Groundwater microbial community and hydrogeochemical patterns in a saline-influenced coastal aquifer

Coastal aquifers may be compromised by various anthropogenic impacts and saline water influences. Diverse inputs of surface and marine waters can consistently influence local hydrological, geochemical, and biological conditions, directly impacting groundwater quality, ecological status, and associated ecosystem services. The aquatic microbial community represents a fundamental component of the groundwater resident biota, playing a major role in nutrient cycling and bioremediation processes. However, the structural and functional traits of the aquatic microbial community have been poorly considered in groundwater quality assessments. This work aims to explore the microbial community responses to groundwater quality variation in a coastal aquifer subject to salinization. The sampling sites were located within the coastal area of Fiumicino (Rome, Italy). The primary physical-chemical characteristics of groundwater samples were examined, including major anions and cations, trace elements, and dissolved organic carbon. The aquatic microbial community was characterized to assess total microbial load (flow cytometry), the microbial metabolic potential (Biolog EcoPlates), and the heterotrophic respiration (Biolog MT2 MicroPlates). The phylogenetic community composition was also characterized by the 16S rRNA gene amplicon sequencing. Results indicated that distinct microbial community profiles, dominated by members of the families Sulfurimonadaceae and Comamonadaceae, were identified within two groups of water characterized by varying salinity and conductivity levels. Our findings underscored the necessity of a cross-disciplinary approach for improved management of groundwater resources, as alterations in the structural and functional dynamics of the groundwater microbial community will directly impact biogeochemical cycles and ecosystem services.