Preferential Transport of a Bromide Tracer Applied in a Pulse of Ponded Water
- D. J. Timlin *,
- L. R. Ahuja and
- G. C. Heathman
The objective of this study was to quantify relations between preferential transport of a solute and initial water content, infiltration rate, and porosity in a field soil where preferential transport was mainly due to soil heterogeneity. We measured the horizontal and vertical distribution of a tracer chemical applied with ponded water to study the flow paths of the tracer. The soil at the site is a Bosville fine sandy loam (fine-mixed, thermic Albaquic Paleudalfs). Strontium bromide (SrBr2) tracer was applied with a dye (methylene blue) in a 100 or 50-mm pulse of water to soil within eight double ring infiltrometers. After 48 h the soil in each infiltrometer was sampled to 0.7 m. Twelve horizontally oriented, continuous soil samples 0.1 m long were collected at each depth. There were very few dye stains of root hairs, root channels, and pores to a depth of about 50 to 80 mm. Recoveries of Br to 0.5 m ranged from 36 to 56% applied. Bromide recovery was negatively correlated with initial water content and positively with total porosity. Below 0.35 m in depth resident solute concentration at a sampling position was positively correlated with concentration in the layer above indicating preferential vertical flow paths. It appeared that a large fraction of solute transport was through the highly porous areas of the cross-section of soil bounded by the infiltrometer ring. The preferential transport of Br in this study was influenced largely by the properties of the clay layer at 0.35 m that had the lowest conductivity and lowest porosity in the profile and appeared to have cracks filled with sand.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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