Analytical approximations for nonlinear adsorbing solute transport in layered soils

Abstract

We consider reactive solute transport in a soil consisting of two layers that have different (bio)chemical properties. Assuming adsorption is adequately described with the Freunlich equation, the degree of adsorption nonlinearity differs. Using simple corrections the fronts are approximated analytically for the case that the top layer adsorbs nonlinearly whereas the subsoil layer adsorbs linearly (case 1) and for the case 2 that the layering order is reversed. By comparison with numerical calculations we show the adequacy of the analytical approximations as well as the effect of layering order on the subsoil front shapes. The layering order appears to affect the fronts which is in disagreement with previously published conclusions by H.M. Selim and coworkers. For the case of a layered soil with nonlinear adsorption and first-order decay, analytical approximations appear to describe the numerically found fronts well.