Project Summary Sheet

Study Title: Interactions of Mercury with Dissolved Organic Carbon in the Everglades
Study Start Date: 10/1/01 Study End Date: 9/30/07
Web Sites: http://sofia.usgs.gov/exchange/aiken/aikenchem.html; http://sofia.usgs.gov/people/Aiken.html
http://sofia.usgs.gov/sfrsf/rooms/mercury; http://sofia.usgs.gov/projects/merc_carbon;
Location (Subregions, Counties, Park or Refuge): Central Everglades; Palm Beach, Broward and Miami-Dade County
Funding Source: USGS Greater Everglades Priority Ecosystems Science (GE PES) Initiative
Principal Investigator(s): George Aiken, graiken@usgs.gov,
Project Personnel: Jarrod Gasper, jgasper@usgs.gov, Kenna Butler, kebutler@usgs.gov, Chase Gerbig, cgerbig@usgs.gov, Doug Latch, delatch@usgs.gov
Supporting Organizations: Florida Department of Environmental Protection, South Florida Water Management District
Associated / Linked Projects: Projects by Krabbenhoft and Orem

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 using a combined field-lab approach. 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

Status:
The project is focusing on 5 major study elements important for future management strategies: 1) Hg-DOM binding and HgS-DOM interaction 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) Determination of the significance of DOM and S geochemistries on Hg cycling in mangrove swamps and coastal areas of the Everglades and Florida Bay; and 5) Characterization and monitoring of changes in DOM and water quality throughout the Everglades system. Recently, the research focus has been expanded to include the influences of DOM and nutrients on the formation and evolution of ridge and slough structures in the Everglades, the influences of DOM on the photochemical reactivity of Hg and the roles of DOM on the transport of other important metals, such as copper (Cu) which is an algaecide.

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.

Waples, J.S., Nagy, K.L., Aiken, G.R., and Ryan, J.N., 2005, Dissolution of cinnabar (HgS) in the presence of natural organic matter, Geochimica et Cosmochimica Acta, Vol. 69, 1575-1588.

Gasper, J., Aiken, G.R., and Ryan, J.N., 2006, A Critical Review of Three Methods Used for the Measurement of Mercury (Hg⁺²)-Dissolved Organic Matter Stability Constants, Applied Geochemistry, accepted for publication.

Planned: 4 journal articles in preparation

Relevance to Greater Everglades Restoration Information [Page numbers listed below are from the DOI Everglades Science Plan. The Science Plan is posted on SOFIA's Web site: http://sofia.usgs.gov/publications/reports/doi-science-plan/]:

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 (pg 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. Methods developed for determining binding in whole water samples. Methods currently being used to determine DOM-Cu binding constants to model Cu geochemistry and bioavailability (DOM-bound Cu is not toxic to algae).
2. DOM exerts strong controls on HgS, a key form of Hg in areas where methylmercury is formed. A large amount of Hg in porewaters exists as colloidal HgS in association with DOM
3. Mesocosm experiments demonstrate direct influence of DOM on the concentrations of dissolved Hg and MeHg; DOM demonstrated to result in greater methylation of Hg and increased bioaccumulation of Hg by fish. Under sulfate reducing conditions, DOM demonstrated to be important factor driving Hg methylation. Strong connection between DOM and S geochemistry.
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; exchange between ridges and sloughs shown to be slow.
6. DOM shown to play important roles in both the reduction and oxidation of Hg⁺² and the reduction of MeHg.