Aggregate formation and Carbon dynamics in minesoils revegetated at the Candiota Coal Mine

Beyond concerns about the significant gas emissions from coal combustion in industry, coal mining is among the most destructive activities for natural ecosystems. The process of soil reconstruction after ore extraction results in minesoil, which has distinct physical, chemical, and biological characteristics compared to undisturbed natural soil. At the Candiota Mine, home to the largest coal reserve in Latin America, the persistent compaction of relocated topsoil over the overburden hinders revegetation. Studies indicate that approximately 90% of soil carbon is stored within aggregates, and a similar pattern is expected in minesoils once biogenic and/or physicogenic aggregates are formed. The classification of aggregates based on different formation pathways has been explored in recent years to assess soil health, as it links physical, chemical, and biological processes involved in soil aggregation. In this study, minesoil aggregates in areas revegetated with perennial grasses were classified into four formation pathways (biogenic, physicogenic, decompressive, and compressive) across two soil layers (0.00–0.05 m and 0.05–0.10 m). Total organic carbon content was analyzed to validate each aggregate class and track the evolution of minesoil properties. It was observed that soil under Urochloa brizantha had a higher proportion of biogenic aggregates and a lower proportion of compressive aggregates, regardless of soil depth. Similarly, biogenic aggregates in this grass showed higher total organic carbon content, indicating greater interaction with soil microbiota, which contributes to aggregate stability and carbon retention. In contrast, compressive aggregates, the least abundant class, had the lowest total organic carbon content across all grass species and soil layers. This confirms that these aggregates form due to soil compaction caused by machine traffic during the minesoil’s topographic reconstruction process. Decompressive aggregates were more abundant than compressive aggregates, regardless of the grass species, highlighting the positive impact of revegetation and/or the presence of a soil biotic community in restoring the physical condition of minesoil. Furthermore, the higher total organic carbon levels in these aggregates support the aggregation theory for minesoils, which suggests that compressive aggregates gradually break down and transition into naturally formed aggregates throughout the revegetation process