projects > interactions of mercury with dissolved organic carbon in the florida everglades > 1998 proposal
Project Proposal for 1998
Project Title: Interactions of Mercury with Dissolved Organic Carbon in the Everglades
Project Chief: George Aiken; Mike Reddy
Project Summary: Interactions of mercury and dissolved organic matter (DOC) play an important role in controlling both the availability of mercury for uptake by living organisms, and the types of chemical reactions that can occur with mercury. The goal of our research is to provide information about the interactions of mercury and dissolved organic matter that will better define this important, albeit, poorly understood process. Effective management strategies will require a more thorough understanding of the processes that control the reactivity, bioavailability and transport of mercury in the Everglades. Ultimately, our research will lead to a more complete model of mercury behavior in the Everglades ecosystem.
Project Justification: Effective management strategies for mitigating mercury contamination of game fish in South Florida requires understanding of factors and processes resulting in the transport and controlling the reactivity and bioaccumulation of Hg in the Everglades. Our project will focus on the effect of DOC on the transport and reactivity of Hg in the Everglades. Results of this research will be used by U. S. Geological Survey, South Florida Ecosystem Initiative scientists, U. S. EPA, Florida Department of Environmental Protection, and the South Florida Water Management District. 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 recognized that the chemical forms of Hg in the water column and sediments are intimately related to bioaccumulation and body burden
Project Objectives: Interactions of Hg with DOC appear to be important in controlling the transport and fate of Hg in the water column. To understand the chemistry of Hg in aquatic systems, better definition of geochemical processes as they apply to DOC is required. Our research will meet this need by focusing on the interactions of the cationic forms of Hg with DOC in a combined field/laboratory study. The characterization of Hg binding resulting from this study will help quantify DOC facilitated transport of Hg in the Everglades. The specific objectives of this research are:
1. To determine the nature and amount of DOC in the Florida Everglades. This work will lead to a more detailed understanding of the influence of hydrologic and seasonal factors on the nature and reactivity of DOC at the field study locations.
Overall Strategy, Study Design, and Planned Major Products: Our project will use a combined field/laboratory approach to assess the significance and strength of DOC-Hg interactions in the Everglades. Temporal variations in DOC concentrations will be measured at appropriate sampling locations to provide a measure of DOC loadings in the system. Major fractions of the DOC will be isolated from the water and characterized by determining chemical composition, molecular weight, and structural characteristics. Whole water samples and the isolated fractions of the DOC will then be used to study interactions of DOC with mercury in laboratory experiments. The goal of these measurements will be to increase our understanding of how mercury interacts with DOC. These measurements will also provide binding constants, which will be used to model the geochernical behavior of mercury in the Everglades. This model will allow us to synthesize the overall effects of the DOC-Hg associations and how they change as the qualitative and quantitative character of the DOC varies in our study systems. The major products of this research will be water quality data published in the form of a USGS Open-file report, journal articles, and a PhD thesis.
Overall: Our project will use a combined field/laboratory approach to assess the significance and strength of DOC-Hg interactions in the Everglades. Both the inorganic composition of, and the DOC associated with, surface water, pore waters, and ground water from the Everglades will be characterized. Temporal variations in DOC concentrations will be measured at appropriate sampling locations to provide a measure of DOC loadings in the system. These measurements will be coupled with determinations of the nature of the DOC under different hydrologic conditions (low and high flow conditions). Major fractions of the DOC will be isolated from the water samples for further analysis. These fractions are composed of a variety of organic compounds, each interacting differently with mercury. The fractions will be characterized by determining chemical composition, molecular weight, and structural characteristics.
Whole water samples and the isolated fractions of the DOC will then be used to study interactions of DOC with mercury in laboratory experiments under a range of pH and concentration conditions. In addition, these measurements will also be made with previously isolated samples from other locations that vary significantly in structural composition. The goal of these measurements will be to increase our understanding of how mercury interacts with DOC. These measurements will also provide binding constants. which are a measure of the strength of the mercury-DOC interactions, that will be correlated with the structural properties of the organic matter to provide inexpensive analytical parameters to be used to estimate the strength of DOC-mercury interactions in the Everglades.
