MONITORING SOLUTE TRANSPORT IN A MULTILAYERED SANDY LYSIMETER USING TIME-DOMAIN REFLECTOMETRY

The lack of detailed and high-quality experimental data on the fate of solutes in soil puts a severe constraint on the development and testing of transport models. This study illustrates how detailed measured solute concentration data, collected by means of time domain reflectometry (TDR), are used to identify the governing transport processes in a vertical heterogeneous soil. A lysimeter was constructed, consisting of an undisturbed three-layered soil monolith placed on an artificial sandy soil column. Tensiometer cups and solution samplers, together with TDR probes, were inserted horizontally at regular depth intervals to monitor pressure head, solution concentrations, soil water content, and bulk electrical conductivity. In the lysimeter, quasi-steady-state unsaturated water flow conditions were established and TDR-estimated transport of solute was monitored during leaching. Solute fluxes at different depths were calculated, resulting in probability density functions of solute travel time to different depths. The first moment of the solute travel time revealed that approximately all soil water was used to transport solute in the top of the lysimeter. The boundary between the top soil and the sandy substratum probably induced instabilities, and hence, preferential flow. The dispersivity increased with depth in the topsoil but approached almost a constant value deeper in the lysimeter.