5 Conclusions
Mg-rich, alkaline dust causes long-lasting soil degradation. The
evidence is the relationship of findings reached in this study with the
results of dust deposition measured during 10 years, 40 years ago.
Sites close to factories 3–4 folds exceeded the natural regional
background content of total Mg in topsoils. 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, along the direction of
the alkaline emissions spreading. Areas close to factory contained up to
14.4–17.4 g kg-1 of available Mg. Studied heavy
metals (Zn, Cu, Pb and Ni) did not exceeded limit values and their
concentration was not in linkage with the content of Mg, as well as
enzymatic activity.
Higher excess of available Mg caused significant increase of soil pH (up
to 9.39) and worsened conditions for the growth of vegetation. Since
plants are the main source of fresh organic matter, their shortage
resulted in low stock of labile soil organic carbon (0.50–0.96 g
kg-1) and consequently weaker enzymatic activity.
Thus, in addition to effective, alkaline emissions capturing filters, an
important measure supporting the microbial activity of affected soil is
enrichment by organic matter.
At present, when the entry of Mg-rich, alkaline dust into the soil has
been significantly reduced (by 99.75% compared to year 1970), the
application of measures can bring more lasting positive results than in
the past.
Nevertheless, classical methods are still the most effective for
reclaiming the most affected areas. The impermeable Mg-rich crust should
be mechanically removed, milled, and provided not containing excess
concentration of heavy metals or other pollutants it can be used as a
magnesium fertilizer. Soil with available Mg exceeded 2,000 mg
kg-1 has to be treated chemically, by incorporating
gypsum compounds, sulphur, as well as high doses of farmyard manure, or
composts, manure-biochar, compost-biochar composite composts.
Recent methods are applicable to less affected areas. These involve the
growing of Mg hyper-accumulating plants that, after composting, can be
used as an organic fertilizer enriched with Mg, or growing plants that
can be used for energy purposes. In the studied area, among naturally
occurring vegetation, only Phragmites australis is characterised
by high biomass production.
Sampling sites, where the available Mg decreased under the critical
level of 1,000 mg kg-1, can be reused for agricultural
production. Over the whole affected area, care must be taken to maintain
a favourable state of natural vegetation. Consistent application of
measures will enable a gradual return of the soil and landscape to a
more productive state.