Project Work Plan

A. GENERAL INFORMATION:

Project Title: Interactions of Mercury with Dissolved Organic Carbon in the Everglades
Project Start Date: 10/1/2000 Project End Date: 9/30/05
Project Funding: USGS Place-Based Studies Initiative

Principal Investigator: George Aiken
Email address: graiken@usgs.gov
Phone: 303-541-3036 Fax: 303-447-2505
Mail address: 3215 Marine Street, Boulder, CO, 80303

Other Investigator(s): Dave Krabbenhoft
Email address: dpkrabbe@usgs.gov
Phone: 608-821-3843 Fax: 608-821-3817
Mail address: 8305 Research Way, Middleton, Wisconsin 53562-3581

Other Investigator(s): Bill Orem
Email address: borem@usgs.gov
Phone: 703-648-6273 Fax: 703-648-6419
Mail address: 12201 Sunrise Valley Drive, MS 456, Reston, VA 20192

Project Summary:

Our project is designed to more clearly define the factors that control the occurrence, nature and reactivity of dissolved organic matter (DOM) in the Florida Everglades, especially with regard to the biological transformation and accumulation of mercury (Hg). This research is relevant because of the high natural production of organic carbon in the peat soils and wetlands, the relatively high carbon content of shallow ground water systems in the region, the interactions of organic matter with other chemical species, such as trace metals, divalent cations, mercury, and anthropogenic compounds, the accumulation of organic carbon in corals and carbonate precipitates, and the potential changes in the quality and reactivity of dissolved organic carbon (DOC) resulting from land use and water management practices. Proposed attempts to return the Everglades to more natural flow conditions will result in changes to the current transport of organic matter from the Everglades Agricultural Area and the northern conservation areas to Florida Bay. In addition, the presence of dissolved organic matter is important in the production of drinking water, contributes to pollutant transport, and will influence ASR performance. Finally, interactions of mercury (Hg) with organic matter play important roles in controlling the reactivity, bioavailability and transport of Hg in the Everglades.

Project Objectives and Strategy:

The primary objectives of our research are (1) to more clearly define the factors that control the occurrence, nature and reactivity of dissolved organic matter (DOM) in the Florida Everglades, and (2) to quantify the effects of DOMDOM on the transport and reactivity of Hg, especially with regard to the biological transformation and accumulation of mercury (Hg) in the Everglades. To meet these objectives, we have adopted a combined field/laboratory approach. In conjunction with other research projects our field efforts are designed (1) to characterize DOM at a variety of field locations chosen to provide information about the influences of hydrology, seasonal factors (wetting and drying events) and source materials (e.g. vegetation, periphyton, peat) on the nature and amount of DOM in the system, and (2) to elucidate the roles of DOM in controlling the reactivity and bioavailability of Hg in the Everglades. Using whole water samples and organic matter isolated from the Everglades, our laboratory studies are designed (1) to determine the strength of Hg-DOM binding constants necessary for geochemical modeling of Hg in the Everglades, (2) to assess the nature and strength of interactions of Hg with DOM in the presence of sulfide, an important Hg ligand assumed to strongly influence Hg bioavailability, (3) to determine the chemical factors that control DOM interactions with Hg, (4) to determine the overall importance of DOM in controlling Hg bioavailability, and (5) to assess the reactivity of DOM with other chemical elements of geochemical significance in South Florida, such as calcite.

Potential Impacts and Major Products:

Effective management strategies for the ecological restoration of the Everglades and for the mitigation of mercury contamination of game fish in South Florida require an understanding of the factors that control the nature, reactivity, distribution and transport of organic matter in the Everglades. It is expected that the information provided by this project, especially with regard to the Hg-speciation model, will be used by management agencies in South Florida to implement remediation strategies. It is well recognized that the chemical forms of Hg in the water column and sediments are intimately related to bioaccumulation and body burden. In addition, this research is important for understanding drinking water, pollutant transport and ASR issues involving DOM.

