[Temporal variations of physicochemical and microbiological parameters in three freshwater ecosystems (southeastern France) invaded by Ludwigia spp].

In France, two amphibious hydrophytes of alien Ludwigia (Onagraceae) have for about the past twenty years been causing serious ecological and economic problems: L. peploides (Kunth) Raven et L. grandiflora (Michaux) Greuter & Burdet.

[A new approach to biodiversity: morphological plasticity of a fresh-water diatom].

Population responses of a planktonic freshwater diatom, Asterionella formosa Hassal, to the hydrodynamic anthropic disturbances were studied at the landscape scale, along a series of nine reservoirs, for a period of 18 months. The analysis of biotic descriptors as cell abundance, cell length and architecture has shown a strong morphological plasticity of this diatom. The morphological variability of A.