European water framework directive, ecological quality status and biological conditions

The objective of the European Water Framework Directive (WFD) is to achieve and maintain a ‘good ecological quality’ in aquatic ecosystems. Ecological quality status is defined as the deviation from near-natural reference conditions and divided into five ecological quality classes. The classes span a biological condition gradient (BCG) whose narrative description is annexed to the WFD. This description also encompasses hydromorphological and physicochemical characteristics along the gradient. BCGs are provided for phytobenthos, phytoplankton, macrophytes, macroinvertebrates, and fishes in lakes, rivers, transitional and coastal waters. This framework provided the basis for the development of freshwater assessment and monitoring systems all over Europe. Many systems have been developed using physico-chemical and hydromorphological parameters to derive environmental gradients of degradation. In a second step, environmental gradients were related to BCG gradients, A large variety of indices and (multi-)metrics are used for assessment, of which, for instance, the German multi-metric standard "PERLODES" is using river macroinvertebrates. The results are expressed as ecological quality ratio (EQR), which is equivalent to the ‘distance’ between the current and the reference condition. The features, advantages and shortcomings of these systems, such as evaluation of uncertainty, definition of class boundaries, intercalibration of systems across Europe, will be discussed.