| In this study,surface sediments of the main trunk stream and its five tributaries of the Yarlung Tsangpo river were studied.In 2016,169 surface sediment samples were collected at 65 sampling points in the basin in three water phases(i.e.The collected samples by inductively coupled plasma emission spectrometer,inductively coupled plasma mass spectrometry,atomic fluorescence spectroscopy and other modern instrument and other modern instrument analysis method for 15(i.e.,Ti?Mn?Cu?Pb?Zn?Cr?Ni?Co?Cd?Li?Mo?Ag?As?Hg?Se)measurement of heavy metal elements.The spatial and temporal distribution characteristics and potential ecological risks of heavy metal elements in the surface sediments of the Yarlung Tsangpo river basin were studied by using mathematical statistics method,ArcGIS kriging interpolation method,principal component analysis method and ecological risk assessment method.The results showed that :(1)the contents of Ti,Mn and Cr in the surface sediments of the Yarlung Tsangpo river basin were significantly higher than those of other measured elements,accounting for 51%,10% and 7% of the total amount of heavy metal elements,respectively.(2)the heavy metal content in surface sediments of the yarlung zangbo river basin was not significantly different with the seasonal change,but the spatial change was significant.The concentration of elements in the synchronic tributary surface sediments was generally higher than that in the mainstream.The contents of heavy metal elements in the surface sediments of nianyang river and Lhasa river are relatively high.(3)the results of multivariate statistical analysis(PCA)showed that the distribution of heavy metals in the surface sediments of the basin was mainly controlled by three factors,namely PC1 and 32.63%(the main load elements were Cd,Pb and Zn).The rich mineral resources in the basin and the mining activities neglected in the early management may be the main influencing factors.PC2,26.49%(main load elements are Ti and Ni).This is mainly due to the remarkable rock weathering and erosion process in the basin.PC3,12.19%(main load elements are Li and As).This indicates that the influence of abundant geothermal resources and related human activities in the basin on the element composition and content of surface sediments cannot be ignored.(4)the calculated results of the cumulative risk index show that the ecological risk of heavy metals in the surface sediments of the Yarlung Tsangpo main stream is low.However,more than half(53%)of the sampling sites of its tributary,the main stream of the Lhasa river,are exposed to medium-level ecological risks caused by high content of Cu in the basin,and high levels of Cu,Pb,Cd and As have caused high ecological risks in its tributary,the niyang river.However,the calculation results of the potential ecological risk index showed that almost all heavy metal elements in the whole basin were at low risk level,that is,slight pollution or no pollution.The comprehensive potential risk index(RI)indicates that,except for the middle risk of individual points,the whole basin still shows a low risk level.According to the calculation of sediment quality reference coefficient(sqg-q),it can be seen that heavy metals in surface sediments of the Yarlung Tsangpo river basin are generally at low and medium ecological risk levels. |
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