PNNL

Abstract

Predicting the impact of flooding from storm surges on coastal ecosystems requires detailed information on changes in soil saturation and salinity in response to the hydrological disturbance. In-situ sensors and sampling commonly used to estimate changes in soil moisture and salinity provide spatially discontinuous datasets, which are limited in monitoring subsurface hydrological processes. Geophysical methods provide highly resolved spatial images of responses sensitive to the changing water and salinity contents and can be used to monitor subsurface hydrology at a continuous spatiotemporal scale. However, extracting quantitative hydrological information from geophysical images remains challenging. Validating and extending current petrophysical models to estimate soil moisture and salinity from electrical measurements addresses this challenge. Using petrophysical models derived from laboratory multi-salinity spectral induced polarization measurements, changes in soil moisture and fluid salinity were estimated in this study from electrical resistivity and induced polarization measurements during an ecosystem-scale simulated flooding experiment. The experiment was conducted across two hydrologically isolated 2,000 m2 2 experimental plots that were simultaneously inundated with freshwater and estuarine water, respectively. Electrical Resistivity and induced polarization were employed to image the propagation of the infiltration front. A modified Archie’s law was used to estimate changes in soil moisture content and salinity. The results demonstrated that the geophysical methods could capture the propagation of the infiltration front through changes in bulk conductivity over time. Additionally, significant changes in imaginary conductivity were observed only in the estuarine plot. Furthermore, moisture content estimated from the resistivity datasets using site-specific petrophysical relationships agrees with measurements from in-situ soil sensors. This study provides a field-scale approach to estimate the propagation of infiltration front and extends the technological capabilities for future hydrological investigations. These outcomes will guide research efforts that investigate the resilience of ecosystems to changing hydrologic disturbance patterns.