An Integrated Approach for Investigating the Salinity Evolution in a Mediterranean Coastal Karst Aquifer

Coastal areas are characterized by considerable demographic pressure that generally leadsto groundwater overexploitation. In the Mediterranean region, this situation is exacerbated by arecharge reduction enhanced by climate change. The consequence is water table drawdown thatalters the freshwater/seawater interface facilitating seawater intrusion. However, the groundwatersalinity may also be affected by other natural/anthropogenic sources. In this paper, water qualitydata gathered at 47 private and public wells in a coastal karst aquifer in Apulia (southern Italy), wereinterpreted by applying disparate methods to reveal the different sources of groundwater salinity.Chemical characterization, multivariate statistical analysis, and mixing calculations supplied thegroundwater salinization degree. Characteristic ion ratios, strontium isotope (87Sr/86Sr), and puremixing modelling identified the current seawater intrusion as a main salinity source, also highlightingthe contribution of water-rock interaction to groundwater composition and excluding influence fromCretaceous paleo-seawater. Only the combined approach of all the methodologies allowed a clearidentification of the main sources of salinization, excluding other less probable ones (e.g., paleoseawater). The proposed approach enables effective investigation of processes governing salinitychanges in coastal aquifers, to support more informed management.