Study on disturbance and restoration of soil organic carbon pool in large-scale open-pit mining areas in Northern China

The large-scale open-pit coal mining has seriously disturbed the landform and soil carbon cycling process of the mining areas. Restoration and improvement of soil organic carbon in open-pit mining areas is in line with the “dual carbon” goal, and is of great significance for improving soil fertility and self-sustaining ecosystems. To reveal the disturbance characteristics of soil organic carbon pool loss caused by open-pit mining, and grasp the influencing factors and improvement strategies of soil organic carbon recovery in mining areas, the Zhungeer mining area, largest open-pit coal mine group in China, was selected as the research area in this study. Sentinel 2 was used to extract the remote sensing images of the damaged area, and 149 soil samples were collected, as well as methods such as statistical interpolation and regression analysis of influencing factors were also adopted. The results indicated that there were significant differences in the physicochemical characteristics, and biological activity between the open-pit mine waste dump soil and natural soil in semi-arid areas. The soil organic carbon content of the newly reclaimed waste dump lacking natural topsoil coverage was extremely low, with an average of 0.19%. Due to non-standard natural topsoil stripping and disorderly mixed discharge, it was estimated that the cumulative loss of organic carbon in the surface soil of this area exceeded 620,000 tons. Regression analysis result showed that total nitrogen (0.559), reclamation period (0.225), and vegetation NDVI (0.172) were the positive factors affecting the recovery of mining soil organic carbon . The survey result also showed that the soil organic carbon content of the composite vegetation restoration model was significantly higher than that of the single vegetation restoration model, while the soil organic carbon content of the grass shrub community composed of sea-buckthorn, alfalfa, and sweet clover was close to the value of natural soil. Under the single vegetation restoration model, the restoration of soil organic carbon content was manifested as follows: shrubs mainly composed of Salix psammophila > trees mainly composed of Pinus tabulaeformis > small trees mainly composed of Rhus typhina > herbaceous plants mainly composed of Medicago sativa. The organic carbon content of the platform and slope soil in the reclamation area of the waste dump increased with escalation of reclamation years. After 5 years of reclamation, the organic carbon content of mining soil exhibited a rapid promotion. The continuous scientific improvement of soil organic carbon is the key to the successful ecological restoration of mining waste dump. Measures such as controlling erosion and fertilizer, adding materials to increase carbon, vegetation carbon sequestration, conservation tillage are the main technical ways to enhance the organic carbon content of mining soil in open-pit mining areas.