Change of carbon of reclamation soil in coal mining subsidence areas with high groundwater in Xuzhou

Under the background of global carbon neutrality, soil carbon accumulation and transformation become a hot topic in academic circles. In the process of land reclamation and restoration, the change and its mechanism of soil carbon pool in coal mining subsidence area under the influence of groundwater are complicated. The study of carbon dynamics in reclaimed soil is an important basis for a scientific restoration of reclaimed soil ecosystem. In this study, the age chronosequense approach and the location-monitoring method were used to study the change of soil carbon pool after the reclamation of coal mining subsidence area in the area with higher level of underground water. Soil samples from the study areas were collected twice, respectively in 2012 and 2020. The content of soil total carbon (CTC, total organic carbon (CTOC), total inorganic carbon (CTIC) were measured, and soil carbon storage of TC pool (STC), TOC pool (STOC), TIC pool (STIC) and rates of carbon sequestration were calculated. The soil properties (i.e., soil bulk density, compaction, porosity and soil structure, etc.) associated with the change of soil carbon were also analyzed simultaneously. The results show that: ① the STC, STOC and STIC of soil in non-subsidence area (CK) were 268.34, 81.63, 186.70 t/hm2 respectively. Land subsidence caused the decrease of STC and STIC, but with no significant change of STOC. ② A quadratic equation curve was shown in the change of soil carbon density and carbon storage in the restoration process of reclaimed soil, the CTC and CTIC of 0−20 cm layer reaching the maximum in 14−18 years after reclamation, and exceeding CK. The STOC could exceed CK in 13−14 years of reclamation. ③ There was no significant difference in carbon density and carbon pool between layers in 0−40 cm of newly reclaimed soil. In the process of restoration after reclamation, the largest increase of carbon density and carbon storage was found in the surface layer (0−10 cm), and there was no regular variation of soil CTIC in the profile for study. ④ The soil CTOC, STOC and CTC were positively correlated with soil porosity, soil clay, fractal dimension (D) and content of aggregate larger than 3.2 mm, but negatively correlated with bulk density, compactness, pH and aggregate content of 2−0.50 mm. There was great potential for carbon sequestration in the reclaimed soil. Soil moisture affected the carbon fixation and transformation of reclaimed soil by influencing soil aeration, aggregate formation and particle change in the area with higher level of underground water. The cultivation could improve soil structure and ventilation condition, promote the growth of plants and soil microorganisms, increase the source of soil organic carbon, and promote the accumulation of reclaimed soil organic carbon by ploughing, crushing, applying organic fertilizer and water level adjustment. © 2023 China Coal Society. All rights reserved.