Impact of Open-cast Coal Mining on Soil Health and Ecosystem Recovery: A Case Study from Acidic Inceptisols of Assam, India.

Open-cast coal mining is a globally prevalent method of coal extraction that significantly disrupts terrestrial ecosystems, particularly through its impact on soil health and biological resilience. The process often results in the exposure of pyrite-bearing strata, leading to Acid Mine Drainage (AMD), nutrient depletion, and disruption of microbial functionality. This study explores how different durations of land uses/types and recovery durations influence soil chemical and biological properties in paddy-growing landscapes of Assam, India. Assam is a region predominantly characterized by strongly acidic Inceptisols, with limited buffering capacity and high vulnerability to degradation. We hypothesized that prolonged recovery time following mining cessation would result in gradual ecological restoration of soil quality. Four categories of land use were studied: C1 (active mining), C2 (recovery for 5 years), C3 (recovery for 10 years), and C4 (uncontaminated paddy field as control). Soils in active mining areas (C1) exhibited severe acidification (pH 4.3–5.3), attributed to AMD, with the lowest pH recorded in C1. This was accompanied by marked depletion of macronutrients—Nitrogen (N), Phosphorus (P), and Potassium (K). Microbial analysis revealed the lowest bacterial populations and Soil Microbial Biomass Carbon (SMBC) in C1, indicating biological stress, whereas C3 showed a partial resurgence in microbial activity and nutrient status. These findings suggest that the cessation of mining activities initiates a slow but measurable trajectory of soil health recovery, defined here as the gradual improvement in soil chemical and biological functions, in post-mining landscapes, though full ecological functionality may require targeted interventions.