ABSTRACT
Plankton of stagnant waters in themselves practically constitutes an autonomous ecosystem, with primary producers, primary and secondary consumers, and bacteria. The types of planktonic organisms are fundamentally the same in running and stagnant waters: algae, protozoa, rotifers, and crustaceans Cladocera and Copepoda. Various models have been designed to simulate the dynamics of phytoplankton in a stream, as a function of water transit time, luminosity, temperature, and nutrients. The model tested on the Lot, downstream of Entraygues, assumes a regularised flow and comprises eight species of algae, each having its own growth characteristics. Plankton of running waters is primarily linked to the current itself, which limits its development on courses with steep slopes, probably by mechanical action. Water transit time is a function of the surface of the submerged section and of the flow, and it determines the possibilities of plankton development.
