Plateau River research: ecological risk assessment of surface sediments in the Yarlung Tsangpo River.

To fully understand the environmental quality of sediments in the Yarlung Tsangpo River Basin, surface sediments of the mainstream of the Yarlung Tsangpo River and its five major tributaries were studied. In 2017, a total of 201 samples from the Yarlung Tsangpo River and its tributaries were collected during three water seasons. Fifteen trace elements (including Cd and heavy metals such as Cr, Cu, Pb, and As), which have great environmental effects, were analyzed. The results show that titanium, manganese, and chromium are the main heavy metals in the sediments of the Yarlung Zangbo River, accounting for 51%, 10%, and 7% of the total of 15 heavy metal elements measured, respectively. There were no significant differences among the heavy metal contents in the sediments of Yarlung Tsangpo River among three water seasons, but there were significant spatial variations. During the same period, the concentration of each element in the tributary sediments was generally higher than that in the mainstream. According to three different ecological risk assessment models, it is calculated that the heavy metal elements in the surface sediments of the river basin are at low or no pollution risk.