Transport of Reacting Solutes Through the Unsaturated Zone

Unsaturated flows within subsurface regions control many large-scale hydrological and environmental processes. This contribution presents and discusses the results of numerical calculations dealing with the flow of water, the chemical reaction at the water-mineral interface and the transport of chemical species caused by such flows. The source of the water flow through the soil is solely the rainfall. The water motion is calculated for two different soil classes and for a typical annual precipitation. The codes which were used are based on the following model: The transport of chemical species is described by a set of partial differential equations, and the homogeneous chemical processes, under the assumption of equilibrium, are described by a set of nonlinear algebraic equations. The source terms of these partial differential equations are given by rate laws of the chemical weathering. Rainfall and chemical weathering are therefore the sources of the transport of reactive multispecies in this model.