Natural restoration of soils on mine heaps with similar technogenic parent material: A case study of long-term soil evolution in Silesian-Krakow Upland Poland

The study focused on the variability in properties and pedogenesis of soils located at post mining sites in the old industrial area in the Silesian-Krakow Upland, southern Poland. The investigated sites were comparable in terms of Zn-Pb mining history, soil texture and climate, but differed in duration of pedogenesis, which started after the waste materials were accumulated and covered 30, 70, 100 and about 400 years of self-restoration. A wide spectrum of soil parameters including: Zn, Pb and Cd contents, dehydrogenase activity, pores space and aggregate formation, organic matter decomposition were studied by chemical and micromorphological image analyses with the aim of tracing the evolution of soils and checking if the results of image analysis could be integrated with results obtained by chemical and biological determinations. Stepwise progressive regression equations were obtained to establish the parameters that varied over time. Zn, Pb and Cd contents exceeded several times permissible values in all soils studied. The evolution of these soils was significantly different from each other. During the process of self-restoration of the soil, the contents of organic carbon and total nitrogen, available potassium and phosphorus including dehydrogenase activity increased with increasing age of soils. Pedogenesis resulted also in the increasing amounts of aggregates of small sizes, which were set close to one another together with narrow pores, which was able to store water. A synchronisation between soil properties, obtained by chemical, biological and micromorphological analyses indicating their usefulness for the demonstration of temporal changes.