Control of alluvial aquifer architecture on reductive and oxidative dechlorination of chloroethenes.

Groundwater quality and ecosystem function are significantly influenced by aquifer-hyporheic zone systems, particularly in cases where such systems interact with influent rivers. This study investigates the impact of the geological structure on natural attenuation of chloroethenes in such connected systems. Our research focuses on understanding the complex interactions between geological features and microbial dynamics, shedding light on perchloroethylene transformation from DNAPL sources. Field investigations were conducted in an alluvial aquifer with fluvial paleochannels dominated by gravels and sands separated by silts and clays in floodplains. A multidisciplinary approach was employed, combining sediment geochemistry, chloroethene isotopic fractionation (δ13C), and microbial community characterization. The results revealed distinct microbial assemblages associated with different geological structures, highlighting hydrogeological heterogeneity's role in shaping microbial diversity and activity. Specific microbial genera involved in chloroethene dechlorination across paleochannels, interchannel areas, and the hyporheic zone on the bank of an influent river were identified, illustrating differential microbial contributions to contaminant degradation. Furthermore, the study elucidated medium factors such as hydraulic conductivity and organic carbon availability that modulate microbial community structure and function. These findings enhance understanding of microbial-mediated contaminant attenuation in heterogeneous subsurface environments, informing groundwater remediation strategies and supporting sustainable groundwater management and environmental protection.