AN ANALYSIS OF SOLUTE ACCUMULATION DURING STEADY-STATE EVAPORATION IN AN INITIALLY CONTAMINATED SOIL

The convective dispersion equation is often used as a functional description of solute transport in soils. In this paper the problem of salt or chemical accumulation near the soil surface under the conditions of an upward evaporative flux is solved analytically for both a constant water content and a depth-dependent water content that is invariant with time. The depth-dependent water content profile is obtained by use of the Gardner solution for steady-state evaporation from a shallow water table. It is shown that under the conditions encountered in the Valais Canton, Switzerland, the concentration profile that develops with time under steady-state evaporative conditions from a shallow water table can be obtained with sufficient accuracy for field conditions using a constant water content. The concentration profile which develops with time depends upon both the upward evaporative flux of water, which concentrates solutes at the surface, and the diffusive-dispersive flux, which tends to move solutes downward against the upward flux of water. Examples illustrate the influence of velocity and dispersion effects on the solute profiles.