Salt Water Contamination On Venice lagoon Mainland: New Evaluation Of Origin, Extension And Dynamics

The Venice Lagoon mainland is affected by salt water contamination in coastal and circum-lagoonal aquifers due to the close vicinity of both the sea and lagoon. The territory, characterized lithologically by alternating layers of silt, clay and sand which have marine, continental and/or marsh origins, is characterized by several critical conditions. These include the existence of paleorivers, lagoonal paleochannels, and rivers which are artificially suspended above the surrounding land by dikes. All of these conditions contribute to an increase in groundwater salinization. Areas with high permeability seem to constitute a preferential way of movement for salt water from the sea or lagoon towards the mainland. Old fossil water seems to be able to reach the surface and contribute to an increase in the process of salt pollution. In fact, during the 1970s, several studies had detected, throughout the territory, the existence of a deep salt water aquifer storing fossil saline water. This aquifer lies at a depth of about 300-450 m in the southern part of the study area and of more than 600 m in the northern part of the Venice mainland. Salt water contamination of subsoil could cause ground salinization and, consequently, desertification of the area, with great economical consequences. These include damaging the large agricultural development of the territory as well as having adverse impacts on the tourist industry. The combined use of adequately validated geophysical and geochemical tools confers a multidisciplinary character to the research and allows for the definition of the phenomenon’s superficial extension. Geophysical analysis based on Vertical Electrical Sounding (VES) and conductivity logs have been performed together with water table measurements and geochemical analysis on samples collected from selected wells. Moreover, a critical review of old geophysical data allowed for the verification of possible saline contamination changes in time. Interesting results have been obtained within the northern sector of the Venice lagoon mainland, specifically within territory of Jesolo. In this case, considering the influence of the Piave and Sile rivers and the presence of a coastal sand dune, it is possible to create a map of salt water contamination to evaluate the agricultural use of superficial water. Therefore, the aim of this research is to define the effective origin of salt water found in the aquifers of the northern lagoon mainland, its distribution, extension and its preferential way of movement within the territory. Thereby, relating all the information acquired to the geological, geomorphological and stratigraphic characteristics of the area.