Impacts of mountaintop removal and valley fill coal mining on C and N processing in terrestrial soils and headwater streams

We measured C and N cycling indicators in Appalachian watersheds impacted by mountaintop removal and valley fill (MTR/VF) coal mining, and in nearby forested watersheds. These watersheds include ephemeral, intermittent, and perennial stream reaches, and the length of time since disturbance in the MTR/VF watersheds was 5 to 11 years. In forest soils compared to VF soils, both denitrification enzyme activity (DEA) and basal respiration (BR) were elevated (factor of 6 for DEA and factor of 1.8 for BR expressed on a weight basis) and bulk density was lower. Organic matter (OM) and moisture were higher in the forest soils, which likely contributed to the elevated DEA and BR levels. Evaluation of soils data from our intermittent watersheds as a chronosequence provides some evidence of soil quality (DEA, BR, and soil moisture) improvement over the course of a decade, at least in the top 5 cm. Across the hydrological permanence gradient, sediment DEA was significantly higher (factor of 1.6) and sediment OM was significantly lower in forested than in VF watersheds, whereas sediment BR did not differ between forested and VF watersheds. Dissolved organic carbon (DOC) concentrations were not different in mining-impacted and forested streams, whereas dissolved inorganic carbon (DIC) concentrations and DOC and DIC stable carbon isotopic compositions (δ¹³C) were significantly elevated in VF streams. The δ¹³C-DIC values indicate that carbonate dissolution was a dominant source of dissolved carbon in MTR/VF mining-impacted streams. The disturbance associated with MTR/VF mining significantly impacts C and N processing in soils, stream sediments, and stream water although our data suggests some improvement of soil quality during the first decade of reclamation.