Characterizing the effects of opencast coal-mining and land reclamation on soil macropore distribution characteristics using 3D CT scanning

Opencast coal mining activities can cause severe changes to terrestrial ecosystems, leading to soil degradation. Soil pores play an important role in the transport and storage of water and nutrients. Soil macropore systems may be used as an indicator of soil quality, and soil macropore characteristics can reflect the quality of reclaimed soil in opencast coal mining areas. In this study, unmined, unreclaimed and reclaimed soils from the Antaibao opencast coal mine of the loess area from China were scanned to acquire information regarding soil macropores using a high-resolution, non-destructive computed tomography (CT) technique. The 3D distributions of different soil macropores were reconstructed using the Matlab platform, and the quantitative characteristics of soil macropores were determined by analyzing the number of individual detached soil macropore and the volume of individual detached macropore. The results indicated that 3D reconstruction technique can visually and accurately characterize the macropore system of compacted soils in opencast coal mining area. The number and volume of individual detached soil macropores can be acquired from a 3D soil model. The macroporosity of unreclaimed soils was poor due to the compaction of heavy machinery during mining activities, and it was about 3% based on CT technique. The macroporosity and functions of reclaimed soils significantly improved with increasing reclamation age. The number of individual detached soil macropores had a good linear relationship with macroporosity. With increasing macroporosity, the diversity of macropore sizes decreased and the volume of the largest individual detached macropore increased. To improve the macropore conditions of compacted soils, land reclamation (including land consolidation, surface soil covering, and vegetation planting) should be carried out as soon as possible.