The KNOW project (implementing the Knowledge of NitrOgen in groundWater) implementation in a NVZ Sardinian area

In EU, nitrate pollution of groundwater is particularly relevant. Through the Nitrate Directive (ND, 91/676/EEC), the EU countries identified Nitrate Vulnerable Zones (NVZ’s), developed protocols of good agricultural practices and set up action programs for the management of farm wastes. However, the ND is emblematic of the asymmetries between the objectives and the effectiveness of its implementation, and the nitrate pollution of EU groundwater has not decreased following over 20 years of ND implementation. The KNOW project1, coordinated by University of Cagliari (Sardinia, Italy) in partnership with NRD (University of Sassari), is framed within research activities of the joint research team for the integrated risk assessment of aquifer pollution of agricultural origin (www.agroscenari.it; www.wadismar.eu; www.uniss.it/nrd). A NVZ was identified in the dairy farming district of Arborea (W-Sardinia). Previous research had shown that nitrate pollution of groundwater in Arborea can have different sources, including chemical and organic fertilizers and urban sewage. This problem is particularly severe in relation to the multi-layer aquifer hosted in the Quaternary sands, that represents one of the most relevant source of freshwater in the study area. Due to its typology, the aquifer is highly vulnerable to pollution. In this framework, KNOW aims to develop integrated knowledge on nitrate flow in groundwater, by means of: a) evaluating the efficiency and effectiveness of geochemical and isotopic tracers (18O, 2H, 15N, 34S and 11B) as indicators of the groundwater recharge areas and nitrate pollution sources in the Arborea NVZ; b) define, by means of mathematical models, the relationship between agricultural practices and the water quality that contributes to recharge the aquifers; c) propose innovative protocols for detection, monitoring and processing of qualitative and quantitative parameters of groundwater resources. The KNOW project is integrating approaches from geochemistry, hydrogeology and agronomy. The research is focused in a transect of 2 x 0.2 km where the groundwater flows and spatial distribution of the nitrate concentration have been assessed in the sandy aquifer through quarterly monitoring conducted in 2007-2009 on 34 wells. Along the transect, farmers were interviewed about the agronomic management practiced in each field in the last 5-years and a bi-monthly sampling of groundwater from 12 wells was made for the chemical and isotopic data determination. The field water balance was assessed with the EPIC model. The actual mean nitrate concentration in the wells was 126 mg L-1; the weighted mean N surplus of the area is 320 kg ha-1 and the mean water surplus 256 mm. If all the N surplus was leached by the percolation water as nitrate, the nitrate concentration would range from a min of 380 to over 650 mg L-1, some five times higher than the actual concentration. The hypotheses being explored to understand the apparent discrepancy include the dilution effect from the upstream groundwater and the self-depuration processes of the aquifer through denitrification. The research activities involve the local farmers’ cooperative (some 200 farmers breeding 35,000 dairy cows) not just as data suppliers but as pro-active stakeholders in addressing the pollution of their own water.