Evaluation of Passive Capillary Wick Samplers for Measuring Deep Infiltration at The Jemez River Basin Critical Zone Observatory

Abstract

Passive capillary wick samplers (PCAPs) are primarily used to sample water from the vadose zone. PCAPs use fiberglass wicks to form a hanging water column that exerts suction on the surrounding soil. Although PCAPs have been used to estimate soil water flux, the accuracy with which PCAPs can estimate flux comes into question due to over/undersampling caused by this applied flux. I used numerical models to explore the effects of a PCAP on flow through the vadose zone. Specifically, I used a two-dimensional axisymmetric flow model of a PCAP embedded in a medium based on HYDRUS. Both steady-state and transient conditions were simulated through the application of various precipitation rates and periods across several soil textures. In this study, I examine soil hydraulic properties, across the soil texture triangle, subject to a range of precipitation events. Results show that the PCAP does over/underestimate water flux. The degree of error is quantified by defining a capture efficiency, which is the ratio of the flux into the plate and the flux that would occur at the same depth with no PCAP present. Higher fluxes and longer time periods resulted in increased convergence of flux into the PCAP, while lower fluxes and shorter durations resulted in divergence of flux from the PCAP. The goal of the study is to understand the behavior of PCAPs under different conditions and to use that knowledge to interpret field measurements in the Jemez River Basin Critical Zone Observatory.