APPLICATION OF THE INTEGRATED LAKE-WATERSHED ACIDIFICATION STUDY MODEL TO WATERSHED LIMING AT WOODS LAKE, NEW-YORK

Woods Lake, in the Adirondack Mountains of New York, was the site of t he Experimental Watershed Liming Study (EWLS) in which base addition w as investigated as a method for mitigation of lake acidity. In an effo rt to predict the duration of effects, the treatment was simulated usi ng the Integrated Lake-Watershed Acidification Study (ILWAS) model. To simulate terrestrial liming, calcite was applied to treated subcatchm ents as a rapidly weathering mineral in the upper horizon. Soil soluti on and lake outlet chemistry showed a response to calcite addition wit hin four months of the start of the simulation. Calcium concentrations , acid neutralizing capacities (ANC), and pH increased in the upper so il layer and aluminum concentrations decreased in the upper three soil layers (0-70 cm). The response of ANC was delayed in lower soil layer s due to proton production associated with aluminum hydrolysis. Moreov er, soil water pH in the third soil layer decreased in response to cal cite treatment due to the displacement of hydrogen ions by calcium add ed to the exchange complex. Calcium concentrations, ANC and pH increas ed and aluminum concentrations decreased in the simulated lake outlet. The modeled effects of calcite treatment on the soil and lake outlet chemistry were not as great as field observations. This was, in part, attributed to the model representation of the watershed, which did not include streams, ponds, or wetlands located in the treated subcatchme nts. Calcite applied to these saturated areas in the field readily dis solved, supplying ANC to lake water. Additionally, incorporation of ca lcite into a thick organic layer in the model diminished the possibili ty of dissolution by contact with overland flow. Observed concentratio ns of calcium, ANC, and pH in the outlet decreased after high values i n the two years after treatment. Although the model failed to match ob served short-term data, it may simulate the long-term response as calc ium is transported through the soil. A long-term simulation of the mod el suggests that effects of base treatment will persist for at least 5 0 years.