FIELD ASSESSMENT OF SOIL PERMEABILITY CHANGES FOLLOWING FRESHWATER AND SALTWATER FLOODING USING INDUCED POLARIZATION METHOD

It is often assumed that hydrological dynamics drive biogeochemical changes in coastal terrestrial-aquatic interfaces (TAI), yet the hydrological responses at TAIs remain poorly quantified due to high spatial heterogeneity. This makes it difficult to predict coastal TAI state changes and represent them in ecosystem models. Understanding how these TAI components respond to hydrological disturbances requires a reliable estimation of soil permeability (k). This study is focused on assessing the use of Induced polarization (IP) measurements at field scale as a potential tool for quantifying changes in soil permeability following freshwater and estuarine water flooding events. The study was conducted on two 40 x 50 meters field plots simultaneously inundated for 20 hours with freshwater and estuary water having fluid conductivities between 10 mS/m and 1,200 mS/m. We acquired time-lapse 2D surface profiles of IP data across both plots, inverted the data in terms of real and imaginary parts of the complex conductivity, and estimated the soil's electrical formation factor (F). Soil k was estimated from fourteen distinct positions by determining saturated hydraulic conductivity along the profile using a dual head infiltrometer (DHI) SATURO instrument in the field, guided by background electrical conductivity data. The field k estimate from DHI was compared to the k estimate from the measured imaginary conductivity and F. Our results show a strong correlation with a coefficient of determination R² of 0.83, with a p-value of 1.0E-5 and RMSE of 0.45 for predicting soil k using the IP dataset in this site. The time-lapse IP results indicate an initial increase in k when the soil is exposed to prolonged flooding, its response leads to subsequent stabilization, thereby resulting in a decline in k over time. Results of this study show that IP can be used to estimate changes in soil k in coastal TAI systems at the field scale following freshwater and saltwater flooding events.