Secondary enrichment of soil by alkaline emissions: the specific form of anthropogenic soil degradation near magnesite processing factories and possibilities of land management

Abstract

Over the past 90 years, anthropogenic degradation of soil caused by alkaline, magnesium-rich dust deposit has presented a serious problem near magnesite processing factories in Jelšava and in Lubeník (Slovakia). The objective of this study was to investigate the chemical and biological soil properties in 14 sampling sites at different distances from factories, and based on the results, to propose further use of affected land. Results revealed that the available Mg 3-68 fold exceeded very high content for texturally medium soils at all grassland sampling sites, and areas close factory contained up to 14.4-17.4 g kg-1. Higher excess of available Mg caused significant increase of soil pH (up to 9.39) and worsened the conditions for the growth of vegetation. As a result, lower stock of newly formed organic matter (0.50-0.96 g kg-1 of labile carbon) with consequently weaker enzymatic activity occurred. Therefore, enrichment by organic matter provides a measure to support the biological activity of soil. The content of monitored heavy metals (Zn, Cu, Pb and Ni) was not related to Mg and did not influence the enzymatic activity of soil. Because alkaline emissions have decreased by 99.8% since 1970, the application of classical measures (mechanical removal of the Mg-rich crust, incorporation of gypsum and manure to the soil), or newer methods (growing of Mg hyper-accumulating plants) can offer more lasting positive effects than those of 50 years ago. This study concluded that Mg-rich, alkaline dust deposition causes long-lasting anthropogenic soil degradation.