Chloride transport in undisturbed soil columns of the loess Plateau

Abstract

In soils containing preferential flow paths, both water and solute can move preferentially, bypassing much of the soil matrix. The object of this study was to examine the effect of preferential solute transport in Changwu (loamy soil) soil and Ansai soil (sandy soil) containing macroporosity. Miscible displacement experiments were conducted with 5 undisturbed soil columns (19.45 cm diameter, 43.5 cm long). Breakthrough curves (BTC’s) of Chloride were measured under water-saturated steady flow conditions. The data were simulated using three conceptual models. The results show that two-flow region model described the preferential solute transport much better than the two-region model and the convection dispersion equation (CDE), especially there were humps in the tailing side. Moreover, distinct double peaks were apparent with the increase of pore water velocity in a loamy soil column. In addition, high pore water velocity and small mass transfer coefficient between the two-flow regions enhanced the development of double BTC peaks. Key words: Breakthrough curves, convection dispersion equation, two-region model, two-flow region model.