Isotopic evidence of enhanced carbonate dissolution at a coal mine drainage site in Allegheny County,Pennsylvania, USA |
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| Institution: | 1. Univ. Nimes, EA 7352 CHROME, rue du Dr Georges Salan, 30021 Nimes, France;2. Aix-Marseille Université, CNRS-IRD-Collège de France, UM 34 CEREGE, Technopôle de l''Arbois, BP80, 13545 Aix-en-Provence, France;3. AREVA NC Malvési, 11102 Narbonne Cedex, France;4. ANDRA, 1-7 rue Jean-Monnet, 92298 Châtenay-Malabry Cedex, France;5. Department of Earth Sciences, University of Waterloo, 200 University Avenue W., Waterloo, Ont. N2L 3G1, Canada;1. Department of Earth and Atmospheric Sciences, Snee Hall, Cornell University, Ithaca, NY 14853, USA;2. Department of Ecology and Evolutionary Biology, Corson/Mudd Hall, Cornell University, Ithaca, NY 14853, USA;1. Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47907, United States of America;2. Idaho Water Resources Research Institute, 875 Perimeter Dr MS 3002, Moscow, ID 83844-3002, United States of America;3. Dept. of Marine, Earth, and Atmospheric Sciences, 2800 Faucette Drive, 5130 Jordan Hall, NC State University, Raleigh, NC 27695-8208, United States of America |
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| Abstract: | Stable isotopes were used to determine the sources and fate of dissolved inorganic C (DIC) in the circumneutral pH drainage from an abandoned bituminous coal mine in western Pennsylvania. The C isotope signatures of DIC (δ13CDIC) were intermediate between local carbonate and organic C sources, but were higher than those of contemporaneous Pennsylvanian age groundwaters in the region. This suggests a significant contribution of C enriched in 13C due to enhanced carbonate dissolution associated with the release of H2SO4 from pyrite oxidation. The Sr isotopic signature of the drainage was similar to other regional mine waters associated with the same coal seam and reflected contributions from limestone dissolution and cation exchange with clay minerals. The relatively high δ34SSO4 and δ18OSO4 isotopic signatures of the mine drainage and the presence of presumptive SO4-reducing bacteria suggest that SO4 reduction activity also contributes C depleted in 13C isotope to the total DIC pool. With distance downstream from the mine portal, C isotope signatures in the drainage increased, accompanied by decreased total DIC concentrations and increased pH. These data are consistent with H2SO4 dissolution of carbonate rocks, enhanced by cation exchange, and C release to the atmosphere via CO2 outgassing. |
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