Water chemistry and greenhouse gases emissions in the rivers of the “Third Pole”/“Water Tower of Asia”

Abstract

With global warming, annual temperature on the Tibetan Plateau, where is also known as the “Third Pole” and the “Water Tower of Asia”, has increased significantly during the last decades. Climate change on the Tibetan Plateau has caused a series of problems, for example, changed hydrographical condition, accelerated glacial melting and expedited permafrost degradation. There is a growing concern that water chemical compositions (e.g. ions, elements, dissolved carbon and nitrogen) in rivers of the Tibetan Plateau will be affected by changes in hydrographical condition as well as human activities. Based on the study in nine rivers of the Tibet Plateau (e.g. the Yangtze River, the Yellow River, the Yarlung Tsangpo, etc.), we found that water ionic chemistry in rivers of the plateau is significantly affected by natural processes such as rock weathering, soil erosion and evaporation-crystallization. Nevertheless, high concentrations of toxic elements (i.e. Hg, Tl, Cd and Pb) that appeared in the Yangtze River and the Yarlung Tsangpo suggested that anthropogenic activities (e.g. mining, factories and tourism) have played critical roles in regional water chemistry budget of the Tibetan Plateau. Chemical substances such as dissolved carbon and nitrogen in rivers will affect GHGs emissions to the atmosphere. In this study, related information in rivers of the plateau are provided. It was found that concentrations of DIN and DON in rivers of the Tibetan Plateau were similar to the world average level, while concentrations of DIC were much higher than that of most other rivers due to intensive water erosion within the catchments. With the first insights of isotope compositions of DOC, we found that the average radiocarbon ages in rivers of the Tibetan Plateau were fairly old, indicating that ancient carbon from the permafrost regions of the plateau might be exported to rivers with its melting/degradation. In addition, despite their low partial pressures, GHGs emission fluxes in rivers of the Tibetan Plateau were demonstrated comparable with many other rivers in the world (e.g. the Amazon and rivers in boreal region) due to large flow velocity and elevated DIC concentrations. Therefore, with climate change in this ecological fragile region, we can come to a safe conclusion that there will be an increasing export of dissolved carbon, nitrogen and GHGs from rivers of the Tibetan Plateau, which will in turn potentially add feedbacks to the regional climate.