Assessing anthropogenic and natural influences on water quality in a critical shallow groundwater system: Insights from the Metauro River basin (Central Italy)

This work aims at the hydro-geochemical and isotopic characterization of the water resource (surface water and shallow phreatic aquifer) of the Metauro River catchment (Marche, Central Italy). The waters of the Metauro River area represent a fundamental resource exploited daily for drinking, agricultural, and industrial uses. The anthropic pressure exposes the water resources to depletion and quality degradation risks, making the study area of high scientific and social interest. The hydro-geochemical approach revealed that the interaction between water and local lithologies led to Ca²⁺-HCO₃^- compositions, with less frequent Na⁺(K⁺)-Cl^- and Ca²⁺-Cl^- hydrofacies and variable salinity (up to 55 meq/L). Most waters showed natural (e.g., halite and evaporite contribution) and anthropogenic (sewage, septic tanks, manure, urban wastewater, and industrial effluents contribution) inputs confirmed by both Na⁺, Cl⁻, NO₃⁻, and SO₄²⁻ enrichments and high Cl/Br ratios. The anthropogenic contributions is further confirmed by the relatively high contents of TPTEs (Total Potentially Toxic Elements), even though these elements individually present values below the Italian Normative Legislative limit. Geochemical issues are mitigated during the year when the surface aquifer is recharged by the river, characterized by a better overall chemical quality. The occurrence of this relationship is of interest to the local authorities in charge of the water resource management. In fact, groundwater exploitation could be increased during specific periods, thus decreasing the anthropic pressure on the river waters, usually exploited for drinking purposes even during the summer seasons when the hydrometric levels drastically drop. The adopted multidisciplinary approach provides an effective tool for accurately determining groundwater processes and can be helpful in improving the balanced and sustainable management of water resources in coastal and non-coastal plains.