The onset of anthropogenic activity recorded in lake sediments in the vicinity of the Horne smelter in Quebec,Canada: Sulfur isotope evidence |
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| Authors: | B Mayer S Alpay WD Gould L Lortie F Rosa |
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| Institution: | 1. Department of Geology and Geophysics, University of Calgary, 2500 University Drive NW, Calgary, Alta., Canada T2N 1N4;2. Geological Survey of Canada, 601 Booth Street, Ottawa, Ont., Canada K1A OE8;3. CANMET, Mining and Mineral Sciences Laboratories, Natural Resources Canada, 555 Booth Street, Ottawa, Canada K1A 0G1;4. National Water Research Institute, Environment Canada, 867 Lakeshore Road, Burlington, Ont., Canada L7R 4A6 |
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| Abstract: | Contents and δ34S values of several S compounds, enumerations of S-reducing bacteria (SRB) and Fe-reducing bacteria (IRB), and Fe, Pb and In concentrations were determined for 210Pb-dated sediment cores from two lakes in Quebec, Canada. Both lakes are located approximately 70 km downwind of the Horne smelter and refinery in Rouyn-Noranda. Increases in Fe, Pb and In concentrations and a decrease in the δ34S values of total S in both lake sediment cores coincide with the start-up of the smelter in 1927. The shift towards more negative δ34S values was primarily caused by an increase in the extent of S isotope fractionation during bacterial (dissimilatory) SO4 reduction due to SO4 loading of the lakes after smelting began. Consequently, an enhanced accumulation of 32S-enriched reduced inorganic S compounds is evident in the sediments. δ34S values of organic S in the sediments decreased only slightly due to the smelter emissions between 1930 and 1980. Hence, due to the sulfide depositing mechanisms, S isotope ratios constitute a useful tracer recording the onset of S pollution in sediments of the two previously SO4-limited lakes investigated. In contrast, total S concentrations alone are not reliable indicators for anthropogenic S loading in lake sediment records. |
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