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The Response of Lake-Watersheds in the Adirondack Region of New York To Decreases in Acidic Deposition and Linkages to Climate Change and Mercury Deposition

Charles T. Driscoll^1*, Kimberley M. Driscoll¹, Karen Roy², Qintao Zhao¹, Afshin Pourmokhtarian¹, Timothy Sullivan³ and Myron Mitchell⁴

Watersheds in the Adirondack region of New York USA are sensitive to air pollution and climate change. In ecosystems there are interesting interactions among acidic and Hg deposition and changing climate. Marked decreases in concentrations of SO₄^2- and H⁺ have occurred in wet deposition at Huntington Forest and Whiteface Mountain since the late 1970s which are consistent with long-term declines in emissions of SO2. Decreases in wet NO₃^- deposition and nitrogen oxides (NOx) emissions have been less over the same interval. All 48 Adirondack Long Term Monitoring (ALTM) lakes, exhibited significant decreases in concentrations of SO₄^2- since 1992 (mean rate -2.31 μeq/L-yr), which coincides with decreases in atmospheric S deposition. Concentrations of NO₃^- have also decreased in 29 of 48 ALTM lakes. This trend is generally consistent with decreases atmospheric N deposition over this period, although others mechanisms may also contribute to this pattern. Decreases in concentrations of SO₄^2- + NO₃^- have resulted in increases in acid neutralizing capacity (ANC) (mean change + 0.98 μeq/L-yr with significant increases in 40 lakes) and pH (mean change 0.20 μeq H⁺/L-yr, with 37 lakes showing significant decreases in H⁺ and two lakes showing increases), and a shift in the speciation of monomeric Al from toxic inorganic species toward less toxic organic forms in some lakes. 23 ALTM lakes have shown significant long-term changes in concentrations of dissolved organic carbon (DOC) (mean change +6.67 μmol C/L-yr, with 20 lakes showing increases and 3 lakes showing decreases). Increases in DOC are likely driven by long-term decreases in SO₄^2-+NO₃^- possible due to increases in pH.

Fish in the Adirondacks exhibit elevated concentrations of Hg. There are interesting linkages between acidic and Hg deposition, including the role of sulfur processing in transformations of Hg, and increases in fish Hg concentrations with acidification.

Model calculations using the biogeochemical model PnET-BGC provide a framework for understanding the response of Adirondack lake watersheds to hypothetical future decreases in acidic deposition and are useful to calculate critical loads of acidity to help guide future emission controls. The responses of ecosystems to decreases in acidic deposition are likely influenced by changes in climate and CO₂. This presentation is linked with a presentation by K. Roy on changes in fish communities in ALTM lakes and the relations of these changes with changes in lake chemistry.

¹ Department of Civil and Environmental Engineering, Syracuse University, Syracuse NY 13244
² New York State Department of Environmental Conservation, Division of Air, Ray Brook, NY
³ E&S Environmental Chemistry, Corvallis OR
⁴ SUNY ESF, Syracuse, NY 13210