Abstract: With low channel transparency and serious eutrophication, it is impossible to directly plant submerged plants at the bottom of the river to purify water. Therefore, a typical eutrophic channel in Shanghai Lingang was restored by constructing a submerged plant bed system of Myriophyllum spicatum. The results showed that the constructed submerged plant bed could reduce nitrogen and phosphorus and improve the transparency of water body via enhancing nutrient uptake by submerged plants and influencing the structure and diversity of microbial community. After 30 days of applying the submerged plant bed, water transparency increased by 152.2% and chlorophyll-a concentration decreased by 87.4%. The average removal rates of total nitrogen (TN), total phosphorus (TP), ammonia nitrogen (NH₃-N), and active phosphorus (PO₄^3--P) concentrations in water were 61.0%, 76.4%, 91.8%, and 76.6% respectively, being significantly different from the control area (P<0.05). The submerged plant bed increased microbial diversity, changed the horizontal community structure at phylum and genus levels, changed the structure of nitrogen-involved bacteria, and increased the abundance of phosphorus-involved bacteria in the water body. Results of redundancy analysis showed that TP, NH₃-N, NO₃^--N, and PO₄^3--P were the main driving factors for the differences of community structure at phylum level in different periods of submerged bed restoration. Proteobacteria, Bacteroidetes, and Firmicutes had significant positive correlation with the concentrations of TP, NH₃-N and PO₄^3--P, but negative correlation with NO₃^--N concentration. The case was opposite for both Actinobacteria and Cyanobacteria. Our results provide theoretical and technical supports for the ecological restoration project of eutrophic rivers.

Key words: constructed submerged plant bed, water transparency, Myriophyllum spicatum, water quality, microbial community.