Early diagenesis of sulfur in the sediments of lakes that receive acid mine drainage

Abstract

Fifteen final-cut strip mine lakes, located throughout the Western Interior, Eastern Interior, and Appalachian Coal Basins in the U.S.A., were selected to represent a wide variety of values for the variables lake-water pH, alkalinity, SO 4 and Fe concentrations, sediment organic matter content, overburden lithology, and lake age. Lake-water, porewater and sediment samples were collected for geochemical analysis. Sequential digestion of sediment samples was used to determine the amount of the inorganic S phases (elemental S, metal monosulfide, metal disulfide, and total) present in the sediment. Authigenic inorganic reduced S minerals were found in the sediments of all 15 lakes that receive acid mine drainage from groundwater input. Authigenic FeS 2 was the largest fraction in most of the lake sediments, but elemental S was larger in some. The amount of C-bonded S, determined by difference, ranged widely but was nearly always less abundant than the inorganic phases. Correlations of the nature and amount of authigenic reduced S minerals to the SO 4 and Fe concentrations in porewater, the organic matter content of the lake sediments, and lake age were tested. The formation of SO 4-reduction end products was not limited by Fe or SO 4 availability. The amounts of reduced S in the sediments correlated with the amount of organic matter in the sediment, indicating that the authigenic mineral formation process is organic-matter limited in these Fe- and SO 4-rich environments. Lake age, which represents a complex function of the diminishing acid-mine-drainage load derived from weathered spoil piles and the generation of alkalinity by biogeochemical reactions in the lake sediments, was a good predictor of the amounts of reduced S mineral in the sediment regardless of geological setting.