Benthic community composition in relation to changes of local hydraulic conditions in diverse european geographic contexts

The variability of hydraulic conditions is a major driver of benthic community composition and has been proven to highly confound the evaluation of ecological quality using biological metrics. The aim of this paper is to investigate if and how local hydraulic conditions act concurrently with other environmental e.g. quality factors in influencing benthic invertebrate assemblages or provide independent effects. The dataset used consisted of almost 150 stream sites located in four broad European geographical contexts: Alps, Central mountains, Mediterranean mountains and Lowland streams. For its wide applicability, the Lotic-invertebrate Index for Flow Evaluation (LIFE) was computed to characterize hydraulic conditions from a biological standpoint. Using River Habitat Survey data, descriptors of hydraulic conditions (LRD), habitat diversification (HQA) and morphological impairment (HMS) were derived, alongside a synoptic Organic Pollution Descriptor (OPD). Relevant amounts of variability and significant relationships between the biological and abiotic hydraulic descriptors (LIFE and LRD respectively) were observed by means of multiple regression models in most of the datasets. Nevertheless, the biological index responded as well to the other environmental descriptors (mainly organic pollution). Correction factors to reduce the influence of sources of variability other than hydraulic conditions on this metrics are thus proposed.