Exploring groundwater microbial communities for natural attenuation potential of micropollutants

Abstract Groundwater is a key water resource, with 45.7% of all drinking water globally being extracted from groundwater. Maintaining good groundwater quality is thus crucial to secure drinking water. Micropollutants, such as pesticides, threaten groundwater quality which can be mitigated by biodegradation. Hence, exploring microbial communities in aquifers used for drinking water production is essential for understanding micropollutants biodegradation capacity. This study aimed at understanding the interaction between groundwater geochemistry, pesticide presence, and microbial communities in aquifers used for drinking water production. Two groundwater monitoring wells located in the northeast of The Netherlands and at 500 m distance from each other were sampled in 2014, 2015, 2016 and 2018. In both wells, water was extracted from five discrete depths ranging from 13 to 54 m and used to analyze geochemical parameters, pesticide concentrations and microbial community dynamics using 16S rRNA gene sequencing and qPCR. Groundwater geochemistry was stable throughout the study period and pesticides were heterogeneously distributed at low concentrations (μg/L range). Integration of the groundwater chemical and microbial data showed that geochemical parameters and pesticides exerted selective pressure on microbial communities. Furthermore, microbial communities in both wells showed a more similar composition in the deeper part of the aquifer as compared to shallow sections, suggesting vertical differences in hydrological connection. This study provides initial insights into microbial community composition and distribution in groundwater systems in relation to geochemical parameters. This information can contribute for the implementation of bioremediation technologies that guarantee safe drinking water production from clean aquifers. Importance section Groundwater is an essential source of drinking water. However, its quality is threathened by the presence of micropollutants. Certain microorganisms are capable of degrading micropollutants. However, groundwater is an unexplored environment, where the biodegradation potential of naturally-present microorganisms is unknown. We thus explore how groundwater microbial ecology in shaped by groundwater composition, namely geochemical parameters and micropollutants. This is a first step towards understanding which microbial communities and environmental conditions support natural attenuation of micropollutants. This study thus provides a first step towards developing in situ bioremediation strategies to remove micropollutants from groundwater used for drinking water production.