A Decade of Microbial Zonation in Remediated Mine Tailings

Organic amendments that consume oxygen can function as reactive barriers, limiting sulfide mineral oxidation in acid-generating tailings; however, they may also promote metal mobilization in surface-oxidized horizons. A decade after applying a 1 meter thick organic cover, we observed notable yet stratified biogeochemical and microbial transformations across the reclaimed profile. The organic layer showed increased nutrient availability alongside declines in organic matter and C:N ratio, reflecting ongoing mineralization and decomposition. Beneath this layer, the interface zone exhibited microbial and geochemical convergence toward more soil-like conditions. Deeper tailings demonstrated slight acidification and an enrichment of sulfur- and iron-oxidizing microbial taxa., potentially indicating continued sulfide weathering. Despite improvements in the interface layer, switchgrass roots largely remained confined to the organic cover, hinting at possible chemical or physical barriers limiting deeper rooting. These findings highlight the short-to-medium-term success of organic covers in enhancing nutrient cycling and fostering microbial succession near the surface. However, persistent weathering underscores the need for complementary strategies, such as deeper amendments or reactive barriers. Given projected climate warming could accelerate organic matter decomposition and sulfide oxidation, increasing the risk of acid generation over time, these findings underscore the importance of sustained organic inputs and adaptive management to ensure long-term reclamation success. Description: This dataset contains microbial community DNA sequence data from a field study evaluating long-term biogeochemical and microbial responses to a 1-m-thick organic cover applied to acid-generating mine tailings. The data support analyses of stratified microbial succession across the organic cover, interface zone, and underlying tailings, as presented in the associated research article. Copyright and License: © His Majesty the King in Right of Canada, represented by Natural Resources Canada, 2025. Released under the Creative Commons Attribution 4.0 International (CC BY 4.0) licence (https://creativecommons.org/licenses/by/4.0/).