Study On The Effect Of Water Purification And Soil Improvement In Constructed Wetland In The Western Lakeside Of Bosten Lake

Imitating natural ones,constructed wetlands is an engineering wetlands decontamination system for sewage treatment.This kind of wetlands is artificially designed to grow plants on a wetland bed consisting of gravel,soil and other materials in depressions with a certain aspect ratio.Flowing into the wetland bed from one side,through the synergy of plants and microorganisms,sewage flows out from the other side to achieve decontamination effect.As a new type of sewage treatment technology,it has many advantages such as low cost,simple process equipment,flexible elements configuration,and high ecological effect compared with the traditional second and third level treatment technology.Therefore,it is widely applied to sewage treatment in rural areas and small-medium cities,non-point source pollution control in agriculture and comprehensive treatment of lakes.Also,it is getting more and more attention.In China,constructed wetlands are often built in the south and the constructing situation in every region differs a lot.Taking the constructed wetland in west bank of Bosten Lake as an object of study,this paper explored the problems of constructed wetlands in arid area and the decontamination effect.The Bosten Lake is a rift lake formed in Neotectonics during the neogene period and it's a typical inland freshwater lake in the Inner Mongolia-Sinkiang Lake Region.In recent years,with the large-scale growth of the local population and the development of industry and agriculture,people developed and utilized the freshwater resource crazily.As a result,the pollution load into the lake increased and the lakeside wetlands were seriously destroyed.Then a series of problems came out--ecological capacity and biomass was reduced,salinity increased,and the reeds in some areas can not grow naturally.To improve the ecological environment of the lake,the Jinhai Reed Group Co.,Ltd in Bohu County took a lead to read relevant documents,visit physical constructed wetlands,and carry out repeated experiments with strong support from governments at all levels.Besides,Xinjiang Normal University actively participated in theoretical research and jointly constructed the wetlands in West Bank of the Bosten Lake.Based on the project,from April to October in 2015,water sampling was carried out at the inlet and outlet gate of each phase of wetland construction,and the changes of the wetland and water pollutants along it were analyzed.Also in April,June and August,soil samples were collected in and outside the wetland,and the changes of soil salinity and nutrients were analyzed.Now the conclusions are listed as follow:?1?After monitoring the water samples both in the constructed wetland in west bank of Bosten Lake and other sampling points from April to October,the results showed that the average concentration abatement of TN,NH₃^-N,NO₃^--N and NO₂^--N in the inlet and outlet of wetland during the seven months were respectively 7.94 mg·L^-1,4.85 mg·L^-1,1.19 mg· L^-1,0.61 mg·L^-1.As to the inlet gate,nitrogen concentration was the highest in August and the lowest in October;while as to the outlet gate,nitrogen concentration was the highest in September and the lowest in June.The concentrations of TN,NH₃^-N,NO₃^--N and NO₂^--N increased first and then decreased both in the inlet and outlet gate.The removal rates of TN,NH₃^-N,NO₃^--N and NO₂^--N were respectively 55.39%,62.96%,71.72%,74.10%.Among them,the removal rates of TN and NH₃^-N increased first and then decreased while NO₃^--N and NO₂^--N showed a decrease-increased-decrease trend.In the water of constructed wetlands,NH₃^-N was the most effective to remove TN and the contribution rate was 61.16%.Based on the comprehensive analysis,it can be seen that the water pollutants in this wetland were effectively removed and the water quality improved obviously.Along the way from inlet to outlet gate of the wetland,the concentration of TN reached V-type and TN,NH₃^-N,NO₃^--N and NO₂^--N all showed a gradually decreased trend.The abatement at the front end of wetland was the largest and the average abatement reached more than 90%.?2?After monitoring the concentration of phosphorus in the constructed wetland in west bank of Bosten Lake,the results showed that from April to June in 2015,the TP concentration abatement in the inlet and outlet gate was 1.66mg·L^-1 and the removal rate was 67.36%.The maximum removal rate appeared in July,which was 91.6%.The removal rate of TP increased first and then decreased and the removal effect was good.The concentration of TP in the water along the wetland gradually decreased from sampling point 1# to 7#.Among them,the concentration of TP from 1# to 3# dropped the most,which was 3.92mg·L^-1.And the abatement contribution rate was more than 90%.?3?The typical organic matter were BOD₅ and COD.After monitoring the water in the constructed wetland in west bank of Bosten Lake,the results showed that from April to June in 2015,the average abatement of BOD₅ and COD concentration were respectively 3.79mg·L^-1 and 22.34 mg·L^-1.The removal rates were respectively 57.85% and 40.12%,and the removal effect of organic matter was poor.The concentration changes of BOD₅ and COD from 1# to 4# tended to be similar--both declined slowly.But after the 4#,BOD₅ increased slightly.?4?Comparing the soil nutrients index in constructed wetlands with that in its control group,we found the two figures differ greatly.The soil nutrients in constructed wetland was higher than that in control group.All sampling points showed that among those nutrients index,the organic matter was rich in its content but other nutrients were relatively poor,which meant the construction of wetlands has indeed improved nutrients content.The salinity content in the soil tended to decrease with the depth of the soil.All kinds of ion content of salinity continued to decrease and presented inverted,in which the most anion was SO₄^2-and the most cation was Na⁺ + K +.?5?By using PCA?Principal Component Analysis?and CA?Correlational Analysis?,this paper analyzed the major factors of water and soil pollution in the constructed wetland in west bank of Bosten Lake.The results showed the major pollution factors in the water were COD,NH₃^-N,and NO₂^-N and the major salinity factors in the soil were SO₄^2-,Na⁺+K⁺,HCO^3-.SO₄^2-showed a significant positive correlation with Na⁺+K⁺,indicating that constructed wetlands were dominated by soluble sodium-kalium salt.BOD₅ showed a significant positive correlation with plant density,water temperature,indicating that moderate nutrients and temperature were necessary to promote plants growth.