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nalysis of Critical Loads and Exceedance with Respect to Projected 2018 Sulfur and Nitrogen Deposition in the Northeastern US

Eric K. Miller1, Paul Miller2 and John Graham2

Determination of pollutant critical loads provides an ecosystem-based reference point for assessment of the magnitude of future deposition reduction goals and a target against which progress in deposition reductions can be evaluated. Considerable prior research and analysis has been conducted in the area of atmospheric deposition, ecosystem impacts, and critical loads of major pollutants in the Northeastern US. Despite extensive prior research, resource managers and policy makers have not yet had the benefit of integrated assessments of aquatic and terrestrial critical loads.

We have identified and mapped specific forested and aquatic ecosystems most sensitive to continued S and N deposition in New York and New England under the anticipated atmospheric conditions in 2018 at full implementation of current state and federal emission control programs. Steady-state terrestrial critical loads were developed using the previously established NEG/ECP regional assessment protocols. Steady-state aquatic critical loads were developed for subset of well-characterized northeastern surface waters using a modified form of the SSWC model employing an empirical correction DOC. Critical loads for all remaining surface waters were estimated using transfer functions developed between the well-characterized subset and watershed parameters developed via the terrestrial critical loads modeling.

Our analysis of critical load exceedance used Community Multiscale Air-Quality Model (CMAQ) results generated by NESCAUM as part of a recent Mid-Atlantic/Northeast Visibility Union (MANE-VU) modeling exercise. Air and precipitation concentration changes derived from the CMAQ results on a 12-km grid were be used in conjunction with Ecosystems Research Group, Ltd.ís High-Resolution Deposition Model (30-meter grid) to estimate deposition on a scale appropriate for critical loads assessment in the complex terrain of the Northeastern United States.

1 Ecoystems Research Group, Ltd
2 NESCAUM