The non-coevolution of DIC and alkalinity and the CO2 degassing in a karst river affected by acid mine drainage in Southwest China

Qingguang Li; Pan Wu; Shilu Wang; Jiangxun Huang; Weiqi Lu; Di Tan; Shangyi Gu; Bailing Fan

doi:10.1016/j.scitotenv.2023.165856

The non-coevolution of DIC and alkalinity and the CO₂ degassing in a karst river affected by acid mine drainage in Southwest China

Sci Total Environ. 2023 Nov 20:900:165856. doi: 10.1016/j.scitotenv.2023.165856. Epub 2023 Jul 28.

Authors

Qingguang Li¹, Pan Wu², Shilu Wang³, Jiangxun Huang⁴, Weiqi Lu³, Di Tan³, Shangyi Gu⁴, Bailing Fan⁵

Affiliations

¹ College of Resources and Environmental Engineering, Key Laboratory of Karst Georesources and Environment, Ministry of Education, Guizhou University, Guiyang 550025, China; State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China.
² College of Resources and Environmental Engineering, Key Laboratory of Karst Georesources and Environment, Ministry of Education, Guizhou University, Guiyang 550025, China. Electronic address: pwu@gzu.edu.cn.
³ State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China.
⁴ College of Resources and Environmental Engineering, Key Laboratory of Karst Georesources and Environment, Ministry of Education, Guizhou University, Guiyang 550025, China.
⁵ College of Eco-Environmental Engineering, Guizhou Minzu University, Guiyang 550025, China.

PMID: 37516187
DOI: 10.1016/j.scitotenv.2023.165856

Abstract

Dissolved inorganic carbon (DIC) in mine water generated during coal mining is a large and potential source of atmospheric CO₂, however its geochemical behaviors under the influence of AMD in relation to CO₂ degassing and carbonate buffering are not well known. In this study, water temperature, pH, DO, alkalinity, Ca²⁺ concentration, and the carbon isotope of DIC were measured monthly from November 2020 to November 2021 and carbonate chemistry and CO₂ emission flux were calculated to reveal the processes of DIC evolution and CO₂ degassing from the Chetian River draining a karst region, which is materially affected by the input of large quantities of AMD. The results showed that carbonate erosion, the mineralization of terrestrial organic matter, and domestic sewage input are all identified to contribute DIC to different degrees to the river. Throughout the year, the Chetian River undergoes high-intensity CO₂ degassing, which is dominated by HCO₃^--neutralized degassing and proton-enhanced degassing in different reaches. The pCO₂ in the river under the influence of AMD is as high as 237,482 μatm, while the F-CO₂ approaches 316.9 g C m^-2 d^-1. Meanwhile, the carbonate system in the downstream karst river buffers an average of 85.2 % of DIC release at the river's outlet. The input of AMD significantly altered the carbon cycle of the surface watershed in the headwaters of tributaries, and greatly enhanced the release of CO₂ from surface water to the atmosphere; meanwhile, the buffering of carbonates on acidity in the water of main streams causes pCO₂ to rapidly reduce over a short distance. Obviously, the carbon emission effect generated by the interaction between AMD and carbonate mainly occurs in the tributary water system. Considering the huge amount of AMD worldwide, this large potential source of atmospheric CO₂ requires a specific and precise quantitative analysis based on actual observations.

Keywords: Acidified mine drainage; DIC transport processes; Degassing scale; HCO(3)(−)-neutralized degassing; Non-coevolution of DIC and alkalinity; Proton-enhanced degassing.