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.