A Soil-Water Repellency Model That Integrates Easily Measurable Soil Physical Parameters.

Soil-water repellency (SWR) is a significant soil phenomenon occurring at the top soil layers affecting the infiltration of water into the subsurface. SWR reduces the infiltration of water onto dry soil but has almost no impact on water infiltration on wet soil. Predicting the SWR behavior across a range of soil moisture conditions and landscapes has many advantages: i) it can be integrated in hydrologic models to estimate the risk of runoff and thus risk of soil erosion and flooding, ii) it can be utilized to improve land management and planning especially when designing green areas and forests, and iii) it provides a tool for remediating SWR soils by clay amendments or surfactants. In this study, soil-water repellency was measured using the Molarity of Ethanol Droplet (MED) method across moisture conditions from air dry to wet conditions on 23 soil samples from 8 transects obtained from a sub hydrological catchment area (Aarup, Jutland, Denmark). A Beta function model was fitted to measured data (SWR vs water content) with the maximum surface tension, the water content at maximum surface tension, and soil water content when SWR is diminished as fitting parameters, in addition to the measured water content and surface tension at air-dry condition. Regression analyses were used to relate the obtained SWR parameters with the easily measurable clay and organic carbon (OC) fractions. The organic carbon OC or the non-complexed OC with clay (or the ratio between the OC/clay) are the main predictors for SWR since the OC overlying varies in vegetations. The predictive model is validated against the data from the same catchment area but at a deeper profile and against data from another transect. The resulting predictive SWR model describes the measurements reasonably well. Furthermore, an attempt is made to fit the model to the wetting and drying loops of the SWR curves in order to explore the model ability to simulate hysteresis behavior.