Responses of primary producers (diatoms, macrophytes) to a mixture of toxicants (river Luzou, SW France)
Réponses des producteurs primaires (diatomées, macrophytes) à une mixture de toxiques (rivière Luzou, SO France)
Résumé
The river Luzou is a small river from the South-West of France, impacted by an industrial seepage. Downstream the factory, high concentrations of cyanide and heavy metals (e.g. zinc, copper) have been recorded since years and a survey of 4 sites selected along the river (2 up- and 2 downstream the factory) was conducted to assess their effects on diatoms and macrophytes. Periphytic biofilms and diatoms were sampled in 2009 from artificial substrates immersed for 15 and 30 days in September and November / December, and macrophytes were collected at the end of September 2009. Quantitative (biomass, chlorophyll, diatom cell densities per substrate surface unit) and qualitative (community structure) descriptors of periphyton were clearly affected by the inputs of the factory, immediately downstream but also 6 km further. Periphytic algal biomass, as well as diatom cell densities, drastically decreased from up- to downstream, while in the growing communities (i.e. sampled after a 15-day immersion), diatom mortality significantly increased (~1.5 fold in September, more 2 fold in November). Downstream Achnantidium minutissimum and Surirella angusta, well known to be tolerant to toxic pollutants, were largely dominant (respectively 57.5% and 21.5%). Achnantidium minutissimum showed many abnormal forms (up to 7.7% relative abundances). Macrophyte communities were quite diversified upstream, Callitriche sp and Fontinalis sp were dominant. Downstream those species disappeared and were replaced by high amounts of the filamentous bacteria Sphaerotilus.