Jean-Claude Druart

Toxic effects of Irgarol 1051 on phytoplankton and macrophytes in Lake Geneva

Irgarol 1051 is a recent herbicidal compound, inhibitor of photosynthesis, used in antifouling paints. This toxic is persistent in aquatic environments, with low abiotic and biotic degradation, highly phytotoxic, and has already been detected in estuaries and coastal areas, with suspected negative impacts on non-target organisms (aquatic plants and algae). We measured the toxicity of Irgarol 1051 to macrophytes and phytoplankton from Lake Geneva (between Switzerland and France) by determining chlorophyll fluorescence yield, and phytoplankton primary production. Long-term toxicity for phytoplankton was estimated in a microcosm study, and growth inhibition tests were performed with isolated algal strains. The concentration of Irgarol 1051 was analysed in the water, and the most polluted site showed a higher level (up to 135 ng/L) than the lowest observed effect concentration for phytoplankton (8-80 ng/L), while the macrophytes appeared to be more tolerant to Irgarol 1051 in short-term tests. The microcosm study showed that phytoplankton structure might be even more sensitive to Irgarol 1051.

Exploring the dynamics of plankton diatom communities in Lake Geneva using emergent self-organizing maps (1974-2007)

Abstract Lake Geneva, situated between France and Switzerland, is a large lake of major importance for the regional economy. As a result, its ecological quality has been monitored using several parameters since 1974. Phytoplankton was one of the items monitored. Diatoms were among the most diverse algae in this compartment. In order to characterize their dynamics, diatoms were explored and clustered using an emergent self-organizing map. Eight different communities were defined on the basis of the U-matrix. Most of them displayed a clear seasonal pattern, some communities were present during the water stratification phase, and others were present during the mixing phase. These communities also displayed a clear inter-annual dynamic pattern. Some were on the decrease, some even disappearing altogether; whereas others tended to increase or to appear. These dynamic patterns were related to the re-oligotrophication of the lake; Lake Geneva was eutrophic in the 70s to mid 80s, and has been meso-eutrophic since the late 90s. A discriminant analysis showed that phosphorus was the determining parameter for diatom communities. These findings confirmed the effectiveness of diatoms for use as a trophic indicator, and their suitability for use in paleolimnological studies on Lake Geneva. Compared to multivariate analyses which only ordinate and had quite undecipherable graphs when data are numerous, e-SOM showed the advantage to cluster and ordinate data in a single analysis and to present a self-evident and intuitive visualization output.

Les Stephanodiscus (Diatomées) du Lac Léman: Description d'une nouvelle espèce, Stephanodiscus irregularis; mise au point taxonomique et distributions saisonnières

The Stephanodiscus (Diatoms) of Lake Geneva: Taxonomic changes, description of a new species (Stephanodiscus irregularis) and seasonal distributions.Both light and electron microscopy have been used to describe the species of Stephanodiscus collected in the plankton of Lake Geneva (Lac Léman, France-Switzerland) during the last few years. Eight taxa have been identified: S. irregularis nov. sp.; S. alpinus Hustedt = S. astraea var. minutula (Kütz.) Grunow; S. binderianus (Kütz.) Krieger var. binderianus; S. binderianus var. oestrupii (A. Cl.) A. Cl.; S. minutula (Kütz.) Round; S. parvus Stoermer & Hakansson = S. subtilis Van Goor var. subtilis; S. neoastraea Hakansson & Hickel; Cyclostephanos dubius (Fricke) Round = S. dubius (Fricke) Hustedt.Seasonal and interannual variations of some of these species are also presented.