Responses of karst ecosystem carbon sinks to climate change and human activities in China

<p indent="0mm">In the study of global change, one of the key issues is the global and regional carbon cycle, and estimating the carbon sink magnitude and determining the spatiotemporal pattern of carbon sources have attracted considerable attention from the academic community and are of great scientific significance. The Chinese karst region, which has considerable potential for carbon sequestration, is the principal area for carbon sequestration in China and even in the world. Changes in temperature and precipitation caused by global warming not only affect the hydrological processes in the karst region but also profoundly impact its carbon sink capacity. Nevertheless, no studies have as yet revealed the magnitude and spatial pattern of carbon sinks in the Chinese karst region, as well as the mechanism of the impact of climate change (<italic>CC</italic>) and human activities (<italic>HA</italic>) on the region. Therefore, to elucidate the spatial and temporal patterns of carbon sinks in Chinese karst ecosystems and reveal their responses to <italic>CC</italic> and <italic>HA</italic>, this paper employed data on climate, lithology, and ion concentration, in combination with a random forest model, a maximal potential dissolution model, and partial derivative analysis. According to the results: (1) during 2000–2020, the average annual flux of the ecosystem organic carbon sinks (NEP) and the total amount were<sc> 148.04 t C km^–2 a^–1</sc> and 374.54 Tg C a^–1, respectively, while NEP showed a steady growth trend with an average annual growth rate of<sc> 2.35 t C km^–2 a^–1.</sc> (2) The average annual flux of carbonate rock weathering carbon sinks (CCSs) and the total amount were<sc> 5.32 t C km^–2 a^–1</sc> and 13.45 Tg C a^–1, respectively, while the average annual growth rate of the CCSs was<sc> 0.04 t C km^–2 a^–1.</sc> (3) The average annual flux of the ecosystem carbon sink was<sc>123.49 t C km^–2 a^–1</sc> and the total amount was 319.24 Tg C a^–1. (4) The carbon sink of the Chinese karst ecosystem exhibited an increasing trend, with an increase rate of <sc>2.16 t C km^–2 a^–1,</sc> while precipitation (<italic>P</italic>), temperature (<italic>T</italic>) and solar radiation (SR) respectively contributed 15.91%, 13.12%, and 17.85% to changes in the ecosystem carbon sink. The contribution of CC to changes in the ecosystem carbon sink was 46.88%, and the contribution of HA was 53.12%. (5) In the karst region, the total increase in the area of the ecosystem carbon sink was<sc> 184.73×10⁴ km²,</sc> while the decrease in the area was<sc>68.27×10⁴ km².</sc> Furthermore, areas of growth in the carbon sinks were considerably larger than areas of decline. As the main factor influencing changes in the ecosystem carbon sink, HA was largely concentrated in the southern karst area, with a principal area of <sc>64.66×10⁴ km².</sc> This study will facilitate the realization of China’s “dual carbon” goal, thereby providing an important reference for diagnosing the country’s global carbon neutrality capacity. By integrating long time series of multisource data and advanced modeling analysis, this study systematically quantified the dynamic changes in ecosystem carbon sinks in China’s karst region with respect to scale, spatial distribution, and driving mechanism. Not only do these results provide a scientific basis for realizing China’s “double carbon” goal, but they also serve as an important reference for the formulation and implementation of global carbon-neutral strategies. To provide more in-depth scientific support for global climate governance in the future, the quantitative assessment of the balance between regional carbon sinks and carbon emissions can be further strengthened to explore the long-term stability of the carbon sink function and the risk of extreme climate events.