Sensitivity Analysis of a Regional Scale Soil Acidification Model

Posch, M. ORCID: https://orcid.org/0000-0001-8649-9129, Kauppi, L., & Kaemaeri, J. (1985). Sensitivity Analysis of a Regional Scale Soil Acidification Model. IIASA Collaborative Paper. IIASA, Laxenburg, Austria: CP-85-045

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Abstract

A dynamic model has been introduced for describing the acidification of forest soils. In one-year time steps the model calculates the soil pH as a function of the acid stress and the buffer mechanisms of the soil. Acid stress is defined as the hydrogen ion input into the top soil. The buffer mechanisms counteract acidification by providing a sink for hydrogen ions. The concepts buffer rate and buffer capacity are used to quantify the buffer mechanisms. The model compares (i) the rate of acid stress (annual amount) to the buffer rate, and (ii) the accumulated acid stress (over several years) to the buffer capacity. These two types of comparisons produce an estimate of the soil pH.

The model has been incorporated into the RAINS model system of the International Institute for Applied Systems Analysis for analyzing the acidic deposition problem in Europe. The data on acid stress, entering the soils, is obtained from the other submodels. Data on buffer rate and buffer capacity has been collected from soil maps and geological maps.

The sensitivity of the model to the forcing functions, parameter values and initialization of the soil variables is evaluated in this paper. The model's sensitivity to initial base saturation appears to be crucial. Base saturation varies widely in forest soils, while the variation of, e.g., total cation exchange capacity is normally not more than +/-50% of the average. Whenever possible, recent measurements about the status of the soil should be used.

The difference of acid stress and the buffer rate of silicates determines whether the soil alkalinizes or acidifies. The sensitivity of the model to that difference varies in time and space, being highest in areas where the deposition rate nearly equals the silicate buffer rate, e.g. at present in Scandinavia.

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