Study On The Purification Effect Of Aquatic Plants On Urban Eutrophic Water

Water eutrophication is the excess of nitrogen,phosphorus and other nutrients in the water body,resulting in a decrease in the dissolved oxygen content in the water body,deterioration of water quality,a large increase in algae and other plankton,and ultimately the death of fish and other animals.In recent years,with the growth of economy,the discharge of domestic sewage,industrial wastewater and agricultural sewage has increased day by day.In view of this,by monitoring the water quality of five urban rivers in Yangzhou,this paper analyzes the eutrophication level of urban river water at different times,studies the purification effect of planting different aquatic organisms in eutrophic water through indoor tests,and discusses the purification effect of eutrophic water under the plant sediment sterilization and plant sediment non sterilization system,The bacterial community structure of water system under different treatments was analyzed by 16S rDNA sequencing,and the correlation between water environmental factors and microorganisms was analyzed.The main results are as follows:（1）The annual changes of DO,pH,TN,NH4+-N,TP and CODcr in the five rivers in the main urban area of Yangzhou were different.Among them,the DO value was the highest in January and the lowest in July;the pH value fluctuated in the range of 6.7-8.9,TN was the highest in January and the lowest in October;the content of NH4+-N showed a trend of fluctuation;the content of TP showed an overall downward trend;CODcr is highest in May and lowest in November.The degree of eutrophication of the water bodies of the five rivers:Baodai River>Xiao Qinhuai River>Ancient Canal>Xincheng River>Erdao River.（2）The Baodai river with serious eutrophication is selected for indoor simulation experiment.The results showed that different types of aquatic plants could survive normally during the experiment.The better removal effect of TN is Hydrilla verticillata,Ceratophyllum demersum and Myriophyllum verticillatum;the removal rate of which was more than 85%.The best removal effect of NH4+-N is Hydrilla verticillata,with a removal rate of 90.96%.The best removal effect of TP was Vallisneria natans with a removal rate of 91.29%.The best removal effect of CODcr was Hydrilla verticillata with a removal rate of 80.46%.The comprehensive evaluation results showed that the purification effect was submerging plants>floating plants>emergent plants.Among them,the submerged plants Hydrilla verticillata and Vallisneria natans have outstanding purification effects..（3）Hydrilla verticillata and Vallisneria natans with good purification effect were selected as experimental materials under the sterilization and non sterilization treatment of sediment.The purification effect of water system with plants is significantly higher than that of water system without plants.The purification effect of non sterilized sediment-plant water system is better than that of sediment sterilization-plant water system,and the purification effect of non sterilized sediment-Hydrilla verticillata water system is the best,followed by that of non sterilized sediment-Vallisneria natans.The results of 16S rDNA sequencing showed that there were differences in the microbial community structure of water purification system between sterilized and non sterilized sediment treatment of different plants,and the bacterial diversity of non sterilized sediment-Hydrilla verticillata water system was the largest.The dominant flora of water system under plant treatment is mainly concentrated in three Phylum:Proteobacteria,Bacteroidetes and Actinobacteria,which are related to nitrogen and phosphorus removal.The results of correlation analysis of water environmental factors showed that the bacterial community composition of the water system in the T1 group was most affected by the TP correlation;the bacterial community composition in the T3 group water system was most affected by the NH4+-N correlation;the composition of bacterial community in the water system of T4 group was greatly affected by DO,pH,TN,and CODcr,and the bacterial community composition at the genus level was positively correlated.