Salt and Water Movement in Unsaturated Frozen Soil

Abstract

Salt and water movement was measured in unsaturated frozen soil columns incubated under a thermal gradient for 3, 6, or 9 weeks. Both water and salt moved from the warmer to cooler areas in the soil, creating a twofold concentration difference over a 24-cm distance. Movement of CaC12, LiI, and K2SO4 was studied in detail Cation exchange reactions and salt solubilities at high concentrations affected the movement. Although the results suggested that mass flow of dissolved salts in a liquid film of water was the principal transfer mechanism, both vapor and salt diffusion were sometimes significant. Thermal diffusion and salt sieving did not appear to be important.Since the vapor pressure of ice controls the water potential in frozen soil, the amount of unfrozen water and matric suction could be calculated from a water release curve and data from ice suspensions in salt solutions. These results led to the conclusion that mass flow in the liquid phase is described by Darcy's law. Thus, salt flow as well as net water transfer can probably be predicted in unsaturated frozen soil using information available from unfrozen systems.Additional Index Words: salinity, salt diffusion, thermal diffusion, salt separation, frost heaving. M OIST UNSATURATED SOIL freezes downward from the surface in the fall and is subject to varied thermal gradients throughout the winter (Benz et al., 1968). As the soil water freezes, small ice crystals form in the pore spaces. Not all of the water freezes under temperatures commonly experienced in the field. A liquid-like film 10 to 40A thick remains at the ice-air interface. Liquid films of varying thicknesses also remain in the soil particleice interfaces and in the soil particle-air interfaces (Anderson, 1970).Since ice crystals freeze out of a solution in a pure state, all soluble salts are forced into the unfrozen water films and may form relatively concentrated brines. The vapor pressure of ice is less than that of pure liquid water. Consequently, water will continue to crystallize from the soil solution until the combined osmotic and matric forces reduce the solution's vapor pressure to that of the ice (Hoeckstra, 1966;Low et al., 1968). Under natural conditions in the field, temperature gradients always exist, and liquid water tends to move from warmer to cooler areas (Fergusen et al., 1964). A spontaneous vapor pressure gradient in this same direction is fixed by the temperature of the ice phase. While some movement is in the vapor phase, most of the flow is in the unfrozen liquid films (Hoeckstra, 1966;Benz et al., 1968 apparent that salt will also move from warmer to cooler areas in the unsaturated frozen soil.Most of the liquid phase movement occurs along the water films adsorbed to the soil particles. While there are liquid films in the ice crystal air interfaces, they comprise a small fraction of the total unfrozen water in unsaturated soil because of the relatively small surface area of the ice crystals compared to that of the soil particles (Anderson, 1970). As the water ...

A new method for calculating frost heave including solute effects

“…The agreement is good, probably fortuitously so in light of the uncertainties in such measurements in both the frozen and unfrozen states. The unfrozen conductivity curve was pub- previously published by Robbins [1977] for the unfrozen soil, while the crosses were calculated from the data of Cary and Mayland [1972] for the frozen soil.…”

“…change per centimeter or difference per time increment. 4, factor to convert temperature to apparent water suction in a freezing soil (approximately -12,000 cm 11 20/'C), i.e., the pressure equivalent to the vapor pressure difference between pure ice and liquid water at any given tempertaure in the range of zero to a few degrees below freezing [Cary and Mayland, 1972].…”

Influence of soil texture on snowmelt infiltration into frozen soils

“…Total infiltration estimated from the numerical simulation was 5.8 mm compared to 6.5 mm measured for the silty clay soil and a simulated infiltration for the sandy loam soil was 15.1 mm while 15.0 mm of infiltration was measured RESULTS FROM NUMERICAL SIMULATION AND DISCUSSIONS In the following sections, the numerical model is used to study the mechanics of infiltration into different-textured frozen soils. Cary andMayland (1972), Miller (1965), Brooks and Cory (1966), Flerchinger and Saxton (1989), 6 Unsaturated liquid hydraulic conductivity Brooks and Corey (1966), Jame andNorum, (1980), Guymon (1981) 7 Capillary pressure Brooks and Corey (1966) 8 Saturations Brooks and Corey (1966), ∂( For personal use only.…”

Is the soil frozen or not? An algorithm using weather records

“…The soil heat flux deficit M may be used to estimate the depth of frost penetration if one also knows the soil water release curve as well as the water content and soluble salt distribution with depth [Cary and Mayland, 1972]. In like manner, if one has this information on the soil properties and is measuring the frost penetration with frost tubes or thermocouples, M can be estimated.…”