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Reduced body size is among the universal ecological responses to global warming. Our knowledge on how altered body size affects ecosystem functioning in ectothermic aquatic organisms is still limited. We analysed trends in the cell size structure of phytoplankton in the middle Danube River over a 34-year period at multiple levels: (1) average cell size of assemblages (ACS), (2) within the centric diatom community and (3) in the dominant centric diatom taxon: Stephanodiscus. We asked whether global warming and human impacts affected the average cell size of phytoplankton. Also, whether the altered size structure affected how chlorophyll-a, as an ecosystem functioning measure, relates to the ACS of phytoplankton. The cell size of phytoplankton decreased significantly at all organisation levels, and the assemblages became more dispersed in cell size over time. Environmental variables related to global warming and human impacts affected the ACS of phytoplankton significantly. The relationship between chlorophyll-a and the ACS of phytoplankton shifted from negative linear to broad and then narrow hump shape over time. Longer water residence time, warming and decline in nutrients and suspended solids decrease the ACS of phytoplankton in the middle Danube and expectedly in other large rivers. Our results suggest that cell size decrease in phytoplankton, especially of centric diatoms, constrains planktic algal biomass production in large rivers, independently of algal density. Such cell size decrease may also affect higher trophic levels and enhance the more frequent occurrence of “clear-water” plankton in large, human-impacted rivers under global change. Electronic supplementary material The online version of this article (10.1007/s10021-019-00467-6) contains supplementary material, which is available to authorized users.

EnglishThe spatial and temporal patterns of phytoplankton in relation to physical and chemical properties were studied in a drinking water reservoir - the Lazberc Reservoir - located in north-east Hungary. The main objectives were to determine the role of the hydrologic regime in structuring algal growth and the effects of physical and chemical variables on the coexistence of a dominant species: cyanobacteria, Microcystis aeruginosa (Kutzing) Kutzing and an eukaryotic dinoflagellates, Ceratium hirundinella (O.F. Muller) Dujardin. The results suggest that nutrients (TP, NH4–N and NO3–N), turbidity, and the hydrologic regime play an important role in regulating the occurrence of investigated species. The rainy summer period resulting in a mixing of the water column, and the low level of nitrogen coupled with the internal release of phosphorus from the lake sediment under brief periods of anoxia promote cyanobacterial bloom. During this period, the water column was characterised by high turbidity, which created favourable conditions for developing a huge C. hirundinella biomass and the simultaneous occurrence of M. aeruginosa. This study also demonstrated - that contrary to what was previously known, deep standing waters in the temperate zone are not only dimictic (mixing twice a year during the spring and the fall), but they can also be mixed during the summer period due to continued rainfall, which equalizes the temperature in the whole water column. This can promote the occurrence of cyanobacterial and eukaryote planktonic organisms portuguesOs padroes espaciais e temporais do fitoplâncton e sua correlacao com as especificidades variaveis fisicas e quimicas, foram examinados no nordeste da Hungria, localizados em um reservatorio tipico de agua potavel no reservatorio de Lazberc. Nosso principal objetivo foi para esclarecer o papel da hidrologia, e os diferentes especificidades fisicas e quimicas na coexistencia de especies dominantes: cianobacteria, Microcystis aeruginosa (Kutzing) Kutzing e Dinoflagellata eucariotica, Ceratium hirudinella (OF Muller) Dujardin. De acordo com os resultados, os nutrientes (TP, NH4-N, NO3-N), turbidez e os condicoes hidrologicas desempenham um papel importante na regulacao da ocorrencia das especies examinadas. O periodo de verao chuvoso que resulta um equilibrio do nivel da agua, o baixo nivel de nitrogenio, juntamente com a liberacao interna de fosforo do sedimento, durante um curto periodo anoxico promove a floracao de cianobacterias. Durante este periodo, a coluna de agua foi caracterizada por alta turbidez, criando condicoes favoraveis para o surgimento de uma enorme expansao da biomassa C. hirundinella e a aparicao simultânea de M. aeruginosa. Este estudo mostrou tambem que as aguas profundas nas areas da zona moderada, nao tem apenas dimictic especialidade (misturando duas vezes por ano, na primavera e no outono), mas tambem durante a estacao do verao pode ser misturada por chuvas continuas que compensam a temperatura em toda a coluna da agua. Isso ajuda a presenca de cianobacterias e organismos eucariotas planctonicos

