A new multimetric macroinvertebrate index for the ecological assessment of Mediterranean lakes

This study outlines the development and application of a new multimetric index (Greek Lake Benthic macro invertebrate Index - GLBiI) for the assessment of the ecological quality of Greek lakes, based on the ecological quality ratio (EQR), under the requirements of the Water Framework Directive. Profundal and sublittoral benthic macroinvertebrates from 18 lakes were biannually sampled across Greece. Additionally, 21 environmental parameters and 5 human pressures were assessed for each lake. The hindcasting approach was used for the establishment of reference conditions after minimizing human pressures. A pool of 84 candidate metrics, representing diversity/richness, sensitivity, functional traits, and taxonomical composition, were tested for the development of the multimetric index. Spearman's rank correlation extracted seven environmental parameters (lake area, mean depth, altitude, alkalinity, dissolved oxygen at bottom and conductivity at bottom) and three human pressures (total phosphorus, population density and non-natural land cover) that were further stepwise linear regressed against each biological metric for pressure-response relationships. Finally, three metrics, the number of taxa and the Simpson's diversity index in the profundal and sublittoral zones, and the relative contribution of Chironomidae (%) family in the profundal zone, were selected as the most appropriate, responding to eutrophication (expressed as total phosphorus and non-natural land cover). The multimetric index GLBiI was expressed as the mean of the EQRs of its metrics following a five class ecological status system. This assessment method may be used in other Mediterranean lakes with similar characteristics.