Modified half-cell method for measuring the solute diffusion coefficient in undisturbed, unsaturated soil
2000
Olesen, T. | Moldrup, P. | Yamaguchi, T. | Nissen, H. H. | Rolston, D. E.
Predictive models for the solute diffusion coefficient, DS, dependency on volumetric soil-water content, θ, are often applied in simulations of solute transport and fate in natural, undisturbed soils. However, all available DS(θ) models have been developed from measurements on sieved, repacked soil. In this study, DS for chloride was measured in both repacked and undisturbed loamy sands at different soil-water contents. The measurements on undisturbed soil were carried out using a modified half-cell method, where the source half-cell is a sieved and repacked soil core and the other half-cell is an undisturbed soil core. Thus, the problems of (i) incomplete contact area at the interface between undisturbed half-cells and (ii) potentially different diffusion properties in undisturbed half-cells can be avoided. The modified half-cell method requires that the diffusion coefficient in sieved, repacked soil is determined separately and that the experimental data is analyzed with a numerical solution to the diffusion equation. No significant difference in chloride DS(θ) between undisturbed and sieved, repacked soil was observed for a Danish (Foulum) loamy sand and a Japanese (Hiroshima) loamy sand. A recently presented soil type dependent DS(θ) model, derived from repacked soil data, shows it to be applicable also for predicting solute diffusion coefficients in natural, undisturbed soils.
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