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 testi ng of transport models. This study illustrates how detailed measured s olute concentration data, collected by means of time domain reflectome try (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 wi th TDR probes, were inserted horizontally at regular depth intervals t o 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 di fferent depths were calculated, resulting in probability density funct ions of solute travel time to different depths. The first moment of th e solute travel time revealed that approximately all soil water was us ed to transport solute in the top of the lysimeter. The boundary betwe en the top soil and the sandy substratum probably induced instabilitie s, and hence, preferential flow. The dispersivity increased with depth in the topsoil but approached almost a constant value deeper in the l ysimeter.