Study On The Removal Of TN,TP,Pb And Cd By Tamarix Ramosissima Under Salt Stress

Constructed wetland is an ecosystem composed of water,matrix,plants and microorganisms based on the principle of natural wetland system.Sewage purification is achieved through filtration,precipitation,adsorption,ion exchange,plant absorption and microbial decomposition.In this study,the present situation and characteristics of wetland pollution in arid and semi-arid areas of North China were analyzed,in order to solve the problem that it is difficult for plants to survive due to the great change of water level and high salinity in the wetland in the arid area,Tamarix ramosissima,a typical halophyte in Bosten Lake wetland in Xinjiang,was selected as the experimental material.By simulating the constructed wetland in 2020,the L₁₆（4⁵）orthogonal experiment was used to study the pollutant removal effect of Tamarix ramosissima wetland systemunder salt stress under flooding and drought conditions.The growth,physiological characteristics and adaptability to salt stress of Tamarix ramosissima under two states were discussed,which provided a theoretical basis for the optimal allocation of saline wastewater constructed wetlands in arid areas.（1）The high increments of the flooding stage are 13.40cm～68.53cm.TDS（total soluble solid）is a highly significant factor of strain high increments（P<0.01）,which is significantly negative（P<0.05）.The stem ranging from 0.65cm～3.91cm,TDS is a significant impact factor（P<0.05）,which is not significantly negative.The removal rate of TN（total nitrogen）by Tamarix ramosissima ranges from-433.77%to97.98%.Under low concentration of TN（20mg/L）,Tamarix ramosissima has poor removal rate of TN in saline wastewater.With the increase of TDS,the TN removal rate of Tamarix ramosissima wetland increased,but with the extension of flooding time,the correlation gradually weakened,and showed a negative correlation in the later stage.The removal rates of TP（total phosphorus）,Pb（lead）and Cd（cadmium）were 48.13%-97.96%,-305.12%-100%and-152.27%-100%,respectively.The greatest impact on the removal rate is the negative correlation of TDS.TDS in the flooding stage is the most important factor affecting the pollutant removal rate of Tamarix ramosissima wetland system.（2）In the drought stage,the increment of plant height and stem diameter of Tamarix ramosissima is-5.20cm～3.90cm,respectively,and the range of stem diameter increment is 0.20cm～2.05cm.Salinity was a significant factor affecting the increment of plant height（P<0.05）,but there was no significant positive correlation（P>0.05）.The removal rates of TN in soil and TP were in the range of-97.64%～47.88%and-11.36%～3.47%,respectively.Salinity was the most significant factor affecting the removal rate of TN and TP,and there was a positive correlation between them.The removal rates of Pb and Cd in soil were-134.90%～59.46%and 4.82%～100%,respectively.Salinity was positively correlated with the removal rates of Pb and Cd.（3）The SPAD values of Tamarix ramosissima leaves in flooding stage and drought stage were8.23～28.53 and 6.02～9.88,respectively.The SPAD values of all treatments in flooding stage were higher than those in drought stage,indicating that the photosynthesis of Tamarix ramosissima in drought stage was worse than that in flooding stage,and the photosynthesis of Tamarix ramosissima increased with the increase of salt content.The range of relative conductivity of Tamarix ramosissima leaves in flooding stage was 57.52%～77.68%,and that in drought stage was 33.10%～48.04%,indicating that the degree of membrane lipid peroxidation in Tamarix ramosissima leaves was high in flooding stage.Salt stress was significantly positively correlated with relative conductivity of leaves in flooding stage（P<0.01）,indicating that membrane permeability of Tamarix ramosissima leaves increased with the increase of salt content.