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.