Saltwater contamination seriously affects water quality and land productivity of reclaimed farmlands along the Venice Lagoon, Italy. To characterize the hydrogeochemical dynamics involved in this phenomenon, a three-year study was carried out in an experimental field located at the southern margin of the Venice Lagoon. Soil matric potential, quality of soil pore water and groundwater, and soil physical and chemical properties were monitored at five monitoring stations. Relationships between Cl−, Na+, Mg2+, Ca2+, K+, SO42−, Br− ionic concentrations, and electrical conductivity of the water samples with the soil characteristics (e.g., texture, exchangeable cations) were investigated. Soil water flux direction was calculated and related to ion concentrations. Moreover, specific molar ratios (Mg/Ca, Na/Cl, Cl/Br, and SO4/Cl) were calculated to identify the main drivers affecting salinity in the field. The study confirmed that the experimental site was strongly affected by soil and water salinity, and two major contamination dynamics were identified. The first one was mainly driven by seawater intrusion from the near lagoon and salty watercourses, while the second was derived by the interactions between the peaty soil and salts that were originally in place, since the area was only reclaimed a few decades ago. The latter highlighted the potentiality of the experimental field to become an acidic sulfate environment. Ionic ratios were implemented and proved to be an important tool for the identification of salinity origin.
<p>Saltwater intrusion in coastal aquifers is a global problem recently worsened by anthropogenic activities (e.g., aquifer overexploitation, hydraulic reclamation and drainage of low-lying areas) and climate change effects (e.g., severe droughts, sea level rise) that contribute to reduce groundwater natural recharge, water quality, and agricultural production. Many low-lying coastal plains facing the Adriatic Sea are strongly affected by saltwater intrusion with serious consequences on agricultural activities and tourism that may become dramatic in a relatively short time due to climate change. In this framework, this work aims to identify monitoring strategies to characterize the process of saltwater intrusion under the effects of climate change and recommend appropriate countermeasures in two Adriatic low-lying coastal plain: south of the Venice Lagoon (north-eastern Italy), and at the Neretva River mouth (south-eastern Croatia).</p><p>Geomorphologic, stratigraphic, hydrogeologic, and agricultural data were collected to characterize the aquifer system at both sites and assess the effects of seawater intrusion on agricultural productivity. Saltwater intrusion was monitored and analysed through monitoring systems that provide qualitative and quantitative information on the processes influencing groundwater and surface water dynamics within the two coastal systems. Moreover, laboratory physical models were developed to serve as benchmarks for the numerical models used to simulate the field results. Numerical modelling reliably implements boundary and initial conditions defined in-situ on both sites, simulates existing states, specifies different scenarios, and predicts salinization dynamic changes caused by climate changes.</p><p>The results of the research activities include the development of specific tools for the management of agriculture-related activities and freshwater resources in coastal areas including vulnerability assessment, mitigation plans, and countermeasures against salt contamination. These results were obtained by integrating the findings gained on both sites, considering differences and peculiarities of the specific areas that are representative of many low-lying plains located on both sides of the Adriatic coast.</p><p>This study has been funded by the contribution from the EU cofinancing and the Interreg Italy&#8211;Croatia Cross Border Collaboration (CBC) Programme 2014&#8211;2020 (Priority Axes: Safety and Resilience) through the European Regional Development Fund as a part of the projects MoST &#160;(AID: 10047742) and SeCure (AID: 10419304).</p>
Estimating the hydraulic properties of the vadose zone is essential to understand soil-water dynamics and achieving appropriate water management in agricultural lands. Inverse modelling methods are commonly used to estimate hydraulic properties from field observations. Unlike the extensively applied local search methodologies, data assimilation techniques can fully account for multiple uncertainties and are becoming a widely used tool for estimating hydraulic parameters. However, only few applications on real field tests are available. The main objective of this study was to estimate the van Genuchten-Mualem (VGM) parameters and the saturated hydraulic conductivity (K s ) of a heterogeneous low-lying farmland at the margin of the Venice Lagoon, Italy, characterized by high peat content, sandy drifts, and a very shallow water table. To this end, two methods were tested, that is, the Ensemble Smoother (ES) and the Levenberg-Marquardt (LM) algorithm associated with hydrological modelling performed with Hydrus-1D. Volumetric water content (VWC) observations were collected at three monitoring sites from May to September 2011. Results on parameters highlighted that the ES technique effectively reduced the uncertainty of α and n, but it was less effective on θ r and K s . The results on VWC showed that the ES efficiency decreased with the increasing non-linearity of the system (e.g., higher sand content) and when the variability of the experimental data was lower (e.g., deepest soil layers where saturation remained permanently close to 1). Both LM and ES allowed to reproduce the VWC observations in the calibration and validation phases, with the former and the latter performing better in the case of sandy and peat soils, respectively. As concerns the method applicability, the ES was less timedemanding as it efficiently updated all the parameters at once and was less dependent on the user choices. Finally, the paper points out the importance of previous knowledge of the VGM parameters (e.g., from lab hydraulic analyses) in defining the constraints for the optimization.
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