Assessment On Accumulation And Transportation Of Soil Heavy Metals By Trees On The Side Of Expressway In Urumqi

In order to select the greening tree species suitable for remediation of heavy metal pollution in the soil of the traffic road area in arid areas,in this paper greening tree species of the river beach expressway were investigated in Urumqi.The different organs of 16 common greening tree species were collected and the content of heavy metals Pb,Zn,Cd,Cr,Cu and Ni were measured to evaluate the pollution degree of heavy metals on the road side.Calculated the enrichment and transport coefficients of various tree species for heavy metals,analyzed the membership function,comprehensively evaluate the cumulative effect of each tree species on heavy metals to further explore the application potential of each tree species.The research results are expected to provide practical support for the selection of tree species under heavy metal pollution.The research shows that:（1）On road sections without greening belts,the peaks of heavy metal content of soil are all within50m from the roadbed.For road sections with green belts,the peak of heavy metal content in the soil is reduced compared to the no green belt,and the distance of the peak is advanced,and the range of the peak appears within 20m.Within 100m from the roadbed,the average value of the comprehensive pollution index of each type of green belt area is W（without greening belts）>H2（North American Begonia and Ulmus pumila L.）>C4（Ulmus pumila L.）>C1（North American Begonia）>C3（Populus bolleana Lauche）>H3（Catalpa speciosa Engelm and Ulmus pumila L.）>C2（Fraxinus rhynchophylla）>H4（Ulmus pumila’Jinye’and Ulmus densa Litw）>H1（Populus bolleana Lauche and Ulmus pumila L.）.（2）Analyzing the total content of heavy metals in each organ,the highest total content in leaves is Ulmus hirsuta(84.81mg·kg^-1),and the highest total content in branches and bark is Picea koraiensis with a value of 106.75mg·kg^-1 and 137.32mg·kg^-1,the highest total content in the root is Xinjiang poplar(112.29mg·kg^-1).The total content of heavy metals in the various organs of the tree species is as follows:bark(104.85mg·kg^-1)>root(92.93mg·kg^-1)>branch(78.29 mg·kg^-1)>leaves(64.43 mg·kg^-1).（3）The analysis of the correlation between the heavy metals in different organs of the tree species showed that there is a significant positive correlation between the heavy metals Zn and Cu in leaves,branches,bark and roots（P<0.05）.The heavy metal Cu in leaves,branches,bark and roots all have a significant negative correlation with the heavy metal Cu in rhizosphere soil（P<0.05）.The green plants and the Pb,Cd,Cr,Ni,and Zn elements in the rhizosphere soil are extremely significantly positively correlated（P<0.01）,and the correlation coefficients are 0.691,0.921,0.649,0.796,and 0.585,which further illustrate that the heavy metals Pb,The sources of Cd,Cr,Ni,Zn and Pb,Cd,Cr,Ni,and Zn in rhizosphere soil may be the same.（4）The enrichment factor（BCF）of green plants for heavy metals is as follows:Zn>Cu>Ni>Pb>Cd>Cr.and the average BCF is that the underground part is larger than the above-ground part.Except for the enrichment coefficient of large leaf Fraxinus rhynchophylla for heavy metal Cu greater than 1,other tree species are less than 1.The overall transport coefficient（BTF）of green plants to heavy metals is Zn>Cu>Pb>Ni>Cr>Cd.Combining the average membership value of the enrichment transport coefficient and the systematic clustering analysis,it is found that Catalpa speciosa Engelm,Picea koraiensis Nakai,Rhus Typhina Nutt,North American Begonia,Salix babylonica,Ulmus densa Litw and Ulmus pumila L have strong enrichment and transport ability for heavy metals.