Finally, using the binding constants determined in the laboratory studies, a computer program will be used to model the geochemical behavior of mercury in the Everglades. This model will allow us to synthesize the overall effects of the DOC-Hg associations and how they change as the qualitative and quantitative character of the DOC varies in our study systems
FY 1997 FY 1998 FY 1999 Activities 1997 1998 1999 1 2 3 4 1 2 3 4 1 2 3 4 Equipment Purchase X X Data Collection X X X X X X X X Data Analysis X X X X X X X X X X Interim Products X X X X Write First Drafts X X X X X Mtg With Clients X X X X X Directors Approval X X X
Planned Outreach Activities: The results of this research will be presented in overall project reviews (Florida DEP, SFWMD), information meetings (USGS), and scientific meetings (ACS, ASLO). Data and results are shared freely with other Ecosystem Initiative projects working in South Florida through project meetings, USGS Open-file report, and upon request.
New Directions, Expansion of Continuing Project (if applicable): It is anticipated that field related studies will continue through FY 1998 in support of the mercury geochemistry work being done as part of the South Florida Ecosystem Initiative. More attention will be given to the ENR, a site that is receiving more attention by the project overall, and sites within WCA2B and WCA3A that were identified in FY 96 as being active with respect to methylmercury. Our field effort will be extended to any new sites to the south of WCA2 that will be potentially added to the study in FY 97.
Increased attention will be given to the role of DOC in the photochemical activity of mercury in the system. This is an important process in the cycling of mercury that is thought to be intimately tied to the reactivity of the DOC. In addition, this process is important for understanding carbon cycling in the Everglades. Preliminary experiments have indicated that the DOC in the surface waters of the Everglades is photochemically active. This work is being done in conjunction with Dave Krabbenhoft (USGS) and Jim Hurley (DNR, Wis.).
Additional research will be done to understand the distribution of Hg among various fractions of the DOC by developing "clean" DOC fractionation techniques, and by combining the DOC fractionation approach with ultrafiltration.
Accomplishments and Outcomes, Including Outreach: FY 97 has been devoted primarily to the collection and characterization of field samples. Three major field trips were undertaken in FY 97 to determine the temporal and spatial variability of (DOC) and water chemistyr at select sites in WCA2 and WCA3. Characterization of these samples is an ongoing task. The preliminary results are rather exciting in that the differences in both the quantity and quality of the DOC in the zones where mercury is most active are different from that noted in other areas under study. In addition, large differences in porewater profiles were noted between wet and dry periods. Prior to the past two spring field seasons the Everglades were uncharacteristically wet preventing the collection of dry-period samples
Jim Hurley of Wisconsin DNR spent 3 months working in Aiken's laboratory during the spring of 1997. This time was spent collaborating on the development of 11 clean" procedures for DOC fractionation, designing studies to understand differences in Hg fractionation by ultrafiltration, and designing both field and laboratory experiments to better define the photochemical behavior of both Hg and DOC. These experiments are scheduled to be carried out during the summer of 1997 and into FY 98.
A collaboration was developed with Carol Kendall to determine the stable isotopic composition of isolates and plant materials in the Everglades. This work is being done in conjunction with a series of plant extractions to help define the sources of DOC in the Everglades. This research will be tied into Carol's efforts to use isotopic analyses to define food-web dynamics and will be an important part of the carbon cycling story.
Also in FY 97, Mahalingam Ravichandran, a graduate student at the University of Colorado, continued his work to determine the mercury-DOC binding constants. This work is funded separately under an agreement with the EPA, however, it is an important element of our mercury-DOC work in the Everglades. This research has focused on the application of an ion-exchange distribution method for the measurement of binding constants and cinnabar dissolution experiments to directly assess the ability of organic matter to compete with sulfide for Hg. Preliminary results indicate that Hg interacts strongly with organic matter isolated from the Everglades.
Deliverables, Products Completed: