ELF - A benthic macroinvertebrate multi-metric index for the assessment and classification of hydrological alteration in rivers

Hydrological alteration prevents unpolluted rivers from reaching acceptable ecological conditions. In Europe, 40% of rivers are degraded due to hydrological alteration but the indices currently used in ecological monitoring cannot quantify the degree of hydrological alteration or discriminate between pollution and hydrological alteration. In this article, we demonstrate the development, calculation and validation of the Hellenic Flow Index (ELF), a new macroinvertebrate-based multi-metric index to assess, quantify and classify hydrological alteration in Greek streams and rivers. 1351 samples collected throughout Greece were partitioned in reference and test datasets and were pre-classified in varying levels of pollution and hydrological alteration. Optimal flow ranges for benthic macroinvertebrates were calculated and flow sensitivity metrics were developed. We tested the predictive accuracy of 607 versions of the ELF index, that is, 607 combinations of seven hydrologically sensitive macroinvertebrate metrics. The developed index is a combination of two ELF versions that had the highest predictive accuracy on two validation datasets. The index developed can assess, quantify and classify hydrological alteration and is also capable of discriminating between pollution and hydrological alteration. The ELF's overall predictive accuracy was 75% and the index was equally accurate in discriminating between clean, polluted and hydrologically altered sites. Within the regular ecological monitoring, water agencies, managers and decision makers can now use a tool that will quickly flag watercourses that specifically need hydrological restoration instead of pollution mitigation measures and thus apply targeted actions towards the ecological restoration of rivers.