Regionalization of soil base cation weathering for evaluating stream water acidification in the Appalachian Mountains, USA.

Estimation of base cation supply from mineral weathering (BC(w)) is useful for watershed research and management. Existing regional approaches for estimating BC(w) require generalized assumptions and availability of stream chemistry data. We developed an approach for estimating BC(w) using regionally specific empirical relationships. The dynamic model MAGIC was used to calibrate BC(w) in 92 watersheds distributed across three ecoregions. Empirical relationships between MAGIC-simulated BC(w) and watershed characteristics were developed to provide the basis for regionalization of BC(w) throughout the entire study region. BC(w) estimates extracted from MAGIC calibrations compared reasonably well with BC(w) estimated by regression based on landscape characteristics. Approximately one-third of the study region was predicted to exhibit BC(w) rates less than 100 meq/m(2)/yr. Estimates were especially low for some locations within national park and wilderness areas. The regional BC(w) results are discussed in the context of critical loads (CLs) of acidic deposition for aquatic ecosystem protection.