Carbon Isotopic and Lithologic Constraints on the Sources and Cycling of Inorganic Carbon in Four Large Rivers in China: Yangtze, Yellow, Pearl, and Heilongjiang

Abstract

Transport of terrigenous carbon by rivers has been affected extensively by climate change and anthropogenic activities in China over the last few decades. Here, we present results on carbon isotopes (13C, 14C) of dissolved and particulate inorganic carbon (DIC and PIC) and combined with major lithologic ions measured in the four largest rivers in China, namely, the Yangtze, Yellow, Pearl, and Heilongjiang rivers, to reveal the sources and transport of terrigenous inorganic carbon in the rivers. The DIC concentrations showed large variations in the four rivers and ranged from 253 to 3,122 μM. The Yangtze, Yellow and Pearl rivers transported high DIC contents that had low Δ14C values of millennium‐aged DIC and very old PIC; however, the Heilongjiang River presented a lower DIC concentration with much younger 14C ages than the global average (1,100 μM). The strong correlations between the DIC isotope values and major lithological ions (Ca2+ and Mg2+) suggest that chemical weathering played important but variable roles in controlling the production and fate of DIC in the rivers. Using dual isotopes and the MixSIAR model, we calculated that the chemical weathering of carbonate rocks contributed 95 ± 5% of the riverine DIC to the headwater of the Yangtze River while silicate rock weathering and riverine organic matter respiration contributed 62 ± 25% and 5 ± 5% of the DIC in the middle and lower reaches of the river, respectively. In contrast, chemical weathering of silicate rocks contributed the dominant fraction of DIC in the Yellow (55 ± 17%), Pearl (61 ± 20%) and Heilongjiang (83 ± 29%) rivers.

CO2 Release Driven by the Combination of Sulfide Oxidation and Carbonate Dissolution in the Upper Changjiang River: Effect of Erosion and Lithology on Chemical Weathering

“…The Changjiang River is the longest river in China and third longest river in the world, with a total flow length of approximate 6,300 km from its headwater in the Himalayas and the Tibetan Plateau (HTP) to the river mouth in Shanghai City (Chen et al., 2002; Chetelat et al., 2008; Noh et al., 2009). The Changjiang River has an annual mean discharge of ∼9.6 × 10 11 m 3 and drains a basin area of 1.8 × 10 6 km 2 , covering approximately 20% total area of China (Shan et al., 2021). The whole Changjiang River basin could be geographically divided into three regions, corresponding to the upper, middle, and lower reaches, which are separated by the Three Gorges Dam (TGD) in Yichang City and Poyang Lake (Chen et al., 2002; Shan et al., 2021).…”

“…The Changjiang River has an annual mean discharge of ∼9.6 × 10 11 m 3 and drains a basin area of 1.8 × 10 6 km 2 , covering approximately 20% total area of China (Shan et al., 2021). The whole Changjiang River basin could be geographically divided into three regions, corresponding to the upper, middle, and lower reaches, which are separated by the Three Gorges Dam (TGD) in Yichang City and Poyang Lake (Chen et al., 2002; Shan et al., 2021). As shown in Figure 2, the upper reaches can be subdivided into the Jinshajiang River and Chuanjiang River, separated by the Yibin City.…”

Source, pattern and flux of dissolved carbon in an alpine headwater catchment on the eastern Tibetan Plateau

“… Note : Atmospheric CO 2 and soil CO 2 source end‐members were measured in the forest catchment of the study area (data un‐published). Carbonate dissolution and OM respiration source end‐members were adopted from Shan et al (2021). …”

“…Models were run with a Bayesian tracer mixing model using the R package ‘MixSIAR’ (Stock et al, 2018). MixSIAR is increasingly used to study DIC source estimation in various freshwater ecosystems (Keskitalo et al, 2022; Shan et al, 2021; Song et al, 2020).…”

“…Note: Atmospheric CO 2 and soil CO 2 source end-members were measured in the forest catchment of the study area (data un-published). Carbonate dissolution and OM respiration source end-members were adopted fromShan et al (2021). Abbreviations: DIC, dissolved inorganic carbon; OM respiration, stream organic matter respiration.F I G U R E 2 Time series of discharge, air temperature, and precipitation during the year of study.…”