Comparison of eutrophication assessment for the Nitrates and Water Framework Directives: Impacts and opportunities for streamlined approaches

Eutrophication of surface water bodies is the most significant water quality problem worldwide. The European Union (EU) has developed an extensive regulatory and policy framework to protect the environment from nutrient pollution. Here, we examine the contrasting approaches of the Nitrates Directive (ND) and the Water Framework Directive (WFD) to assessing eutrophication status, comparing for the first time the different physico-chemical and biological criteria. We found inconsistencies in nutrient assessment criteria used to assess eutrophication between the two directives, with nitrogen often linked to less stringent drinking water standards rather than to ecologically relevant criteria. A comprehensive overview of the biological elements used as indicators across the EU for both directives was assembled for the first time. Biological assessment varied considerably with some Member States using only physico-chemical criteria underlining the need for the expansion of biological indicators used in the nitrates directive. Major inconsistencies exist among countries in the thresholds for nutrients for both directives with higher values used by countries with greater percentages of agriculture. There is a need to review and place thresholds appropriately to support good ecological status. It is imperative that both directives use similar eutrophication assessment criteria to achieve consistent implementation of management measures. Action should therefore be taken to harmonise eutrophication relevant definitions, criteria (parameters, metrics and thresholds) and report data in a disaggregated way. This will streamline approaches and better inform water quality aspects of a resilience strategy to meet current and future water management challenges.