MODELING LONG-TERM ACIDIFICATION TRENDS OF FORESTED SANDSTONE CATCHMENTS IN THE BLACK-FOREST (SW GERMANY)

An extensive database from eight Triassic (Bunter) sandstone catchment s in the Black Forest, SW Germany, was used to apply the MAGIC model a nd simulate long-term acidification trends Using the ion ratio (Ca+Mg) /(SO4+NO3) as criterium (values < 1.5 indicate an acidified state), hi ndcast simulations showed that the brooks of three catchments have rea ched values <1.5, three catchments are approaching 1.5, and two catchm ents (carbonate bearing upper Bunter) are still well above this limit The different acidification state of the catchments is mainly caused b y the amount of acidic deposition and bedrock geology. Other differenc es (shallow or deep groundwater circulation, sulphate sorption and soi l parameters) are less significant. To simulate the future evolution, three scenarios were tested: a pessimistic, an optimistic and a most p robable case. The latter leads to a still progressing but decelerated acidifcation in the next 100 years. In the pessimistic case, acidifica tion rates will be accelerated in two of the catchments. Even in the o ptimistic case,the initial state, prior to acidification, cannot be re stored up to the year 2130. However,the forecasting of the future evol ution is still markedly hampered by the significant uncertainty in the evaluation of nitrogen-driven acidification, a process which today al ready predominates in parts of the Black Forest.