Describing soil SO42- dynamics in the Solling roof project with 4 two different modelling approaches

The release of previously stored soil SO42- is tightly connected with the reversibility of soil and water acidification. Thus soil SO42- dynamics have to be included when predicting the reversibility acidification. Our aim was to compare two modelling approaches: The model MAGIC (Cosby ct at, 1985) describes SO42- dynamics with the Langmuir sorption isotherme. In the SO-MODEL (Prenzel, 1991) a precipitation/dissolution of jurbanite is defined. Even though it was possible to calibrate both models to lysimeter data of the Selling D1 site in 1 m depth, the prognosis for SO42- concentrations in the soil solution differed significantly. While MAGIC predicted the observed gradual decrease of SO42- concentration with decreasing deposition, the SO-MODEL calculated stable concentrations up to the year 2026 followed by a sudden drop. Because the prognosis established with the SO-MODEL is incompatible with observed field data, we concluded that the predicted SO42- dynamic of the SO-MODEL was unrealistic.