Long-term trends in the chemistry of precipitation and lake water in the Adirondack Region of New York, USA

Abstract

Long-term changes in the chemistry of precipitation (1978–94) and 16 lakes (1982–94) were investigated in the Adirondack region of New York, USA. Time-series analysis showed that concentrations of SO4 2−, NO3 −, NH4 + and basic cations have decreased in precipitation, resulting in increases in pH. A relatively uniform rate of decline in SO4 2− concentrations in lakes across the region (1.81±0.35 μeq L−1 yr−1) suggests that this change was due to decreases in atmospheric deposition. The decrease in lake SO4 2− was considerably less than the rate of decline anticipated from atmospheric deposition. This discrepancy may be due to release of previously deposited SO4 2− from soil, thereby delaying the recovery of lake water acidity. Despite the marked declines in concentrations of SO4 2− in Adirondack lakes, there has been no systematic increase in pH and ANC. The decline in SO4 2− has corresponded with a near stoichiometric decrease in concentrations of basic cations in low ANC lakes. A pattern of increasing NO3 − concentrations that was evident in lakes across the region during the 1980's has been followed by a period of lower concentrations. Currently there are no significant trends in NO3 − concentrations in Adirondack lakes.