An Expedited Procedure to Highlight Rapid Recharge Processes by Means of Nitrate Pollution Dynamics in the Northern Italy Plain

In recent decades, increasing anthropogenic pressure and climate change have made the protection and sustainable management of groundwater resources essential. In this context, the identification of aquifer recharge zones, especially those characterized by rapid groundwater flow and high vulnerability to surface pollution sources, becomes a priority for the protection of underground resources. In the Po Plain (northern Italy), based on the lithological, geometric, hydraulic, and hydrodynamic characteristics of the aquifers, the recharge areas are mainly located in the alluvial fans of the Alpine and Apennine foothills. Due to the high hydraulic conductivity of the aquifer, the shallow depth of the water table and the agricultural activities, groundwater resources are vulnerable to nitrate (NO3−) contamination. Given this background, the present study introduces a novel methodological approach based on the geochemical signature of groundwater, indicated by the presence of bicarbonate (HCO3−) and NO3− ions, aimed at identifying aquifer recharge areas. Specifically, by analyzing time series of NO3− and HCO3− concentrations for the period 2012–2023, and applying criteria of an HCO3−/NO3− ratio < 10 and NO3− > 30 mg/L, it was possible to identify areas where aquifer recharge processes are clearly evident. These recharge processes are rapid, as confirmed by the hydraulic gradient, the high hydraulic conductivity of the aquifers, and further supported by the isotopic composition of groundwater, especially tritium concentrations. Furthermore, due to the hydrogeological characteristics of the surveyed region, which resemble those of alluvial basins in close proximity to mountain ranges, the methodology and findings of this study can be used as an unconventional and expedited method for similar research conducted globally, offering hope for the future of groundwater research.