Chemical characteristics and temporal trends in eight streams of the Catskill Mountains, New York

Abstract

Discharge to concentration relationships for eight streams studied by the U.S. Geological Survey (USGS) as part of the U.S. Environmental Protection Agency's (U.S. EPA) Long-Term Monitoring Project (1983–89) indicate acidification of some streams by H2SO4 and HNO3 in atmospheric deposition and by organic acids in soils. Concentrations of major ions in precipitation were similar to those reported at other sites in the northeastern United States. Average concentrations of SO4 2− and NO3 − were similar among streams, but base cation concentrations differed widely, and these differences paralleled the differences in acid neutralizing capacity (ANC). Baseflow ANC is not a reliable predictor of stream acidity at high flow; some streams with high baseflow ANC (>150 Μeq L−1) declined to near zero ANC at high flow, and one stream with low baseflow ANC (<50 Μeq L−1) did not approach zero ANC as flow increased. Episodic decreases in ANC and pH during peak flows were associated with increased concentrations of NO3 − and dissolved organic carbon (DOC). Aluminum concentrations exceeding 300 Μg L−1 were observed during peak flows in headwater streams of the Neversink River and Rondout Creek. Seasonal Kendall Tau tests for temporal trends indicate that SO4 2− concentrations in streamwater generally decreased and NO3 − concentrations increased during the period 1983–1989. Combined acid anion concentrations (SO4 2− + NO3 −) were generally unchanged throughout the period of record, indicating both that the status of these streams with respect to acidic deposition is unchanged, and that NO3 − is gradually replacing SO4 2− as the dominant acid anion in the Catskill streams.