HR: 0800h
AN: B11B-0397    [Abstracts]
TI: Mercury Methylation, Demethylation, and Bioavailability in the Hyporheic Sediments of a Northern Wisconsin Wetland
AU: * Creswell, J E
EM: jcreswell@wisc.edu
AF: Environmental Chemistry and Technology Program, University of Wisconsin - Madison, 660 North Park Street, Madison, WI 53706, United States
AU: Babiarz, C L
EM: babiarz@cae.wisc.edu
AF: Environmental Chemistry and Technology Program, University of Wisconsin - Madison, 660 North Park Street, Madison, WI 53706, United States
AU: Shafer, M M
EM: mmshafer@facstaff.wisc.edu
AF: Environmental Chemistry and Technology Program, University of Wisconsin - Madison, 660 North Park Street, Madison, WI 53706, United States
AU: Roden, E E
EM: eroden@geology.wisc.edu
AF: Department of Geology and Geophysics, University of Wisconsin - Madison, 1215 West Dayton Street, Madison, WI 53706, United States
AU: Armstrong, D E
EM: dearmstr@facstaff.wisc.edu
AF: Environmental Chemistry and Technology Program, University of Wisconsin - Madison, 660 North Park Street, Madison, WI 53706, United States
AB: It is generally accepted that wetland sediments have a high potential to produce methylmercury, yet the factors controlling the relevant chemical transformations are poorly understood. Previous studies suggest that sulfate- reducing bacteria play an important role in methylation, but iron-reducing bacteria may also participate in this process. Methylation rates are influenced by both the concentration of Hg(II) and its speciation, which affects its bioavailability. Net accumulation depends also on demethylation rates, rates which may be significant in these systems. The objective of this study is to gain a better understanding of the main factors controlling the bioavailability of inorganic mercury for the production of methylmercury in wetland hyporheic zones. Stable isotopes of mercury are being used to investigate potential methylation and demethylation rates in the hyporheic sediments of Allequash Creek, near Boulder Junction, WI. Other techniques that are being applied to examine the chemical and biological drivers of mercury methylation and bioavailability include tin-reducible mercury "titrations" to measure the concentration of strong mercury-binding ligands in porewater, ¹⁴C-acetate uptake assays to determine the activity of the native microbial consortia , ion exchange resin experiments to explore the role of dissolved organic carbon in mercury binding, and inhibition studies (e.g. molybdenum amendments) of sulfate-reducing bacteria to assess their role in producing methylmercury. Manipulations of environmental conditions in laboratory microcosms are used to determine the relative importance of physical factors, such as temperature, and biogeochemical factors, such as sulfate, sulfide, dissolved organic carbon (DOC), and iron levels, on the fate of mercury in hyporheic systems. Preliminary results show that while significant levels of inorganic mercury are present in the hyporheic groundwater, strong mercury-binding ligands in the wetland porewaters at a high carbon site may limit the bioavailability of mercury. Measurements of chemical parameters such as DOC, iron, sulfate, and sulfide concentrations in field samples will further clarify whether conditions exist that promote the microbial methylation of mercury.
DE: 0404 Anoxic and hypoxic environments (4802, 4834)
DE: 0409 Bioavailability: chemical speciation and complexation
DE: 0432 Contaminant and organic biogeochemistry (0792)
DE: 0448 Geomicrobiology
DE: 0461 Metals
SC: Biogeosciences [B]
MN: 2007 Fall Meeting