Longitudinal and seasonal patterns of stream acidity in a headwater catchment on the Appalachian Plateau, West Virginia, USA

The chemical composition during baseflow was used to elucidate the fundamen tal processes controlling longitudinal and seasonal patterns of stream acid ity in Yellow Creek, a chronically acidic headwater (pH range 3.7-4.2) on t he Appalachian Plateau in northeastern West Virginia. Sulfate concentration s controlled the variability of stream acidity within the Yellow Creek catc hment. Decreases in stream free H+ acidity with decreasing elevation likely resulted from SO42- retention in riparian wetland areas as well as spatial variation in dominant tree species. Seasonal variations in free H+ and ino rganic monomeric aluminum (Aln+) concentrations appeared related to seasona l fluctuations in baseflow discharge which was controlled by vegetative act ivity. Baseflow stream discharge, as well as H+ and Aln+ acidity, gradually declined during the growing season (June through October), likely reflecti ng microbial SO42- reduction in saturated anaerobic environments within rip arian wetlands. A marked pulse of stream H+, Aln+, and SO(4)(2-)coincided w ith an abrupt increase in baseflow discharge resulting from the cessation o f transpiration after leaf-fall in November. This seasonal pattern suggests that autumn may be a critical period for eastern brook trout in streams dr aining wetlands on the Appalachian Plateau.