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Urban rivers often contain elevated concentrations of contaminants such as organic pollutants and heavy metals which can be amplified in lotic ecosystems receiving effluents from wastewater treatment plants (WWTP). However, the impact of WWTPs on the microbial parameters of the urban river sediments has not been well documented compared to urban surface water. Collecting sediment samples at five different locations over a 9,000 m transect during four sampling periods, we investigated spatiotemporal variations of microbial parameters in sediments of lower Des Plaines River; the largest effluent-dominated stream in the United States and the effects of sediment physicochemical properties on the variations were explored. We reported reduced microbial biomass, CFUs, and distinct bacterial communities at the WWTP outfall compared to other sites, indicating that WWTP effluents have the potential to moderate bacterial community structure. Seasonal variations in the sedimentary bacterial community structure were evident regardless of the spatial variations imposed by the effluents. Our community-level physiological profiling of the sedimentary bacterial community structure indicated that temperature was more important than water chemistry, whereas total microbial biomass by phospholipid phosphate analysis responded to the influences of both temperature and water chemistry. Metal concentrations showed values that fall within the “fair” to “very poor” range of biological conditions outlined by the Midwest Biodiversity Institute. We posit that the increased sediment metal loads select for metal-tolerant microorganisms that help to maintain microbial biomass. In the spring, sequencing of bacterial 16S rRNA genes revealed significant effects of effluent on bacterial community composition at the WWTP outfall, showing increases in abundances of Caldilinea, Candidatus, Allochromatium, Sulfuritalea, and Nitrospira sequences, linked to anthropogenic inputs from WWTP effluents. Given that human dependence on effluent-dominated ecosystems for water resources will increase with rapidly increasing urbanization, studies focusing on remediation and policy changes are dire to develop effective management of existing urban rivers.


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