Investigating Soil Organic Matter Complexation in Natural Analog Systems Using Geoelectrical Methods

Soil organic matter (SOM) interactions with minerals, such as ferrihydrite, are fundamental to processes that control carbon sequestration, nutrient cycling, and maintaining soil health. This study investigates the sensitivity of geoelectrical methods, such as induced polarization (IP), to the formation of organo-mineral complexes, focusing on ferrihydrite (a common mineral in soils), and pentaglycine (a component of the SOM). Multiscale experiments (millifluidic system and column) using ferrihydrite-coated sand, ceramic beads, and a polydimethylsiloxane (PDMS) pore network show a large increase in imaginary conductivity (an IP parameter), following the initial pentaglycine injection, which may be attributed to surface complexation reactions. Subsequent decreases in the imaginary conductivity suggest surface saturation or reduced adsorption site availability. Complementary scanning electron microscopy (SEM) imaging revealed morphological changes on the ferrihydrite aggregate surface, supporting IP measurements. Notably, a consistent strong IP response is observed across both the millifluidic and column systems, validating the reproducibility of these measurements under controlled conditions. Overall, these findings demonstrate the potential of geoelectrical methods such as IP as a noninvasive tool for monitoring complex interactions at the mineral-fluid interface.