基于水-碳耦合循环过程的岩溶碳汇评价方法

Karst carbon sink effect is the carbon cycle and transfer process which driven by the karst water circulation. It is an important part of the global carbon cycle. Previous study of evaluation of karst carbon sink is based on the dynamics equation, who think the carbon content of atmospheric CO2 source and carbonate rock source in karst water is equivalent.In this case, the air source includ free air and soil air. However, it is found by isotope study on hydrology geochemistry that isotope in the karst water carbon is lighter than expected. In other words, The contribution form those 2 carbon sources is not equal to the karst water carbon, and the carbon quality form air is more than carbonate rocks. So, the karst carbon sink is underestimated obviously by using old evaluation method in early studies. In this study, the karst spring system in covered karst region is choosen as study object because their water-carbon transfer path is clear relatively. The isotope dating techniques and water chemical mixture model are used to build the karst water circulation model in covered karst region. Based on Rayleigh fractionation theory, we take the carbon stable isotope as tracer factor to discusses the water-carbon coupling cycle in study area. Then, the necessary corrections is made to the traditional methods of karst carbon sink evaluation. Based on the research, the karst water carbon contribution ratio from air and carbonate rocks is calculated newly, and the karst water carbon sources is identified.

岩溶碳汇效应是由岩溶水循环驱动的碳迁移过程，是全球碳循环的重要组成部分。以往岩溶碳汇评价是基于岩溶动力学方程，认为大气CO2和碳酸盐岩两个端元对岩溶水中的碳量的贡献比为1:1。其中大气包括自由空气和土壤空气。然而，同位素水文地球化学研究发现，岩溶水中碳同位素比预想的偏轻。这说明两个碳源对岩溶水中碳的贡献并不相等，大气源的贡献比要高于碳酸盐岩。因此，以往的岩溶碳汇评价方法明显的低估了岩溶水循环的碳汇效应。本项目选择水-碳运移路径较为清晰的覆盖型岩溶泉系统为研究对象，拟运用同位素测年技术和水化学混合模型构建工作区覆盖型岩溶水循环模型；以13C作为示踪因子，基于碳稳定同位素瑞利平衡分馏研究，探讨工作区水-碳耦合循环模式。进而对传统的岩溶碳汇评估方法进行必要的修正。计算碳酸盐岩和大气两个端元的碳对岩溶动力系统的贡献比，藉此甄别岩溶水中碳的来源。

选择了不同植被、土壤覆盖条件下的4个研究地点进行采样，分别为贵州茂兰自然保护区（代表顶级岩溶森林生态系统）、广西南宁马山弄拉和桂林丫吉（代表次生林覆盖区）、广西贺州和柳州农耕区（代表农业生产区）。共采集了水样全分析样品56件、水样D和18O同位素样品24件、水体14C样品5件、CFCs样品21件、水体13C样56件、87Sr/86Sr样品21件。2017年在茂兰国家级森林保护区内建设监测站1处，装配有矩形堰和Aqua TROLL 600多水质参数仪。通过项目实施，基本完成了既定的研究目标。通过水文监测和同位素示踪，探讨了不同植被条件下岩溶水循环方式及变化趋势；分析了不同植被演化阶段的岩溶碳汇机理；初步建立了不同植被、土壤覆盖条件下，由岩溶水循环碳循环驱动的岩溶碳循环过程模型，建立了岩溶水中碳的来源的甄别技术方法，改进了岩溶碳汇评价方法。