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 average annual rainfall at the site 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 combined to form a 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 oC), ground and sieved through 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; electrical conductivity (EC) using a Conductometer HANNA DiST 6; hydrolytic acidity by method of Kappen in solution of 1 mol dm-3 CH3COONa (dry soil to solution ratio 1:2.5) and was quantified with 0.1 mol dm-3NaOH; the content of available magnesium and calcium were analysed by method of Mehlich III (Mehlich, 1984); total soil organic carbon (CT) was analysed by the Tyurin method (Kononova, 1966) by 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 concentrations of heavy metals and content of total magnesium and calcium were assayed after mineralisation of the samples in the mixture of HF and HClO4 (Crock & Severson, 1980); and available forms of heavy metals were extracted with 1 mol dm-3HCl according to Rinkis method (Novozamsky et al., 1993). The total contents and available forms were determined by applying the method of atomic absorption spectroscopy with a PU 9100X spectrometer (Philips).
Activities of some redox and hydrolytic soil enzymes were determined according to standard methods, namely dehydrogenase activity (DEH) [E.C.1.1.1] was assayed with the Thalmann method (1968), and catalase activity (CAT) [E.C. 1.11.1.6] by the Johnson & Temple method (1964). Alkaline phosphatase (AlP) [E.C. 3.1.3.1] and acid phosphatase (AcP) [E.C. 3.1.3.2] were performed with the Tabatabai & Bremner (1969) method.
2.4 Statistical analysis
Each analysis was completed in three replications. Results shown in Tables 1, 3, and 5 represent the average values (mean ± SD). One-way analysis of variance (ANOVA) and the least significant difference (LSD) method 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, electrical conductivity, hydrolytic acidity, 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).