Date Published: October 25, 2018
Publisher: Public Library of Science
Author(s): Angéla Földi, Éva Ács, István Grigorszky, Luc Ector, Carlos Eduardo Wetzel, Gábor Várbíró, Keve Tihamér Kiss, Péter Dobosy, Zsuzsa Trábert, Andrea K. Borsodi, Mónika Duleba, Suzannah Rutherford.
The spatial response of epiphytic diatom communities to environmental stress was studied in a moderately saline wetland area located in the plain of Danube-Tisza Interfluve, Hungary. The area is characterised by World War II bomb crater ponds and can be regarded as an excellent ecological model system where the dispersion of species is slightly limited by distance. To study the effect of environmental variables on the communities, canonical correspondence analysis was applied. Salinity, pH, total suspended solids, total phosphorous and depth proved to be significant environmental drivers in this analysis. The ecological status of the ponds was assessed with Ziemann’s halobity index, as the trophity-depending metric cannot be applied to these habitats (due to the naturally high phosphorus content). Ponds in “good” ecological status significantly differed from those appertaining to water quality category of “not-good” ecological status considering characteristic of natural astatic soda pans (e.g. salinity, pH, ammonium, total phosphorous concentration, nitrogen:phosphorous ratio and turbidity). The differences between epiphytic diatom communities inhabiting the ponds were detected using non-parametric multidimensional scaling. The samples formed three groups according to the types of ponds (“transparent”, “transitional” and “turbid”) based on the width of the macrophyte belt around them. Indicator species related to the ecological status of the ponds and diatom communities contributing to the separation of groups of ponds were identified. One of the indicator species differed from species already described. Light and scanning electron microscopy features and phylogenetic analyses based on three genes (18S and 28S rRNA genes, rbcL) proved that it was a new species of Nitzschia genus, closely related to Nitzschia frustulum and Nitzschia inconspicua. Therefore, description of a new species, Nitzschia reskoi Ács, Duleba, C.E.Wetzel & Ector is proposed. We concluded that the increasing abundance of Nitzschia reskoi was a signal of the degradation of the intermittent saline wetlands.
Global warming affects the structure, function and stability of lake ecosystems throughout the world . Small, shallow ponds are especially vulnerable, but the habitat loss due to the contraction is also detectable in large shallow lakes . In limnological studies, the small, shallow lakes, the intermittent lakes and puddles have not been highlighted against large lakes for a long time. Investigations over the last decades have pointed out that there are significant differences between the ecology of small and large lakes [2,3]. The small lakes are labile because of the low water volume; consequently, they rapidly indicate the change of the environmental conditions (e.g. climate change). Huge numbers of astatic soda pans have decreased during the last decades all over the world, especially in the Carpathian Basin due to human activity and global warming .
According to Reese et al. , a true “extreme” environment on Earth would be hot brine having high pH. Some of the studied bomb crater ponds (first of all the members of “turbid” group) had high salinity, pH and turbidity, their waterbody could warm up and the suspended matter content was extremely high, so the light availability for the algae was very low. Following the proposed terminology of Reese et al. , we can say that these ponds are really extreme habitats and the indicator diatoms of these ponds are true “boundary organisms”. These results highlight the importance of studies finding rules that explain the composition and abundance of coexisting species, which is a central issue of community ecology.