Characterization of Acidic Coal Mine Drainage Sediments: Approaches to Improving Biological Properties for New Soil Formation.

Acid mine drainage (AMD) results from natural geochemical processes that occur when metal sulfides such as pyrite (FeS₂) are exposed to air and water through mining. Terrestrial environments are affected when AMD from abandoned mines flows overland, coating soil surfaces with acidic precipitates, eradicating vegetation, and creating “kill zones” that remain barren for decades. In former coal mining areas, AMD that emerges from underground abandoned mine seeps tends to become channelized within the kill zones, leaving behind mounded, oxidized sediments supporting no plant growth. In this study, cores were collected in an AMD kill zone from three areas (gray, orange and red) having different hydrologic properties and layers of Fe-oxide precipitates accumulated over nearly 100 years. Drainage from abandoned underground coal mines emerges at the site in Clearfield County, central Pennsylvania, and eventually enters the West Branch of the Susquehanna River. The aim of this research was to evaluate how AMD precipitates can be modified as a parent material for development of new soils to support reforestation. The deep cores were taken after the fourth year of three different remediation treatments (lime, lime+27 tons/ha compost, and lime+54 tons/ha compost), all of which included a first-year nurse crop of oats derived from straw mulch. We compared pH, rooting depth, carbon contents, acid generation potential and colony-forming units of culturable microorganisms in cores with depth. We found that doubling the compost rate had little effect on plant cover or numbers of culturable microorganisms at the surface. Although surface soils amended with the lower rate of compost in the red area had lower pH (3.2-4.6) than soils in the orange (4.6-5.5) and gray areas (7.0-7.3), the red area supported highest plant diversity yet at least tenfold lower numbers of culturable microorganisms, These findings suggest that AMD sediment removal and high levels of nutrient addition are not necessary to achieve good plant growth. Low input remediation efforts can therefore be effective in sustaining diverse vegetation in these formerly barren zones.