Organic matter remineralization in the sediment of two acid mine drainage lakes
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Acid mine drainage is a significant environmental problem throughout the world. At Rocky Forks Conservation Area near Columbia, MO numerous lakes have formed from old coal mining pits. Most of these lakes have a pH near 7, presumably buffered by the limestone bedrock except one, nicknamed Red Lake, which is consistently acidic. A comparison study was done from July 2012 to January 2013 between Red Lake (pH 3.4) and Green Lake (pH 7.4) to determine the rate of organic matter is remineralization in the sediments of both lakes. Pore water equilibrators were used to obtain concentration depth profiles of ferrous iron (Fe2+), sulfate (SO42-), manganese (Mn2+), and dissolved inorganic carbon (DIC) and to model rates. Results showed Red Lake had significantly higher Fe2+, Mn2+, and SO42- concentrations in the pore water than Green Lake. Iron and sulfate reduction occurred in both lakes, but manganese reduction was not observed in either. Sulfate reduction dominated in Green Lake, which resulted in higher rates of DIC production than in Red Lake. Iron reduction was observed in Red Lake for the summer, but does not account for a majority of DIC produced. In the winter, sulfate reduction is observed deeper in the sediment column accounting for 100% of the DIC produced in Red Lake. However, plants, organic matter, and iron cycling may be altering iron and sulfate reduction and the biogeochemistry in Red and Greek Lakes, accounting for differences in DIC production rates between the two lakes.