Variability of aquatic macrophyte populations in large watercourses: first results on the Adour-Garonne hydrosystem

Abstract

Macrophytes are an important functional group of rivers. They are primary producers such as habitats for many organisms. They are also used to assess running water quality through the Macrophyte Biological Index for Rivers (I.B.M.R.). In rivers downstream areas, macrophytes distribution seem to be more likely determined by physical factors (out-flows, substrates, depth, turbidity~). Natural discontinuities (confluence) but especially artificial ones (such as dams) can greatly influence these physical parameters and then the aquatic vegetation. As part of the ECOBAG program, started in 2000 in the Cemagref, eight study sites, located upstream and downstream to discontinuities, were chosen in two rivers of South West of France (Dordogne and Garonne). Macrophytes are regularly sampled on these sites during summer. First results illustrate interrelations between macrophytes development and physical parameters and allow us to present some ecological trends.