Bringing European river quality into line: an exercise to intercalibrate macro-invertebrate classification methods

Intercalibration requires the value of the boundary between high and good status classes, and that between good and moderate status as defined by national biological assessment systems, to be consistent with definitions outlined in the Water Framework Directive and comparable between Member States. This intercalibration, the first attempted at such a wide European scale, was performed on the response of river macro-invertebrates to multiple stressors using national data from fifteen Member States belonging to the Central Baltic Geographical Intercalibration Group (CBGIG). Member State based their boundaries on samples that are not directly comparable because of differences in sampling methods and defined their boundaries using different biotic indices. In order to facilitate a comparison of boundaries, values of national classification systems were expressed as ecological quality ratios (EQRs: ratio between the measured status of the biological quality element and the expected value of the biological status at reference state) and translated to a common metric. Mean ecological boundary values were calculated from national boundary values that were agreed for adoption by the Member State, provided the boundary values and assessments systems on which they were based complied with a stringent list of criteria. A range representing an acceptable degree of uncertainty around the mean high/good and good/moderate boundary values, known as the ¿harmonisation band¿ (mean boundary value ± 0.05 EQR units) was defined to account for variation between national methods. In order to ensure comparability of ecological status, Member States with boundary values below this band were required to adjust their boundary value to fall within the harmonisation band.JRC.H.1-Water Resource