The Catskill region of New York experiences the highest rates of acidic deposition of any region of the United States with low acid neutralizing capacity (ANC) surface waters. Surface waters are represented almost entirely by streams, whose chemical compositions are strongly affected by discharge. Many streams exhibit ANC ≤ 0 µeq L−1 during high-flow events; a few are acidic at baseflow. The sum of Ca2+ and Mg2+ concentrations exceeds ANC in all streams by a consistent 120 to 140 µeq L−1; differences between ANC and [Ca2+ + Mg2+] are attributable mainly to high SO42− concentrations, which result from acidic deposition. Nitrate concentrations increase during high-flow events. Depressed ANC values during snowmelt and storms are the result of dilution of base cations, relatively consistent SO42−, and increased NO3− levels.
Site-specific studies indicate that stream SO42− is matched very closely by SO42− concentrations in precipitation, when adjusted for dry deposition and evapotranspiration. Stream nitrate yield is exceeded by atmospheric deposition on an annual basis. Biological processes may play important roles in controlling the amount of NO3− supplied to Catskill streams during high-flow events.
Long-term monitoring data (1922 to the present) indicate that ANC values are increasing, largely as a result of an increasing trend in base cations. Sulfate concentrations are decreasing, but any positive effect this might have on ANC is balanced by a sharply increasing trend in NO3−. Limited data indicate that acidic deposition has had no deleterious effects on Catskill stream biota.
KeywordsBase Cation Acidic Deposition Brook Trout Acid Neutralize Capacity Stream Discharge
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