Chapter 10: Movement of Solutes in Soil: Computer-Simulated and Laboratory Results

Abstract

Mechanisms that determine the rate at which chemicals move through soils include processes such as diffusion/dispersion, adsorption, decay, and intra-aggregate diffusion. Exact analytical solutions can be derived for some of these processes, such as for linear adsorption and linear decay. However, for nonlinear cases, analytical methods cannot be used to obtain the exact solutions of the transport equations, and approximate methods must be employed. The use of numerical techniques helps in modeling the transport of solutes in such cases. Numerical and analytical approaches can and should complement and augment each other. For example, an analytical solution may be used to check the accuracy of a numerical program. On the other hand, a numerical solution may be used to demonstrate the appropriateness (or shortcoming) of a particular assumption necessary in the development of an analytical solution. This chapter discusses some of the transport equations currently used to describe the movement of chemicals in soils and presents solutions based on both numerical and analytical techniques. The chapter discusses the influences of several mechanisms affecting solute transport phenomena, such as nonlinear adsorption, hysteresis in the equilibrium isotherms, and decay.