Effects of cadmium stress on periphytic diatom communities in indoor artificial streams

1. Two experiments were performed with periphytic diatoms originating from the River Lot (France) and allowed to grow on clean substrata within indoor artificial streams. Three cadmium (Cd) levels (control, low Cd=10 mug L-1 and high Cd=100 mug L-1 ) were used to test the effects of Cd on (i) the settlement and development of diatom communities (Experiment 1, 4 weeks Cd exposure) and (ii) predeveloped communities grown over a 2-week period without contamination (Experiment 2, 2 weeks Cd exposure). 2. Experiment 1 revealed that growth and taxonomic composition of diatom communities clearly differed with Cd exposure. Biofilms were more adpressed to substrata under low Cd concentration, and were thinner and patchy under high Cd concentration. 3. Exposure of developed diatom communities (Experiment 2) to Cd revealed only minor variations in taxonomic composition, possibly linked to the protective role of the developed organic matrix against metal stress. 4. These results support the validity of periphytic diatom communities as indicators of metal pollution, although significant structural changes would take longer within developed communities.