MEASUREMENT OF WATER AND SOLUTE DYNAMICS IN FREEZING SOIL COLUMNS WITH TIME-DOMAIN REFLECTOMETRY

Two soil columns (Davos sand, Alptal loam) were subjected to a cycle o f one-dimensional freezing and thawing from both ends towards the midd le of the columns. The freezing characteristic curves were determined at different levels in the columns and used to estimate parameters in a physically based mathematical model. Measurements of liquid soil wat er content with time domain reflectometry (TDR) were influenced by cal ibration restrictions related to the experimental setup. A model devel oped by Van Loon et al. (1991, Transp. Porous Media, 6: 391-406) was u sed to calculate the salt concentration in the liquid water phase from TDR measurements of the soil electrical conductivity. Measured bulk s alt concentrations (salt content per volume soil) were found to be ver y sensitive to the liquid water contents, especially at low values, Re sults indicate a freezing-induced redistribution of the salt in the co lumn: first, there was a convective flow of salt towards the cold ends ; second, diffusion occurred in the opposite direction owing to develo ping concentration gradients. Conceptually, the setup presented can be applied to field conditions to detect in situ redistribution of salt induced by soil frost.