Harmonisation of a new assessment method for estimating the ecological quality status of Greek running waters

During the last decades, a great number of indices have been developed throughout Europe to fulfil the requirements of the Water Framework Directive (WFD) and to assess the ecological impacts of anthropogenic pressures. The development of a methodology for assessing the ecological quality status of Greek rivers and streams was urgently needed because the existing European indices were not adapted efficiently to the particular hydrological and climatic conditions of this Mediterranean region. After selecting the most appropriate typological system, four systems were tested using a different number of reference samples based on a vast number of criteria from impaired to at least impaired sites. The most suitable typological system was found to be the river types (IC) from the Mediterranean Intercalibration exercise. Reference or minimally disturbed sites to evaluate the Ecological Quality Ratio (EQR) for each river type were selected previously to the development and selection of the most appropriate metrics or biotic index based on benthic communities for the assessment of the ecological quality of the rivers. In this frame, 42 European metrics and indices, were tested against a) their response to three quality gradients (undisturbed, slightly disturbed and disturbed), b) their acquisition of a low interquartile coefficient and c) a low Spearman's correlation between the metrics and indices. Hence, 9 metrics and indices were examined for their response to human pressures and the Hellenic Evaluation System 2 (HESY2) was selected and successfully intercalibrated with the assessment methods of the other countries, using the option of indirect comparison based on near-natural reference sites (reference benchmarking). This index showed a significant correlation with some anthropogenic pressures (e.g. P-PO43−, artificial and agricultural areas) in all IC types. HESY2 estimates also more than 86% of the moderate samples correctly and beside this, it provides a precise, explicit and simply applicable assessment of the ecological quality status in Greek streams and rivers. HESY2 is applied for the assessment of the ecological quality in Greek running waters and will be further justified considering the results of the forthcoming National Monitoring Program (2017-2022).