EXPERIMENTAL STUDIES AND MODELING OF ENHANCED ACIDIFICATION AND RECOVERY

During the last three decades the experimental manipulations of whole ecosystems have been shown to be a useful and widely used tool for inv estigation of the effects of air pollution, air pollution reduction st rategies and management practices on the health and productivity of fo rests and the acidification of catchments and fresh waters. Generally the aims have been to investigate the impact of a continued or increas ed load of air pollutants on the ecosystems, and the possibilities of reversing the acidifying effects by soil amelioration, addition of buf fer acting substances or by removal of the air pollutants. Along with the field experiments, models have been developed to predict future ef fects and dynamics in the ecosystems under different air pollution sce narios. The present paper gives an overview of experimental field mani pulation studies and examples of results obtained with the acidificati on model MAGIC. All the acidification recovery studies performed so fa r have shown that a reduced input of S to the ecosystem immediately fr om the first year resulted in reduced output, although the expected pa rallel reduction in output of Al and H+ did not occur until some years later, or not at all. The MAGIC model generally predicts the results of both acidification and timing field experiments very well, apart fr om minor discrepancies in year-to-year variability around the observed trends. Several experimental studies have confirmed that reduced inpu t of acidity or increased input of base cations caused no or only slig ht changes in the pH in the soil. The buffer processes of the soil may cause the effects to be restricted to the very top soil layer, unless the manipulations were very strong. It is concluded that experimental field studies have increased our understanding of the complexity of t he ecosystem and highlighted the need for studies integrating field an d laboratory work.