Study On The Purification Of Stagnant Water By Submerged Plants And Their Combinations

In view of the problem that the water purification effect of Potamogeton crispus,the main submerged plant in Lianshi lake of Yongding River,Beijing,is reduced due to the succession in summer,the purification effect of TN,TP,NH₃-N,NO₃-N and other water quality indexes in the water is studied by using Elodea nuttallii,Hydrilla verticillata,Hydrilla verticillatanatans,Myriophyllum verticillatum and their combination,and the combination suitable for the water purification and the succession of Potamogeton crispus is selected according to the test results.The results show that:?1?The treatment capacity of TP was Hydrilla verticillata 9.74mg/plant>Hydrilla verticillatanatans 8.63mg/plant>Myriophyllum verticillatum 8.17mg/plant>Elodea nuttallii8.03mg/plant,and the best was the combination of Hydrilla verticillatanatans+Hydrilla verticillata+Myriophyllum verticillatum..The average treatment capacity of each plant was11.11mg/plant;the treatment capacity of TN was Myriophyllum verticillatum 99.91mg/plant>Elodea nuttallii 90.86mg/plant>Hydrilla verticillata 89.08mg/plant>Hydrilla verticillatanatans80.09mg/plant,and the best was Elodea nuttallii+Hydrilla verticillata+Myriophyllum verticillatum.The average treatment capacity of each plant was 141.36mg/plant for the combination;The treatment capacity of NH₃-N was Hydrilla verticillatanatans 78.41mg/plant>Hydrilla verticillata 70.21mg/plant>Myriophyllum verticillatum 70.1mg/plant>Elodea nuttallii64.45mg/plant,and the best was the combination of Hydrilla verticillatanatans+Hydrilla verticillata+Myriophyllum verticillatum..The average treatment capacity of each plant was96.12mg/plant.?2?The absorption of TP by Hydrilla verticillata is the best,The absorption of TN reduction by Myriophyllum verticillatum is the best,and The absorption of NH₃-N by Hydrilla verticillatanatans is the best,and the combination of Hydrilla verticillatanatans+Hydrilla verticillata+Myriophyllum verticillatum capacity of TP,TN and NH₃-N is 11.11mg/plant,122.64mg/plant and 96.12mg/plant respectively,which is greater than that of single planting,combined with the growth of each plant Therefore,the combination of Hydrilla verticillatanatans+Hydrilla verticillata+Myriophyllum verticillatum should be selected as the succession plan of Potamogeton crispus in summer in Lianshi lake.?3?In the process of shallow water and deep water experiments,the growth states of different submerged plants are also different.Hydrilla verticillatanatans and Hydrilla verticillata are more suitable for shallow water planting,while Elodea nuttallii and Myriophyllum verticillatum are more suitable for deep water planting.At the same time,considering the effects of competition and inhibition,Elodea nuttallii and Hydrilla verticillata are not suitable for planting too close,and the density should not be too large,Hydrilla verticillatanatans and Myriophyllum verticillatum can form a good vertical growth relationship,with little interaction.Under the condition of different water depth in the lake bottom,it is better to optimize the planting layout of Hydrilla verticillatanatans,Hydrilla verticillata and Myriophyllum verticillatum from the plane point of view,so as to give full play to the purification effect of submerged plants.?4?According to the general formula of pollutant attenuation and comprehensive analysis of treatment capacity,all the test combinations can be used as the combination of short-term and rapid treatment of water quality:TN treatment for the combination of Elodea nuttallii+Hydrilla verticillatanatans;NH₃-N treatment for a single combination of Hydrilla verticillata;TP treatment for the combination of Elodea nuttallii+Hydrilla verticillatanatans.The combinations that can be used for long-term maintenance and treatment of water quality are:TN treatment for the combination of Hydrilla verticillatanatans+Hydrilla verticillata+Myriophyllum verticillatum.TP treatment for the combination of Elodea nuttalli+Hydrilla verticillata+Myriophyllum verticillatum.NH₃-N treatment for the combination of Hydrilla verticillatanatans+Hydrilla verticillata+Myriophyllum verticillatum.?5?Potamogeton crispus can still maintain a good growth state at 29?,and it begins to decay slowly at 31?,and the decay situation is intensified at 33?.Therefore,when the water temperature reaches 29?,it is necessary to harvest and salvage Potamogeton crispus to avoid secondary pollution caused by the decay of Potamogeton crispus.It is suggested that the harvesting time of Potamogeton crispus should be from the middle of May to the middle of May.The submerged plants that can connect the succession of Potamogeton crispus in terms of growth and time are Hydrilla verticillata,Hydrilla verticillatanatans and Elodea nuttallii.