Compositions of suspended particulates in typical urban river of Shanghai, China and its significance for ecological restoration

Although the water quality of urban rivers in Shanghai, China has been improved significantly in the past decades, their transparency is still unsatisfactory. To clarify the turbidity and its possible mechanisms, the characteristics of suspended particulate matters (SPM) are analyzed carefully, which reveals that suspended microbes dominate the component in urban rivers with high turbidity. Based on the principal component analysis and random forest analysis, nutrients and organic pollutants is revealed to promote the turbidity by promoting the growth of suspended algae and microbes. Furthermore, high-throughput sequencing is used to analyze the microbes in bulk water of urban rivers and iris rhizosphere of ecological floating bed. It reveals that there are significant differences between the microbial communities in bulk water and iris rhizosphere, suggesting that microbes immobilized in iris roots are not derived from bulk water. The metabolic function enrichment analysis based on PICRUSt shows that rhizosphere microbes mainly concentrate on the metabolism of plant secretions, while suspended microbes in bulk water mainly concentrate on the metabolism of pollutants. Since microbial diversity, metabolic richness, and interactions of rhizosphere microbes are much higher than those microbes in bulk water, it suggests that rhizosphere microbes may reduce suspended microbes in water via their competitive effects, thus purify pollutants and reduce turbidity in bulk water (improve transparency). These findings reveal the theoretical basis of water ecological restoration, thus might be helpful to technological innovation in the ecological restoration of urban rivers with high turbidity.