Measuring flow variability in a layered, volcanic vadose zone using a conservative tracer and nitrate isotopic analysis

Abstract

Due to textural changes in the volcanic materials, coupled with hydrophobic conditions, non-equilibrium flow dominates the unsaturated transport through the vadose zone at the investigated site (Fig.1). As a consequence, high spatial variability is evident in the drainage volumes measured using automated equilibrium tension lysimeters (AETLs) installed at different depths in the vadose zone. By using the subsurface recoveries of a conservative Br tracer applied on the surface, the flow variability through the vadose zone can be quantified. The tracer experiment, along with isotopic analysis of the nitrate through the vadose zone also permits us to investigate an incongruity in the measured drainage volumes at the Taupo Ignimbrite-Palaeosol interface. This study helps understanding the processes controlling spatial and temporal variability of contaminant leachate rates from volcanic soils.