Abstract: Guidelines on ecological thresholds for temperature, low flows, and nutrients in European rivers.
The European Water Framework Directive (WFD) includes nutrient status, thermal conditions, and quantity and dynamics of flow as required quality elements for assessing ecological status in rivers. This document provides guidelines on developing upper and lower boundaries of Good Ecological Status (GES) thresholds for these three elements. It does prescribe generic fixed thresholds, as Member States are characterised by a range of climatic and geographic features, and there are no universal standards that can be applied to all rivers across Europe. We report on information received from 18 out of 28 Member States, revealing previously unreported established thresholds, as well as a lack of consistent measurement.
Separate typologies may need to be developed for each quality element according to the relationship between river typology and the characteristics of the element. A flexible system of nutrient monitoring and thresholds is needed, such as the method for phosphorus monitoring developed by UKTAG using site-specific values of alkalinity and altitude. Many Member States currently use the standards set out for rivers in the Nitrates Directive as a default for nitrate monitoring. However, these values may not be suitable for every river basin Member States need to develop thresholds that will allow them to meet the goals of the WFD. Co-limitation of nitrogen and phosphorus is an important concept to consider when developing management plans. Relevant temperature thresholds and monitoring systems for rivers must go beyond static values applied to all rivers and specific to only one taxon (fish), and move towards more dynamic approaches such as using species sensitivity distribution curves. The development of environmental flow standards has been largely overlooked thus far and almost no Member States have set these thresholds. Incorporating methods such as look-up tables and functional analysis approaches like the building block method provide a basis for developing dynamic and effective flow standards for EU rivers.