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While phytoplankton studies on large potamal rivers have increased in number in recent years, upper river sections have received considerably less attention. However, in order to better understand processes that govern the development of dominance of euplanktonic elements in the lower river sections, detailed studies of the upstream areas are necessary. We studied the composition, diversity and recruitment of the planktonic algal communities in the River Sajo and in its main tributary River Hernad, two characteristic rhithral river systems in Central Europe. Results revealed that diatoms are dominant elements of the phytoplankton in the upper river segments both in terms of taxa richness, and relative abundance. We found that composition of the phytoplankton showed the closest resemblance to that of benthic communities of soft substrates, highlighting the key role of riverbed characteristics in river phytoplankton recruitment. The occurrence of euplanktonic elements was not restricted to human impacted river segments, these taxa also occurred in pristine headwaters. Accordingly, planktonic algae potentially colonise small headwater streams naturally, although their dominance is expected to occur only at downstream reaches following impounded river segments. Diatom metrics used in ecological state assessment were calculated for the rithroplankton. These metrics fell in the range of values calculated for diatom flora on the hard substrates. However, the potential use of rithroplankton for quality assessment might be limited, because the high variability of index values at site level would result in misclassification of the ecological status.

The question of how species richness depends on the area is one of the most intensively studied subjects in biogeography. Many studies have reported this pattern for terrestrial and macroscopic taxa; however, microscopic and aquatic communities have received much less attention in the literature. The aim of our study was to reveal the relationship between the habitat size and richness of freshwater benthic diatom assemblages. We hypothesized that if the size of studied water bodies covers wide spatial scales, the species-area relationship (SAR) could be described by a sigmoid model. Benthic diatom assemblages were investigated in pools, ponds and lakes of various sizes (10−2–108 m2). We demonstrated that although the SAR in the log-log space can be described by a linear model, the linear breakpoint regression provides better fit to data. Using this technique a characteristic small island effect (SIE) could be distinguished. The SIE fell in the range of 10−2–104 m2. We also demonstrated that species richness of the diatom guilds is remarkably different in the various size ranges of the water bodies. We also demonstrated that the slope of the SAR (z value) is similar to those values that have been reported for other microbial organisms.

As lake biota are basically determined by hydromorphological characteristics of the lake basin, estab- lishment of a lake typology is the first step in lake quality assessment and management. Based on descriptor vari- ables (size, depth, lake bed material, water-regime and macrophyte coverage), 16 hydromorphological lake-types were established for the Pannonian Ecoregion. Our analyses revealed that descriptor variables have considerable effect both on biomass and composition of phytoplankton. As the phytoplankton biomass of several lake-types can be merged, a simplified typology can be proposed. Since the phytoplankton composition of various lake-types dif- fered significantly in terms of diversity and relative abundance of functional groups, well delineated composition- based types cannot be established for Pannonian lakes. Although the Pannonian Ecoregion is the westernmost part of the Eurasian steppe zone, the proposed typology of the studied area can be extended to lakes of the greater Pannonian region.

800x600 Diatom composition of the rheoplankton (phytoplankton) in the Sajo- Hernad river system (Slovakia and Hungary) was studied. Forty two sample sites were designated on the watershed from source to mouth of the two rivers and their tributaries. Samples were taken in July 2012. Altogether, 258 diatom taxa were identified. The microflora was dominated by tychoplanktonic elements. According to the relative abundance of the occurring taxa, four groups could be distinguished. Differentiation of these groups was confirmed by differences in the habitat characteristics, viz. altitude, width of watercourse, macrophyte coverage and river bed material. Diversity of diatom taxa in the phytoplankton was also studied. A positive relationship was found between the macrophyte coverage and the Simpson and the Shannon indices. In contrast, a negative relationship was shown between the macrophyte coverage and Berger-Parker diversity, in which metric the role of the dominant taxa is emphasized. Although the phytoplankton in rhithral rivers is influenced by stochastic events, our results reveal that geographical and hydromorphological characteristics of the rivers and coverage of macrophytes can also play role in shaping the composition and diversity of the phytoplankton. Normal 0 21 false false false HU X-NONE X-NONE MicrosoftInternetExplorer4