Abstract
Understanding the solute effect on soil water dynamics during soil freezing is important for managing soil water and nutrients and for controlling groundwater pollution. In this study, we performed a column experiment, using variably saturated sand with NaCl solution, to estimate the solute effect on soil water flow and hydraulic properties. The sand column (i.d.: 78mm; length: 350mm), which was instrumented with seven thermocouples and seven time domain reflectometry probes, was cooled from the top to form a frozen layer.We monitored temperature, liquid water content, and solute concentration.Water flow from the unsaturated region to the frozen region and solute accumulation in the frozen region due to convection were observed. When the soil contained solutes, the frost reached deeper and frost-induced water flow decreased. Applying a capillary bundle model to the column experiment showed that pore-ice formation resulted in a decrease in the hydraulic conductivity of the frozen sand. The frozen sand showed the same relationship between unfrozen water content and hydraulic conductivity irrespective of the soil solute concentration, but the relationship between temperature and unfrozen water content varied depending on the solute concentration.
