Hydrogeological characterization of small coastal wetlands and forests in the Southern Po Plain (Northern Italy).

This study is aimed to characterize the shallow groundwater system in the coastal area between the Uniti and Bevano rivers (southern part of the Po plain), where salinization is threatening the coastal ecosystems and posing a major environmental issue for the phreatic water management in the coast. A thin rainwater lens is present at the top of the aquifer in the backshore area and its extent has a seasonal variability. These few centimetres of freshwater represent a thin interface between sea water and the delicate coastal ecosystems, such as those of dunes and wetlands. To have a better understanding of the changes in groundwater chemistry, we performed a seasonal monitoring of the water quality at the top of the aquifer. Effective concentrations of chemicals and actual values of physical-chemical parameters in the rainwater lens could be measured by means of auger holes. The analysis of the cation-exchange process in the aquifer was made through the application of the Base Exchange index (BEX index) of Stuyfzand (2008), an indicator of salinization or freshening of waters. The results pointed out that a salinization process is taking place in the largest part of the aquifer. Extension and chemical composition of the rainwater lens are strongly influenced by anthropogenic factors such as drainage and land use. The surface water bodies are all brackish to salty and characterized by anoxic and reducing conditions. At present, only halophytes are present around the dune slacks, which have turned into brackish to hypersaline lakes.