Stratigraphic Influence on the Groundwater Dynamics in a Salt-contaminated Phreatic Aquifer at the Southern Margin of the Venice Lagoon, Italy

Complex freshwater-saltwater exchanges characterize Holocene aquifers in low- lying coastal plains, such as the phreatic aquifer at the southern margin of the Venice Lagoon, object of this study. This is due to the contribution of several factors that control groundwater dynamics, including the high variability of Holocene coastal deposits and water management practices. The stratigraphic architecture of the coastal area at the southern front of the Venice Lagoon consists of sandy paleochannels and littoral ridges and fine lagoon sediments. The relationships between the sedimentary deposits and vertical changes in salinization of the phreatic aquifer are poorly studied, although they are of paramount importance for the sustainable use of water resources. This work is aimed to demonstrate the influence of morpho-sedimentary constraints (i.e. stratigraphic discontinuities) on the salt- fresh water dynamics of the salt contaminated aquifer at the southern margin of the Venice Lagoon. The adopted methodology is based on the comparison between stratigraphic logs (in terms of Facies Analyses) and Electro Conductivity profiles (in which the EC has been taken as a proxy of salinity) acquired into the aquifer. The results show that buried channelized sandy deposits can reduce the salinity of the phreatic aquiferwhen a sufficient freswater supply is simultaneously present.