Assessing the influence of surface water intrusion on shallow groundwater wells using water quality measurements, stable water isotopes, and microbial community analysis

Intruding surface water can negatively impact the physicochemical and microbiological quality of groundwater. Understanding these impacts is important because groundwater provides about 25–50% of the world's potable water supply, and reduced quality is a potential public health risk. In this study, we monitored six shallow groundwater wells and three surface water bodies in the North Ostrobothnia region of Finland twice-monthly for 12 months (October 2021–October 2022) via (i) on-site and off-site measurements of physicochemical water quality parameters, (ii) determination of stable water isotope compositions, and (iii) analysis of microbial communities (via amplicon sequencing of the V3–V4 16S rRNA gene sub-regions).