Effect of Managed Aquifer Recharge with Potable Reuse Water on Aquifer Microbial Community Profiles

Abstract

Managed Aquifer Recharge (MAR) using reclaimed water is a promising approach for replenishing groundwater resources. However, the effects of MAR on aquifer microbial communities; including dynamics during injection, subsurface storage, and recovery, remain poorly understood. This study evaluated the impact of MAR of advanced reuse water produced using an advanced carbon-based treatment on the microbiome of the PAS. The study was conducted at the Hampton Roads Sanitation District's 1MGD Sustainable Water Initiative for Tomorrow (SWIFT) facility, which has been injecting advanced reuse water into the aquifer since 2018. Using 16S rRNA gene amplicon sequencing, we characterized microbial compositions across four injection-recovery tests conducted over an 18-month period and compared to a downgradient monitoring well known to be influenced by SWIFT water and a USGS background monitoring well (control) that had not yet been influenced at the time of the study. Substantial shifts were expected given that the SWIFT water is aerobic, while the PAS is anaerobic. Beta diversity analysis (unweighted UniFrac) confirmed that microbial community profiles of injected SWIFT water were distinct from groundwater pumped back from the aquifer during the recovery phases. Some variances in the degree of microbial community similarity between the SWIFT water and recovered groundwater were observed across the four test dates, with greatest overlap in composition observed during the June 2025 test (p = 0.1017) and least overlap during the April 2024 and November 2024 tests (p = 1E-04; p = 1E-04) according to PERMANOVA analysis of 16S rRNA gene profiles. Thus, there was not a sequential shift in the groundwater bearing stronger resemblance with the SWIFT water with time at the injection well, rather it varied dynamically, likely as a function of changing composition of the SWIFT water. The monitoring well and recovered water had high degree of similarity (PERMANOVA test, p = 1E-04), emphasizing the shift in microbial activity as facultative anaerobes and aerobes are expected to thrive better with time as the aquifer shifts from anaerobic to aerobic. The composition of the monitoring well microbial communities was more stable relative to recovery water as traveling through the aquifer offers some degree of buffer before it reaches the monitoring well, whereas SWIFT water's composition is continually changing at the injection well site. Notably, the monitoring wells and background Control groundwater showed no taxonomic overlap with each other. Differential abundance analysis (DAA) identified specific microbial families that diverged the most among water types and revealed taxonomic groups that are hypothetically involved in clogging of the injection well with time. These included: Pseudomonadaceae, Mycobacteriaceae, Sphingomonadaceae, and Thiotrichaceae, suggesting that future researchers should further investigate. This study provides new insight into how the injection of anaerobic aquifers with aerobic advanced treated reuse water influences native groundwater microbiomes and implications for associated geochemical and operational impacts.