Field-scale solute transport — spatially interpolating the parameters of a transfer function model

The results from a solute transport study done near Basel, Switzerland are reported. The experimental site was a 3.25 ha corn field consisting of well drained silt loam. A bromide tracer was applied to the surface of 40 plots, located at regular intervals on a grid. Soil cores were taken twice at each plot during the experiment. The first time, samples were collected at 10 cm intervals from the surface to 50 cm. During the second sampling, soil cores were taken to a depth of 100 cm in 20 cm increments. Four plots were sampled twice each time to assess small-scale heterogeneities. Solute transport was described as a convective-dispersive process with highly variable parameters within the test field. A poor correspondence between the apparent fraction of the soil volume that is active in transport and volumetric water content was found. This was interpreted as resulting from effects such as stagnant water, locally three-dimensional flow and infiltration water which bypasses the regions of the soil which contain the main mass of the tracer. The spatial distribution of the transport parameters within the test field could not be explained on the basis of soil physical properties. The fields of the transport properties showed spatial dependence and locally estimated parameters were interpolated over the entire test field by kriging.