Geostatistical evaluation of lead and zinc concentration in soils of an old mining area with complex land management

This study is aimed at detailed statistical and geostatistical investigation of lead and zinc concentration in an old mining area located in the eastern part of the Upper Silesian Industrial Region. This area is rich in lead and zinc ores whose intense extraction dates back to the tenth century ad. The complexity of the area results from historical and current mining activities, as well as from a variety of different types of land management and complex geological conditions. Almost 1,000 collected soil cores were divided into two subsets: those collected at the depth of up to 20 cm and the those collected at the depth from 40 to 60 cm. Extensive analyses considered geological substrata in terms of spatial variability and spatial distributions, the type of land management, geoaccumulation indexes and enrichment factors. Lead and zinc concentration was several times higher on depths ranging from 40 to 60 cm beneath the soil surface than in the 20-cm topsoil. The results showed that clearer spatial dependence was observed for deeper soil layers then for the topmost ones, especially near mines where anthropogenic factors predominated over lithogenic ones. Weak spatial dependence was accompanied by high values of the geoaccumulation index. The lowest concentrations of pollution with geoaccumulation index below 0 and enrichment factor up to 5 observed in the forest were caused by low anthropogenic pressure and the presence of sandy soils, less capable of accumulating heavy metals