Successional Changes in Some Physicochemical Properties on an Age Series of Overburden Dumps in Raniganj Coalfields, West Bengal, India

Opencast mining replaces natural vegetation of an area with huge quantities of overburden dumps called mine spoils. The natural plant succession on these dumps improves the dump features after an interval of time. The present work reports successional changes in some physicochemical properties of an age series of overburden dumps (0, 1, 3, 9, 12, 18, 21 years) formed from open-cast mining in Bansra and Sonepur Bazari colliery of Raniganj Coalfields. Dump pH remained near neutral in all the dumps. As the age of the overburden dumps increased, there was an initial increase in clay, silt, water holding capacity, and moisture content. Organic carbon, calcium, potassium, and electrical conductivity also increased with dump age, but the increase of only two parameters—total nitrogen and mineral nitrogen was significantly related to the dump age. No improvement occurred in dump phosphorus concentration with time. Among exchangeable cations, magnesium and sodium decreased, while calcium and potassium increased with age. The net annual accumulation rate of total nitrogen and organic carbon was 12.59 ppm and 300 ppm, respectively. Growth curve of mean dump parameter indicated that the parameter increased with time up to 9 years but decreased afterward. Time period required by the overburden dumps to reach a nearby native forest soil condition was estimated at approximately 19 years. Anthropogenic disturbances in the intermediate successional stages might be responsible for decline in some dump features at 12th year of succession.