EGU21-3682, updated on 04 Mar 2021
https://doi.org/10.5194/egusphere-egu21-3682
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Assessing the effects of oxidation of pyrite and reducing nitrogen fertilizer on chemical weathering and the carbon cycles in a karst river system by using multiple isotopes

Sen Xu1, Si-Liang Li1,2,3, Jing Su1, Fu-Jun Yue1,3, Jun Zhong1, and Shuai Chen1
Sen Xu et al.
  • 1School of Earth System Science, Institute of Surface-Earth System Science, Tianjin University, Tianjin, China (correspondent: Siliang.li@tju.edu.cn)
  • 2State Key laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin, China
  • 3Tianjin Key Laboratory of Earth Critical Zone Science and Sustainable Development in Bohai Rim, Tianjin University, Tianjin, China

Pyrite is the most common sulfide mineral occurring in sedimentary and igneous rocks and globally contributes a greater flux of sulfate. Large quantity of reactive nitrogen as fertilizers for agricultural production has been released into the environment in China over recent decades. Sulfuric acid formed by oxidative weathering of pyrite (OWP) and nitric acid formed by oxidation of reducing nitrogen fertilizer (ONF) through neutralization with carbonate minerals can counteract CO2 drawdown from chemical weathering. Here, we use the multiple isotopes (13C-DIC, 34S and 18O-SO42–, 15N and 18O-NO3, and 18O and D-H2O) and water chemistry, as well as historical hydrochemical data to assess the roles of strong acids in chemical weathering and the carbon cycle in a karst river system (Chishui River, southwestern China). The variations in alkalinity and the δ13C-DIC along with theoretical mixing models demonstrate the involvement of strong acids in carbonate weathering. However, the strong acid weathering flux determined by δ13C-DIC and mixing models is considered to be overestimated due to the effects of photosynthesis and degassing of CO2 on δ13C-DIC signal. The protons liberated from OWP and ONF can be constrained by water chemistry and isotope techniques with the use of a Bayesian isotope mixing model. The strong acid weathering flux determined using proton information is higher that determined by δ13C-DIC and mixing models. This suggests that the additional protons derived from OWP and ONF might be consumed in other ways without affecting the δ13C-DIC signals, such as the neutralization of acidic waters. These results indicate that OWP and ONF coupled with carbonate dissolution significantly enhanced the coupling cycles of carbon, nitrogen and sulfur in this river system.

How to cite: Xu, S., Li, S.-L., Su, J., Yue, F.-J., Zhong, J., and Chen, S.: Assessing the effects of oxidation of pyrite and reducing nitrogen fertilizer on chemical weathering and the carbon cycles in a karst river system by using multiple isotopes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3682, https://doi.org/10.5194/egusphere-egu21-3682, 2021.

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