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STREAMWATER ACID-BASED CHEMISTRY AND CRITICAL LOADS OF ATMOSPHERIC SULFUR DEPOSITION IN SHENANDOAH NATIONAL PARK, VIRGINIA
Citation:
SULLIVAN, T. J., B. COSBY, J. R. WEBB, R. L. DENNIS, A. J. BULGER, AND F. A. DEVINEY, JR. STREAMWATER ACID-BASED CHEMISTRY AND CRITICAL LOADS OF ATMOSPHERIC SULFUR DEPOSITION IN SHENANDOAH NATIONAL PARK, VIRGINIA. ENVIRONMENTAL MONITORING AND ASSESSMENT. Springer, New York, NY, 137(1-3):85-99, (2008).
Impact/Purpose:
The National Exposure Research Laboratory's (NERL's) Atmospheric Modeling Division (AMD) conducts research in support of EPA’s mission to protect human health and the environment. AMD's research program is engaged in developing and evaluating predictive atmospheric models on all spatial and temporal scales for forecasting the Nation's air quality and for assessing changes in air quality and air pollutant exposures, as affected by changes in ecosystem management and regulatory decisions. AMD is responsible for providing a sound scientific and technical basis for regulatory policies based on air quality models to improve ambient air quality. The models developed by AMD are being used by EPA, NOAA, and the air pollution community in understanding and forecasting not only the magnitude of the air pollution problem, but also in developing emission control policies and regulations for air quality improvements.
Description:
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 <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.