Reconstruction of water acidification in a forested catchment, western Harz Mountains, Germany

Abstract

A dynamic model based on the precipitation of aluminium hydroxosulf ate minerals was used to reconstruct a hypothetical history of catchment acidification. The effects of 140 a of increased atmospheric S deposition into the Lange Bramke valley, western Harz Mountains, was simulated. The model includes the following processes: complexation of several hydroxo- and sulfato-compounds ; ion exchange based on selectivity constants for all uncomplexed cations; carbonic acid equilibria reactions system assuming a given partial pressure of CO 2 ; and the precipitation/dissolution equilibria for gibbsite (Al(OH) 3 ), alunite (KAl 3 (OH) 6 (SO 4 ) 2 ) and jurbanite (AlOHSO 4 ). The adequacy of the model was demonstrated by applying it to 4 a of deposition, soil water and streamwater chemistry data from the Lange Bramke area. The model indicated that the measured S retention in the catchment can be explained by precipitation of alunite and jurbanite.