Evaluation of the use of Water Framework Directive typology descriptors, reference sites and spatial scale in macroinvertebrate stream typology

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The aim of this study was to test the effect of the Water Framework Directive typology descriptors on a macroinvertebrate-based stream typology, the use of reference sites in comparison to the use of degraded sites, and both degraded and reference sites. The EU research projects AQEM and STAR provided 1660 samples of 48 stream types sampled all over the major geographical gradients in Europe. The samples included gradients from reference conditions to samples with bad ecological quality. These stream types fit the WFD typological demands. The macroinvertebrate data were analysed by using Detrended Correspondence Analysis (DCA). The observed macroinvertebrate distribution was tested against the WFD river typology by a graphical interpretation of the ordination diagrams. The major macroinvertebrate distribution patterns in European streams were based on climate (temperature), slope (current velocity), and stream size. The WFD descriptors ‘System A' for stream types are too rigid and should be replaced by temperature, current, and size. The differences in average numbers of taxa between the 1660 sites distributed over Europe were either caused by differences between local environmental factors or by sampling effort, not by temperature, elevation, stream order or latitudinal position. The distribution patterns using all samples, only reference samples, and only degraded samples showed that human stress diminished the natural differences between stream communities and typologies should therefore be based on reference conditions.

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