Hydrogeochemical and isotopic characterization of the Gioia Tauro coastal Plain (Calabria - southern Italy): A multidisciplinary approach for a focused management of vulnerable strategic systems.

This work pursues the hydro-geochemical and isotopic characterization of the complex groundwater system of the Gioia Tauro Plain, one of the most important industrialized and agricultural coastal areas of southern Italy. The anthropic pressure exposes the water resources at risk of depletion and quality degradation making the plain groundwater a system of high scientific and social interest. The plain is characterized by a shallow aquifer, mostly recharged by local rains and a deep aquifer apparently less influenced by local precipitation. Both aquifers are mainly Ca-HCO3 waters except for localized sectors where Na-HCO3, Na-Cl and Ca-SO4 waters are present. In deep aquifer, both prolonged interaction with sedimentary rocks, mainly deriving from the erosion of crystalline rocks, and direct cation exchange represent the primary factors controlling the formation of Na-HCO3 waters. Mixing processes between these waters and either connate brine and/or deep thermal waters contribute to the formation of isolated high salinity Na-Cl-rich waters. In shallow aquifer, inputs of N-rich sewage and agriculture-related contaminants, and SOx emissions in proximity of the harbor are responsible of the increasing nitrate and sulphate concentrations, respectively. The Cl/Br and NO3/Cl ratios highlight contamination mainly linked to agricultural activities and contribution of wastewater. Along the northern boundary, the warmest groundwater (Na-Cl[SO4]) were found close to a bend of the main strike-slip fault system, locally favouring the rising of B- and Li-rich deep waters, testifying the influence of geological-structural features on deep water circulation. Despite the high-water demand, a direct marine intrusion is localized in a very restricted area, where we observed an incipient groundwater-seawater mixing (seawater contribution ≤7 %). The qualitative and quantitative conditions of the shallow aquifer still have acceptable levels because of the relatively high recharge inflow. A reliable hydrogeochemical conceptual model, able to explain the compositional variability of the studied waters, is proposed.

A multivariate non-parametric approach for estimating probability of exceeding the local natural background level of arsenic in the aquifers of Calabria region (Southern Italy).

The concept of natural background level (NBL) aims at distinguishing the natural and anthropogenic contributions to concentrations of specific contaminants, as groundwater management and protection tools. This is usually defined as a unique value at a regional scale, even when the hydrogeological and geochemical features of a certain territory are far from homogeneous. The concentration of target contaminants is affected by multiple hydrogeochemical processes. This is the case of arsenic in the Calabria region, where concentrations are definitely variable in groundwater. To overcome the limitation of a traditional approach and to include the intrinsic hydrogeological and geochemical heterogeneity into the definition of the natural contribution to As content in groundwater, an integrated probabilistic approach to the NBL assessment combining aquifer-based preselection criteria and multivariate non-parametric geostatistics was proposed. In detail, different NBL values were selected, based on the aquifer type and/or hydrogeochemical features. Then, these aquifer-based NBL values of arsenic were used in the Probability Kriging method to map the probability of exceedance and to provide contamination risk management tools. This multivariate geostatistical approach that takes advantage of the physico-chemical variables used in the aquifer-based NBL values definition allowed mapping the probability of exceedance of As in a physically-based way. The hydrogeochemical diversity of the study area and all the processes affecting As concentrations in the aquifers have been considered too. As a result, the obtained map was characterized by a short-range and long-range variability due to local hydrogeochemical anomalies and water-rock interaction and/or atmospheric precipitation. By this approach, the NBL exceedance probability maps proved to be less "noisy", because the local hydrogeochemical conditions were filtered, and more capable of pointing out anthropogenic inputs or very anomalous natural contributions, which need to be investigated more in detail and properly managed.