Impact of the residual flow on the physical characteristics and benthic community (algae, invertebrates) of a regulated Mediterranean river: the Durance, France

The Durance is a large regulated Mediterranean river characterized by a greatly reduced residual flow. A limnological study was conducted on a 4-km section of the middle course of the regulated river. The main environmental consequences of residual flow were: the high daily and annual thermal amplitudes and the reduction of the diversity of available habitats. The benthic communities (algae and macroinvertebrates) were characterized by lower diversity and density, if compared with homologous non-regulated rivers of the same zone; this was considered to be a consequence of channel constriction and the disappearance of numerous aquatic habitats (side arms, back-waters, etc.). The invertebrate community, represented by eurythermic and psychrostenothermic species, showed distinct seasonal dynamics which were an expression of its adaptation to the important hydrothermal variations during the annual cycle. The eurythermic species—which are polyvoltine, were present throughout the year. The stenothermic species—which are monovoltine species, with a short life cycle developed during the winter and spring months in which thermal conditions were still favourable for them.