Environmental geochemical characteristics and the provenance of sediments in the catchment of lower reach of Yarlung Tsangpo River, southeast Tibetan Plateau

Abstract

Loess-like deposits and soils distribute extensively along the wide valleys across the Yarlung Tsangpo River (YTR) catchment in southern Tibetan Plateau. They provide insights into pedogenetic processes and environmental changes. The climate of the low reach area of the YTR catchment is currently relatively wet and warm compared with the middle and upper reaches. To reconstruct climate and environmental changes in the source region, we carried out major and trace elements measurements on various types of sediments collected from the catchment of the lower part of YTR and its tributaries, i.e., Nyang, Po, Yigong and Parlung Tsangpo river (YPT). We find that CaO and MgO are more enriched in the YPT catchment than in the upper continental crust (UCC). Surface and profile sediments across the lower reach of the YTR show elevated As, Cd, Pb and Cs levels, which present potential health risks to local residents and should be considered in health policies. We also found that the sediments are predominantly sourced from local felsic bedrocks. Across the lower part of the YTR, surface sediments only underwent incipient chemical weathering. Steep slopes and heavy precipitation likely removed the sediments quickly and minimized the exposure of minerals to chemical weathering. Elevated As, Pb and Cs contents were found in sediments deposited during the wetter and warmer period from the early-middle Holocene compared with those deposited in modern times. Thus, climate might be an important factor for heavy metals release into the soils of southern Tibetan Plateau by modulating the extent of chemical weathering of their parent rocks.