Lake assessment strategy in European Union (EU): Case study of European large lakes

Assessment of the ecological quality of lakes and setting targets are key elements of lake management. The European Commission Water Framework Directive (WFD; EC 2000) requires development and harmonisation of the ecological status assessment systems for all surface waters (lakes, rivers, coastal, and transitional waters) and all biological quality indicators (phytoplankton, macrophytes, benthic fauna, and fish). The aquatic WFD classification for ecological status includes 5 criteria: “high,” “good,” “moderate,” “poor,” and “bad”. Ecological status is measured as a deviation from type-specific reference conditions defined as a biological, chemical, and morphological condition associated with no or very low human pressure. Good status means a slight deviation from reference conditions, providing a sustainable ecosystem and acceptable conditions for human uses. The general mandate of the WFD is to achieve good status for all surface waters by 2015. The implementation of the WFD raises challenges widely shared by the EU member states and includes an extremely demanding timetable, but an incomplete technical and scientific basis. A large number of fundamental issues need further elaboration to make the transition from principles to practical implementation. To address the challenges in a cooperative and coordinated way, the EU member states, Norway, and the European Commission agreed on a Common Implementation Strategy (EC 2001) for the Water Framework Directive. This process has resulted in a number of guidance documents that form the basis for the development of ecological classifications and Intercalibration process (EC 2003a, 2003b, 2003c, 2005a). The Intercalibration process has been coordinated and scientifically led by the European Commission Joint Research Centre in close collaboration with the WFD Ecological Status Working Group and the expert networks. Our aim is to describe a novel approach for Europe-wide classification of the ecological quality of surface waters and harmonisation of the classification systems required by the WFD. We focus on the establishment of reference conditions and quality class boundaries for European lakes according to a phytoplankton indicator – the concentration of chlorophyll a. The approach is illustrated through a case study in which the ecological status of 54 European large lakes was evaluated according to the proposed criteria.