How to relevantly characterize hydraulic properties of saline and sodic soils for water and solute transport simulations

Abstract

Proper sets of soil hydraulic parameters are important for modeling water flow and solute transport. Using field saline water and laboratory tap water, this study systematically analyzed and compared laboratory saturated hydraulic conductivity, Kls and soil water retention curve, SWRC of saline soil within three soil multi-layered profiles to find out the adequate initial hydraulic parameter set of a hydrological model. Falling and constant head methods were applied on three undisturbed samples per pedogenic horizon. SWRC were established on the same samples, using both saline and tap water. Results showed the spatial variability of hydraulic properties in vertical and horizontal dimensions when comparing soil profiles' properties. The constant head method with saline water resulted in the highest Kls values followed by the falling head method with saline water, the constant head method with fresh water, and the falling head method with fresh water. The differences in Kls were up to two orders of magnitude when comparing all datasets. Fresh water reduced soil water retention significantly. A significant correlation between the hydraulic properties and some physical and chemical properties suggests that the effects of soil texture, structure, calcium carbonate and gypsum content, and CEC (clay mineralogy) were larger than those of salt content. The change in hydraulic properties and the dependency on the procedure use may be attributed to aggregate breakdown and plugging of macropores, clay heterogeneity and dispersion, calcium carbonate and gypsum dissolution, all damaging soil structure. Simulation runs illustrated that hydraulic properties obtained with saline water resulted in better model performance than when using the conventional procedures with fresh/tap water. A proper set of initial hydraulic parameter values is an important step in model calibration and thus must be characterized correctly. Therefore, to hydraulically characterize saline soil, procedures should be standardized. Moreover, the approach and results of this study may provide a reference for characterization of soil hydraulic properties of saline and sodic soils effectively.