Effects of hydrological regime on the drift algae in a regulated Mediterranean river (River Verdon, southeastern France)

The lower part of the River Verdon is profusely regulated by hydroelectric impoundments and the exploitation of canals by the water supply company. This study is an attempt at determining the effects of mean daily flow on the suspended algae in this river. The sampling sectors were localized downstream to the last hydroelectric dam. Two patterns of hydrological regime were analyzed in this hydrosystem: the river manifests a stable and low residual flow and the canal is characterized by a stronger and annually variable flow. In the canal, the algal community has a lower species richness, cell density and diversity than in the river. The abundance of drift algae decreases significantly with the flow. The composition of the algal community also varies in accordance with the flow. The response of drift algae to hydrological regime shows strong seasonal variations; the hydrological disturbance was heavily linked to the freshwater needs. Copyright © 2001 John Wiley & Sons, Ltd.