Three watershed–lake systems of the Integrated Lake–Watershed Acidification Study (ILWAS) were investigated to determine the effects of atmospheric deposition on the chemical compositions of oligotrophic lakes in the Adirondack Mountains of New York. Using the principles of watershed mass balance and electroneutrality of solutions, the following conclusions were drawn. (1) Annually, about 90% of the NH4+ and 50% of the NO3− from atmospheric deposition were retained in the systems. (2) In the Woods system, Cl− was in steady state with respect to atmospheric deposition although both Panther and Sagamore systems had net losses, indicating watershed sources of Cl−. (3) The losses of base cations from Panther and Sagamore were substantially greater than from the Woods system, reflecting the shallow soils of the latter. (4) The concentrations of SO42− in the waters of the three systems were controlled by the atmospheric deposition of anthropogenic sulfur; in Woods and Panther, inputs (atmospheric deposition) equalled outputs (discharges from the lake outlets); in Sagamore, outputs exceeded inputs. (5) In 1978–80, concentrations of SO42− were four to five times higher than historical values. These increased concentrations had caused either decreased alkalinities of surface waters or increased concentrations of base cations (Ca2+, Mg2+, Na+, K+) or both. The former directly affects aquatic ecosystems; the latter directly affects terrestrial ecosystems because of increased rates of loss of the nutrients Ca, Mg, and K in the absence of resupply from primary weathering.
Target loads of atmospheric sulfur and nitrogen deposition for protection of acid sensitive aquatic resources in the Adirondack Mountains, New York
