Field translocation of diatom biofilms impacted by Cd and Zn to assess decontamination and community restructuring capacities

Metal wastes have been repeatedly shown to significantly disturb periphytic communities. This study considers an industrial contamination site subjected to remediation processes since 2007. With the aim of finding relevant bioindicators of the restoration capacity of such impacted hydrosystems, this study focussed on biofilm and diatom recovery kinetics. Biofilms were colonised at a reference site and in parallel at a metal-contaminated site. After 24 days, contaminated biofilms were translocated to the reference site to study the biofilm recovery potential for 9 weeks under natural conditions. Analyses from the community level – measures of metal bioaccumulation, cell densities and taxonomic investigations – to the individual level – measures of teratological forms – were performed. The results showed that Zn and Cd contents were rapidly depurated, reaching reference levels 3 and 9 weeks after translocation, respectively. A Principal Response Curve (PRC) analysis enabled to see the fast evolution of diatom communities, with species specific to the reference site growing in decontaminated biofilms from the 3rd week. After 9 weeks, we estimated that diatom community restructuring was complete, based on measurements of biovolumes and teratological form rates which both decreased to reference levels in decontaminated biofilms throughout the experiment. The different teratological types appeared to be good bioindicators of biofilm contamination and shed light on the duration of contamination. According to these results, different criteria can provide information on the recovery potential of periphyton. Biofilms proved to be good bioindicators of metal recovery and diatoms proved to be good bioindicators of community recovery.