Although metacommunity dynamics of lentic phytoplankton are relatively well-documented, studies on the role of environmental and spatial processes in shaping phytoplankton communities of large rivers are still scarce. Here, we examined six phytoplankton data sets, which were collected in 1978-2017 from large river-scale segments (mean spatial extent 1117 km) in the Danube River. Our aim was to elucidate role of climatic, spatial and temporal predictors in variation of phytoplankton beta diversity using variance partitioning for compositions of species and functional groups sensu Reynolds. We hypothesised that phytoplankton beta diversity (measured as average distance to group centroid) would be positively related to both climatic heterogeneity and spatial extent used as a proxy for dispersal limitation. Additionally, we tested alternative dispersal models to evaluate different spatial processes structuring phytoplankton community. Our results revealed that spatial variables were more important than climatic factors in controlling both species and functional group composition. Climatic heterogeneity showed significant positive relationship with beta diversity. In contrast, there was no significant relationship between beta diversity and spatial extent, suggesting that spatial effect on beta-diversity was attenuated by anthropogenic disturbance. The better performance of non-directional model compared to model of water directionality suggested that spatial dynamics of phytoplankton metacommunity was in large part regulated by differences in the regional species pools. Spatial and temporal variables outperformed environmental (including climatic) factors in explaining phytoplankton metacommunity structure, indicating that phytoplankton exhibited strong biogeographical patterns. Thus, dispersal limitation interfered with species-sorting processes in determining phytoplankton community structure. In conclusion, our findings revealed that the development of a more reliable bioassessment program of the Danube River should be based on separation into basin regions.

The morphology and ontogenetic allometric trends of a rare diatom Fragilaria heidenii Ostrup and the morphologically related Staurosira tabellaria (W. Smith) Leuduger-Fortmorel were compared using conventional and semilandmark-based geometric morphometric analyses. Fragilaria heidenii was studied in detail by light and electron microscopy using type material and recent samples from Lake Ladoga and Lake Ilmen (north-western Russia). The taxon is transferred into the genus Staurosira Ehrenberg as Staurosira inflata comb. nov. on the basis of its valve morphology. This taxon is characterized by the absence of rimoportulae, lack of perforated copulae, spines located on the interstriae, internal vola occlusion in the areolae and the features of the areolae and apical pore fields. Conventional morphometric analysis showed considerable overlapping of S. inflata and S. tabellaria in their frustule characteristics such as length, width, length-to-width ratio and striae density. Moreover, at later stages of...

Diatoms are widely applied in the ecological status assessment of aquatic ecosystems using indices calculated from pollution sensitivity and indicator values of species. Traditional, morphology-based identification of species requires in-depth taxonomic knowledge and expertise. Identifying taxa according to their barcode sequences obtained with high-throughput sequencing (metabarcoding) would be a promising alternative. In this pilot study, we tested the applicability of metabarcoding of benthic diatom assemblages for the ecological status assessment of Hungarian water bodies, comparing its performance to that of morphology-based identification of species. The barcode region of the rbcL gene was investigated in samples from running waters with various trophic states and unique lentic habitats, namely soda pans. For running waters, the Specific Pollution Sensitivity Index (IPS) and for soda pans the H index and the Indice Biologique Diatomees (IBD) were calculated from the morphology- and sequence-based abundances. The ecological quality ratio was determined for running waters. Overall, more infrageneric taxa were found with microscopy than with metabarcoding in the lotic and lentic samples. The correspondence between taxon lists detected by the two methods was relatively low but increased considerably in the case of morphologically dominant taxa. Community composition based on microscopy and DNA sequence analysis showed a significant correlation and was determined by the same main environmental drivers. Morphology-based indices strongly correlated with sequence-based indices. Both aspects indicated the same ecological status class for more than half of the lotic samples. In other cases, a status shift from good to moderate was frequent, a phenomenon that could prove problematic because the Water Framework Directive prescribes intervention for waters with a moderate or worse status. Considering discrepancies between the results obtained with microscopy and metabarcoding, using both methods in parallel could be proposed until the reference database has been suitably updated.

