Carbon dioxide partial pressures and emissions of the Yarlung Tsangpo River on the Tibetan Plateau

Abstract

Rivers are important routes for material and energy transport between terrestrial and marine ecosystems. Recent global-scale assessments of carbon (C) have suggested that C emission fluxes to the atmosphere are comparable to the fluvial C fluxes to the ocean. However, many previous studies only collected data from inland rivers in low altitude regions. Therefore, it remains unclear how plateau rivers affect C flux. In this study, 20 monitoring sites were set up along the Yarlung Tsangpo (YT) River on the Tibetan Plateau and detailed observations were carried out in the wet and dry seasons. The riverine CO2 fluxes exhibited significant seasonal patterns which ranged from 597.12 ± 292.63 μatm in the wet season to 368.72 ± 123.50 μatm in the dry season. The CO2 emission flux (FCO2) obtained from floating chamber method, ranging from 8.44 ± 6.94 mmol m−2 d−1 in sunmmer to 3.62 ± 6.32 mmol m−2 d−1 in winter, with an average value of 6.03 mmol m−2 d−1. Generally, the river was a weak carbon source with respect to the atmosphere. However, the pCO2 and FCO2 were much lower than that for other large rivers around the globe, which were obviously restrained by the weak microbial activities due to the low primary productivity and carbonate buffer activities in the carbonate background. Carbon loss via atmosphere exchange in the YT River on the plateau accounted for 2.2% and 10.6% of the riverine dissolved carbon fluxes (67.77 × 109 mol a−1) according to the floating chamber and thin boundary layer methods, respectively. The YT River probably acts as a “pipeline” to transport weathered nutrients from the plateau to downstream areas. Our results demonstrated the characteristics of a “weak outgassing effect and a high transport flux of carbon” for the plateau river, which is different from rivers on plains. Considering the global relevance of Tibetan Plateau, further studies with enhanced spatiotemporal resolution are needed to better understand the important role of plateau rivers on carbon budgets and climate change over both regional and global cycles.

Chemical weathering in the upper and middle reaches of Yarlung Tsangpo River

“…This suggests that the impact of human activities on carbon emissions in Tibet peaked in 2015 and is expected to gradually diminish in the foreseeable future. However, the annual carbon sequestration of the five tributaries is estimated to be about 62.38 × 10 9 mol/y, or 2.74467 × 10 9 kg/y, accounting for 49.7% of the TCE in 2014 and 7.7% of the TCE in 2015 in Tibet, underscoring the potential significance of river-based carbon sequestration as a vital CO 2 treatment sink (Yu et al, 2021;Bao et al, 2023). These findings suggest that river-based carbon sequestration could play a crucial role in achieving carbon neutrality objectives in Tibet.…”

“…G. Jiang et al, 2015). The study area of this paper is in the middle and upper reaches of the Yarlung Tsangpo River, with its geographical location of 27 °48′-31 °18′ N and 85 °18′-112 °24′ E, covering an area about 216,000 km 2 , and its elevation ranges from 3,543 to 7,068 m, 4,878.5 m on average (Bao, 2019;Bao et al, 2023;Lyu et al, 2023). The Indian Ocean monsoon is weakened in the region by the resistance of the Himalaya Mountains, so while the study area is located in a plateau region with intense radiation and long sunshine, the total accumulated heat is low, making the average temperature in the hottest month ranging from 11.2 °C to 17.0 °C, and the temperature of the coldest month below 0 °C (Guo et al, 2023;Hu et al, 2022;Yu et al, 2021).…”

“…Frontiers in Environmental Science frontiersin.org types of chemical weathering among the tributaries were quite different. The weathering of pyrite and weathering and dissolution of evaporite are the two main sources of sulfate in the rivers in the study area (Bao, 2019;Bao et al, 2023;L. G. Jiang et al, 2015).…”