Borrow Pit Disposal of Coal Mining Byproducts Improves Soil Physicochemical Properties and Vegetation Succession

The way of disposing of rock mineral material has a significant impact on subsequent spontaneous vegetation succession, soil properties, and respiration. We compared seven spontaneously vegetated samples from a large (2 km2) borrow pit used to dispose of the byproducts of a hard coal mine with seven plots from four coal mine spoil heap piles. We used BIOLOG EcoPlates to assess the microbial catabolic activity of the substrate. The substrate in the borrow pit was characterized by higher water content and lower temperature compared to the heap pile substrate. The borrow pit had a more diverse plant community structure. Higher Rao's quadratic entropy, functional richness, and functional divergence were also calculated from plant functional traits in borrow pit samples. Although borrow pit samples showed higher total microbial biomass, bacteria/fungi ratio, and gram+/gram- ratio, and heap pile samples showed higher soil enzymatic activity, microbial functional diversity, and catabolic activity, these differences were not significant. Soil respiration from the borrow pit substrate was two folds higher. The borrow pit method of disposing of rock mineral material can be suggested to speed up spontaneous vegetation succession. This research provides new insights into the effects of burying hard coal byproducts in borrow pits and offers guidance for the management of hard coal mining.