3 Results
3.1 Influence of alkaline dust fallout on basic chemical characteristics
and quantity of heavy metals in soil
Alkaline dust generated during magnesite processing contains beside
magnesium also the calcium, therefore Figure 2a, b and c presents the
total and available contents of Mg and Ca determined at all 14
investigated sites. Results showed that sample sites close to factories
3–4 folds exceeded the natural regional background content of total Mg
in topsoils (9.1–15.2 g kg-1).
Consequently, the available Mg 3–68 fold exceeded very high content for
texturally medium soils (>0.255 g kg-1)
at all grassland sampling sites, even at distance of 10 km from
factories. The dynamics of changes in total as well as available Mg
concentration in soil (depending on the direction of prevailing winds
and therefore alkaline emissions spreading) are clearly documented in
the quadratic polynomial trend (Figure 3a and b). While both forms of Ca
showed no trends (Figure 3c and d), the highest contents of total Mg
were found in the sampling sites near both magnesite processing plants,
particularly in Jelšava. The contents of available Mg gradually
increased in the direction of predominant winds, beginning near the
factory in Lubeník, and the highest concentration was determined near
the factory in Jelšava. The same sampling sites also had the highest pH
values and carbonate content (Figure 3e and f).
Sites situated in close proximity to both sources of pollution recorded
the highest values of soil pHH2O 7.60–9.39. With
increased distance from the factories, pH values, together with Mg
content, demonstrated a decreasing tendency (pHH2O7.04–7.98). Soil pH was highly significantly affected by the content of
total and available magnesium (r = 0.788; r = 0.894; P<0.001) respectively, while calcium did not result in
significant increase of soil pH. Accordingly, no significant
relationship was found between total Mg and Ca and also between
available Mg and Ca (Table 1). Increased carbonate concentration
(CO32-) more or less followed the
localities heavily loaded by Mg-rich dust fallout and correlated with
the available and total Mg content in the soil (Table 1, Figure 2).
Conversely, there was no linkage between carbonate content and total or
available calcium.
Figure 4 displays the concentrations of total and available zinc,
copper, lead, and nickel on studied soils. The contents of analysed
metals varied by sampling sites. This was also confirmed by analysis of
variance. Increase of available Ni content was associated with an
increase in the total Ca concentration (r = 0.663; P <
0.01) not Mg (r = 0.335; P > 0.05). In addition, the
concentration of available Ni (r = 0.811; P < 0.001)
and Cu (r = 0.566; P < 0.05) significantly correlated
with the content of available Ca. We found no statistically significant
relationship between total or available Mg and total or available forms
of monitored heavy metals (Zn, Cu, Pb, and Ni).
3.2 Influence of alkaline dust deposition on the storage of soil organic
matter and enzymatic activity
Soil degraded by high amount of Mg-rich, alkaline dust fallout,
especially in localities where a solid Mg-rich crust has been formed on
the surface, is characterised by low stock and altered quality of soil
organic matter. Total organic carbon (CT) was in range
5.4–24.3 g kg-1, i.e. low content predominated
(Figure 5a).
The dynamics of changes in total as well as labile carbon
(CL) content depending on the direction of alkaline
emissions spreading is documented in the quadratic polynomial trend
(Figure 6). The lowest contents of CT and especially
CL were found in sampling sites 6–9 close to the
factory in Jelšava. The same sampling sites contained the highest
quantity of total but mainly available Mg (Figure 2a and b). Although
the CT content was lower in the localities most polluted
with alkaline dust fallout (Figure 5a), there was no significant
relationship between CT and total and available Mg
(Table 1). Conversely, there was a significant negative correlation
between the labile fraction of organic matter (CL) and
the available Mg (r = -0.617; P < 0.05), suggesting
that in the most affected areas, limited formation prevails and
therefore a low quantity of new, labile organic matter. Formation of
new, labile organic compounds was significantly impeded also by high
pHH2O values (r = -0.602; P < 0.05), as
shown in Table 1.
ANOVA test disclosed significant differences in enzymatic activities on
the sampling sites. The highest activity of dehydrogenases, catalase,
alkaline as well as acid phosphatases were reported in the soil
collected from sites 11 and 13, which also contained the highest
quantity of CL (Figure 5).
We determined a significant decrease in soil enzymatic activity because
of increased Mg content (Table 1). In particular, depending on the
available Mg content, the alkaline phosphatase, acid phosphatase,
dehydrogenase and catalase activities significantly decreased (r =
-0.613; -0.640; -0.574; -0.610; P < 0.05). Moreover,
the activity of acid phosphatase was negatively influenced by increased
pHH2O (r = -0.608; P < 0.05).
Conversely, alkaline phosphatase activity increased in accordance with
the content of available Ca (r = 0.538; P < 0.05).
Thus, in the affected area, the excess of available Mg, as well as
increased pH values, and decreased content of labile soil organic matter
were associated with Mg-rich, alkaline dust deposition and caused a
significant decrease in soil enzymatic activity.