Our research also provides important contributions to understanding the chemistry of organic matter reactivity, an area of considerable interest to environmental chemists, engineers and geochemists. The data gathered by our project are published primarily in the form of journal articles that contribute to the basic understanding of the 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 in the Everglades. The U. S. Geological Survey, U.S. EPA, Florida Department of Environmental Protection, and the South Florida Water Management District will use results of this research.

Collaborators:

Dave Krabbenhoft, USGS, WRD, Wisconsin
Bill Orem, USGS, GD, Reston
Cynthia Gilmour, Academy of Natural Sciences, Benedict Estuarine Lab
Joseph Ryan, University of Colorado

Clients: U. S. Geological Survey, South Florida Ecosystem Initiative scientists, U. S. EPA, Florida Department of Environmental Protection, and the South Florida Water Management District will use results of this research. It is expected that the information provided by this project, especially with regard to the Hg-speciation model, will be used by management agencies in South Florida to implement remediation strategies.

B. WORK PLAN

Title of Task 1: Interactions of DOM with Hg in the Everglades
Task Funding: USGS Place-Based Studies Initiative
Task Leaders: George Aiken
Phone: 303-541-3036
FAX: 303-447-2505
Task Status (proposed or active): active
Task priority: High
Task Personnel: Jarrod Gasper

Task Summary and Objectives: Identification of the mechanisms by which Hg interacts with DOM and quantification of these interactions are critical elements for modeling Hg transport and reactivity in the Everglades. The objectives of this task are to provide binding constant data for Hg with DOM in the Everglades and to assess the reactivity and speciation of Hg in the presence of DOM and sulfide.

Work to be undertaken during the proposal year and a description of the methods and procedures:

FY04:

1. Continue lab-based studies on DOM-Hg binding constants. We have recently completed development of dialysis technique for measuring binding constants (2 papers accepted at Environmental Science and Technology, Masters thesis in preparation). This method is the only reliable method we have found for measuring binding constants. Method will be used with other fractions of the DOM from F1 and other locations in the Everglades to determine binding of DOM with Hg and MeHg.
2. Continue lab-based studies on the interactions of DOM with HgS. HgS is assumed to be an important species controlling Hg bioreactivity. Greater definition of DOM-HgS interactions is critical for understanding factors that control methylation of Hg. We previously demonstrated the strong influence of DOM on the chemistry of HgS complexes (papers published in Environmental Science and Technology), although the processes are poorly defined. Paper in preparation for publication in FY 04 (Geochimica et Cosmochimica Acta). Efforts in FY 04 and FY 05 will provide data to better understand these processes and assess the role they play in controlling Hg bioavailability. This work is important for understanding results of mesocosm studies (see Task 2).
3. Efforts to publish information in appropriate outlets (e.g. SOFIA site, Environmental Science and Technology, Geochimica et Cosmochimica Acta) will continue.

Planned Outreach: Publication of results in peer-reviewed literature will continue. Results are provided for the SOFIA website, regularly shared with colleagues and interested parties in the Florida Department of Environmental Protection and South Florida Water Management District, and presented at scientific meetings of national/international significance (ACS, AGU) and meetings in Florida (e.g. GEER conference). It is anticipated that work will begin on draft report for USGS 5-year Science Report.

Title of Task 2: Effects of DOM on Hg cycling in the Florida Everglades
Task Funding: USGS Place-Based Studies Initiative

Task Leaders: George Aiken
Phone: 303-541-3036
FAX: 303-447-2505
Task Status (proposed or active): active
Task priority: High
Task Personnel: Jarrod Gasper, Kenna Butler

Task Summary and Objectives: The overall effects of DOM on Hg cycling in the Everglades are influenced by hydrology, sources of organic matter and the presence of inorganic species, such as sulfate. Our objectives in this task are to assess the effects of hydrology and source materials on DOM reactivity and to ascertain the overall influence of these factors on the cycling of Hg in the Everglades. This work is primarily field based and carried out in collaboration with other scientists (Krabbenhoft, Hg; Orem, S geochemistry; Gilmour, Hg methylation)

