Application of source-sink theory and MCR model to assess hydrochemical change risk in Lhasa River basin, Tibet, China

The Lhasa River, one of the tributaries of the Yarlung Zangbo River on the Tibetan Plateau, provides water for the vast majority of residents in Tibet. The main purpose of this study is to identify regional environmental risk factors that may be affecting the Lhasa River basin. The minimum cumulative resistance (MCR) model was used to determine the “source-sink” risk pattern of the Lhasa River by identifying the sources of metal ions and trace elements in the basin. The results show that loss of soil ions, climate conditions and environmental factors contribute to the hydrochemical characteristics of the Lhasa River basin. The distribution of soil type greatly overlaps with the likelihood of soil ions loss. The low-risk and high-risk zones mainly consist of calcic soils and litho soils, respectively. In terms of the climate and environmental risk factors, rainfall erosivity poses the greatest risk during the low-flow season, vegetation coverage during the high-flow season, and freeze-thaw erosivity during the normal-flow season. High-risk sources and low-risk sources were identified by the MCR model. The high-risk sources were the vegetated and unused lands, which are vulnerable to weathering of Ca and Mg rich sedimentary and mixed rocks, while low-risk sources were the urban, construction, industrial and mining areas and forest land. This study can contribute to the development of policies for the sustainable management of water resources and the protection of the water environment in the Lhasa River Basin.