Assessing Nitrate Concentration and Groundwater Hydrodynamics in Veneto Region : A Multi-Decade Analysis Using Spatial, Stratigraphic, and Isotopic Approaches

Nitrates are naturally occurring molecules in the environment, but their concentrations have become increasingly concerning due to agricultural activities. This is partially due to the widespread use of nitrogen fertilizers and manure, which convert to nitrates, significantly decreasing groundwater quality. This issue prompted the European Union to introduce the “European Nitrate Directive” in 1991, setting a nitrate concentration limit of 50 mg/L in groundwater. Spatial and temporal data on annual nitrate concentrations were collected across the Veneto region by the Regional Environmental Agency over a 20-year period (2003-2023). Understanding groundwater hydrology and retention times is essential to evaluate whether the measures implemented by EU member states are improving water quality. This study focused on the sub-region of Veneto plain to the east of the Brenta river extending from the pre-Alpine foothills to the Venice Lagoon characterized by unconfined aquifers and a multi-aquifer system. For the multi-aquifer system, accurately defining the depth and extent of each layer was crucial to constructing an accurate model to describe the fate of nitrates in groundwater. In the study area, data from more approximately 800 boreholes were analyzed to define the subsoil stratigraphy accurately. However, data discrepancies were occasionally observed, making a detailed analysis and reorganization of the dataset essential to achieve representative results. To further investigare subsurface dynamics, isotope analyses provided insights into water retention times and groundwater flow. Isotopes such as ¹⁸O, ³H, ³He/⁴He, Ne, ¹⁴C , ¹³C and ⁸⁷Sr/⁸⁶Sr quantified in the 1970s and 2000s proved particularly valuable in the understanding the hydrodynamics of the subsurface domain of interest.