No abstract

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.

The Indice de Polluo-Sensibilité Spécifique (IPS) is one of the most frequently used diatom index. Beside this, according to some studies in streams and small rivers the diatom ecological guilds might be effective tools for ecological quality assessment in the future, but the usability of them is not always clear. Our main goal was to compare the robustness of the IPS index and diatom ecological guilds in a large river. For this i) a temporary study was carried out to investigate if there were some differences between how the nutrient content affected the IPS values and guilds proportions in the Danube River; ii) spatial studies were conducted to investigate the effects of the different water depths (different light intensity and current velocity) on biological metrics (IPS and guilds, as well); iii) we studied whether the IPS index or guild proportions were influenced more by the substrate type.As for the results of the temporal study only the motile and planktic guilds had significant connections with phosphate-phosphorus concentration. However, the high profile and the low profile taxa showed correlations neither with nutrient concentration nor water discharge. Nevertheless, the higher abundances the low profile guild reached the lesser values of the IPS index were. In spatial studies the guild abundances (especially the motile taxa) altered in different water depths. This could be caused by 2 different microhabitats characterised by disparate current velocity, and by different types of bed material along the cross-section. Contrary to guilds, there were no relevant differences in IPS values along the cross-sections. We experienced similarities in the study on shells and in spatial study: there were significant differences between guild abundances on different shell surfaces, but not so in the IPS. On the whole the IPS is robust enough to be a suitable index for the ecological water quality assessment and diatom ecological guilds could not be used instead of the diatom index (IPS) in large rivers. However, the trait based methods could be useful supplements of the ecological status assessment.

25While phytoplankton studies on large potamal rivers have increased in number in recent years, upper 26 river sections have received considerably less attention. However, in order to better understand 27 processes that govern the development of dominance of euplanktonic elements in the lower river 28 sections, detailed studies of the upstream areas are necessary. We studied the composition, diversity