Comparison of base cations in streams and soils in two small western Maryland watersheds

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Hydrologic response, vegetation, nutrient cycling, and soil structure are some of the ecosystem properties affected when a watershed is strip-mined for coal and subsequently reclaimed. The present study sought to quantify the impacts of strip-mining and reclamation on the base cation pools and cycling within a watershed. To that end, a paired watershed study was conducted comparing a strip-mined watershed (TMat1) to a second-growth forested watershed (TNef1). Base cation input-output budgets were constructed for two watersheds using precipitation collection and stream sampling techniques. Soil base cation pools and cation exchange capacities were measured, and lysimeter samples were analyzed for calcium, magnesium, potassium, and sodium. In-stream silica concentrations were also measured to help discern whether base cation export was due to a silicate mineral weathering source or from the soil exchange complex. Although it was difficult to determine the source of base cations, TMat1 was exporting vastly greater quantities of all four base cations than was TNef1. Mineral soil exchangeable Ca, Mg, and Na were significantly greater at TMat1, due to mining and exposure of mineral surfaces such as limestone and other bedrock. Mineral soil CEC was not significantly different between the two sites. Similarly, 15 cm deep lysimeters also had significantly higher levels of Ca, Mg, and Na at TMat1 than TNef1. From this research, it is clear that reclamation has not restored TMat1 to its original condition and that there is a large amount of base cation export to the stream in this watershed. Prolonged cation export could cause long-term nutrient depletion, but could also serve to neutralize mineral acidity associated with acid mine drainage and acid rain at TMat1.