Harmonization of the assessment method for classifying the ecological quality status of very large Greek rivers

The intercalibration exercise is required by the European Water Framework Directive (WFD) to harmonize the national ecological class boundaries across Member States. It is applied to individual types of water bodies, comparing WFD-compliant biological assessment methods using specific quality elements. This study addresses the harmonization of the STAR_ICMi index for the ecological status assessment of very large Greek rivers in compliance with the completed intercalibration exercise for European very large rivers. River sites were sampled biannually for benthic invertebrates (as biological quality element) and environmental data during different surveys. The water quality of the samples ranged from high to bad. STAR_ICMi was significantly correlated to the Combined Abiotic Pressure index (CAPi) and its component pressures channelization, riparian vegetation alteration, and to a lesser extent to organic pollution. During the intercalibration approach benchmark standardization was applied to the component metrics of the intercalibration index prior to boundary comparison to minimize typological differences. The Greek class boundaries of high/good and good/moderate ecological status were compared and harmonized with the “Global Mean View” defined in the completed European intercalibration exercise. Similarity percentage analysis of biological community variation was performed for sites in high, good, and less than good ecological status according to the intercalibrated Greek classification.