SULFATE SORPTION IN SOILS UNDER ACID DEPOSITION - MODELING FIELD DATA FROM FOREST LIMING

Sulfate sorption can modify the reaction of a soil to acid depositions. Different models of this process exist. In a preceeding paper the adsorption isotherm and the solubility product modeling approach have been compared and a solubility product model has been introduced. The latter model is tested using a forest liming experiment. Concentration data from canopy drip and seepage covering a 20-yr observation period are used as 3-yr moving averages. The model assumes a steady seepage flow and uses only one 1-m compartment. The model considers joint chemical equilibria for gibbsite, jurbanite, cation exchange, and complexation. The seepage pH and concentrations of Al and sulfate under the unlimed reference plot can be modeled if a reduced CEC and a free parameter function for alkalinity production are used. The sulfate desorption caused by liming can be explained by the model. It is concluded that sorbed sulfate contributes to the lime requirement of an acidified soil.