Hydrogeochemical surveys of shallow coastal aquifers: A conceptual model to set-up a monitoring network and increase the resilience of a strategic groundwater system to climate change and anthropogenic pressure

Salinization is a main concern for coastal aquifers due to climate change and incremental anthropogenic pressure. The Mediterranean area is particularly sensitive to this process, being several coastal aquifers already affected by seawater intrusion. The Fano coastal aquifer, located in the northern part of the Adriatic Sea (Italy), has a regional importance since it supplies drinkable water to the local communities and may be subjected to salinization given its intrinsic vulnerability and the awaited human and climate pressure. In this work, for the first time a detailed hydrogeochemical and isotopic study on the Fano shallow aquifer is presented to highlight the quality of this groundwater system. The hydrological, geochemical and isotopic data indicate a strong nitrate contamination in the central part of the basin, forcing the local water management company to inject low-NO3 waters from the main river course (Metauro River) to reduce the impact due to the N-bearing species. Differently from other coastal aquifers located along the Adriatic Sea where the seawater wedge is deteriorating most groundwater systems, our results and geochemical modeling suggest that the shallow aquifer of Fano is not apparently affected by salinization. This achievement makes this aquifer suitable for assessing whether the groundwater system might be evolving toward a seawater-contaminated aquifer. According to the proposed hydrogeochemical conceptual model, a monitor network should be deployed by the local authorities and the water management company to take appropriate measures to minimize the risk of seawater intrusion, should the hydrogeochemical and isotopic parameters indicate an incipient ingression of seawater.