COMPARISON OF MEASURED AND SIMULATED CHANGES IN BASE CATION AMOUNTS USING A ONE-LAYER AND A MULTILAYER SOIL ACIDIFICATION MODEL

Biogeochemical processes describing nutrient cycling strongly affect t he development of different soil horizons and soil acidification. Howe ver, in many soil acidification models these processes are not directl y simulated, and spatially distributed soil properties are lumped into average values. This paper describes the extension of a one-layer soi l acidification model (SMART) to a multi-layer model (SMARTEX) by incl uding nutrient cycling, and the performance of both models regarding t heir ability for the assessment of the effects of acid deposition on f orest soil. This was done by comparing simulation results of the two m odels with respect to changes in base cation amounts to historical dat a from sites in south Sweden. The results showed that the multi-layer model gives better results for the top soil, whereas the one-layer mod el gives better results for the rootzone and the total profile. Since the top soil is most important, the extended model is more suited to r elate acid deposition to forest growth than the more general results o f the one-layer model. However, the sensitivity of the multi-layer mod el to some parameters is large. A change in these parameters had stron g effects on the separate layers, whereas the effects were cancelled o ut over the total profile. This sensitivity requires a careful paramet erization of the model which might be troublesome to lack of data.