An important tool in the evaluation of acidification damage to aquatic and terrestrial ecosystems is the critical load, which can be defined as the level of acidic deposition below which ecological damage would not be expected to occur. The critical load for protection of aquatic biota is generally based on maintaining surface water ANC at an acceptable level. This E&S study included calibration and application of the watershed model, MAGIC, to estimate the sensitivity of 66 watersheds in the Blue Ridge Province to changes in atmospheric S deposition. The principal objectives of this research report were to:
In general, the model projected that soil and stream chemistry have changed substantially since pre-industrial times, but that future changes in response to emissions controls will be small. Simulation results suggested that modeled watersheds would not change to a large degree with respect to stream ANC or soil % base saturation, depending on the extent to which emissions are reduced in response to three emissions control scenarios (Base Case, Moderate, and Aggressive Additional Controls).
In order to aid in the process of extrapolating MAGIC model critical loads simulation results to watersheds within the study area that were not modeled, we developed a suite of multiple regression equations to estimate critical loads from variables that are more widely available across the region than are the MAGIC model results. Separate multiple regression prediction efforts were conducted to estimate critical load from 1) landscape variables represented spatially in the GIS, 2) a combination of landscape variables and stream chemistry variables, and 3) streamwater chemistry only. Based on these relationships, critical loads were estimated for the broader region. Project completion date was October 2007.