An algorithm of successive approximation used to calculate Ca2+concentration and pH in soil solutions at arid areas

摘要

In modeling the processes of CaCO3 dissolution and deposition in soils, Ca2+ concentration and pH in soil solution must be calculated based on the principles of thermodynamic equilibrium. However, it is difficult to calculate them directly because some parameters (e.g. ionic activity coefficients in soil solutions) are unavailable, which leads to the use of computer simulations to model these processes. An algorithm of successive approximation is presented in this paper to address this problem. With esimtaes of CO2 partial pressures in soil air and temperature, the algorithm enables computation of Ca2+ concentrations and pH in soil solutions of arid areas, resulting in a significant advancement of computer simulations of soil CaCO3 eluviation. This method has been applied and verified using CAEDP model (A model for CaCO3 eluviation in arid area soils). The results show that our method based on theory is accurate, robust, and simple.