MODELING THE CONCENTRATION OF ALUMINUM IN SURFACE WATERS

Although the increased mobilization of aluminum from soils to surface waters is widely recognized as one of the most important ecological ef fects of acidic deposition, lumped-parameter mathematical models of ac idification response typically overestimate the change in Al concentra tion under changing deposition by a considerable margin. The assumptio n of equilibrium with gibbsite (Al(OH)(3)) in the MAGIC model and othe r models of acid-base chemistry is shown to be inconsistent with measu red values for a large variety of lake and stream databases. A modifie d algorithm for predicting Al concentration, based on empirical relati onships evident in field data: provided superior estimates of changes in Al concentration in three long-term monitoring data sets and under experimental conditions at two experimental watershed manipulation sit es.