Identification of ecological thresholds from variations in phytoplankton communities among lakes: contribution to the definition of environmental standards.

In aquatic ecosystems, the identification of ecological thresholds may be useful for managers as it can help to diagnose ecosystem health and to identify key levers to enable the success of preservation and restoration measures. A recent statistical method, gradient forest, based on random forests, was used to detect thresholds of phytoplankton community change in lakes along different environmental gradients. It performs exploratory analyses of multivariate biological and environmental data to estimate the location and importance of community thresholds along gradients.

Characterization of Freshwater Diatom Communities: Comparing Taxonomic and Genetic-Fingerprinting Approaches.

Benthic diatom assemblages from five sampling sites located on two rivers were characterized simultaneously by means of traditional microscopic observations and PCR-DGGE fingerprinting with primers specifically designed for Bacillariophyceae. Community structure, richness, and diversity assessed by both methods were compared. Diatom lists obtained from morphological identification were separated into subsets, depending on (i) the taxonomic level considered (genus, species, variety) and, for each of them, (ii) the relative abundance (RA) of each component (the whole data set, RA > 1%, RA > 2%).

Assessing the impact of chloroacetanilide herbicides and their metabolites on periphyton in the Leyre River (SW France) via short term growth inhibition tests on autochthonous diatoms.

The Leyre River is the main tributary to the Bassin d'Arcachon lagoon. Herbicides belonging to the chloroacetanilide class have been found in the river (S-metolachlor and acetochlor) as well as some of their metabolites at higher concentrations. As the environmental toxicity of these molecules is not well known, ecotoxicological tests have been carried out on river periphyton at different levels of biological diversity: from the clone of one diatom species (Nitzschia nana) to the population of the same species (several clones) up to the multi-specific species community dominated by diatoms.

Variations of periphytic diatom sensitivity to the herbicide diuron and relation to species distribution in a contamination gradient: implications for biomonitoring.

Diatoms are commonly used as bioindicators of trophic and saprobic pollution in rivers. However, more knowledge is needed concerning their sensitivity to toxicants such as agricultural herbicides. In this study, seven species of periphytic diatoms were isolated from the Morcille River (Beaujolais area, France) which presents a streamward contamination gradient by pesticides and particularly diuron.

Evaluation of single and joint toxic effects of diuron and its main metabolites on natural phototrophic biofilms using a pollution-induced community tolerance (PICT) approach.

This study assessed the single and joint acute toxicity of diuron and two of its metabolites (DCPMU and 3,4-DCA) on natural phototrophic biofilms using a PICT approach with photosynthesis bioassays. River biofilm communities were collected at three sampling stations exhibiting increasing concentrations of diuron, DCPMU and 3,4-DCA from upstream to downstream. Applied individually, the parent compound was more toxic than its metabolites, with DCPMU being more toxic than 3,4-DCA which only inhibited photosynthesis at very high concentrations (EC25 at about 5 mg/l).