Water application frequency effects on steady-state solute transport parameters

Abstract

In many studies, data from transient or quasi steady-state solute transport experiments are modeled using steady-state models. Few investigations, however, have been carried out to verify the validity of this approach. In this paper, we study the effects of water application frequency on the parameters derived using steady-state models. Bromide transport was studied in an undisturbed soil column of loamy sand exhibiting fingered flow. Four solute displacement experiments were carried out under quasi steady-state flow conditions. The mean water flux in all experiments was 1.42 cm d −1, but water was applied at different time intervals for each; that is one, two, three, or six times daily. Water content and solute concentration were measured following an in situ calibration, using time domain reflectometry (TDR) probes at nine different depths. The TDR probes were placed in two alternate directions, with every second probe being orthogonal to the first. The convective–dispersive (CDE) and the convective log-normal transfer function (CLT) models were fitted to the solute transport data. The CDE model best described the solute transport. The dispersivity decreased when water was applied more often. The decrease can largely be attributed to lesser variability of the water flux velocity, especially in one of the probe directions. The mass recovery was about 40% for all depths and did not change with the differing intervals between water applications. Solute transport heterogeneity was also constant during the experiments. These observations lead to the conclusion that preferential flow paths in this soil were consistent and independent of application frequency.