Streamwater acid-base chemistry and critical loads of atmospheric sulfur deposition in Shenandoah National Park, Virginia |
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Authors: | T J Sullivan B J Cosby J R Webb R L Dennis A J Bulger F A Deviney Jr |
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Institution: | (1) E&S Environmental Chemistry, Inc., P.O. Box 609, Corvallis, OR 97339, USA;(2) Department of Environmental Sciences, University of Virginia, Charlottesville, VA, USA;(3) Air Resources Laboratory, National Oceanic and Atmospheric Administration, Research Triangle Park, NC, USA |
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Abstract: | A modeling study was conducted to evaluate the acid-base chemistry of streams within Shenandoah National Park, Virginia and
to project future responses to sulfur (S) and nitrogen (N) atmospheric emissions controls. Many of the major stream systems
in the park have acid neutralizing capacity (ANC) less than 20 μeq/L, levels at which chronic and/or episodic adverse impacts
on native brook trout are possible. Model hindcasts suggested that none of these streams had ANC less than 50 μeq/L in 1900.
Model projections, based on atmospheric emissions controls representative of laws already enacted as of 2003, suggested that
the ANC of those streams simulated to have experienced the largest historical decreases in ANC will increase in the future.
The levels of S deposition that were simulated to cause streamwater ANC to increase or decrease to three specified critical
levels (0, 20, and 50 μeq/L) ranged from less than zero (ANC level not attainable) to several hundred kg/ha/year, depending
on the selected site and its inherent acid-sensitivity, selected ANC endpoint criterion, and evaluation year for which the
critical load was calculated. Several of the modeled streams situated on siliciclastic geology exhibited critical loads <0 kg/ha/year
to achieve ANC >50 μeq/L in the year 2040, probably due at least in part to base cation losses from watershed soil. The median
modeled siliciclastic stream had a calculated critical load to achieve ANC >50 μeq/L in 2100 that was about 3 kg/ha/year,
or 77% lower than deposition in 1990, representing the time of model calibration. |
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Keywords: | Acidification Critical load Sulfur Stream chemistry Modeling |
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