[Spatial Differentiation Characteristics of Heavy Metals in the Sediments in the Main Stream and Tributaries in the Upper Reaches of Yarlung Zangbo River].

Understanding the spatial distribution and sources of heavy metals in river sediments on the Qinghai-Tibet Plateau is of great significance for revealing the global geochemical processes of heavy metals. Taking the upper reaches of the Yarlung Zangbo River as the research object, surface sediment samples were collected from the upper reaches of the Yarlung Zangbo River in July 2023, and the content and particle size composition of seven heavy metals (Cr, Ni, Cu, Zn, As, Cd, and Pb) that have great impact on the environment and human body were analyzed. The results showed that the grain size of the sediments in the study area was dominated by sand (57.3%), coarse silt (23.2%), fine silt (11.9%), and clay (7.6%). The sediment sand proportion was higher the closer to the river source. The proportion of sand in the north bank was larger than that in the south bank. The contents of Cr, Ni, As, Cd, and Pb in the sediments of the study area were higher than those of the soil background values of the Qinghai-Tibet Plateau. There were significant differences in the distribution of heavy metals in the sediments of tributaries on the north and south banks. The contents of Cr, Ni, and As in the north bank tributaries were significantly higher than those in the south bank. This spatial difference was related to the rock types of the parent rocks of different tributaries and the different intensities of human activities. According to the results of PMF model analysis, natural and human factors contributed for 78.0% and 22.0%, respectively, in the sediment of tributaries on the south bank of the study area. Natural sources and sources of heavy metals contributed for 85.1% and 14.9%, respectively, in the sediments of the north bank tributaries. This study can provide reference for understanding the geochemical processes of heavy metals in Yarlung Zangbo River sediments under factors and human activities.