Assessment of soil quality degradation impacted by topsoil stockpiling of a surface mining operation in a Tropical climate.

Abstract

Topsoil stripping and storage are primarily carried out before mining, yet the main problem of returning this stockpile post-mining is the decline in soil quality. This study investigated the impact of varying storage durations on soil biogeochemical properties and the presence of heavy metals in stockpiled topsoils of four different ages (3, 8, 13, and 18 years) compared to a native forest at the Newmont Ghana Gold Limited, Ghana. Soil samples were collected on the various stockpiles to evaluate soil pH, total nitrogen, organic carbon, nitrate and ammonium nitrogen, exchangeable cations, bacterial population, and microbial biomass carbon (MBC), Fe, Pb, Cd, Cu, and Zn. Our findings revealed that prolonged storage duration considerably diminishes soil quality relative to the natural forest. Notably, MBC significantly decreased from 49.00 mg C kg^-1 soil in the 3-year-old stockpile to 39.00 mg C kg^-1 soil in the 8-year-old stockpile. However, MBC increased dramatically from 12.82% to 49.49% in the 13- and 18-year-old stockpiles respectively. The bacteria population decreased by 15.01%, 40.00%, and 40.90% when the storage age increased from 3- to 8-, 13-, and 18-year-old stockpiles. All the stockpiles recorded higher contamination factors, pollution load indexes, and Igeo indexes for measured heavy metals except Cd. The increase in stockpile ages beyond 3 years resulted in an increased deterioration index compared with the natural forest. The principal component analysis revealed that MBC, bacteria, NO₃^- -N, fungi, and earthworm populations were the most sensitive soil indicators affected by stockpiling. The decline in stockpile quality may significantly hamper reclamation efforts, necessitating that land managers and mining firms consider stockpile age, nutrient content and biological indicators for effective restoration. Additionally, amendment applications to 8 years and above stockpiles could optimize nutrient availability, facilitating ecosystem restoration.