Developing Critical Loads of Acidity for Stream Ecosystems in the Adirondack Region of New York State

Shuai Shao1, Charles T. Driscoll2, Douglas A. Burns3, Gregory B. Lawrence4 and Timothy J. Sullivan5

The Adirondack region of New York has high inputs of acidic deposition and many acidic streams. The PnET-BGC is an integrated biogeochemical model formulated to simulate the response of soil and surface waters in northern forest ecosystems to changes in atmospheric deposition. In this is study, the model was applied to twenty-one streams in the Adirondacks to simulate the effects of past and future (1000-2200) changes in atmospheric sulfur (S) and nitrogen (N) deposition on stream water chemistry. The model was calibrated using observed stream water and soil chemistry data. The results indicated model simulated stream water chemistry generally agreed with the measured data at all sites. Model hindcasts indicated that stream water in the Adirondack are inherently sensitive to acidic deposition. The average of model simulated stream ANC is 175 μeq/L (range 48 to 335 μeq/L) before anthropogenic disturbances are applied to the model (1850) and it decreased in response to historical acidic deposition to 59 μeq/L (−37 to 242 μeq/L) in 2015. The model was run under a range of future scenarios from 2016 to 2200 of changes in sulfate, nitrate, and combination of sulfate and nitrate deposition to evaluate how the stream water chemistry might respond to emission control strategies. Future model projections suggested that decreases in sulfate deposition is more effective in increases in stream ANC compared with equivalent decreases in nitrate deposition; nevertheless, the simultaneous controls on nitrate and sulfate deposition are more effective way to restore stream ANC than individual control of nitrate or sulfate deposition. However, only ten of the twenty-one sites will restore the stream ANC to the preindustrial level under the most aggressive deposition reduction scenarios. The model results were used to determine the critical loads of acidity (CLs, the level of atmospheric deposition above which the harmful ecosystem effects occur) for all twenty-one sites.


1Syracuse University,
2Syracuse University,
3U.S. Geological Survey,
4U.S. Geological Survey,
5E&S Environmental Chemistry,