Comparison and harmonization of eutrophication assessment criteria under the WFD and the Nitrate Directives

Eutrophication of surface water bodies is the most significant water quality problem worldwide. The EU has developed an extensive regulatory and policy framework to protect the environment from nutrient pollution. Although efforts have been made to integrate and create connections between directives, the various requirements and implementation regarding monitoring, assessment and reporting may be different thus hindering the efficient implementation of water policy. The Nitrates Directive (ND) aims at the protection of European surface and ground waters from agricultural pollution due to nitrates, and to promote good agricultural practices. All surface waters should be classified regarding their eutrophication status thus contributing to designation of Nitrate Vulnerable Zones where nutrient management measures are implemented. Since the ND does not stipulate the methodology to assess eutrophication, a plethora of eutrophication assessment criteria have been used by countries which have not been compiled and analysed so far. On the other hand, the Water Framework Directive (WFD) is a comprehensive legislation that mandates the assessment of ecological status of all surface waters based on a variety of elements. It is important that both directives use similar eutrophication assessment criteria achieving consistent implementation of management measures. In this study, for the first time, the criteria used to assess eutrophication under the WFD and the ND are compared and analysed. Furthermore, two case studies are used in order to evaluate the differences. The results show that eutrophication criteria used under different legislations are often incompatible and lead to dissimilar designation of the status of water bodies.