Diffusion of Sorbed Solutes in Gas and Liquid Phases of Low‐Moisture Soils

Abstract Organic solute diffusion through the soil matrix is strongly affected by the moisture content of the soil. The solute diffusion coefficient in the commonly used one‐dimensional diffusion model, in which local equilibrium is assumed, is modified to include a semiempirical model for solute adsorption. The proposed approach accounts for the experimentally observed rise in the solute diffusion coefficient with moisture content, at low moisture content levels, and the decrease in the diffusion coefficient with increasing moisture above a critical moisture level. Finally, three tortuosity models are explored to examine their influence on the solute diffusion‐coefficient model over the entire range of possible soil moisture levels.