Groundwater biofilms

Stormwater infiltration systems (SIS) have been developed to limit surface runoff and urban flooding. The impacts of such practices on the ecological and biological quality of groundwater ecosystems remain poorly studied due to the lack of efficient methodologies to assess microbial qualities of aquifers. In the present study, a method based on the incubation of artificial substrates (clay beads) is presented to evaluate microbial biomass, microbial activity and bacterial community structures. Three urban water types (stormwater surface runoffs, and SIS-impacted or not impacted groundwaters) collected from 6 sites were considered. Total proteins, dehydrogenase and hydrolytic activities were used to monitor biofilm development on clay beads. Analyses based on next generation sequencing (NGS) of partial rrs (16S rRNA) PCR products (V5-V6) were used to compare operating taxonomic units (OTUs, defined as groups of DNA sequences sharing more than 97% identity) of 10 day-old clay beads biofilms with those of waters collected from the same sampling point. Clay beads biofilm biomass and enzymatic activities were found indicative of biodegradable dissolved organic carbon transfers from the surface to the SIS-impacted groundwaters. Biofilms developing on clay beads also allowed determining the impact of SIS on groundwater bacterial genetic community structures. Although rrs OTU profiles of clay bead biofilms did not perfectly match the diversity of the waters collected from the same sampling points, they were found to have captured the most abundant OTUs. They also captured OTUs not detected in these waters, suggesting exposure prior the sampling time and demonstrating the integrative character of this approach. Monitoring biofilms developing on clay beads allowed a tracking of bacterial genera containing species representing health concerns such as Bordetella and Legionella, and genera involved in key functional processes such as Nitrospira involved in nitrification and Azospirillum involved nitrogen-fixation. Clay beads were found efficient germcatchers that could be used to investigate the incidence of SIS management practices on the connected aquifer microbiological state.