## 4 Discussion  
Reduction of the abundance and species' richness of oribatid mites in soils close to industrial factories is a well-known phenomenon. The effects of metal pollution from different sources on the community structure of soil arthropods have been demonstrated by many researchers [53; 54; 55; 56]. The authors underlined that oribatids generally seemed to be more susceptible to toxic metals than most of the other arthropods [12; 57; 58; 59; 60]. A generally observed pattern was that communities were impoverished with increasing metal concentration since most species decrease in abundance, although some species may survive even the most polluted sites [61; 62]. We can confirm this claim as we detected very low mite abundance at contaminated sites with one dominating species, _T. v. sarekensis_. The reduced number and low abundance of some species in the oribatid community at the MOD might indicate that this community is resistant, with reduced self-regulation possibilities. There are more reasons why oribatids' abundance and diversity were strongly affected at the polluted sites. First, many pollutants quickly accumulate in the soil, which is the living space for many oribatid species. Second, fungal hyphae, known to accumulate metals effectively, are the primary food source for many species [63]. In MOS and MOD  
Figure 3: Dendrogram resulting from a clustering procedure using the Bray–Curtis method and showing the similarities of the oribatid mite community at the study’s four sites. samples, we repeatedly tried to cultivate microscopic fungi, which are considered a required component of juveniles' diet of Oribatida, but without success. The pond's and dam's sediment did not favor the development of microscopic fungi, which also reflected in the abundance of oribatid mites. The MOS and MOD samples showed meaningfully lower diversity and equitability than meadow and forest samples. On the other hand, even though the diversity values were much higher in the natural soil than in the technogenic sediments, we can consider the oribatocoenosis at this site relatively poor. The abundance of mites and species' number of Oribatida were also highly reduced in the MOS and MOD, gradually increasing toward the natural, unpolluted sites, MOM and MOF. To a certain degree, the soil protects mites against pollutants and, therefore, whole absence of Oribatida was observed only in highly polluted ash sediments. Our study revealed that the recorded values of pollutants (especially the concentrations of As, Cu, Ni, Co) influenced the mite communities' structure in the ash pond and its dam (Table 4). _T. v. sarekensis_ was found to resist a wide range of toxic metal pollution. It was the only species that thrived in high abundance in heavily polluted samples of forming Technosol MOD. According to [PERSON] [63], it was the only oribatid species observed as comparatively abundant at highly polluted sites. _T. v. sarekensis_ is considered an opportunistic herbo-fungivorous species. It is also well known for belonging to a group of parthenogenetic r-selected organisms, which can recolonize areas where sexual reproduction may be hindered by environmental conditions [64]. Its life strategy and high tolerance allow it to occupy free niches after the displacement of other species and acquire a highly dominant position in the community [4; 65; 66; 67; 68]. Most oribatid species are, although defined as K-selected organisms with low dispersion ability [69]. They cannot adapt to new conditions, escape easily from the stress of disturbance, or quickly recolonize disturbed habitats. Only a few eruppotent species from oribatocoenoses, usually Oppiidaea and Brachychthoniidae, can survive in permanently stressed biotopes. The technogenic substrates often form an unfavorable microhabitat for mites because of the low amount of SOM, low humidity, and wide C/N range.