APPLICATION OF THE SAFE MODEL TO THE SOLLING SPRUCE SITE

A dynamic geochemical simulation model, SAFE, was applied to a Norway Spruce stand in Selling, Germany. The model performance was evaluated with respect to base saturation, base cation (Ca + Mg + K) and aluminu m concentration in soil solution, weathering rate, and soil solution p H. Four acid deposition scenarios were evaluated with respect to base saturation and molar ratio of aluminum to base cations in soil solutio n. Base cation and aluminum concentrations were in agreement with data , while pH was slightly underestimated. The predicted weathering rate of base cations was close to rates estimated from budget studies and s tudies of depletion of minerals in the soil column. Release of K was o verestimated, possibly because congruent dissolution of illite rich in Mg and K was assumed. The scenario analysis shows that continued acid deposition stress at the 1990 level will cause no further depletion o f the soil exchange complex, while 95% reductions in acid deposition w ould lead to an increase in base saturation from 3% to 10% during the period 1990 to 2050. In this case, the BC to Al ratio would exceed one at all depths of the soil profile by the year 2012. A scenario based on emission reductions as agreed upon by a number of European countrie s in the UN-ECE Convention on Transboundary Air Pollution and in natio nal abatement plans would lead to minor improvements in base saturatio n and BC to Al molar ratio, but the BC to Al ratio would stabilize at a value as low as 0.3.