Quantification of preferential flow in undisturbed soil columns using dye tracers and image analysis

Solute transport studies are increasingly being used to characterise flow mechanisms in both the field and laboratory. Realisation that solutes may move preferentially through soil into groundwaters has meant that research in this area has increased in importance. Chloride and Brilliant Blue tracers were applied to large undisturbed soil cores (8000 cm 3 ) inserted with time domain reflectometery probes (TDR). Following the collection of serial digital images, it was possible to examine the nature of the dominant water flow mechanisms in terms of dye-stained pathways and quantify the spatial distribution of dye concentration in two dimensions using image analysis. A high level of variability of flow patterns observed from dye and solute tracers was noted between soil types, between replicates and within replicates. These patterns were further explored using X-ray Computed Tomography to obtain 3-D visualisations of soil macropore architecture.

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