Mercury Cycling in Stream Ecosystems. 2. Benthic Methylmercury Production and Bed Sediment&#8722

时间：2009-04-19  阅读：    我要评论:

Mark Marvin-DiPasquale*^†, Michelle A. Lutz^‡, Mark E. Brigham^§, David P. Krabbenhoft^‡, George R. Aiken, William H. Orem and Britt D. Hall^‡# U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, U.S. Geological Survey, 8505 Research Way, Middleton, Wisconsin 53562, U.S. Geological Survey, 2280 Woodale Drive, Mounds View, Minnesota 55112, U.S. Geological Survey, 3215 Marine Street, Suite E-127, Boulder, Colorado 80303, U.S. Geological Survey, 12201 Sunrise Valley Drive, Reston, Virginia 20192Environ. Sci. Technol., 2009, 43 (8), pp 2726–2732DOI: 10.1021/es802698vPublication Date (Web): March 11, 2009Copyright This article not subject to U.S. Copyright. Published 2009 by the American Chemical Society * Corresponding author phone: 650-329-4442; e-mail: mmarvin@usgs.gov., †

USGS, Menlo Park, California.

, ‡

USGS, Middleton, Wisconsin.

, §

USGS, Mounds View, Minnesota.

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USGS, Boulder, Colorado.

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USGS, Reston, Virginia.

, #

Current address: Department of Biology, University of Regina, 3737 Wascana Parkway, Regina, Saskatchewan, Canada S4S 0A2.

Abstract

Mercury speciation, controls on methylmercury (MeHg) production, and bed sediment−pore water partitioning of total Hg (THg) and MeHg were examined in bed sediment from eight geochemically diverse streams where atmospheric deposition was the predominant Hg input. Across all streams, sediment THg concentrations were best described as a combined function of sediment percent fines (%fines; particles < 63 μm) and organic content. MeHg concentrations were best described as a combined function of organic content and the activity of the Hg(II)-methylating microbial community and were comparable to MeHg concentrations in streams with Hg inputs from industrial and mining sources. Whole sediment tin-reducible inorganic reactive Hg (Hg(II)_R) was used as a proxy measure for the Hg(II) pool available for microbial methylation. In conjunction with radiotracer-derived rate constants of ²⁰³Hg(II) methylation, Hg(II)_R was used to calculate MeHg production potential rates and to explain the spatial variability in MeHg concentration. The %Hg(II)_R (of THg) was low (2.1 ± 5.7%) and was inversely related to both microbial sulfate reduction rates and sediment total reduced sulfur concentration. While sediment THg concentrations were higher in urban streams, %MeHg and %Hg(II)_R were higher in nonurban streams. Sediment pore water distribution coefficients (log K_d’s) for both THg and MeHg were inversely related to the log-transformed ratio of pore water dissolved organic carbon (DOC) to bed sediment %fines. The stream with the highest drainage basin wetland density also had the highest pore water DOC concentration and the lowest log K_d’s for both THg and MeHg. No significant relationship existed between overlying water MeHg concentrations and those in bed sediment or pore water, suggesting upstream sources of MeHg production may be more important than local streambed production as a driver of water column MeHg concentration in drainage basins that receive Hg inputs primarily from atmospheric sources.

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