Study on the N Purification of Eutrophic Water by Floating Plant-sediment-microbial System

Floating plantsare characterized by suspendingthemselves on the water surface. They have great adaptability to water depth and distinctive capacityfor reproductive and nutrients absorption. Besides, they are easy for planting, harvesting and daily management. As we know, water eutrophication is an increasing problem in China. Because ofthe excellent features, floating plants are widely used in the construction of wetlands to control water eutrophication. In addition to the direct absorption and indirect rhizosphericeffects of aquatic plants, the adsorption and interception of sediments, and microbial degradation couldsignificantly remove water pollutants. Yet, the roles of aquatic plants, sediments and microorganisms in nutrient removalwithin the same natural experimental system are still unclear. By simulating wet land ecosystem, this research studied the changes of nitrogen (N) content in water, plants and sediments as well as the rhizosphere microbial community structure, aiming to clarify the purification approach of N in eutrophic water by plant-sediment-microbial system.The results show that after 40 d treatments, the removal rates of NH₄⁺-N, NO₃^--N and TN in both control and plant treatments were higher than 87% in medium and high N systems. In most cases, no significant difference was found between the two groups. Nymphaea tetragona was more suitable to grow in high N system that was demonstrated by the greatest biomass and N accumulation among 4 tested plants.In low and medium N systems, sediments inorganic nitrogen (IN) content in control was significantly higher than that in the plant treatments. However, in the high N system, there was no significant difference between control and plant treatments where the IN concentration showed an increasing trend.In addition, there were no significant differences in the rhizosphere bacteria α diversity index and community structure between the plant and control groups. Compared with unsterilized treatments, sediments sterilization significantly increased the contents of NH₄⁺-N and TN in water as well as IN in sediments. It can be concluded that, besides the plant absorption, the N could besignificantly removed by microbial function and sedimentation in this experimental system, which provides a scientific basis for efficient purification of eutrophic water in wetland ecosystem.