Use of whole-community bacterial indicators to monitor ecological health, function and variability within freshwater stream biofilms.

This study describes the extent of variability in biofilm bacterial community structure across a broad range of spatial and temporal scales and assesses whether this may be used as an indicator of stream ecological health and function. A community DNA fingerprinting technique (Automated Ribosomal Intergenic Spacer Analysis - ARISA) was used to examine the structure of bacterial communities within freshwater stream biofilms. When compared with macrobenthic invertebrate community assemblages using multi-dimensional scaling techniques, similar broad-scale trends in population structure were revealed between organisms at these different trophic levels. For both communities, spatial variability in community structure was greater between streams than within each site, or compared to temporal variability measured over 1 year. Distance-based redundancy analysis of both bacterial ARISA and macroinvertebrate data estimated that the largest cause of variation in community structure was due to differences in catchment land-use, rather than any single water quality parameter (e.g. ph or ammoniacal nitrogen). Multidimensional scaling of ARISA data also revealed significant differences in community structure between urban, and less impacted stream sites, providing evidence that whole-bacterial communities could be used as an indicator of freshwater ecological health, analogous to the way that macroinvertebrate communities have been used for many years. In conclusion, we propose the analysis of whole bacterial communities as a cost-effective, high throughput alternative indicator of freshwater ecological health.