Hydrostratigraphic setting and groundwater dynamics in high salinized low-lying farmlands at the southern margin of the Venice Lagoon

<p><strong>Hydrostratigraphic setting and groundwater dynamics in high salinized low-lying farmlands at the southern margin of the Venice Lagoon</strong></p><p><strong>¹</strong> Institute of Geosciences and Earth Resources, National Research Council, Padova, Italy</p><p>² Institute of Marine Sciences, National Research Council, Venice, Italy</p><p>³ Department of Geosciences, University of Padova, Padova, Italy</p><p>⁴Regione Veneto - Soil Defence Regional Directorate, Venice, Italy</p><p>⁵Land Reclamation Authority Adige Euganeo, Este-Padova, Italy</p><p>&#160;</p><p>* Corresponding author: chiara.cavallina@igg.cnr.it</p><p>&#160;</p><p>Key words: salt-water intrusion, groundwater dynamics, coastal plain, Venice</p><p>The coastal plain at the southern margin of the Venice lagoon is a low-lying territory, which is the result of river diversions, channeling, and hydraulic reclamation that took place over the last centuries. The mechanisms controlling the exchanges between surface water and groundwater progressively shifted from natural to artificial ones. Presently, most of this territory lays at ground elevation up to 3 m below the mean sea level and a complex network of drainage channels and pumping stations regulates the depth of the water table both to prevent flooding-waterlogging and to allow irrigation. Being at the lagoon margin and next to the sea, the aquifers of this area are heavily affected by salt-water intrusion that jeopardizes the farmlands productivity and specifically damages the crop yield. Focusing on the geology and stratigraphic architecture of the first 25-meters of the subsoil, in which the shallow aquifers are included, the sedimentary record consists in Pleistocene alluvial deposits and Holocene deposits. The latter show the typical transgressive wedge including prodelta, littoral and back barrier depositional environments. Specifically, the Holocene littoral sands contain the unconfined aquifer, which is almost continuous along the whole coastal strip. &#160;Sedimentary bodies as paleo-channels and remnants of littoral ridges, commonly hosting unconfined aquifers, are present all over coastal plain. Pleistocene alluvial deposits contain the first locally confined aquifer.</p><p>Several past studies have revealed the complexity of freshwater-saltwater exchanges imposed by the concomitance of various forcing factors. However, a specific study on the dynamic of saline contamination of the groundwater is still missing. We present here the preliminary results of an ongoing research aimed to characterize the groundwater dynamics and disentangle mechanisms that control groundwater salinity in the shallow aquifer system of the low-lying farmlands adjacent to the southern Venice lagoon margin and the Brenta-Bacchiglione river mouth. The results of detailed analyses from various perspectives (based on sedimentary cores, continuous hydrological and hydrogeological data, geophysical surveys) are properly integrated to describe the dynamics in the shallow aquifer system. Particular attention is payed to the hydro-morpho-stratigraphic system in relation to the mechanisms driving the freshwater-saltwater exchanges. This research is developed in the frame of the Interreg Italy-Croatia project MoST (Monitoring Sea-water intrusion in coastal aquifers and Testing pilot projects for its mitigation), which addresses to improve the quality and sustainability of the human management of water resources in coastal areas.</p>