GEOPHYSICAL INVESTIGATION OF IRON-SULFUR REDOX DYNAMICS IN SULFIDIC SOILS: A CASE STUDY FROM ZODLETONE SPRING, OKLAHOMA

Abstract

This study investigates subsurface iron-sulfur redox dynamics in anaerobic acidic sulfate soils at Zodletone Spring in southwest Oklahoma by integrating noninvasive geophysical method electromagnetic induction (EMI) and Indicator of Reduction In Soil (IRIS) devices. EMI was used to collect apparent electrical conductivity (ECa), which was processed through inversion modeling to better estimate true electrical conductivity (EC) and generate a three-dimensional model of the subsurface. Slices of the model revealed distinct redox transitions between 0.4-0.6m across majority of the study area. IRIS devices confirmed strongly reducing conditions through the removal of iron oxide paint (FeOOH) and precipitation of iron monosulfides (FeS). A statistically positive correlation was observed between elevated EC and FeS coverage (R2 = 0.52, p = 0.008), while remaining FeOOH showed a negative correlation with EC (R² = 0.59, p = 0.003), supporting the use of EMI as a noninvasive proxy for monitoring redox activity. These findings demonstrate the value of EMI for identifying redox transition zones in acidic sulfate soils, with important implications for monitoring acidification through oxidation and supporting wetland remediation. The findings also suggest broader relevance for planetary exploration, where subsurface iron-sulfur cycling in low oxygen environments may serve as a biosignature of microbial habitability.