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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-310
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-310
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 13 Nov 2019

Submitted as: research article | 13 Nov 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Temporary and net sinks of atmospheric CO2 due to chemical weathering in subtropical catchment with mixing carbonate and silicate lithology

Yingjie Cao1,3,4, Yingxue Xuan2, Changyuan Tang1,2,3, Shuai Guan5, and Yisheng Peng1,3 Yingjie Cao et al.
  • 1School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China
  • 2School of Geography and Planning, Sun Yat-Sen University, Guangzhou, China
  • 3Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-Sen University, Guangzhou, China
  • 4Southern Marine Science and Engineering Guangdong Laboratory, Zhuhai, China
  • 5Guangdong Research Institute of Water Resource and Hydropower, Guangzhou, China

Abstract. The study provides the major ion chemistry, chemical weathering rates and temporary and net CO2 sinks in the Beijiang River, which was characterized as hyperactive region with high chemical weathering rates, carbonate and silicate mixing lithology and abundant sulfuric acid chemical weathering agent with acid deposition and AMD origins. The total chemical weathering rate of 85.46 t km−2 a−1 was comparable to other rivers in the hyperactive zones between the latitude 0–30°. Carbonate weathering rates of 61.15 t km−2 a−1 contributed to about 70 % of the total. The lithology, runoff and geomorphology had significant influence on the chemical weathering rate. The proportion of carbonate outcrops had significant positive correlation with the chemical weathering rate. Due to the interaction between dilution and compensation effect, significant positive linear relationship was detected between runoff and total, carbonate and silicate weathering rates. The geomorphology factors such as catchment area, average slope and hypsometric integral value (HI) had non-linear correlation on chemical weathering rate and showed significant scale effect, which revealed the complexity in chemical weathering processes. DIC-apportionment showed that CCW (Carbonate weathering by CO2) was the dominant origin of DIC (35 %–87 %) and that SCW (Carbonate weathering by H2SO4) (3 %–15 %) and CSW (Silicate weathering by CO2) (7 %–59 %) were non-negligible processes. The temporary CO2 sink was 823.41 103 mol km−2 a−1. Compared with the temporary sink, the net sink of CO2 for the Beijiang River was approximately 23.18 × 103 mol km−2 a−1 of CO2 and was about 2.82 % of the temporary CO2 sink. Human activities (sulfur acid deposition and AMD) dramatically decreased the CO2 net sink and even make chemical weathering a CO2 source to the atmosphere.

Yingjie Cao et al.
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Short summary
About half of the global CO2 sequestration due to chemical weathering occurs in warm and high runoff regions. To evaluate the temporary and net sinks of atmospheric CO2 due to chemical weathering, we selected a typical subtropical catchment as our study area and did filed work to sample surface water along the main channel and major tributaries in one hydrological year. The result of mass balance calculation showed that human activities dramatically decreased the CO2 net sink.
About half of the global CO2 sequestration due to chemical weathering occurs in warm and high...
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