Evaluation of moisture flux from chloride data in desert soils

Scanlon, B.R., 1991. Evaluation of moisture flux from chloride data in desert soils. J. Hydrol., 128: 137-156. Chloride-concentration data from 10 soil profiles in a 40 km2 area of the Chihuahuan Desert of Texas were used to assess chloride mass balance methods of evaluating moisture flux. The relative importance of advective and diffusive transport mechanisms was determined. Moisture fluxes were calculated from measured chloride concentrations on the basis of a steady-state flow model. To evaluate controls on unsaturated flow, moisture fluxes from this study were compared with those from other regions. The chloride profiles displayed large variations in concentrations and had (a) low chloride concentrations ( ≤ 100 g m–3) near land surface, (b) maximum chloride concentrations (1,900 to 9,300 g m–3) at depths of 1.3 to 4.6 m, and (c) gradually decreasing chloride concentrations with depth below the peak. Steep concentration gradients (up to 12,000 g m–3 m–1), characteristic of chloride profiles in these desert soils, indicate a potential for molecular diffusion; however, low moisture contents ( ≤ 0.1) in the zone of steep concentration gradients resulted in diffusive fluxes that were 2 to 3 orders of magnitude lower than the advective fluxes; therefore, diffusive fluxe