Wastewater Treatment Plant Effluent Alters Particle-Associated Bacterial Assemblages in an Intermittent Stream
Wastewater Treatment Plants (WWTPs) can be point-sources of nutrients, organic matter, anthropogenic contaminants, and microbes to lotic environments, and the input of WWTP effluent can alter the activity and composition of stream microbial assemblages in the benthos and water column. Within the stream benthos, fine particulate matter (FPM) supports especially high levels of microbial activity, but the effect of WWTP effluents on the microbial communities specifically associated with benthic FPM in rivers has not been studied. The present work sought to address this knowledge gap by analyzing FPM quantity, nutrient content, associated microbial activity, and bacterial assemblage composition in FPM samples  collected from sites upstream and up to 800 m downstream of a WWTP effluent input into an intermittent Mediterranean stream. Sampling was conducted on two sampling dates (November and July) and the study included both amplicon and metagenomic sequencing in order to assess both the taxonomic and functional gene composition of the particle-associated bacterial assemblages. Effluent input resulted in increased stream water nutrient concentration and nutrient content of FPM, which was correlated with an increase in microbial metabolic activity immediately downstream of the WWTP. There was a significant decrease in the diversity of the bacterial assemblages associated with the fine particles as well as changes in their taxonomic and functional gene profiles. Taxa associated with wastewater treatment (Rhodocyclaceae and Xanthomonadaceae), the metabolism of anthropogenic contaminants (Sphingobacteriales), and the human gastrointestinal system (Bacteroidaceae and Helicobacteraceae), and genes associated with multidrug efflux pumps and denitrification were more abundant immediately downstream of the WWTP. However, the effects of effluent were short-lived and decreased with distance downstream, especially in November when the upstream flow moderated the effects of effluent. Our results indicate that WWTP effluent impacts natural microbial communities by altering environmental conditions and sourcing new microbes. In intermittent streams, limited dilution by natural flow can constrain common stream microbes and allow higher abundance of WWTP-associated pathogenic microbes.
Wastewater Treatment Plants (WWTPs) can be point-sources of nutrients, organic matter, anthropogenic contaminants, and microbes to lotic environments, and the input of WWTP effluent can alter the activity and composition of stream microbial assemblages in the benthos and water column. Within the stream benthos, fine particulate matter (FPM) supports especially high levels of microbial activity, but the effect of WWTP effluents on the microbial communities specifically associated with benthic FPM in rivers has not been studied. The present work sought to address this knowledge gap by analyzing FPM quantity, nutrient content, associated microbial activity, and bacterial assemblage composition in FPM samples  collected from sites upstream and up to 800 m downstream of a WWTP effluent input into an intermittent Mediterranean stream. Sampling was conducted on two sampling dates (November and July) and the study included both amplicon and metagenomic sequencing in order to assess both the taxonomic and functional gene composition of the particle-associated bacterial assemblages. Effluent input resulted in increased stream water nutrient concentration and nutrient content of FPM, which was correlated with an increase in microbial metabolic activity immediately downstream of the WWTP. There was a significant decrease in the diversity of the bacterial assemblages associated with the fine particles as well as changes in their taxonomic and functional gene profiles. Taxa associated with wastewater treatment (Rhodocyclaceae and Xanthomonadaceae), the metabolism of anthropogenic contaminants (Sphingobacteriales), and the human gastrointestinal system (Bacteroidaceae and Helicobacteraceae), and genes associated with multidrug efflux pumps and denitrification were more abundant immediately downstream of the WWTP. However, the effects of effluent were short-lived and decreased with distance downstream, especially in November when the upstream flow moderated the effects of effluent. Our results indicate that WWTP effluent impacts natural microbial communities by altering environmental conditions and sourcing new microbes. In intermittent streams, limited dilution by natural flow can constrain common stream microbes and allow higher abundance of WWTP-associated pathogenic microbes.
NOVA University Lisbon