Résumé
Spatial variability in the microbial community composition of the riverine biofilm was investigated in a small river, using two spatial scales: one monitored the upstream-downstream pesticide contamination gradient, referred to as the "between-section variability", and the other monitored a 100-m longitudinal transect (eight sampling sites per section) within each sampling section, referred to as the "within-section variability". Periphyton samples were collected in spring and winter on artificial substrates. DGGE was used to assess the prokaryotic and eukaryotic community composition and HPLC pigment analysis to assess the global taxonomic composition of the photoautotrophic community. To reduce the variability due to differences between the physical conditions within each sampling section, and to provide a better comparison of the three sampling sections, nine plates (three per sampling section) subjected to similar physical conditions were chosen, and the results for these plates were compared to those based on all 24 plates. As shown by DGGE and by HPLC analyses, using these three substrate plates with similar environmental conditions did indeed reduce the within-section variability and maximize the between-section variability. This sampling strategy also improved the evaluation of the impact of pollutants on the periphytic communities, measured using short-term sensitivity testing.