Larval Odonata distribution as a describer of fluvial ecosystems: the Rhône and Ain rivers, France

Odonata larval populations have been sampled during spring and summer in 8 old beds of the Rhône River and in 8 old beds of its tributary, the Ain River, upstream of Lyon (France). The method consists of a series of hand-net samples evenly distributed along the old beds. It does not provide high numbers of larvae in each sample, but the great number of samples allows the comparison of numerous environments in the study area. This research reveals how Odonata larval populations may describe some features of the hydrosystem functioning, e.g. links with the main stream, the rate of groundwater supply, the astaticism of the water bodies and the succession of the old riverbeds toward semi-aquatic and terrestrial conditions.