Geophysical Imaging for Scaling Understanding of Hydro-Biogeochemical State Changes Across Coastal Interfaces
Authors
Kennedy O. Doro1* (kennedy.doro@utoledo.edu), Moses B. Adebayo1, Efemena Emmanuel1, Solomon Ehosioke1, Peter Regier2, Anya Hopple1, Fausto Machado-Silva2, Kenton Rod1, Xingyuan Chen2, Patrick J. Megonigal3, Nicholas D. Ward2, Michael N. Weintraub1, Vanessa L. Bailey2
Institutions
1University of Toledo, Toledo, OH; 2Pacific Northwest National Laboratory, Richland, WA; 3Smithsonian Environmental Research Center, Edgewater, MD
URLs
Abstract
Geophysical methods provide highly resolved spatial images of responses sensitive to subsurface state changes and can be used to monitor subsurface hydrology at a continuous spatiotemporal scale. However, extracting quantitative hydrological and biogeochemical information from geophysical images remains challenging. This study uses repeated measurements of natural and induced electrical potential fields to quantify changes in soil moisture, salinity, and redox potential at coastal interfaces along the Chesapeake Bay and Lake Erie. At the Chesapeake Bay, researchers used petrophysical models derived from laboratory multi-salinity electrical measurements to estimate changes in soil moisture and fluid salinity from electrical resistivity and induced polarization measurements during a simulated flooding experiment. The experiment was conducted across two hydrologically isolated 2,000 m2 plots simultaneously inundated with freshwater and estuarine water. Time-lapse electrical resistivity and induced polarization measurements were used to image the propagation of the infiltration front. The team used a modified Archie’s law to estimate changes in soil moisture and salinity in response to the simulated flooding event. Researchers found that the geophysical methods could capture the propagation of the infiltration front through changes in bulk electrical conductivity over time. Additionally, significant changes in imaginary conductivity were observed only in the estuarine plot, which correlated with the increasing soil salinity. Estimates of the soil moisture and salinity contents from the resistivity and induced polarization datasets agreed with measurements from in situ soil sensors. At the Lake Erie area, researchers used repeated co-located measurements of natural electrical currents (Self-Potential) and redox potential to show that the electrochemical contribution of Self-Potential correlates with redox potential, providing an alternative approach to estimate spatial changes in soil redox potential. The results of this study extend the use of geophysical imaging for improving spatial estimates of soil moisture, salinity, and redox potential changes across coastal interfaces.