High-Resolution Monitoring of Vertical Solute Transport in the Unsaturated Zone

Groundwater risk assessments concerning contamination by nutrients and organic pollutants have traditionally been based on groundwater sampling. However, limited attention has been devoted to quantifying the accumulation of solutes in the unsaturated zone and assessing the temporal dynamics of solute fluxes from this zone to the underlying aquifers. Vertical transport in the unsaturated zone is governed by two principal components: solute concentration and water flux.

While pore water sampling has long been applied to determine solute concentrations, direct in-situ quantification of water transport remains challenging, as it requires comprehensive characterization of soil physical properties such as grain size distribution, bulk density, and the soil water retention curve. The latter has historically posed significant methodological difficulties. To overcome these challenges, DMR has developed a novel soil-water sampler capable of automated pore water collection while simultaneously logging volumetric water content and soil matric potential, thereby enabling high-resolution determination of the soil water retention curve.

This innovative instrumentation establishes a new standard for continuous measurement of water fluxes in the unsaturated zone and offers unprecedented insights into the spatiotemporal variability of solute leaching driven by precipitation events and near-surface nutrient inputs.