A Molecular and Spectroscopic Approach to Reclamation of Coal Mine Soil Using Tree Species: a Case Study of Gevra Mining Area, Korba, India

Loss of topsoil and mechanical mixing of soil horizons of mining land causes depletion of huge amounts of carbon (C). Biological reclamation of the soils of mining land helps in soil organic carbon (SOC) sequestration. Therefore, to quantify the quality and quantity of soil organic carbon sequestered through biological reclamation, a chronosequence study consisting of 8- and 25-year-old reclaimed mine soil substrates planted with three different plant species, viz Azadirachta indica , Gmelina arborea and Dalbergia sissoo was undertaken at Gevra, Chhattisgarh, India. Microbial biomass carbon (MBC) and mean SOC stock were recorded highest for A. indica (1468.45 mg C kg −1 soil substrate and 334.72 Mg C ha −1 respectively) after 25 years of reclamation. All the three tree species contributed significantly in raising the non-labile SOC pool among which, the contribution of A. indica (88.25%) was found highest. SOC stock (69.82 Mg C ha −1 ) was found highest for topsoil substrate of 25-year-old re-vegetated site. This increase in SOC in topsoil substrate associated with a higher carbon input and the lower rates of SOC decomposition following revegetation indicated accumulation of more stable SOC forms with time. The nitrogen (N) content ( r = − 0.51, p < 0.01) and C/N ratio ( r = 0.56, p < 0.05) in the litter were an important controlling factor for TSOC. SOC molecules became more aromatic with a higher degree of substitution by reactive functional groups in the 25-year-old restored minesoil substrates as observed from spectroscopic analysis ( E 4 / E 6 and A 253nm / A 220nm ). After 25 years of reclamation, similar Fourier transform infrared (FT-IR) absorption bands were observed for all tree species. However, the intensities at 1618- 1651 cm −1 in humic acid (HA) of G. arborea were higher, indicating presence of aromatic C=C, ascribed to the higher complexity of the HA fraction for G. arborea . The results indicated that spectroscopic methods (FT-IR, UV–vis, E 4 / E 6 ratio) were clearly able to distinguish between restored minesoil substrates on the basis of the characteristics of SOC molecules and can be useful to shedding light on SOC dynamics and sequestration processes.