Work to be undertaken during the proposal year and a description of the methods and procedures:

FY 04:

1. Continue work using field based mesocosms to address issues concerning partitioning and reactivity Hg in the Everglades with regard to the roles played by DOM in the system. Mesocosm experiments have been very successful demonstrating the influence of DOM on methylation and bioaccumulation of Hg. In this work organic matter isolated from areas with reactive DOM is added to mesocosms, in addition to other constituents (sulfate, Hg) to assess impacts on Hg partitioning, methylation and bioaccumulation. These experiments will continue throughout FY 04. Research of interest to SFWMD and Florida DEP.
2. Continue work assessing the roles of drying and wetting of peat soils on the generation of DOM and MeHg. Research is both lab and field based. DOM concentrations and changes in the reactivity of the DOM are determined as a function wetting and drying, a common natural condition and one of great importance in managed wetlands, such as the STAs. DOM characterization methods established by USGS labs are used. This research of interest to SFWMD and Florida DEP.
3. Begin study of DOM in new Storm Treatment Areas ( STA’s). The STAs are critical for restoration efforts. Key management decisions on the operation of the STAs require data on performance under different conditions. DOM characterization methods established by USGS labs will be used.
4. Continue assessment of water quality changes in Everglades by participation in ACME Site Survey work. This is done in conjunction with Krabenhoft and Orem. Our project is responsible for DOM measurements and characterization throughout the Everglades.
5. We plan to continue overall project support with regard to DOM analyses and isolate availability for experimentation and to continue efforts to publish information in appropriate outlets (e.g. SOFIA site, Environmental Science and Technology, Geochimica et Cosmochimica Acta).

Planned Outreach:

Publication of results in peer-reviewed literature will continue. Results are provided for the SOFIA website, regularly shared with colleagues and interested parties in the Florida Department of Environmental Protection and South Florida Water Management District, and presented at scientific meetings of national/international significance (ACS, AGU) and meetings in Florida (e.g. GEER conference). It is anticipated that work will begin on draft report for USGS 5-year Science Report. 

C. BRIEF DESCRIPTION ON HOW PROJECT TASKS SUPPORT THE DOI AND USGS EVERGLADES RESTORATION SCIENCE PLANS

This project is relevant for the following items in the USGS Science Plan in Support of Everglades Restoration:

1. Restoration Goal 1A:
   • SO1 (Hydrology: How does the Everglades ecosystem function? Understand ecosystem structure and processes),
   • SO4 (Hydrology: How is the Everglades system changing? Monitor ecosystem response to change),
2. Restoration Goal 1B: SO1 (Water quality: Understand ecosystem structure and processes),
   • SO3 (Water quality: Establish ecosystem baselines and variations for restoration targets),
   • SO4 (Water quality: Monitor ecosystem response to change),
   • SO5 (Water quality: Predict ecosystem response to anthropogenic and natural changes),
3. Restoration Goal 3, Foster Compatibility of the built and natural systems: SG 1 (How does the Everglades system function?), SG 4 (How is the Everglades system changing?).

1. The data generated on Hg-DOM interactions are critical for the water quality models describing/predicting the system's response to different stresses that control Hg methylation,
2. Our studies of the nature DOM are important elements of water quality studies throughout the Everglades. This component is critical to meet the objectives for WCA 3 (C. Decompartmentalization of WCA 3), Loxahatchee (H. H. Arthur Loxahatchee NWR Internal Canal Structures), and has relevance for ASR elements of the plan. Overall, this information is critical for understanding a number of ecosystem responses (CERP Monitoring and Assessment Plan — What is needed).
3. In addition to modeling noted above, our Hg-DOM research is of fundamental importance in understanding the factors that control Hg-methylation and have relevance for understanding bioaccumulation,
4. Our work on the effects of wet/dry cycles on Hg methylation are important for the hydrologic management practices used to operate the Stormwater Treatment Areas (STAs), and,
5. Work commencing in FY 04 will focus on water quality issue in the STAs.