Longitudinal and seasonal patterns of stream acidity in a headwater catchment on the Appalachian Plateau, West Virginia, U.S.A.

The chemical composition during baseflow was used to elucidate the fundamental processes controlling longitudinal and seasonal patterns of stream acidity in Yellow Creek, a chronically acidic headwater (pH range 3.7-4.2) on the Appalachian Plateau in northeastern West Virginia. Sulfate concentrations controlled the variability of stream acidity within the Yellow Creek catchment. Decreases in stream free H⁺ acidity with decreasing elevation likely resulted from SO₄/^2- retention in riparian wetland areas as well as spatial variation in dominant tree species. Seasonal variations in free H⁺ and inorganic monomeric aluminum (Al(n)⁺) concentrations appeared related to seasonal fluctuations in baseflow discharge which was controlled by vegetative activity. Baseflow stream discharge, as well as H⁺ and Al(n)⁺ acidity, gradually declined during the growing season (June through October), likely reflecting microbial SO₄/^2- reduction in saturated anaerobic environments within riparian wetlands. A marked pulse of stream H⁺, Al(n)⁺, and SO₄/^2- coincided with an abrupt increase in baseflow discharge resulting from the cessation of transpiration after leaf-fall in November. This seasonal pattern suggests that autumn may be a critical period for eastern brook trout in streams draining wetlands on the Appalachian Plateau.