Contribution of the Soil Macro- and Microstructure to Organic Matter Stabilisation in Natural and Post-Mining/Industrial Soils under Temperate Climatic Conditions

The soil organic matter (SOM) content and stability in natural gypsum soils and mining/industrial soils were compared to check the effects of selected soil properties (mainly macro- and microstructure) on SOM stability and determine whether the old brownfield soils regardless of being highly polluted with trace metals could store high amounts of SOM. The mining/industrial soils were 50–400 years old and so had been left sufficiently long for full self-restoration. Despite having very different origins, both natural and brownfield soils stored similar amounts of SOM and had similar pH values, calcium carbonate contents, and textures but differed in SOM stabilisation, which was expressed by higher C/N ratios, lower aggregate water resistance index, lower dehydrogenase activity, and greater areas of undecomposed or slightly decomposed plant residues in mining/industrial soils compared to gypsum ones. However, the differences diminished with time, and in the oldest (150–400 years) brownfield soils, these parameters were similar to those in natural soils. Multiple regression analysis indicated that under the study conditions, SOM amounts, besides CaCO 3 contents and dehydrogenase activity were also strongly affected by porosity and microaggregation. In the research we showed the role of degraded soils in the sustainable use of the environment.