Solute transport through the vadose zone: A field study and stochastic analyses

Solute concentration and water content profiles were measured within an area of 3 x 6 m(2) to a depth 1.7 m in an unsaturated soil, Spatial variabilities of soil water content and concentration were analyzed based on the field data and stochastic models. During the 33-day field experiment under constant leaching, the soil water movement showed an approximately steady-state flow. The effect of soil variability on soil water distributions was relatively small. On the other hand, the concentration distribution exhibited a profound variability in the field, especially within the zones with peak values in the vertical profiles. Immobile water content calculated from the experimental data was about one-third of the total water content. Stochastic and deterministic models were used to simulate solute transport through the vadose zone. Comparison of the simulation results with the field experimental data showed that the models described the mean concentration reasonably well without considering the pore scale dispersivity. However, the pore scale dispersivity had a significant impact on the estimation of the concentration variance.