Dragonflies (Insecta: Odonata), indicators of the diversity and ecological integrity of alluvial river ecosystems?

After decades of regulation, sectors of the French Upper Rhône River were restored. In this study, we aim to assess the ecological status of a set of seven floodplain channels of the area of Belley using a relatively inexpensive bioindicator: adult Odonata. Surveys were carried out during summer 2019 by following the RhoMeO Odonate protocol. The number of observed species (19) was low compared with a theoretical list of expected species (31). Several existing indices based on adult Odonata assemblages led to different characterisations of the floodplain, with an ecological status varying from bad to good, which highlights the divergence between indices depending on their thresholds and focus. A comparison with other bioindicators sampled between 2003 and 2019 as part of the monitoring of the restoration revealed correlations between adult Odonata and macrophytes in terms of alpha diversity. An analysis of beta diversity showed that variations in adult odonate community composition between sites reflect different levels of lateral hydrological connectivity within the floodplain. This perspective is the same as for other aquatic macroinvertebrates. Moreover, an analysis of links between macroinvertebrates and water temperature showed negative correlations between macroinvertebrate taxonomic richness and maximum water temperature or annual temperature range as well as a positive correlation between macroinvertebrate abundance and minimum summer temperature