Étude comparée de la dynamique du zooplancton de trois réservoirs d'altitude et d'un lac naturel dans les Pyrénées

Abstract

L'étude comparée du peuplement zooplanc tonique en milieu naturel et en milieu perturbé, permet de préciser l'influence des modalités d'exploitation de ces retenues sur le développement de la communauté pélagique. En particulier, elle met en évidence pour la série lacustre considérée, un changement de structure de la communauté zooplanc tonique, un appauvrissement spécifique de cette communauté, et une diminution progressive de la productivité de ces milieux.A comparative study of zooplankton in three high-altitude reservoirs and one natural lake in the Pyrenees.Keywords : Zooplankton, kinetic, biomass, production, reservoirs, discharge, Pyrenees. The population dynamics and production of zooplankton have been evaluated in three neighbouring reservoirs (lake Aumar, Orédon, Aubert) and compared with previous results from the natural lake Port-Bielh (2 285 m) which had zooplankton that were specifically similar (dominant species : Polyarthra vulgaris, Mixodiap torn its laciniatits, Cyclops strenuns, Daphnia longispina).The chief difference between the three reservoirs was their thermal regime due to their morphometric and hydrological characteristics.All characteristics can be used to define a series, Port-Bielh-Aumar-Orédon-Aubert, characterised by a progressive diminution in the thermal climate and an increasing instability in the environment. This comparative study of zooplankton populations in a natural and perturbed environment shows precisely the effects of managing these reservoirs on the development of the pelagic community. In particular, the lake series is shown to exhibit a gradual change in the structure of the zooplankton community, a gradual impoverishment of species in the community and a progressive decrease in productivity.As far as the oligotrophic factor is concerned, the discharges and their modalities must be taken into account in the management of the reservoirs.