1 Introduction
Slovakia belongs to one of the countries with economical-valuable occurrence of natural- crystalline magnesite, and behind China, Russia, North Korea and Turkey belongs to the largest producer of magnesite in the world. Production is localised at two sites: Jelšava (Slovak magnesite processing plant) and Lubeník (Slovmag). Mining of magnesite and its processing to refractory materials is a very dusty operation that negatively influences whole ecosystems including biota. Landscapes have been changed, and craters, waste dumps and heaps have been formed (Huttmanová et al., 2015). Unfortunately, after the installation of new technologies and effective filters, considerably less attention was paid to the research of the locality than in the past. Therefore, some scientific literature used in this research is older and mostly written in Slovak.
Contrariwise with situation in Slovakia, Yang et al. (2012) had claimed that magnesite processing has expanded around the world mainly during the past 30 years, mainly in China, which nowadays accounts 44 % the production in the world. Despite relatively short period of production, the environment is already severely damaged in the surrounding of magnesite mining and calcination plants (Fu et al., 2011). In Slovakia, magnesite has been mined and processed for more than 90 years therefore there are many long-term experiences in the degradation of environment, but also in the reclamation of affected soil. Therefore, some methods successfully applied in land reclamation may be useful also on localities recently contaminated by magnesite dust. Soil contamination by Mg-rich, alkaline emissions is a serious, long-lasting problem.
The magnesite processing plant in Jelšava (founded in 1923) and in Lubeník (founded in 1934) did not produce large amounts of clinker and the common technology of shaft furnaces caused moderate dustiness. However, since 1958, a change in the processing technology (from shaft to rotation furnaces), increased production in new enterprise and insufficient filtration, caused significant dustiness in the surroundings of the factories, mainly along the direction of predominant winds from the north-west to the south-east. From a mineralogical perspective, Mg-rich, alkaline emissions contained 35%–50% amorphous MgO and 10%–20% of other minerals (such as periclas, dolomite, and calcite) (Šály & Minďáš, 1995). Near magnesite processing factories, the maximum permitted concentration of 150 t km-2year-1 (i.e. 12.5 g m-2 per 30 days) of alkaline dust deposition has been exceeded during 50 years. However, after installing new technologies and improved dust filters (Amertherm in 1984), the situation has improved (Bobro & Hančulák, 1997).
Alkaline dust emitted during magnesite processing has caused the anthropogenic alkalinisation of more than 12,700 ha of agricultural land and 6,600 ha of forests, as well as the contamination of water and damage of soil biota. In particular, the finest dust fractions (0.04–0.063 mm) contain the highest proportion of free MgO particles emitted furthest from the source. Because MgO particles and amorphous MgO have a large surface area, they are highly active, have high absorption ability for gases and liquids, and react chemically with substances in the soil and plant tissues. In the affected area, mainly highly active amorphous MgO has caused an increase in the original soil pH from slightly acidic (5.5–6.5) to alkaline (8.5–9.5) (Hronec et al., 1992).
Alkaline emissions reduce the production of plant biomass through direct devastation of vegetation by dustiness, as well as by damage to assimilatory organs. Alkaline solutions formed by the reaction of alkaline emissions with air humidity also directly harm the leaves and bark of plants (Machín & Navas 2000). Indirect damage to vegetation includes anthropogenic alkalinisation of soil with alkaline dust fallout, leading to the unavailability of macro- and micro-nutrients (Yang et al., 2012; Wang et al., 2015a) and thus decreased biological activity and diversity (Katuz et al., 2001; Mihál et al., 2015). In closer surroundings of magnesite processing plants, considerable deposition of Mg-rich, alkaline dust has caused vast damage of local plant communities. Currently, only several resistant species are present (Fazekaš et al., 2018). In localities most affected by alkaline dust deposition, the vegetation completely disappeared and a tight, solid Mg-rich, 5–8 mm thick crust was formed on the soil surface, inhibiting the proper soil functioning (Hronec et al., 1992; Fazekaš et al., 2019).
Previous information has demonstrated that all components of the environment near magnesite processing factories are considerably deteriorated, and despite the adoption of many measures, this unfavourable state continues. The amount of Mg-rich, alkaline fallout depends on both the distance from the source and the direction of predominant winds carrying and spreading alkaline emissions. Hence, in this work we investigated and evaluated the anthropogenic degradation of selected chemical and biological soil properties caused by alkaline emissions coming from magnesite processing factories in Lubeník and Jelšava. Soil properties were assessed along the direction of the prevailing winds (carrying and spreading alkaline emissions), at different distances from factories. Based on obtained results, an approach to land use in the studied localities was proposed.