Modelling the effects of acid precipitation on soil leachates: A simple approach

A model is proposed to provide a simple, yet quantitatively valid perspective for the extent of soil (and lake) acidification to be expected for chemically and biologically active soils under the threat of acid precipitation. The model attempts to predict the acid (H⁺ + Al³⁺ + Fe³⁺) and base (Na⁺ + K⁺ + Mg²⁺ + Ca²⁺) cation losses from the soil, calculated from the rate and amount of acid cation retention when the rate of acid cation input is constant. It is assumed that the total amount of acidity retained by the soil is limited and qualitatively follows a Freundlich-type “absorption” isotherm. Required input information for the model includes (i) the total amounts of acid and base cations received by the soil via precipitation and weathering (minus normal leaching losses), (ii) the exchangeable base cation content and total number of cation exchange sites of the soil prior to the onset of acid precipitation.