Metal concentrations in stream biofilm and sediments and their potential to explain biofilm microbial community structure

Concentrations of metals associated with sediments have traditionally been analysed to assess the extent of heavy metal contamination in freshwater environments. Stream biofilms present an alternative medium for this assessment which may be more relevant to the risk incurred by stream ecosystems as they are intensively grazed by aquatic organisms at a higher trophic level. Therefore, we investigated zinc, copper and lead concentrations in biofilms and sediments of 23 stream sites variously impacted by urbanisation. Simultaneously, biofilm bacterial and ciliate protozoan community structure was analysed by Automated Ribosomal Intergenic Spacer Analysis and Terminal Restriction Fragment Length Polymorphism, respectively. Statistical analysis revealed that biofilm associated metals explained a greater proportion of the variations observed in bacterial and ciliate communities than did sediment associated-metals. This study suggests that the analysis of metal concentrations in biofilms provide a good assessment of detrimental effects of metal contaminants on aquatic biota.

► Zn, Cu & Pb concentrations in biofilm and sediments from 23 streams were assessed.
► Bacteria and ciliate protozoa were simultaneously used as biological indicators.
► Zn & Cu were generally enriched in biofilm compared to sediments.
► Metals in biofilm provide a useful assessment of freshwater ecosystem contamination.
► Results highlight the likely ecological importance of biofilm associated metals.