Migration and Transformation Mechanisms of $\mathrm{HCO}_{3}^{-}$ in Soil-groundwater System of Karst Small Watershed : Yaji Experimental Site in Guilin
1 College of Earth Sciences, Guilin University of Technology, Guilin 541006, China
2 Institute of Karst Geology, Chinese Academy of Geological Sciences / Key Laboratory of Karst Dynamics, MNR and GZAR / 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 Pingguo Guangxi, Karst Ecosystem, National Observation and Research Station, Pingguo 531406, China
4 School of Environmental Studies, China University of Geosciences, Wuhan 430074, China
The sources and transformation mechanisms of $\mathrm{HCO}_{3}^{-}$ in outlet water bodies of typical karst watersheds are crucial for conducting karst carbon sink accounting and assessing carbon sequestration capacity. Taking the Yaji Experimental Field in Guilin, Guangxi as the research subject, an earth system science perspective was adopted, combining high-resolution monitoring with monthly sampling techniques. Continuous measurements temperature, electrical conductivity (EC), and CO2 were conducted at soil depths of 10 cm, 40 cm, and 90 cm. Simultaneously, soil water, air, and spring water samples were collected for the analysis of pH, CO2, δ13CDIC, $\mathrm{HCO}_{3}^{-}$, and other hydrochemical parameters. By coupling mathematical models with hydrogeochemical techniques, data-driven linear mixing models and hydrochemical was utilized to systematically analysis and interpret the sources, influencing factors, and migration characteristics of $\mathrm{HCO}_{3}^{-}$ within the soil-groundwater system. The proportion of $\mathrm{HCO}_{3}^{-}$ derived from soil CO2 was found to be 80.00% in soil water and 70.06% at the karst spring outlet (S31), indicating that soil CO2 is the dominant source of $\mathrm{HCO}_{3}^{-}$ in the soil-groundwater system. Soil CO2 levels were primarily influenced by meteorological conditions, soil temperature, soil EC, and biological activity. During the rainy season, increased soil CO2 and enhanced karst dissolution resulted in simultaneous rises in Ca2+ and $\mathrm{HCO}_{3}^{-}$ concentrations in S31. Based on the hydrochemical facies, calcite saturation index, and CO2 degassing characteristics, it was found that the $\mathrm{CO}_{2}-\mathrm{HCO}_{3}^{-}-\mathrm{CaCO}_{3}$ system in the soil-groundwater continuum reaches a dynamic equilibrium. Overall, the dynamics of $\mathrm{HCO}_{3}^{-}$ in the karst small-watershed soil-groundwater system are governed by the coupled processes of “soil CO2 generation, water-rock reaction, and hydrological transport”. This system exhibits a migration-transformation pattern characterized by “rapid generation in upper layers, enrichment in the middle layers, and stable output at the spring outlet”. Moreover, reprecipitation at the karst spring outlet acts as a mechanism for reducing $\mathrm{HCO}_{3}^{-}$ concentrations. The results are expected to provide scientific guidance for quantifying karst carbon sink fluxes and assessing carbon sequestration potential.
FAN Ya-fei, GUO Yong-li, CHI Fu-xiang, CHEN Fa-jia, LIU Fan, ZHU Qi.
Migration and Transformation Mechanisms of $\mathrm{HCO}_{3}^{-}$ in Soil-groundwater System of Karst Small Watershed : Yaji Experimental Site in Guilin[J].
Science Technology and Engineering, 2026, 26(27): 11636-11648 DOI:10.12404/j.issn.1671-1815.2600155
方解石饱和指数(saturation index of calcite,SIc)可用于判断水体径流路径“溶解↔再沉淀”过程[18],明晰${\mathrm{HCO}}_{3}^{-}$的生成区(SIc ≤ 0)与泉口再沉淀削减区(SIc > 0),确定${\mathrm{HCO}}_{3}^{-}$的生成和迁移转化。SIc的计算公式为
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