Spatial and temporal dynamics of mercury in Precambrian Shield upland runoff |
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Authors: | CJ Allan A Heyes NT Roulet VL St Louis JWM Rudd |
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Institution: | (1) Dept. of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, NC 28227, USA;(2) Dept. of Geography, McGill University, 805 Sherbrooke St. W., Montreal, Quebec, H3A 2K6, Canada;(3) Dept. of Microbiology, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada;(4) Dept. of Fisheries and Oceans, Freshwater Institute, Winnipeg, Manitoba, R3T 2N6, Canada |
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Abstract: | Methylated and total Hg, and TOC concentrations were measured in precipitation and runoff in a first order Precambrian Shield watershed, and in precipitation, throughfall, shallow groundwater and runoff in a zero Precambrian Shield watershed. Plots dominated by open lichen-covered bedrock and another containing small patches of conifer forest and thin discontinuous surficial deposits were monitored within the zero order catchment. Methyl (3–10 fold) and non-methyl (1.4–2.8 fold) Hg concentrations changed irregularly during rainfall and snowmelt runoff events in all catchments. Temporal patterns of Hg concentration in runoff included flushing and subsequent dilution as well as peak concentrations coinciding with peak or recession flow. Mercury export was highest from lichen-covered bedrock surfaces as a result of high runoff yields and minimal opportunity for physical retention and in the case of MeHg demethylation. Forest canopy and lichen/bedrock surfaces were often net sources for Hg while forest soils were mostly sinks. However, upland soils undergoing periodic reducing conditions appear to be sites for the in situ production of MeHg. |
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Keywords: | dissolved organic carbon episodic runoff methyl mercury |
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