Chironomid (Insecta: Diptera) Assemblages from a Gradient of Lotic and Lentic Waterbodies in River Floodplains of France: A Methodological Tool for Paleoecological Applications

International audienceGandouin et al. 2006. Chironomid (Insecta: Diptera) assemblages from a gradient of lotic and lentic waterbodies in river floodplains of France: a methodological tool for paleoecological applications. Abstract The chironomid species inhabiting a natural dead arm (the Pilet dead Arm), two artificial backwaters (the Saxy Dyke field and the Ranchier Dyke Field) and the main channel of the lower Rhoˆne River (South of France) were studied. A between-class (between-station) Correspondence Analysis (CA) showed that, on the scale of the alluvial plain, habitat is a major factor influencing the species assemblages. The assemblage composition on the transversal floodplain gradient was compared with existing data on assemblages from the main channel of the Garonne River (South of France) and three of its floodplain waters (two side arms and one oxbow lake). In order to work at the level of taxonomic determination commonly used in paleoecological studies, the overall dataset (lower Rhoˆne + Garonne) was analyzed to the genus level. The genus level analysis confirmed that chironomid assemblages can be used to characterize the connectivity of small waterbodies with the main river channel and 44 chironomid genera were classified according to their hydrological preferences (lentic habitat taxa, ubiquitous taxa and lotic habitat taxa). This classification was then applied to a paleoecological dataset from the Saint-Omer basin (North of France) in order to test the potential of chironomids for paleoecological studies on fluvial environments. The results presented here highlighted this potential and indicate that river chironomid assemblages can be used as descriptors for alluvial habitats, and allow researchers to evaluate the level of connectivity of these habitats with the main river channel during floods. River chironomid assemblages are a promising tool for reconstructing past hydrological changes and for obtaining information on paleoflood periodicity