Short-term reestablishment of soil water repellency after wetting: Effect on capillary pressure-saturation relationship

Soil water repellency is known to be a dynamic property, which varies in the short term or between seasons. In the short term, its temporal nature is often studied based on soil water content, assuming that it is reestablished after the sod dries out. In this study, we examined the reestablishment of soil water repellency after wetting and subsequent drying. The reestablishment process was studied on: (i) natural water-repellent soils (WRS) subjected to different leaching rates; and (ii) wettable sand subjected to wetting-drying cycles with dissolved organic matter (DOM) solution. After air drying, the sods were packed in columns, rewetted, and from the maximum height of capillary rise for the target sod (H-eq1) and that of a "reference sod" (H-eq0) the equilibrium (static) contact angle (omega(eq1)) was calculated, assuming that for the reference sod e contact angle omega(eq0) = 0. Increasing the leaching fraction of an initially WRS resulted in a decrease in omega(eq1) values. For an initially wettable soil, increasing wetting-drying cycles with DOM solutions resulteqd in an increase in omega(eq1). The variations in cos omega(eq1) were reflected in a similar ratio for the capillary-pressure-saturation relations (CSR). The prediction from scaling the "reference soil" CSR curve by cos omega(eq1) was found to be satisfactory, but more accurate where the effective saturation S < 0.5. At S > 0.5, organic matter is more likely to detach and dissolve, changing the properties of the soil solution by altering its surface tension and the sod particles' surface, i.e., omega(eq1).