Fig. 3. The SO^2-₄ adsorption isotherms (upper graph) and relationships between SO^2-₄ and H⁺ adsorption (lower graph) of the fourth layer soil at Solling, calculated by the Extended Constant Capacitance Model (ECCM) for a liquid phase SO^2-₄ concentration range of 0.1 to 3.0 mmol L^-1