LEITÃO M. & L. LEGLIZE (2000) Long-term variations of epilimnetic phytoplankton in an artificial reservoir during a ten-year survey. Hydrobiologia, 424 : 39-49

Vieux-Pré is an artificial reservoir in the north-east part of France (61 Mm3), created in 1986 for hydraulic management. The phytoplankton and several environmental parameters in the upper part of the lake were monitored at a mid-lake station, from 1988 to 1997. The specific composition of the community changed during this period, from a predominantly pennate-diatom phytoplankton (Asterionella formosaFragilaria crotonensis), the lake passed to dominance by a sparse, motile nanoplankton (Mallomonas akrokomosM. caudataCryptomonas erosaChroomonas/Rhodomonas, a.o.) and then by large colonies of small-celled species (Uroglena americanaDinobryon spp., Radiocystis geminataAphanothece clathrata, Coelosphaerium kuetzingianum a.o.). This paper describes the algal successions involved and shows the decisive effects of the decrease of trophic level from an eutrophic stage to an oligo-mesotrophic condition. In the beginning, externally imposed disturbances (flooding and dewatering) were frequent, while now the lake has stabilised as a deep, stratified pelagic system. Under these conditions, autogenic phytoplankton appear to dominate.