A laboratory-scale physical model for freeze-thaw studies in soil columns under simulated climate change conditions

Responses of soils to climate warming during winter can be studied by monitoring soil temperature variations in the vadose zone. Freeze-thaw cycles during winter can have a significant impact on soil biogeochemical and physical processes. Observing soil temperature at different depths offers important insights into heat availability, which influences biogeochemical activity and solute movement driven by temperature gradients. However, it is difficult to replicate the relevant processes in soil columns without maintaining freezing temperatures with an unfrozen soil layer below the freezing interface. This paper describes the development and experimental verification of a laboratory-scale physical model to assess the effect of freeze-thaw cycles on biogeochemical processes in unsaturated soil. The results show that the experimental design can (i) induce cyclical freezing of soil down to desirable depths, (ii) maintain vertical temperature gradients and (iii) ensure the rest of the column remains unfrozen below the freezing interface for pore water sampling. The rate of freezing is suitable for quick freeze-thaw cycles (0.19 °C/min). This setup can be further developed to observe solute transport and attenuation in variably-saturated soil and soil moisture status for different freeze-thaw regimes under simulated climate change scenarios.