Comparative analysis of carbon sink effects in karst water systems in three-dimensional climate zones: Taking the Lijiang Basin-the Jinshajiang karst area as an example

To actively address global climate change and achieve the strategic goals of carbon peak and carbon neutrality, Chinese geologists have recently confirmed from multiple perspectives that the potential of karst carbon sinks is substantial. Studying the factors influencing karst processes is fundamental to accurately quantifying the intensity of karst carbon sinks. This study took multiple karst springs within the same aquifer, characterized by similar land use but different elevations in the Lijiang Basin–the Jinshajiang karst area as the research objects. Based on hydrological and hydrochemical data, the mass concentration of CO₂ consumed by carbonate rock weathering and the carbon sink flux at each level of the groundwater system were calculated by the hydrochemical-runoff method.

The results show that climatic conditions are the main factors controlling karst carbon sink effects. The mass concentration of CO₂ consumed by carbonate rock weathering is mainly influenced by temperature and is negatively correlated with altitude. In other words, the lower the altitude, the higher the mass concentration of CO₂ consumed by carbonate rock weathering. Additionally, the rate of increase in the mass concentration of CO₂ consumed by carbonate rock weathering tends to rise as altitude decreases. The carbon sink flux is mainly controlled by temperature and precipitation. In high-altitude mountainous regions where carbonate rocks are mainly affected by freeze-thaw weathering, the carbon sink flux is mainly controlled by precipitation and shows a positive correlation with altitude; that is, higher altitude receive greater precipitation, resulting in an increased carbon sink flux. Conversely, when carbonate rocks are primarily affected by chemical weathering, the carbon sink flux is mainly controlled by temperature and affected by precipitation, exhibiting a negative correlation with altitude. In this case, lower altitudes correspond to a greater carbon sink flux from carbonate rock weathering, with an increasing trend in magnitude. However, this change is less pronounced than the variation in the mass concentration of CO₂ consumed by carbonate rock weathering, which decreases due to the reduction of precipitation. This indicates that the variations in altitude in a three-dimensional climate zone give rise to different climate types,such as precipitation form and amount, temperature, air pressure, evaporation, sunshine, etc.,thereby controlling the distribution of vegetation types and organisms, the intensity of weathering, and indirectly controlling the development and formation processes of karst and distribution of soil. Therefore, differences in altitude alter nearly all external environmental factors that control and affect karst development except for the hydraulic gradient. This results in the formation of diverse karst morphologies and distinct karst water system characteristics, which further amplify variations in karst features and carbon sink intensity. This is the main reason for the differences in karst and carbon sink intensity observed within the same area. The hydrological characteristics of karst water systems, along with vegetation and soil cover conditions, are important factors influencing the mass concentration of CO₂ consumed by carbonate rock weathering and the carbon sink flux. These factors can even have a greater impact than climatic conditions. Therefore, human modifications of the external environment can change the intensity of karst carbon sinks, supporting strategic goals related to carbon peak and carbon neutrality. This study provides a geological basis for accurately assessing the intensity of karst carbon sinks, which is of great significance for understanding the global carbon cycle and advancing efforts toward carbon peak and carbon neutrality.