Prediction of soil chemistry changes due to acidic deposition with a dynamic model - model description and application to soil acidification experiments

摘要

A dynamic model that mainly includes chemical reactions taking place in the soil was developed to simulate the soil acidification triggered by acidic deposition. The model was applied to soil acidification experiments in order to confirm the applicability of the model and to evaluate the contributions of each buffering mechanism. In the experiment, pH-adjusted sulfuric acid was added to twelve soil samples for four years. In case of the simulated acid rain with pH3, the estimated temporal change ofsoil chemistry corresponded well with the measurements except for exchangeable aluminium. Selectivity coefficients of cation exchange showed a clear positive correlation with the soil pH for each soil sample, and change in exchangeable aluminium could be predicted by expressing selectivity coefficients as a function of soil pH. According to the results of the model estimation, the main buffering mechanisms were Al hydroxide dissolution and/or release of exchangeable base cations, and acid was neutralized mainly in the surface soil layer (10 cm) by these processes. For the acid rain with pH4, decreased rates of exchangeable base cation were sometimes less than the observed ones. This disagreement was considered to be caused by the uncertainty of the data on mineral weathering and nitrification rates.