Redox zonation and bioclogging interaction in managed aquifer recharge systems: A laboratory-scale investigation

Managed aquifer recharge (MAR) processes induce dynamic changes in groundwater redox conditions, which subsequently affect the formation of bioclogging during subsurface infiltration. To explore this relationship, we conducted controlled laboratory column experiments simulating both aerobic and anaerobic recharge scenarios. By integrating monitoring of changes in hydraulic conductivity, quantification of bacterial growth, assessment of metabolic activity, and analysis of redox-sensitive indicators, we characterized bioclogging patterns and revealed the associated hydrochemical transformations. The results indicated distinct spatial distributions of bioclogging under varying redox recharge conditions. Aerobic recharge led to more severe bioclogging, with deeper penetration along flow paths compared to anaerobic conditions (p < 0.001 for differences in bacterial biomass). Conversely, the accumulation of extracellular polymeric substances (EPS) exhibited an inverse trend, with concentrations under anaerobic recharge reaching 4.2 times those observed under aerobic conditions. Redox zonation analysis revealed that aerobic infiltration maintained weakly oxidizing conditions (ORP: 5.7 – 109.8 mV), whereas anaerobic recharge resulted in progressive transitions from initial weak oxidation (ORP: 1.3 – 103.9 mV) to reducing conditions (ORP: −29.4 – −10.2 mV). These redox gradients facilitated sequential biogeochemical reactions: the aerobic system displayed bacterial-mediated oxygen respiration followed by nitrate attenuation (denitrification) and sulfate reduction, whereas the anaerobic environment favored concurrent oxygen respiration and nitrate reduction (dissimilatory nitrate reduction to ammonium, DNRA), followed by sulfate depletion. Our findings elucidate the interrelated hydrogeochemical mechanisms that govern redox evolution and bioclogging dynamics during MAR operations. This research provides empirical evidence that can inform the optimization of recharge strategies to mitigate clogging risks while preserving groundwater quality.