Monitoring saltwater intrusion in the area surrounding the Grado lagoon (NE Italy)

Coastal aquifers are heavily influenced by seawater intrusion, a phenomenon exacerbated by current climate change, which is affecting the availability of freshwater for drinking and irrigation purposes. This occurrence also leads to a progressive salinization of agricultural lands, adversely affecting crop yields. Despite the importance of groundwater salinization management for coastal agriculture in the Friuli Venezia Giulia region (NE Italy), there is currently a lack of detailed study on the topic. To partly fill this gap, a first field campaign was carried out in the inland areas surrounding the Grado lagoon, as part of an ongoing PhD project focusing on the regional issue. The Grado lagoon is a low energy environment characterized by higher salinity compared to the Adriatic Sea and the nearby Marano lagoon, due to shallower depth and limited presence of freshwater tributaries. In the inland regions of the Grado lagoon, which are mainly situated below sea level and predominantly utilized for agriculture, ensuring environmental sustainability rely heavily upon effective water resource management. In order to tackle this challenge and manage the water resource effectively, it is crucial to establish a comprehensive hydrogeological model of the area. Non-invasive geophysical investigation techniques have commonly been employed for this purpose in similar contexts. In this study, Electromagnetic induction (EMI) technique has been utilized for studying saline intrusion in the subsurface, thanks to its ability to explore large areas in relatively short times, detecting depth and lateral variations in electrical conductivity which can be associated with soil salinity changes. During this campaign, more than 30 km electrical conductivity profiles were collected along the lagoon margin, highlighting electrical conductivity variations, directly linked to the presence of saltwater in the aquifers closer to the saltwater body. The data obtained from EMI surveys were validated through Electrical Resistivity Tomography profiles performed in selected location and through direct sampling of groundwater, conducted via manual boreholes drilled to varying depths relatively to the groundwater level. The material retrieved from the drillings also enabled us to obtain short stratigraphic logs, which have contributed to a better understanding of the salinity distribution in the coastal aquifers. The combined approach has demonstrated its worth by providing crucial insights into the extent of salinization in the coastal phreatic aquifers. A thorough understanding of seawater intrusion is essential for future strategic planning of water resource management and agricultural development in the study area.