A multi-disciplinary approach to characterize groundwater systems in coastal areas: the case studies of the Muravera Plain (Sardinia, Italy)

A multi-disciplinary approach for the hydrogeological assessment and characterization of groundwaters in a coastal area with high anthropogenic pressure and ongoing seawater intrusion phenomena is presented. Such phenomena are increasingly widespread in coastal areas all over the world and could seriously threaten groundwater resources and socio-economic development of territories. The coastal plain of Muravera, in south-eastern Sardinia (Italy), has been studied since the sixties because of important seawater intrusion phenomena. Over the years, many research and studies, including geological, geophysical and geochemical, have been carried out, but dynamics and processes controlling the groundwater flow system were not fully understood. To define a three-dimensional (3D) hydrogeological conceptual model, all the available existing data were integrated within a 3D GIS environment along with those collected during new field surveys, including piezometric, hydrochemical and multi-isotope data, namely deuterium and oxygen isotopic composition of water (δ2H and δ18O), tritium(3H), strontium (86Sr/87Sr), and boron (δ11B). Stratigraphic logs and geophysical, interpreted according to a geological–depositional model based on sequential stratigraphy, allowed to constrain the geometry of the groundwater system, resulting in a complex multilayer aquifer, mostly phreatic and locally confined. Results from bulk chemistry and isotopes provided information regarding recharge sources, flow paths and residence times of groundwaters. Four main flow paths, including lateral recharge from bedrock, surface water infiltration from the Flumendosa river and Rio Flumini Uri, and the occurrence of young mixing processes between fresh and sea waters were recognized. Moreover, a major contribution of meteoric water to groundwater recharge has been documented. The proposed approach improves the understanding of the aquifer system under investigation and reduces uncertainties about main groundwater dynamics. Moreover, results of the conceptualization become new input information and data required in the development of a groundwater flow numerical model. The latter represents a useful tool for an efficient management of groundwater resources aimed at improving the quality and availability of water resources by local government.