Solute transport and chemical processes: The present state of the unsaturated zone component of the SHE modelling system

A numerical model for solute transport in the unsaturated zone has been developed. The model is based on the basic equation for soil water flow in one dimension and the general convection-dispersion equation. These equations are solved by numerical techniques and coupled under the assumption that the flow equation can be solved independently. Options for solute-soil reactions are included in the model comprising immobile water, adsorption, ion exchange, decay, complexation, precipitation, ionic strength effects on species activity and carbonate system governed pH. The model can simultaneously account for five anions and four cations. Furthermore, the plant uptake of anions and cations are considered.