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Anthropogenic Copper Inventories and Mercury Profiles from Lake Superior: Evidence for Mining Impacts
Affiliation:1. Instituto Cavanilles de Biodiversidad y Biología Evolutiva and Departamento de Microbiología y Ecología, Edificio de Investigación, Campus de Burjassot, Universitat de Valencia, E-46100 Burjassot, Spain;2. Laboratoire de Glaciologie et Géophysique de l''Environnement-CNRS UMR 5183, 54, rue Molière, Domaine Universitaire, B.P. 96, Université Joseph Fourier-Grenoble 1 F-38402, Saint Martin d''Hères, France;3. Departamento de Biología, Universidad Autónoma de Madrid, E-28049, Madrid, Spain;1. Department of Physical and Environmental Sciences, University of Toronto, Toronto, ON M1C 1A4, Canada;2. Environmental Monitoring and Reporting Branch, Ontario Ministry of Environment and Climate Change, Toronto, ON M9P 3V6, Canada
Abstract:During the past 150 years, the mining industry discharged more than a billion tons of tailings along Lake Superior shorelines and constructed numerous smelters in the watershed. Given the vast size of Lake Superior, were sediment profiles at locations far offshore impacted by nearshore activities? Did copper and associated precious metal mining modify regional fluxes for copper and mercury? Samples from thirty sediment cores document that background concentrations of copper are high (mean 60.9 ± 7.0 μg/g), due to the proximity of natural ore sources. Anthropogenic inventories uncorrected for focusing also are high, ranging from 20 to 780 μg/cm2 (mean 187 ± 54 μg/cm2). Focusing factor corrections decrease the mean estimate and reduce variance (144 ± 24 μg/cm2). Several approaches to estimating inputs suggest that only 6 to 10% of historic copper deposition originated directly from atmospheric sources, emphasizing terrestrial sources. Moreover, coastal sediment cores often show synchronous early increases in copper and mercury with buried maxima. Around the Keweenaw Peninsula, twenty-two cores trace high copper and mercury inventories back to mill and smelting sources. Direct assays of ores from thirteen mine sites confirm a natural amalgam source of mercury in the stamp mill discharges. Core records from inland lakes (Michigamme Project) also reveal patterns of copper and mercury inputs from a variety of mining sources: historic tailing inputs, amalgam assay releases, and atmospheric smelter plumes.
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