Organic matter accumulation as a driver of pedogenic microstructure in Technosols developing from iron-sulfide mine wastes

Technogenic soils contain organic matter derived from recent natural inputs as well as industrial compounds. Although the environmental behavior and fate of these compounds have been widely studied, the role of soil organic matter (SOM) accumulation in the development of pedogenic microstructure remains poorly understood. This study investigates micromorphological evidence of pedogenesis in a Spolic Technosol formed from iron-sulfide mine wastes and developed over approximately 200 years. Emphasis is placed on the influence of SOM accumulation on microstructural evolution. A soil profile in southern Poland was examined using thin sections of impregnated soil blocks, which were observed under petrographic microscopes. Pedogenic microstructure was most pronounced in the A horizon, where field observations revealed a well-developed granular structure and dense root systems. Micromorphological analysis showed a crumb microstructure with compound packing voids, resulting from the combined effects of biological activity (root growth and soil fauna) and physical processes (shrink–swell and freeze–thaw cycles). These processes progressively transformed the original massive fabric of the reclaimed mine material into aggregated structures. The close association between granular microstructure development and increased SOM content in the A horizon underscores the central role of organic matter in aggregation and structural evolution of Technosols derived from iron-sulfide mine wastes.