ecosystem structure and function (p 85) through research designed to elucidate the links between the carbon and sulfur cycles and mercury bioavailability. This research also supports the needs to understand the factors that control mercury methylation and bioaccumulation (p 89).

The study also indirectly supports Research into Potential Effects of Copper on Periphyton (p 89) by better defining the reactivity of DOM with metals and has implications for addressing water quality needs in Florida Bay (p 78) and identification of Threats Associated with ASR and In-Ground Reservoirs (p 87) by providing fundamental information of the roles played by DOM in the functioning of the Everglades ecosystem.

Key Findings:

  1. Strong Hg-DOM constants, critical for geochemical and biochemical models, successfully determined.
  2. DOM exerts strong controls on HgS, a key form of Hg in areas where methylmercury is formed.
  3. Mesocosm experiments demonstrate direct influence of DOM on bioaccumulation of Hg by fish.
  4. Drying/rewetting of Everglades results in increased rates of Hg methylation.
  5. Amount and reactivity of DOM strongly dependent on hydrologic conditions and nutrient inputs to the Everglades.

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