Soil Saturation Response to Changing Hydrological Regimes at Coastal Interfaces


Kennedy O. Doro1* (, Moses B. Adebayo1, Solomon Ehosioke1, Fausto Machado-Silva1, Bing Li2, Xingyuan Chen2, Anya M. Hopple3, Allison N. Myers-Pigg2, Peter Regier2, Patrick J. Megonigal3, Nicholas D. Ward2, Inke Forbrich1, Michael N. Weintraub1,2, Vanessa L. Bailey2


1University of Toledo, Toledo, OH; 2Pacific Northwest National Laboratory, Richland, WA; 3Smithsonian Environmental Research Center, Edgewater, MD



Coastal interfaces are increasingly experiencing changes in their hydrological regimes with more dynamic wetting and drying frequency and duration caused by increased storm surges, flooding events, lake level fluctuations, and sea level rise. This results in high temporal and spatial variation in soil saturation, which impacts ecological functions from plant growth to biogeochemical cycling. Improved measurements and models are required to capture varying soil-water saturation dynamics and quantify changes in storage. This study aimed to delineate soil stratigraphic connectivity and capture hydraulic state changes during hydrological perturbations across the coastal interface using geophysical models validated with in situ soil cores and hydraulic parameter measurements. The team also developed a hydro-geophysical framework combining geophysics and an advanced terrestrial simulator (ATS) flow model to capture the variation in soil saturation at coastal interfaces. Researchers combined electrical resistivity and ground penetrating radar to estimate lateral and vertical variation in soil hydro-stratigraphic properties. A sand-silt-clay stratigraphy characterized the Chesapeake Bay area with a silty clay unit at 1.5 m depth, constraining vertical flow. In contrast, shallow occurrences of glacial till along with silty clays limit vertical flow along the Lake Erie coastal soils. Furthermore, the team used time-lapse electrical resistivity imaging to monitor changes in soil water and solute content during a simulated flooding experiment at a coastal upland forest along the Chesapeake Bay. Resistivity changes of 50% to 85% were attributed to changes in water and solute content revealing fresh and estuarine water infiltration fronts. The flow simulation from ATS captures both saturation and concentration curves extracted from soil sensors and the timelapse geophysical imaging. This study shows the efficacy of using geophysical methods in monitoring hydrological state changes at an ecosystem-scale. The high spatial resolution of geophysical measurements, when converted to hydrological variables, also provides data to calibrate the ATS models. Future work will focus on hydrological investigations coupled with biogeochemical data to mechanistically understand how soil and groundwater dynamics control fluxes and transformations of carbon, nutrients, and greenhouse gasses across coastal terrestrial-aquatic interfaces.