Response of six European forest sites to decided and proposed air pollutant emission reductions
Two acid deposition scenarios were simulated for six European forest sites situated in Germany, Denmark, Russia, Switzerland, Spain and Ireland. Three models were used in combination; the RAINS (Regional Acidification INformations and Simulation) model, the SAFE (Simulating Acidification in Forest Ecosystems) model and the MakeDep model. The scenarios used were based on results from international negotiations (the Oslo and Sofia protocols) and on calculations of what could be achieved using the best available technology at a reasonable cost. The parameters chosen for studying the course of acidification were base saturation, BC:Al molar ratio in soil solution and pH. Furthermore, the sites were compared with respect to deposition regimes as well as ion exchange and weathering rates, nutrient uptake and nutrient cycling. The results show, that all sites have undergone acidification. Three of the sites show BC:Al molar ratios below or very close to the threshold value of 1. Currently accepted reductions in S and N emissions will lead to a halt in acidification in all cases and a partial regeneration of the soil buffer capacity in some cases. Introducing maximum feasible reductions would improve soil conditions remarkably at all six sites. The differences in degree and course of acidification can be derived from differences in weathering rate and soil buffer capacity as well as from the deposition regimes. Detailed information on future anthropogenic base cation deposition is shown to be less important for the outcome of the scenarios than expected.