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Sci Total Environ. 2016 Oct 15;568:727-738. doi: 10.1016/j.scitotenv.2016.03.044. Epub 2016 Apr 27.

Mercury and methylmercury in aquatic sediment across western North America.

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United States Geological Survey, California Water Science Center, 6000 J St., Placer Hall, Sacramento, CA 95819, USA. Electronic address:
United States Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, USA.
United States Geological Survey, Forest and Rangeland Ecosystem Science Center, Corvallis, OR, USA.
United States Geological Survey, Western Ecological Research Center, Dixon Field Station, 800 Business Park Drive, Suite D, Dixon, CA 95620, USA.
United States Geological Survey, 8505 Research Way, Middleton, WI 53562, USA.
United States Geological Survey, California Water Science Center, 6000 J St., Placer Hall, Sacramento, CA 95819, USA.
Department of Biology, University of Regina, 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada.
United States Environmental Protection Agency, 1200 6th Ave, St. 900, OEA-095, Seattle, WA 98101, USA.


Large-scale assessments are valuable in identifying primary factors controlling total mercury (THg) and monomethyl mercury (MeHg) concentrations, and distribution in aquatic ecosystems. Bed sediment THg and MeHg concentrations were compiled for >16,000 samples collected from aquatic habitats throughout the West between 1965 and 2013. The influence of aquatic feature type (canals, estuaries, lakes, and streams), and environmental setting (agriculture, forest, open-water, range, wetland, and urban) on THg and MeHg concentrations was examined. THg concentrations were highest in lake (29.3±6.5μgkg(-1)) and canal (28.6±6.9μgkg(-1)) sites, and lowest in stream (20.7±4.6μgkg(-1)) and estuarine (23.6±5.6μgkg(-1)) sites, which was partially a result of differences in grain size related to hydrologic gradients. By environmental setting, open-water (36.8±2.2μgkg(-1)) and forested (32.0±2.7μgkg(-1)) sites generally had the highest THg concentrations, followed by wetland sites (28.9±1.7μgkg(-1)), rangeland (25.5±1.5μgkg(-1)), agriculture (23.4±2.0μgkg(-1)), and urban (22.7±2.1μgkg(-1)) sites. MeHg concentrations also were highest in lakes (0.55±0.05μgkg(-1)) and canals (0.54±0.11μgkg(-1)), but, in contrast to THg, MeHg concentrations were lowest in open-water sites (0.22±0.03μgkg(-1)). The median percent MeHg (relative to THg) for the western region was 0.7%, indicating an overall low methylation efficiency; however, a significant subset of data (n>100) had percentages that represent elevated methylation efficiency (>6%). MeHg concentrations were weakly correlated with THg (r(2)=0.25) across western North America. Overall, these results highlight the large spatial variability in sediment THg and MeHg concentrations throughout western North America and underscore the important roles that landscape and land-use characteristics have on the MeHg cycle.


Aquatic sediment; Mercury methylation; Spatial mercury patterns; WNAMS; Western North American Mercury Synthesis

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