Chapter Four - Inorganic components in river waters in the Third Pole

Abstract

The “Third Pole,” centered on the Tibetan Plateau, is also known as the “Water Tower of Asia.” The Third Pole region feeds more than 10 large rivers (e.g., the Yellow River, the Yangtze River, the Yarlung Tsangpo, the Indus, the Amu Darya, etc.) in Asia and there are more than one billion people dependent on the water resources provided by these river basins. In this chapter, an overview of the water chemistry and the geochemical mechanisms that govern the characteristics of major ions and trace elements in rivers of the Third Pole are presented. In general, most rivers of the Third Pole have an alkaline water environment with an average pH of 8.7. As a result of intensive rock weathering within the catchments, the averaged total dissolved solids (~380mgL−1) in the rivers of the Third Pole are much higher than the global median level. It was found that the dissolved contents in rivers of the Third Pole are dominated by Ca2+, Mg2+, HCO3−, Cl−, and SO42− with a spatial heterogeneity due to the different climates, hydrography, and geology conditions over the region. The main mechanisms that control the water chemistry in the rivers of the Third Pole are natural processes, such as rock weathering, ground discharge, and evaporation-crystallization, and most of the rivers remain pristine. However, it should be noted that due to human factors, such as urbanization and mining operations, toxic elements such as As, Cd, Hg, Mn, and Pb concentrations in some of the rivers in the Third Pole are higher than the permissible limits for drinking water as established by the WHO. With increasing anthropogenic activities and changes within the river basins of the Third Pole, further monitoring of the hydrochemical compositions in rivers over this eco-fragile region is warranted.