Speaker
Description
Managed aquifer recharge (MAR) strategies hold potential for improving groundwater quantity for crop irrigation, yet they also pose risks to groundwater quality. The introduction of exogenous water into the subsurface, whether by flooding or well injection, creates geochemical gradients in redox potential, pH, and major ion compositions. In turn, these gradients can induce dissolution reactions in the aquifer matrix that can mobilize geogenic contaminants with the percolating water. This work aims to elucidate the impact that MAR has on redox shifts in the vadose zone, understanding that this change is at the heart of both arsenic and uranium mobilization. We pose that redox potential transients arise from the interplay between imbibition of the vadose zone with oxygenated water, limitations in atmospheric gas exchange across the soil-water interface, and oxygen respiration by microbial activity. We simulate water infiltration dynamics and reactive transport of oxygen from a drywell at a typical wetting-draining schedule and compare the timescales of biological reaction to those of physical transport to explain the observed trends. Our results reveal that the magnitude and persistence of redox shifts are limited in spatial extent and duration, whereby microbial respiration and dilution work together to efficiently mitigate the geochemical changes caused during MAR. A deep understanding in the controls for biogeochemical shifts is imperative to provide substantive guidance on sustainable water management strategies and to reduce potential long-lasting impacts on contaminant mobilization.
| Country | United States |
|---|---|
| Water & Porous Media Focused Abstracts | This abstract is related to Water |
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