2 Materials and methods
2.1 Study area
The territory affected by alkaline dust deposition extends in the valley along the River Muráň (48º60’–48º66’ N, and 20º15’–20º27’ E, about 270 m a.s.l.). It is located in the Revúcka Highland, a geomorphological complex of the Slovak Ore Mountains, and a sub-province of the Inner Western Carpathians. Long-term annual average rainfall at the area is 728 mm, and the average annual temperature is 8.2 °C. Prevailing winds in the territory are in the direction from north-west to south-east (Climate-Data.Org, 2019). The geology of the loaded area is very complex. The older Paleozoic is represented by granite, and the younger by magnesite, on which were developed Cambisols. Rendzic Leptosols were formed on Mesozoic limestones, dolomites, and shales. Cambisols were formed on Neogene gravel, Luvisols on Pleistocene loam, and Haplic Fluvisols were formed on Holocene alluvial deposits (Geological map, 2019).
2.2 Soil sampling and samples preparation
Soil sampling sites (Figure 1) were designed based on the quantity of fallen alkaline dust (g m-2 30 days-1) for the period 1980–1990. Values were published by Turčan Consulting (1992), and results were map processed. The studied area started in the north-west, approximately 1 km before the first magnesite processing factory in Lubeník, and continued down the alluvium of the River Muráň alongside the factory in Jelšava and finished in the south-east, behind the village of Gemerské Teplice. Following the direction of prevailing winds (north-west to south-east), 14 sampling sites covered by natural vegetation were selected. At each site, soil-sampling plots (30 m × 30 m) were designated, and from these, networks of 10 m × 10 m were assigned to collect nine soil subsamples per each plot (resulting in 126 subsamples). To represent the average conditions of the plot, the 9 soil subsamples were pooled and formed composite sample for each of the 14 sampling sites. Because in the past, most of the studied area was used as arable land, soil samples were collected from the topsoil (0–30 cm).
In the laboratory, soil samples were air dried at laboratory temperature (20 °C), ground and sieved via a mesh diameter of 2 mm, and for determination of organic carbon with a mesh size of 0.25 mm.
2.3 Soil analysis
Soil pH was measured potentiometrically in a 1:2.5 suspension of dry soil to distilled water; carbonates (CO32-) volumetrically using 10% HCl; the content of available magnesium and calcium were analysed by method of Mehlich III (Mehlich, 1984); total soil organic carbon (CT) was determined using the method of Tyurin (Kononova, 1966) by soil sample oxidation in the mixture of K2Cr2O7 and H2SO4; and labile carbon (CL) i.e. oxidisable by 5 mmol dm-3KMnO4 in an acidic medium of 2.5 mmol dm-3 H2SO4 according to Loginow et al. (1987).
Total content of heavy metals, magnesium and calcium were assayed after samples mineralization in the mixture of HF and HClO4(Crock & Severson, 1980); and the available forms of heavy metals were extracted with 1 mol dm-3 HCl according to Rinkis method (Novozamsky et al., 1993). Subsequently, the elements were determined by atomic absorption spectroscopy using PU 9100X spectrometer (Philips).
For the determination of soil enzymatic activity were used standard methods, namely dehydrogenase activity (DEH) [E.C.1.1.1] was determined using method of Thalmann (1968), and catalase activity (CAT) [E.C.1.11.1.6] by method of Johnson & Temple (1964). Alkaline phosphatase (AlP) [E.C.3.1.3.1] as well as acid phosphatase (AcP) [E.C.3.1.3.2] by method of Tabatabai & Bremner (1969).
2.4 Statistical analysis
Each analysis was completed in three replications. Results shown in Figures 2, 4, and 5 represent the average values (mean ± SD). One-way analysis of variance (ANOVA) and the least significant difference (LSD) were used to compare investigated parameter means for the different sampling sites at P ˂0.05. A correlation matrix was used to assess the relationship between pH, content of carbonates, total and labile organic carbon, and the contents of total and available magnesium and calcium, enzymatic activity, and total and available forms of Cu, Ni, Pb, and Zn. For the expression of total and available Mg content dynamics following the direction of prevailing winds, quadratic polynomial regression models were used. All statistical analyses were performed using Statgraphics Centurion XV.I software (Statpoint Technologies, Inc., USA).