ELECTRICAL SIGNALS AS PROXIES FOR WETLAND SOILS CHARACTERISTICS AND HYDRO-BIOGEOCHEMICAL PROCESSES

The water retention and nutrient cycling function of wetlands and their role in moderating soil carbon storage and greenhouse gas emissions have increased interest in understanding the hydrological and biogeochemical processes within them. These processes vary with the soil characteristics, making capturing their spatial and temporal variability essential for understanding wetland functions. Recent advances in sensors allow resolving temporal variation in soil properties at less than a millisecond scale. However, multiple sensors are required to capture vertical and lateral changes at a field scale. Hence, understanding the distribution of soil state variables and processes will benefit from fast, minimally invasive techniques, including electrical geophysical methods. The flow of water and biologically mediated chemical gradients create natural electrical gradients termed self-potential within soils whose amplitude reflects the source intensity. Also, the movement of ions induced by an external electric field, termed electrical conductivity, depends on the soil pore fluid conductivity and charge storage at the grain-fluid electrical double layer, termed polarization. Therefore, self-potential, electrical conductivity and induced polarization signals of wetland soils contain inherent signatures that can be used to unravel the soil characteristics. This study present recent advancements and challenges in using these geophysical signatures to characterize and monitor wetland soil properties and processes. Case examples from wetlands in Northwest Ohio are used to show correlations between soil self-potential and electrical conductivities with wetland soil texture, organic matter, and moisture content. A petrophysical model that decouples the real and imaginary components of electrical conductivity and experimental estimates of the soil formation factor and surface conductivity is used to assess the merit and demerit of using electrical conductivity as a proxy to estimate soil properties and processes at the field scale.