ASSESSMENT OF BIOGEOCHEMICAL MATURATION OF OVERBURDEN DISTURBED BY SURFACE MINING

The homogenization and replacement of the overburden during surface mining disrupts rock weathering, soil formation processes, and the biogeochemical cycling of elements. The ultimate goal of reclamation is to re-establish a diverse, functional ecosystem post disturbance, which is dependent on the geochemical characteristics of the disturbed overburden material. In southeastern Ohio, the Meigs Creek No. 9 coal seam was progressively surface mined beginning in 1968 and ending in 2001. The overburden of the coal seam consisted of limestone and shale containing 1.5% - 5% pyrite. Using these progressively mined regions as snapshots of overburden weathering we examined time dependent geochemical changes in the overburden 9, 14, and 27 years post-disturbance. Soil cores, reaching a maximum depth of approximately 50 to 70 cm from the surface, were extracted from each region and analyzed to establish pH, water content, organic and inorganic carbon content, acid-extractable Fe(II), Fe(III), Mn(II), and Mn(III/IV) concentrations, and porewater chloride, sulfate, phosphate, and nitrate anion concentrations. All disturbed overburden sediments contained elevated Fe(II), Mn(II), and pH in comparison to undisturbed soil at comparable depths. With increasing time post disturbance, Fe(II) content and sediment pH decrease concurrently with an increase in porewater sulfate concentration, suggestive of oxidation of overburden-associated iron sulfide phases. Shifts in microbial communities associated with the geochemical maturation will also be examined using culture-dependent enumerations and nucleic acid based approaches.