Regional model projections of future effects of sulfur and nitrogen deposition on streams in the southern Appalachian Mountains

We constructed a model‐based evaluation of current and future effects of atmospheric S and N deposition on aquatic resources in the eight‐state southern Appalachian Mountains region. Modeling was conducted with the MAGIC model for about 40 to 50 sites within each of three physiographic provinces, stratified by stream water acid neutralizing capacity (ANC) class. Simulations were based on assumed constant future atmospheric deposition at 1995 levels and on three regional strategies of emissions controls provided by the Southern Appalachian Mountains Initiative (SAMI), based on the Urban to Regional Multiscale One‐Atmosphere model. The National Stream Survey statistical frame was used to estimate the number and percentage of stream reaches in the region that were projected to change their chemistry in response to the emissions control strategies. There was a small decline in the estimated length of projected acidic (ANC ≤ 0) streams in 2040 from the least to the most restrictive emissions control strategy, but there was little difference in projected stream length in the other ANC classes as a consequence of adopting one or another strategy. However, projections of continued future acidification were substantially larger under a scenario in which S and N deposition were held constant into the future at 1995 levels. Model results suggested that the percent of potentially acid‐sensitive streams having chemistry that is chronically unsuitable for brook trout would increase slightly between 1995 and 2040 under all except the most restrictive emissions control strategy.