Assessment of soil carbon pool, carbon sequestration and soil CO₂ flux in unreclaimed and reclaimed coal mine spoils

Surface coal mining inevitably deforests the land, reduces carbon (C) pool and generates different land covers. To re-establish the ecosystem C pool, post-mining lands are often afforested with fast-growing trees. A field study was conducted in the 5-year-old unreclaimed dump and reclaimed coal mine dump to assess the changes in soil CO₂ flux and compared with the reference forest site. Changes in soil organic carbon (SOC) and total nitrogen stocks were estimated in post-mining land. Soil CO₂ flux was measured using close dynamic chamber method, and the influence of environmental variables on soil CO₂ flux was determined. Woody biomass C and SOC stocks of the reference forest site were threefold higher than that of 5-year-old reclaimed site. The mean soil CO₂ flux was highest in 5-year-old reclaimed dump (2.37 μmol CO₂ m⁻² s⁻¹) and lowest in unreclaimed dump (0.21 μmol CO₂ m⁻² s⁻¹). Soil CO₂ flux was highly influenced by environmental variables, where soil temperature positively influenced the soil CO₂ flux, while soil moisture, relative humidity and surface CO₂ concentration negatively influenced the soil CO₂ flux. Change in soil CO₂ flux under different land cover depends on plant and soil characteristics and environmental variables. The study concluded that assessment of soil CO₂ flux in post-mining land is important to estimate the potential of afforestation to combat increased emission of soil CO₂ at regional and global scale.