Developing the Critical Loads for the Acidification of Some Lake- Watersheds in the Adirondack Region of New York

Qingtao Zhou1*, Charles T Driscoll1, Timothy J.Sullivan2 and Bernard J.Cosby3

Critical loads are a useful tool to guide emission control strategies that will lead to the recovery of ecosystems in response to decreases in atmospheric deposition. In an ongoing study, we are developing critical loads and target loads of acidity for lake-watersheds in Adirondack region of New York. We examined the response of lake-watersheds to a range of future scenarios of decreases in atmospheric nitrate and sulfate deposition. The projects involves examining critical and target loads for 20 lake-watersheds. For this presentation we present results for Constable Pond, a chronically acidic, thin till drainage lake and Arbutus Lake, a moderate ANC, medium till drainage lake as case studies. The project was conducted with the dynamic watershed model PnET-BGC. We ran the model under different scenarios of combinations of decreases in atmospheric nitrate and sulfate deposition ranging from 0% to 100% that was ramped down from 2008 to 2020 and remained constant thereafter until steady-state was attained. Critical loads were determined from steady-state values, while target loads were determined for various years approaching steady-state. Model calculations suggest that Adirondack lake-watersheds have become sensitive to ongoing inputs of acidic deposition due to the long-term loss of exchangeable base cations in soil from historical acidic deposition. As a result the ANC and soil %base saturation (BS) of the lake-watersheds following decreases in acidic deposition never reach values that occurred prior to the Industrial Revolution (before the onset of acidic deposition). The target and critical loads of Adirondack lakes greatly depend on rates of base cation supply, and the resulting initial ANC and soil base status. Our results show that recovery of lake ANC and soil %BS is accomplished most effectively by equivalent decreases in sulfate deposition compared to nitrate deposition. As part of this study we also examine aquatic and forest biological indicators of acidification stress.

*Corresponding author. Address: Department of Civil and Environmental Engineering, Syracuse University, Syracuse NY 13244. Phone:(315)-882-4516. Email Address:
1 Department of Civil and Environmental Engineering, Syracuse University, Syracuse NY 13244,
2 E&S Environmental Chemistry, Corvallis OR 97339,
3 Department of Environmental Sciences, University of Virginia, Charlottesville VA 22904.