Keeping it simple: Benefits of targeting riffle-pool macroinvertebrate communities over multi-substratum sampling protocols in the preparation of a new European biotic index

Abstract

Abstract The purpose of this study was to test the performance of a new sampling strategy for bioassessment of water quality. The macroinvertebrates living in the mineral substrata of geomorphological unit riffles strategy (MMS-GUR) concentrates sampling effort on certain geomorphologically and hydrobiologically representative units within survey sites and refines the level of taxonomic sorting of pertinent macroinvertebrate communities therein. Previous data have demonstrated that the mineral substrata of geomorphological unit riffles (GURs) harbour a wide variety of macroinvertebrates and pollution-sensitive taxa [Beauger, A., Lair, N., Reyes-Marchant, P., Peiry, J.-L., 2006. The distribution of macroinvertebrate assemblages in a reach of the River Allier (France), in relation to riverbed characteristics. Hydrobiologia 571, 63–76]. These units are typical of alluvial rivers and are easily identified from the bank and easily sampled. The objectives of the present study were to specify the sampling effort required to obtain representative taxonomic data from these communities, and to compare the performance of the new protocol with that of an established multi-substratum sampling methodology (XS). Two sampling series were carried out on two rivers within the same hydro-ecoregion. Two separate data were compiled from each site, incorporating taxon lists and relevant biological, ecological and physiological trait (BEPT) information, one using conventional (XS) methodology and the other from the MMS-GUR protocol. Macroinvertebrates sampled from three GURs of the River Allier ranged from pollution-tolerant to pollution-sensitive taxa. A comparison between the two methods (MMS-GUR and XS) conducted on the Allier and the Loire confirmed the validity of GURs as representative features, showing that pollution-sensitive taxa were better represented on mineral substrata and pollution-tolerant taxa were not over-estimated. The XS method is characterised by eight samples, while preliminary studies on the Allier suggested that a maximum of 13 samples were required to obtain sufficient taxonomic richness using the MMS-GUR methodology. However in river sections where pollution-sensitive taxa were numerous, the number of MMS-GUR samples required for analysis could be reduced to 10 or 8. In the context of the EU Water Framework Directive and associated AQEM project, the MMS-GUR protocol may facilitate the comparison of different rivers by sampling macroinvertebrate communities from similar rhithron or epipotamon habitats and focussing on pollution-sensitive taxa. It has the further advantage of reducing the time and effort spent in sampling and sorting. Increasing the resolution of taxonomic information to the genus level may also improve the standard of water quality assessment.