Study On The Enrichment Of Metallic Element In Different Parts Of Phragmites Australis In The Main Wetland Of Lhasa River Basin

In order to learn the health status of wetland,the potential risk of sediment,and the regularity of enrichment of metal elements in different parts of Reed in the Lhasa River basin.Three main natural wetlands in Lhasa basin,such as the Lhalu Wetland,Bagarxue Wetland and Chabalang Wetland,were studied,and 25 sampling sites were set up in three wetlands?7 sampling sites in Lhalu Wetland,7 sampling sites in Chabalang Wetland and 11 sampling sites in Bagarxue Wetland?.The water environment,sediment and different parts of Phragmites communis?Root,Stem,Leaf,Flower?of three natural wetlands,which content were analyzed and evaluated.The distribution,enrichment coefficient and transfer coefficient of metal elements in different parts of Reed plants in the main natural wetlands in the Lhasa River basin were also discussed,the pollution risk and its influencing factors of natural wetland sediments were assessed preliminarily.The results showed that the concentration of all the elements in each sampling site was up to the requirement of class I water standard except for Zn element at LHL03sampling point and Sb element at LHL07 sampling point in the water environment of Lhalu wetland,the concentration of all the elements in the water environment of the Bagarxue wetland and the Chabalang wetland meets the requirements of class I water standard.Through the comparison of inlet and outlet,it is found that the removal rate of elements in wetland is also different,among which,the removal rate of Hg element in Lhalu wetland is the highest,83.33%,and the removal rate of Cr is the highest of Bagarxue Wetland,which is up to 65.91%.the highest removal rate of Ca was 29.10%in Chabalang wetland.Through the comparison of 12metal elements?Cu,Pb,Mo,Cd,Co,Cr,Fe,Ba,Zn,Hg,As,Sb?in Lhalu wetla-nd with Bagarxue Wetland and Chabalang Wetland,the results showed that the contents of three metal elements?Cu,As,Cr?in Bagarxue Wetland and Chabalang Wetland were higher than those in Lhalu Wetland due to the influence of chemical fertilizer and pesticides,and the other elements were lower than those in Lhalu Wetland.This indicates that the pollution degree of urban wetlands may be slightly higher than that of wetlands far away from the city.The ion composition of Bagarxue Wetland and Chabalang Wetland mainly comes from the weathering process of rock,the dominant cations are Ca²⁺,and the hydrochemical type is mainly Ca²⁺.Compared with the standard values of PEL,seven elements,such as As,Cr,Cd,Cu,Ni,Pb,Zn in the surface sediments of Bagarxue Wetland and Chabalang Wetland,were lower than the standard values of PEL at each point.According to the comprehensive pollution index,the maximum of Bagarxue Wetland was 2.40 at BGS03 sampling point,and the main influencing factor was Cu element.The maximum of Chabalang Wetland was 2.78 at CBL01 sampling point,and the main influencing factor was Sb element.Through comparing different elements with different parts?root,stem,leaf and flower?of Phragmites communis in three Wetland,which showed that most of the elements except individual elements accord with the rule of root>flower>leaf>stem.In Lhalu Wetaland,the strongest element of TF is Ca,as high as 3.29,the enrichment of Fe elements was the most significant,especially in the roots,which was more than five million times.In Bagarxue Wetland,it was found that,the strongest transfer ability was Ca up to 9.27,the biological enrichment coefficient of U in the root of Reed was the highest,as high as 7.51;In Chabalang Wetland,the transfer ability of Zn element was the strongest,which was 3.62,the root of Phragmites australis has the strongest enrichment ability to Cr elements,and the enrichment coefficient is as high as 10.21.