Monitoring and evaluation of carbon sink capacity in comprehensive soil and water conservation measures in micro-watersheds of purple soil areas, southwestern Hunan

Background This study monitors and evaluates the carbon sink in micro-watersheds of purple soil areas in southwestern Hunan, aiming to provide technical support and methodologies for assessing the carbon sink capacity of soil and water conservation projects, and to offer insights for carbon sink research in soil and water conservation within purple soil areas of Southwest China. MethodsThrough on-site sampling and analysis, the vegetation carbon pool, soil carbon pool, and soil and carbon conservation amounts in Huangniqiao and Sipingxi small watersheds in Cili County, Zhangjiajie, from 2004 to 2024 were accounted for, so as to evaluate the carbon sequestration capacity of their soil and water conservation measures. Results① After 20 years of comprehensive management, the carbon storage in Huangniqiao and Sipingxi small watersheds in Cili County increased by 4.67×105 t, with an average annual growth of 1.95×104 t.② From 2004 to 2024, after soil and water conservation measures, the soil carbon storage in the small watersheds increased by 11.89% compared with the baseline scenario, the vegetation carbon storage increased by 54078.62% compared with the baseline scenario, and the soil and carbon conservation amount was 52.54 t.③ Different soil and water conservation measures—including exclosure management, afforestation of soil and water conservation forests, and terracing projects on slopes—vary in their capacity to enhance carbon sequestration. Among these, exclosure management demonstrates the most significant enhancement of soil carbon sequestration under Phyllostachys edulis and Bambusa spp. stands. Meanwhile, afforestation of soil and water conservation forests with Pinus elliottii yields the highest vegetation carbon sequestration density. Although the slope-to-terrace project is less effective in improving carbon sequestration capacity than the first two, it is still of great significance for soil protection and reducing erosion. Conclusions Various soil and water conservation measures demonstrate significant effects in carbon preservation, carbon sequestration, and carbon sink enhancement. Among them, afforested areas with species such as Pinus elliottii, Pinus massoniana, and Cunninghamia lanceolata exhibit high carbon sequestration capacity, effectively improving the overall benefits of comprehensive soil and water conservation management.