Abstract
The Zenne River in Brussels (Belgium) and effluents of the two wastewater treatment plants (WWTPs) of Brussels were chosen to assess the impact of disturbance on bacterial community composition (BCC) of an urban river. Organic matters, nutrients load and oxygen concentration fluctuated highly along the river and over time because of WWTPs discharge. Tag pyrosequencing of bacterial 16S rRNA genes revealed the significant effect of seasonality on the richness, the bacterial diversity (Shannon index) and BCC. The major grouping: -winter/fall samples versus spring/summer samples- could be associated with fluctuations of in situ bacterial activities (dissolved and particulate organic carbon biodegradation associated with oxygen consumption and N transformation). BCC of the samples collected upstream from the WWTPs discharge were significantly different from BCC of downstream samples and WWTPs effluents, while no significant difference was found between BCC of WWTPs effluents and the downstream samples as revealed by ANOSIM. Analysis per season showed that allochthonous bacteria brought by WWTPs effluents triggered the changes in community composition, eventually followed by rapid post-disturbance return to the original composition as observed in April (resilience), whereas community composition remained altered after the perturbation by WWTPs effluents in the other seasons.
Highlights
Rivers flowing through cities are often used as receiving body for treated and untreated urban wastewaters all over the world [1,2]
The objectives of the present study were : (1) to study the spatial and temporal variations of the bacterial community composition (BCC) along a sewage polluted urban river; (2) to identify the main environmental factors driving the microbial population dynamics in the watercourse; (3) to compare the river BCC before and after the discharge of major wastewater treatment plants (WWTPs) effluents; and (4) to analyze the fate and dynamics of different functional groups of sewage related bacteria once discharged into the river
This effect is marked after Brussels-North WWTP considering its high volumes of effluent discharge into the river
Summary
Rivers flowing through cities are often used as receiving body for treated and untreated urban wastewaters all over the world [1,2]. Some of these sewage-contaminated rivers are amongst the most extreme examples of ecosystems disturbed by human activities. The UN predicted that, for 2050, 70% of the world population will be living in cities and this urban growth will mainly occur in less developed countries, where wastewater treatment facilities are scarce [2]. Considering the importance, scarcity and fragility of freshwater ecosystems, research about the impact of the release of high amount of sewage on rivers functioning and ecological health is essential to preserve and have a rational management of this resource over a long term period
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