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Elevated concentrations of methyl mercury in streams after forest clear-cut: a consequence of mobilization from soil or new methylation?
Umeå University, Faculty of Science and Technology, Chemistry.
2009 (English)In: Environmental Science and Technology, ISSN 0013-936X, Vol. 43, no 22, 8535-8541 p.Article in journal (Refereed) Published
Abstract [en]

Concentrations of inorganic, mercuric mercury (HgII), methyl mercury (MeHg) and ancillary chemistry measured in first-order streams draining 0-4 (N = 20) and 4-10 (N = 27) year-old clear-cuts of former Norway Spruce Picea abies (Karst.) forest stands were compared with concentrations in streams draining >70 year-old Norway Spruce reference stands (N = 10). Concentrations of MeHg, and ratios of MeHg TOC-1 and HgII TOC-1, were significantly (p < 0.01) elevated in 0-4 year-old clear-cuts, as compared to references. The only ancillary variable showing a significant elevation for 0-4 year-old clear-cuts was Mn (p < 0.02). The 4-10 year-old clear-cuts showed intermediate concentrations with nonsignificant differences as compared to references. pH, nitrate, sulfate, Ca, Fe, TOC, TON, and the aromaticity of TOC (SUVA254 nm) showed nonsignificant differences between clear-cut age classes and references. Assuming that MeHg and HgII are mobilized from soil to stream to a similar relative extent as a consequence of clear-cutting, a calculation showed that 1/6 of the elevated MeHg concentration was due to enhanced mobilization from soil and 5/6 was due to new methylation of HgII 0-4 years after clear-cut. New methylation after clear-cut is suggested to be stimulated by an increased availability of electron donors for methylating bacteria, as a consequence of degradation of logging residue ("slash") and soil organic matter. A subdivision of sites situated above and below the highest postglacial coastline (HC) revealed a significant elevation of MeHg, MeHg TOC-1 and HgII TOC-1 (p < 0.05) beyond their references in 0-4 year-old clear-cuts above (but not below) the HC. This suggests that postglacial deposits of FeS(s) and FeS2(s) were not an important factor for elevation of MeHg after clear-cut.

Place, publisher, year, edition, pages
American Chemical Society , 2009. Vol. 43, no 22, 8535-8541 p.
URN: urn:nbn:se:umu:diva-32986DOI: 10.1021/es900996zOAI: diva2:308133
Available from: 2010-04-06 Created: 2010-04-06 Last updated: 2010-04-06Bibliographically approved

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