Microbial Community Diversity of an Effluent Dependent Stream Ecosystem

Nutrient enrichment in freshwater ecosystems is a rapidly growing environmental crisis. Excess supply of these nutrients results in the increase of algal biomass production and the disruption of important ecosystem functions. In this study, we collected streambed rocks within 3 study reaches of the Cibolo Creek watershed (Boerne, TX, USA) monthly with different influences of wastewater discharges (1 control site upstream of discharge, 1 site immediately below discharge sites at a confluence, 1 site ~500-m downstream of discharge) from May 2021 to September 2021 (5 sampling periods). At each site, streambed rocks were sampled for algal biomass, total biofilm organic matter, and biofilm bacterial/archaeal communities via targeted (16S rRNA genes) amplicon Illumina MiSeq sequencing. Both chlorophyll a and biofilm OM was greatest in the most downstream location impacted by wastewater effluent. Overall, wastewater-fed sites (down-1, down-2) were depleted in Acidobacteria (p < 0.001), Deltaproteobacteria (p < 0.001) and Firmicutes (p < 0.001) and enriched in Cyanobacterial bacterial phyla. In addition, Clostridium was surprisingly a dominant Genus only in the upstream location that was not impacted by human wastewater effluent. This suggests that the upstream location may not be an adequate "reference" or that Clostridium is not a good fecal indicator for treated effluent in this region and may serve as a better indicator for wildlife waste. This data indicates that there is a complex relationship between autotrophic and heterotrophic biomass in this study and that other environmental factors (e.g. waterfowl and wildlife fecal contamination) besides wastewater effluent that are impacting microbial diversity shifts in this ecosystem.