Valutazione dei meccanismi di degradazione dei nitrati durante il processo di infiltrazione e trasporto nelle acque sotterranee come verifica della efficacia delle misure di mitigazione della contaminazione nelle Zone Vulnerabili da Nitrati

The increase in intensive agriculture and animals has led to the widespread application of fertilizers in soils. This practice has resulted in the release of various chemical pollutants into the soil, which are then transported into the water table through the leaching action of rainwater. Despite the implementation of strict regulations outlined in the Nitrate Directive, no noticeable improvement in groundwater quality has been observed in many Nitrates Vulnerable Zones. The study area, the plain of Arborea (Sardinia), has been identified as a NVZ since 2005, and this phenomenon is clearly observable there. The unsaturated zone is a fundamental part of the hydrological cycle, capable of storing water, providing water for vegetation, transporting solutes, and breaking down pollutants before they reach the aquifer. The main objective of this research project is to assess the influence and role of the pedological and hydrological characteristics of soils on the timing and processes of transport and/or reactive mitigation of nitrates during the infiltration of water from the surface to the aquifer in an area characterized by significant use of nitrogen fertilizers. A multidisciplinary methodological approach has been adopted, including the acquisition of geological, pedological, hydrological, isotopic data, and experimental activities in an experimental plot located in Arborea. In the plain, an agricultural field was chosen as a pilot site, in which a monitoring system of the unsaturated zone was set up to obtain information on the processes taking place in the soil. TDR probes were installed to measure the volumetric water content, while suction cups were placed at different depths to sample pore water for analysis of ionic nitrogen species and nitrate isotopes. The experimental approach was coupled with the use of a physically based flow and transport model in the unsaturated zone, FLOWS, for simulating the flow and transport of nitrate at the pilot site. The Soil Water Balance (SWB) code and the isotope soil pore water profile method were employed to evaluate both the rate of groundwater recharge and the time lag between infiltration and water table attainment. The monitoring of the unsaturated zone combined with the determination of travel time and the models are a useful factor for the understanding of the processes occurring in the transported solutes and are an effective tool for the reduction of their leaching into groundwater and for the optimization of agricultural practices.