Rapid Pedogenesis in Appalachian Coal Mine Spoils and Its Implications.

Mine soil morphology and genesis in Appalachian mine spoils has been studied extensively since the 1970’s. While initial soil physical and chemical properties are controlled by lithology, distinct A horizons form in months, transitional AC horizons form in years and Bw horizons can form in decades in finer textures spoils. Significant weathering of sand to silt+clay has been noted in < 5 years along with disintegration of rock fragments in surface layers. Iron oxides accumulate rapidly and may fix P over time, limiting plant availability.  While spoils high in sulfides are excluded from use, initial and long-term pH are controlled by interactions among trace pyrites and carbonates and differences in their reaction rates can produce unusual swings in pH over time.  Organic C and N accumulate rapidly, but their accurate analysis is complicated by geogenic forms (fossil coal and carbonate rock cements) and by Fe+Mn interferences in conventional Walkely-Black analyses. Multiple regional studies have predicted annual C-sequestration rates of 1.0 to 3.0 Mg/ha, but recent conservative analyses corrected for coal and carbonates indicate much lower annual rates. Regardless of other physical and chemical properties, the long term productivity of these soils is most frequently limited by densic layers. Pre-weathered brown overburden strata from zones close to the original surface produce lower pH and rock fragments which favors establishment of native forest species while unoxidized gray strata from deeper cuts produce higher pH, soluble salts and rock fragments which favors herbaceous species. These differences in pre-mining weathering also have great implications for the material’s tendency to produce total dissolved solids, primarily Ca and sulfate, which have been implicated as stressors in receiving streams. Thus, increasing emphasis is being placed upon understanding the underlying chemical weathering mechanisms and runoff/leaching interactions of these materials on final reclaimed surfaces and in valley fills.