Effect evaluation of remediation in three typical rivers with Vallisneria natans under different pollution and spatial characterization of functional microorganisms

Abstract Submerged plants can improve water quality, but the evaluation of practical engineering applications and the research on the characterization of functional microorganisms in the ecosystem are still insufficient. Three typical rivers (gradient pollution, persistent point pollution, and non external pollution) planted with Vallisneria natans in Guangzhou, China, were selected for monitoring to evaluate the restoration effect by measuring ralated environmental parameters and pollutant indexes, while microbial sequencing was used to analyze the spatial characterization of functional microbial composition. The results showed that Haizhu wetland phase III had a higher pH (9–10) and Xinshichong had a relatively lower concentration of dissolved oxygen (0.23–6.29 mg/L) varied with the intensity of light. Nitrogen pollution level followed the order of Xinshichong > Haizhu wetland phase I > Haizhu wetland phase III generally. The nitrate removal rate in Haizhu wetland phase I reached over 88%. 16S rRNA sequencing analysis showed that the sediment, leaves, and water bodies had different microbial community structures and Proteobacteria were abundant in all samples. Cyanobacteria attached to the leaves of Vallisneria natans, thereby inhibiting the growth in the water and sediment. Sulfur and iron circulation functional bacteria were mainly found in the sediment, while iron-oxidizing bacteria also presented on the leaves. The sediment from Xinshichong also contained abundant methane-related functional bacteria. The distributions of nitrogen cycling-related functional bacteria in the sediment and water, and on the leaves varied according to the different pollution levels at the sites. Therefore, Vallisneria natans can regulate DO environment, improve water quality, and work as an important attachment site for functional microorganisms in the ecosystem to prevent the waterbodies from black and odor. Additional work will be necessary to explore the process on the production of black and odor and the synergistic mechanism of microorganisms.