HR: 0800h
AN: B11B-0410    [Abstracts]
TI: Coupled Hydrological and Biogeochemical Controls on Methylmercury Production and Export from a Boreal Wetland
AU: * Heyes, A
EM: Heyes@cbl.umces.edu
AF: University of Maryland Center for Environmental Science, 1 William St P.O. Box 38, Solomons, MD 20688, United States
AU: Krabbenhoft, D P
EM: dpkrabbe@usgs.gov
AF: U.S. Geological Survey, 8505 Research Way, Middleton, WI 53562, United States
AU: Branfireun, B A
EM: brian.branfireun@utoronto,ca
AF: University of Toronto at Mississauga, 3359 Mississauga Rd N, Mississauga, ON L5L 1C6, Canada
AU: Gilmour, C C
EM: gilmourc@si.edu
AF: Smithsonian Environmental Research Center, 647 Contees Wharf Rd, Edgewater, MD 21037, United States
AU: Mitchell, C P
EM: mitchellc@si.edu
AF: Smithsonian Environmental Research Center, 647 Contees Wharf Rd, Edgewater, MD 21037, United States
AU: Tate, M T
EM: mttate@usgs.gov
AF: U.S. Geological Survey, 8505 Research Way, Middleton, WI 53562, United States
AU: Richardson, M
EM: murry.richardson@utoronto.ca
AF: University of Toronto at Mississauga, 3359 Mississauga Rd N, Mississauga, ON L5L 1C6, Canada
AB: Through long-term addition of a mercury (Hg) stable isotope to a wetland, we have begun to unravel the complexity of Hg and methylmercury (MeHg) cycling in a Boreal wetland. As part of the METAALICUS project being conducted at the Experimental Lakes Area, the lake 658 wetland was annually amended from 2001-2006 with a mercury isotope at a level approximately 5 times the annual anthropogenic deposition. However, wetlands not only receive Hg directly from atmospheric deposition, but also from upland runoff and from adjacent water bodies during periods of inundation. As METAALICUS is a whole watershed experiment, both the adjacent lake and uplands were each amended with a different mercury isotope. This has allowed us to study the cycling of Hg within the wetland in a watershed context. What is clear from this integrated approach is Hg cycling is dependent on the complex interplay of hydrodynamic and biogeochemical factors which will form the focus of this presentation. The Lake 658 wetland is classified as a basin oligotrophic swamp, and is surrounded on three sides by steeply sloping uplands and on the fourth by a lake. The morphology of the wetland causes large portions of the wetland to be hydrologically disconnected for long periods during dry periods in the summer and by ice in winter. When flow occurs, it is along defined channels rather than by sheet flow, which is partially an artifact of the basin morphology. Thus, wetland form influences the wetland volume that contributes to Hg and MeHg export. The majority of the Hg isotope added to the wetland has been retained in the vegetation and upper few centimeters of peat, with less than 1% exported despite the substantial export of both inorganic ambient Hg and MeHg. As little newly deposited Hg, represented by the amended isotope has been exported, we hypothesize that Hg export from wetlands is strongly coupled to decomposition and the fate of dissolved organic carbon which binds both Hg and MeHg. While MeHg is found throughout the wetland, MeHg concentrations and potentials (measured by short-term assays) were greatest in areas that are hydrologically connected to the lake or upland. These methylation assays correlate well with sulfate reduction and methane production. However, high concentrations of MeHg can be present in areas of the wetland when methylation assays reveal no measurable activity suggesting a pool of recalcitrant MeHg exists in wetlands. We hypothesize that the hydrologically interconnected areas of the wetland are most important in producing and exporting MeHg. However, the slow release of Hg isotope from the 658 wetland indicates Hg retention, thus response to changes in Hg deposition, is at least on the order of years and probably decades.
DE: 0330 Geochemical cycles (1030)
DE: 0489 Trace element cycling (4875)
DE: 0496 Water quality
DE: 1879 Watershed
DE: 1890 Wetlands (0497)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting