Assessing nitrate groundwater hotspots in Europe reveals a severely inadequate designation of Nitrate Vulnerable Zones

Abstract Monitoring networks show that the European Union Nitrates Directive (ND) has had mixed success in reducing nitrate concentrations in groundwater. By combining machine learning and monitored nitrate concentrations (1992-2019), we estimate the nitrate hotspot area in Europe to be 401,000 km2, with 47% occurring outside of Nitrate Vulnerable Zones (NVZs). We also found contrasting increasing or decreasing trends, varying per country and time periods. We estimate that only 5% of the 122,000 km2 of hotspots in 2019 will meet nitrate quality standards by 2040 and that these may be offset by the appearance of new hotspots. Our results reveal that the effectiveness of the ND is limited by time-lags between the implementation of good practices and pollution reduction and an inadequate designation of NVZs. Significant improvements in the designation and regulation of NVZs are necessary, if the objectives of EU legislation to protect groundwater are to be achieved.