| This paper analyses the state of the water source ecosystem and assesses the improvement of water quality in the water source,proposes the optimization of plant combinations to improve the efficiency of water treatment based on the problems of the water source ecosystem,and then explores the optimum conditions required for the ecological restoration of the submerged plant eel grass.A feasibility study was carried out on the ecological restoration of eel grass in this wetland type alternative water source.After identifying the areas suitable for the ecological restoration of eel grass,a comparison was made between the water purification effects of the Yellow calamus-Eel grass aquatic plant system and that of the Arundo donax var versicolor and Hydrilla verticillata plant system,and the former was identified as a more suitable solution for the optimisation of the water source ecosystem.The main components include the following:1.After the Pretreatment area(Precipitation area,Ecological filter wall Ⅰ),Compound wet area(Ⅰ area,Ⅱ area,Ⅲ area,Ecological filter wall Ⅱ)and Deep purification area successively,the water quality of the source wetland was improved from class Ⅳ～Class Ⅴsurface water to Class Ⅲ surface water,which has a high reduction effect on the main water quality indexes CODMn,TN,TP,NH4+-N.The average annual removal rates were 24.3%,62.8%,65.4%and 25.9%,respectively.In each unit,the complex wet area and deep water purification area are the main places to remove the above indexes.2.The water emergent plant varieties used in the water source wetland mainly include barracuda grass,shallot,reed,Mosaic reed,repower flower,cattail,calamus,Arundo donax var versicolor,while the submerged and floating plants mainly include chlorophyta,goldfish algae,Hydrilla verticillata,eel grass,water horn,duckweed,water hyacinth,etc.There are some problems of poor growth and too short plant height of the emergent water plant reed.Cattails,scallions and other lodging phenomenon,all affect the water purification effect.In submerged water and floating leaf plants,Hydrilla verticillata grows excessively and then rots,which leads to the deterioration of water quality at the end of complex wet area and the front end of deep water purification area,accompanied by a substantial increase in organic matter and TN content in sediment.In addition to physical methods,it is also suggested to change the plant species.For the poor growth of reed,toppling cattails and scallions,it is suggested to change to yellow calamus.In addition,it is suggested to restore the ecosystem of eel grass and restrain the flooding of aquatic plants such as Hydrilla verticillata.3.Under constant light and continuous light,the critical light intensity for the growth of eel grass is 150 Lux,that is,water grass can only grow when the light intensity is greater than 150 Lux;Under the simulated day-night alternations,that is,12 hours of light and 12 hours of darkness,the critical light intensity for the growth of eel grass is 900 Lux,that is,water grass can only grow when the light intensity is above 900 Lux.4.The monitoring data of underwater light intensity in the water source wetland show that the underwater light conditions in the complex wet area gradually become better along the flow direction,and the maximum daytime highlight intensity in the first half reaches 2200 Lux,and the average daytime light intensity in different weather ranges from 64 to 1145 Lux,but has not yet reached 900 Lux completely.The average light intensity in the second half of the complex wet area was 4943～6478 Lux in the sunny day,and higher than 2587 Lux in the cloudy day,both of which greatly exceeded the critical light intensity of 900 Lux for the growth of eel grass.In the deepwater purification area,the water turbidity is small,the transparency is high,and the underwater light intensity is high,and the light intensity before and after the deepwater area is similar.The light intensity within 1.4m water depth in sunny days is greater than 900 Lux,and within 0.7m water depth in rainy days is greater than 900 Lux.5.The growth situation of eel grass in water source was basically consistent with the conclusion of light intensity monitoring experiment:the activity of eel grass in the first half of the complex wet area gradually decreased until it died within half a year after planting,so it was not suitable for ecological restoration of eel grass.The connection between the second half and the first half of the complex wet area belongs to the excessive area,while the activity of eel grass in the latter part changes with the seasons,with decreased activity in winter and increased activity in summer and stable growth.Therefore,the second half of the complex wet area is suitable for the ecological recovery of eel grass.If the planting time is spring,it is conducive to the survival of eel grass,and the transition area can also be used as the ecological recovery area of eel grass.In the depth of water less than 1.2m,the grass planted on the bank slope of the deep water area can achieve normal growth.6.In order to determine the optimization scheme of the ecosystem of wetland type water source,a comparison was made between the combination of Yellow calamus and Eel grass and the original combination of Arundo donax var versicolor and Hydrilla verticillata in water source.According to the reduction effect of the two plant systems in the artificial wetland simulation device,the water quality indexes of inlet and outlet water under different temperature conditions can be seen:The treatment of CODMn,total nitrogen and total phosphorus in the Yellow calamus-Eel grass wetland system was significantly better than that in the Arundo donax var versicolor and Hydrilla verticillata wetland system.However,the treatment effect of Arundo donax var versicolor and Hydrilla verticillata wetland system was slightly better than that of Yellow calamus and Eel grass wetland system.In summary,the wetland system of Yellow calamus and Eel grass is more suitable for the optimization of water source ecosystem. |
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