Regional Acidification Model for Forest Soils

Regional model calculations of forest soil acidification in Finland for different future energy use and emission reduction input scenarios are compared. The calculations have been made with the Finnish Acidification Assessment Model (HAKOMA) consisting of modules for emissions, emission abatement costs, atmospheric dispersion, transformation and deposition, and impacts on forest soils and lakes. The impact modules include time-dependent simulations of forest soil and lake acidification processes which consider the dynamic nature of ecosystems. The existing buffering capacity and its depletion are assumed to have ecological impacts. In forest soil acidification the depletion of the nutrient cation inventory in soil by acid deposition and through tree harvesting is considered. Cations are supplied by atmospheric deposition, estimated by measurements, and mineral weathering. The distribution of soil types is estimated on the basis of the national forest inventory. The cation contents for each soil class are derived from measurement programmes.

The results of the pilot studies show the most critical areas regarding acidification to be in the areas of high deposition in southwestern and southeastern Finland. To minimize the acidification, considerable emission reductions seem to be necessary both in Finland and in the areas of high emissions in the neighbouring countries. The results were also relatively sensitive to the parameter values in the soil model.