HR: 16:20h
AN: B14B-02 INVITED    [Abstracts]
TI: Biogeochemical Controls on Mercury Methylation: A compilation of Data Across Fresh and Saltwater Wetlands
AU: * Gilmour, C
EM: gilmourc@si.edu
AF: Smithsonian Environmental Reseearch Center, 647 Contees Wharf Rd., Edgewater, MD 21037, United States
AU: Heyes, A
EM: heyes@cbl.umces.edu
AF: U. Maryland, Chesapeake Biological Lab., 1 Williams St., Solomons, MD 20688, United States
AU: Mitchell, C
EM: mitchellc@si.edu
AF: Smithsonian Environmental Reseearch Center, 647 Contees Wharf Rd., Edgewater, MD 21037, United States
AU: Krabbenhoft, D
EM: dpkrabbe@usgs.gov
AF: USGS, 8505 Research Way, Middleton, WI 53562, United States
AU: Orem, W
EM: borem@usgs.gov
AF: USGS, National Center, Reston, VA 20192, United States
AU: Aiken, G
EM: graiken@usgs.gov
AF: USGS, Marine Street Science Center 3215 Marine Street, Boulder, CO 80303, United States
AU: Mason, R
EM: robert.mason@uconn.edu
AF: U. Connecticut, Dept Marine Sciences 1080 Shennecosset Road, Groton, CT 06340,
AB: Over the past decade, we have examined the biogeochemical controls on net methylmercury production across a number of wetland ecosystems, including salt marshes in Chesapeake Bay, the freshwater and estuarine Everglades, and a variety of boreal freshwater wetlands in Ontario. The balance between sulfate and sulfide is key for understanding Hg methylation rates among these ecosystems. Sulfate stimulates Hg-methylating sulfate- reducing bacteria (SRB) while sulfide creates charged mercury-sulfide complexes that are unavailable for uptake by SRB. Sulfate-stimulation of methylation has been demonstrated in experimental studies that range from pure culture, to sediment and soil amendments, to large-scale field additions. Stimulation of methylation by sulfate has also been demonstrated in freshwater ecosystems impacted by sulfur pollution derived from atmospheric deposition, agriculture and mining. This presentation will present a compilation of field and laboratory studies on the impact of sulfate and sulfide on MeHg production to create a simple, general model for the control of net Hg methylation in surfaces sediments and wetland soils that includes microbial activity (sulfate reduction rate), dissolved sulfide, dissolved organic matter and and soil organic matter. In particular, the model focuses on the balance between sulfate and sulfide, and the optimal concentrations of each for methylation across studies and ecosystems. Data to be presented will include new information from high sulfate and sulfide coastal ecosystems in Chesapeake Bay. Optimal sulfate concentrations for methylation appear to range widely among ecosystems, while the optimal sulfide concentrations are more constant, and often quite low, often in the low micromolar range. However, recent data from estuarine and marine systems suggest that net methylation can proceed at somewhat higher sulfide concentrations when microbial activity is particularly high. By compiling these data, we can begin to predict the magnitude of net MeHg production across different wetland types, the sensitivity of different types of wetlands to mercury inputs, the role of wetlands in MeHg budgets for different types of aquatic ecosystems, and impact of wetland reconstructions and mitigations on MeHg budgets.
DE: 0432 Contaminant and organic biogeochemistry (0792)
DE: 0448 Geomicrobiology
DE: 0461 Metals
DE: 4840 Microbiology and microbial ecology (0465)
DE: 4875 Trace elements (0489)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting