The Long Term Response of Adirondack Surface Waters to Reductions in Acidic Deposition

Kristin A. Waller1*, Charles T Driscoll1, Jason Lynch2 and Dani Newcomb2

After years of adverse impacts to the acid sensitive regions of the United States, the US EPA formulated Title IV of the 1990 Clean Air Act Amendments to regulate sulfate emissions from power plants with the goal of decreasing acidic deposition. Post implementation, large scale decreases in sulfate emissions and deposition concentrations have been readily evident; however, due to the complexity of surface water systems, ecosystem recovery has been more elusive and less apparent in the immediate data. The Temporally Integrated Monitoring of Ecosystems (TIME) is a long term monitoring project developed in 1990 to sample statistically chosen subpopulations of lake and stream regions across the eastern US to compare regional trends in surface water chemistry to changes in air deposition. Forty-three TIME lakes were selected to represent the surface waters of the Adirondack ecosystems in upstate New York. Using the TIME and NADP data available from 1991-2007, substantial decreases in sulfate were confirmed for local wet deposition and lakes throughout the Adirondacks. Corresponding to a -1.04 meq/m2-yr average regional trend in sulfate deposition for the time period, lake sulfate concentrations have decreased at an average rate of - 1.92 µeq/L-yr and fluxes have decreased at an average rate of -1.19 meq/m2-yr. Additionally, the percentage of these 43 lakes considered to be acidic (ANC <0 µeq/L) has decreased from 16.3 to 14.0 percent over the last ten years. Previous analysis of Adirondack TIME data, conducted in the late 1990s, concluded that although sulfates were decreasing appreciably, ANC recovery was limited by large decreases in base cation concentrations. While lake trends in ANC continue to show a dependence on changes in base cations, more than 80% of the TIME lakes now exhibit considerable increases in ANC at an average rate more than two-fold greater than previously reported (+.76 µeq/L-yr). The past seventeen years of Adirondack TIME data suggest that the surface water ecosystems are finally showing recovery from acidification. However, analyses of the four most recent years of data (2004 to 2007) reveal that several lakes are now experiencing increasing levels of sulfate deposition and decreasing DOC concentrations. It is possible that these unexpected trends coincide with increases in precipitation, which may advocate a need for stricter sulfate

1*Corresponding Author, Email: , Phone: 609-575-0085
1Department of Civil and Environmental Engineering, Syracuse University, 151 Link Hall, Syracuse, NY 13244, USA
2Office of Air and Radiation Office of Atmospheric Programs