1-3 Investigating Microbially Mediated Manganese Removal and Mobilization Mechanisms during Managed Aquifer Recharge

Session: Advances in Managed Aquifer Recharge

Presenting Author:

Authors:

Abstract:

Managed aquifer recharge (MAR) can benefit communities by increasing groundwater yields, preventing land subsidence, and reducing saltwater intrusion in coastal areas. However, introducing water with a different chemical composition than an aquifer’s native groundwater may result in unintentional releases of geogenic contaminants into groundwater, including manganese (Mn) and others. The Hampton Roads Sanitation District in Virginia implemented an MAR initiative in 2018 called the Sustainable Water Initiative for Tomorrow (SWIFT) to address the overuse of groundwater in the Potomac Aquifer and reduce the nutrient load to the Chesapeake Bay.  The SWIFT project involves the injection of oxygenated, highly treated wastewater into the sub-oxic to anoxic Potomac Aquifer. Our overarching hypothesis is that this change in redox conditions has the potential to stimulate biogeochemical transformations of Mn, which occurs naturally within the Potomac Aquifer.

To test our hypothesis, we are constructing microbial microcosm experiments using Potomac Aquifer sediments, Potomac Aquifer groundwater, and SWIFT recharge water. During these experiments, we are exploring the capacity of the native microbial community within the Potomac Aquifer to reduce and oxidize Mn under different redox conditions. In the oxic experiment, we supplement microcosms with both Mn (II) and oxygen. In the anoxic experiment, we supplement microcosms with synthetic δ-MnO₂ and maintain anoxic conditions. These microcosms will be incubated for 1 month and sampled throughout the incubation period for dissolved Mn (II). Additionally, samples will be taken for 16S DNA sequencing to profile the microbial community present in each microcosm. Sediments from the microcosms will be analyzed with X-ray photoelectron spectroscopy, energy dispersive spectroscopy, and Raman spectroscopy to characterize the mineralogical changes that occurred during incubation. Results of these experiments will provide insight into Mn removal and mobilization mechanisms acting in a large-scale MAR operation and will inform operational conditions to minimize release of geogenic contaminants during the SWIFT and other MAR efforts worldwide.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-5409

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