Earth Science Frontiers ›› 2023, Vol. 30 ›› Issue (5): 510-525.DOI: 10.13745/j.esf.sf.2023.2.66

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Chemical weathering and its associated CO2 consumption on the Tibetan Plateau: A case of the Lhasa River Basin

XIE Yincai1,2(), YU Shi1,2,*(), MIAO Xiongyi1,2, LI Jun3, HE Shiyi1,2, SUN Ping’an1,2   

  1. 1. Ministry of Natureal and Resources & Guangxi Key Laboratory of Karst Dynamics, Institute of Karst Geology, Chinese Academy of Geological Sciences, Guilin 541004, China
    2. International Research Centre on Karst under the Auspices of UNESCO/National Center for International Research on Karst Dynamic System and Global Change, Guilin 541004, China
    3. Hebei Key Laboratory of Water Quality Engineering and Comprehensive Utilization of Water Resources, Hebei University of Architecture, Zhangjiakou 075000, China
  • Received:2022-09-06 Revised:2022-10-31 Online:2023-09-25 Published:2023-10-20
  • Contact: YU Shi

Abstract:

In order to study chemical weathering and its effects on CO2 consumption and climate change on the Tibetan Plateau, hydrochemical data were collected bi-monthly, over a hydrological year between November 2019 to October 2020, at selected hydrological monitoring stations across the Lhasa River Basin. Combined with δ13CDIC and $\partial^{34}\mathrm{S}_{\mathrm{SO}_4}$ data, the hydrochemistry of the river basin and its major influencing factors were investigated. Mass-balance and forward-model approaches were applied to calculate the end-member contribution, chemical weathering rate, and atmospheric CO2 consumption flux in the river basin. The main ionic species in river water were Ca2+ and $\mathrm{NO}_3^{-}$, and the hydrochemical type was HCO3-Ca. The cation contribution percentages from atmospheric input, human activities, silicate weathering, and carbonate weathering were 6%, 4%, 21% and 70%, respectively. Chemical weathering is largely caused by sulfuric acid corrosion, where coal strata and sulfide deposits each contributed 50% sulfides, as evidenced by the chemical composition of river water, and δ13C (-8.78‰--1.35‰) of dissolved inorganic carbon and $\partial^{34}\mathrm{S}_{\mathrm{SO}_4}$ (-2.26‰--1.10‰) of sulfate in river water; and the sulfuric acid involvement in carbonate weathering was significantly stronger in dry season than in rainy season. By estimation, the annualized weathering rate and CO2 consumption flux were 5.20 t·km-2·a-1 and 118 × 103 mol·km-2·a-1 respectively for silicate, and 22.5 t·km-2·a-1 and 202 × 103 mol·km-2·a-1 respectively for carbonate, excluding the impact of sulfuric acid. With sulfuric acid involvement, the annualized weathering rate for carbonate increased by 31% to 29.4 t·km-2·a-1, and CO2 consumption flux for carbonate and silicate combined reduced by 35% to 207 × 103 mol·km-2·a-1. This work revealed that sulfuric acid-mediated weathering can change the regional carbon cycle and should be taken into consideration in carbon cycling modeling.

Key words: chemical weathering, CO2 consumption, carbon cycle, sulfuric acid, carbon and sulfur isotope, Lhasa River

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