Characterizing the Transport of the Stable Isotopes of Water in Unsaturated Soils
infiltration. The peak shift method is used to calculate a net percolation rate by finding the location of isotope peaks. The literature applying the peak shift methods is plentiful. However, when extensive spreading occurs by diffusion and dispersion and a well-defined peak is no longer present the peak shift method is not applicable and another method of analysis is needed. The goal of this work was to develop a better understanding of the diffusive and dispersive movement of isotopes within an unsaturated soil. Isotopes can be partitioned to the vapour phase where they can be stored and transported in addition to the aqueous phase. A dual phase relationship was derived to analyze isotope profiles where significant spreading has occurred. A dual phase (i.e. vapour and liquid) diffusion – water content relationship was developed using water isotope, carbon dioxide, and oxygen gas diffusion literature including gaseous and aqueous phase tortuosities. This relationship was evaluated using the results from a set of double half-cell diffusion cells. Each cell allowed for a diffusion coefficient to be measured at specific volumetric water content. The experimental procedures proved to be challenging and required several iterations to collect quality data. Interpretation of the diffusion cell data resulted in a best fit dual phase model, using the gaseous phase tortuosity model of Penman (1940) and the aqueous phase tortuosity model recommended by Padilla et al. (1999) with the saturated tortuosity from Maxwell (1881). The proposed diffusion model was also evaluated using the observations from a column test used to simulate infiltration under simple field conditions. Simulated rainfall was allowed to infiltrate and diffuse. Isotope values were measured over the column elevation at different times. These observations were used to verify the dual-phase diffusion model as well as several different dispersivity-water content relationships. The diffusion behavior observed in the column experiment was consistent with the combined dual-phase model selected from the diffusion cells.
DegreeMaster of Science (M.Sc.)
DepartmentCivil and Geological Engineering
SupervisorBarbour, S Lee; Hendry, M Jim
CommitteeMaule, Charles; Ferguson, Grant; de Boer, Dirk
Copyright DateOctober 2017
Stable Isotopes of Water