Editorial handling by A. Kolker a b s t r a c t 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 (d 13 C DIC ) 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 13 C due to enhanced carbonate dissolution associated with the release of H 2 SO 4 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 d 34 S SO4 and d 18 O SO4 isotopic signatures of the mine drainage and the presence of presumptive SO 4 -reducing bacteria suggest that SO 4 reduction activity also contributes C depleted in 13 C 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 H 2 SO 4 dissolution of carbonate rocks, enhanced by cation exchange, and C release to the atmosphere via CO 2 outgassing.

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