Application of the safe model to the Solling spruce site

Abstract

A dynamic geochemical simulation model, safe, was applied to a Norway Spruce stand in Solling, Germany. The model performance was evaluated with respect to base saturation, base cation (Ca + Mg + K) and aluminum concentration in soil solution, weathering rate, and soil solution pH. Four acid deposition scenarios were evaluated with respect to base saturation and molar ratio of aluminum to base cations in soil solution. 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 studies of depletion of minerals in the soil column. Release of K was overestimated, 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 of the soil exchange complex, while 95% reductions in acid deposition would 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 countries in the UN-ECE Convention on Transboundary Air Pollution and in national abatement plans would lead to minor improvements in base saturation and BC to Al molar ratio, but the BC to Al ratio would stabilize at a value as low as 0.3.