Abstract

To assess contaminant fluxes in the vadose zone water flux and solute concentrations must be known but they are seldom measured simultaneously at the same location. A water fluxmeter (WFM) with divergence control was modified to measure solute concentrations by adding a funnel and collection vial to the bottom of the meter. Laboratory experiments using coarse and fine sands showed that measured solute concentrations and known water fluxes can be combined to provide estimates of solute flux. Water containing a NO3 tracer was applied at a rate of 1.97 × 10−8 m s−1 (621 mm yr−1), and water flux was simultaneously measured along with NO3 concentrations in the outflow water. The general agreement in fitted and measured pore-water velocities suggests that the breakthrough curves of NO3 measured using the drainage through the WFM can be used to estimate the pore-water velocity of the soil. Solute travel-time through the 60-cm-long wick was <10% of the travel time through the sands and could be neglected. Flow divergence was examined by measuring the soil water content and pressure head at different positions and by measuring the water flux passing through and around the WFM. Divergence was controlled by a 15-cm-high barrier such that more than 80% of the flow passed through the fluxmeter in both soils. Results show that the modified SFM can provide a convenient method for long-term monitoring of contaminant flux.

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