Recent and potential future changes in the chemistry of surface waters of the Adirondack region of New York in response to decreases in atmospheric deposition

Charles Driscoll1, Shuai Shao2, Habibollah Fakhraei3, Gregory Lawrence4 and Doug Burns5

Historical acid deposition has contributed to the acidification of soil and surface waters in acid-sensitive regions of the U.S.  Over past several decades, however, controls on sulfur dioxide and nitrogen oxide emissions in the U.S. have reversed this process, resulting in decreases in acid deposition that have led to decreases in sulfate and nitrate concentrations and increases in the acid neutralizing capacity (ANC) in surface waters of acid-sensitive regions like the Adirondacks of New York.   Concentrations of dissolved organic carbon (DOC) in surface waters have also increased in response to decreasing acid deposition. As recovery from acid deposition proceeds, changing climate is also becoming an important potential driver of changes in surface water chemistry. We present an analysis of long-term observations of lake chemistry in the Adirondacks in response to decreases in acid deposition. This analysis is complemented by the application of the watershed biogeochemical model, PnET-BGC, to an intensive study site in the Adirondacks, Buck Creek, to examine future decreases in acid deposition coupled with projected changes in meteorological conditions. PnET-BGC has been modified to include an algorithm that depicts changes in the mobility of DOM (dissolved organic matter) with changes in soil acid-base chemistry. Analysis of chemical trends in Adirondack lakes show ongoing decreases in sulfate, nitrate, calcium and inorganic monomeric aluminum, and increases in ANC. Coincident with lake recovery from acid deposition are marked, but spatially variable increases in DOC concentrations. The supply of DOM provides naturally occurring organic acids that offset increases in ANC. Results show mean lake DOC concentrations and changes in lake DOC concentrations increase with increases in watershed to lake surface area ratio and decreases in lake hydraulic residence time. The PnET-BGC modeling of Buck Creek is consistent with ongoing lake trends. Likely future decreases in acid deposition are projected to continue to decrease stream sulfate and nitrate concentrations and increase ANC, but recovery of soil percent base saturation will be delayed.  Model simulations also examine effects of DOM mobility and changing climate on recovery of soil and surface waters.

 

1Syracuse University, ctdrisco@syr.edu
2Syracuse University, sshao@syr.edu
3Syracuse University, hfakhrae@syr.edu
4U.S. Geological Survey, glawrenc@usgs.gov
5U.S. Geological Survey, daburns@usgs.gov