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.

Specimens of a very small diatom were found in a dead oxbow of Tisza River (Hungary), in Eula River (Germany) and Parroy Pond (France). After SEM studies we identified all of them as Eolimna archibaldii J.C. Taylor et Lange-Bert., which is currently regarded as endemic species to South Africa. Furthermore, the results of Principal Components Analysis of morphometric characters clearly demonstrated an overlap between the type material and European populations. Therefore this diatom cannot be considered endemic to South Africa. Moreover, E. archibaldii and a very similar species, E. becaresii are transferred to the genus Sellaphora. Our results confirm the benefit of SEM for verifying the identity of small-sized diatoms, especially for routine monitoring, and allow more precise ecological assessment.

The stress dominance hypothesis (SDH) postulates that strong environmental gradients drive trait convergence in communities over limiting similarity. Previous studies, conducted mostly with terrestrial plant communities, found controversial evidence for this prediction. We provide here the first test for SDH for epiphytic diatoms. We studied community assembly in diatom communities of astatic ponds. These water bodies serve as a good model system for testing SDH because they exhibit stress gradients of various environmental factors. Functional diversity of diatom communities was assessed based on four traits: (1) combined trait reflecting the trade-off between stress tolerance and competitive dominance, (2) cell size, (3) oxygen requirement and (4) N-uptake strategy. According to our results, salinity, pH and the width of the macrophyte belt appeared as significant predictors of the trait convergence/divergence patterns presumably acting through influencing the availability of carbon dioxide and turbidity. Lower trait diversity was found in turbid, more saline and more alkaline ponds and functional diversity was higher in transparent, less saline and less alkaline ponds. Overall, our results supported the stress dominance hypothesis. In habitats representing increased environmental stress, environmental filtering was the most important community assembly rule, while limiting similarity became dominant under more favourable conditions.

(1) Urbanization significantly influences the ecosystems of rivers in various ways, including the so-called loading effect of wastewater production. Benthic diatoms are used in ecological status assessments of waters. Beside species composition, traits can be used as indicators. We aimed to evaluate how the loading of the large city of Budapest manifests in the physico-chemical variables of the River Danube and what species composition and trait response this loading results in for the benthic diatom communities. (2) Weekly samplings were performed at points upstream and downstream of Budapest on both riverbanks. Samples were compared, based on general physical-chemical variables and the concentration of thirty-four elements, as well as species composition and seven traits of species of diatom communities. Ecological status was assessed using the Specific Pollution Sensitivity Index (IPS). (3) Only a few measured environmental variables showed differences between the sampling points, suggesting that the nutrient loading has significantly decreased due to the installation of several efficiently working wastewater treatment plants since the introduction of the European Union Water Framework Directive. In contrast, the species composition and traits of species showed the effect of land use. Benthic diatoms indicate the environmental changes caused by land use in the longer-term, while chemical measurements reflect instantaneous status.

Centric diatom taxa in the Cyclotella ocellata and C. comensis complexes show high morphological variability and often apparently continuous morphological transitions. In this study, we investigated natural assemblages of the C. ocellata/C. comensis complex from Hungarian and Croatian lakes and from Turkish streams using morphological and molecular methods. The studied assemblages contained cells with morphologies resembling C. ocellata as well as other, closely related, species: C. comensis, C. pseudocomensis, C. costei, and C. trichnoidea. The goal of our paper was to assess whether the observed morphological differences were due to intraspecific variability or suggest the existence of several, putatively distinct species.Ten morphometric characters were measured, which, either individually, or in pairs, did not differentiate the nominal taxa in our assemblages. However, multivariate discriminant analysis has revealed a group including C. ocellata and C. trichonidea morphologies could be separated from another containing C. comensis, C. pseudocomensis and C. costei.A nuclear (18S rDNA) and a chloroplast (rbcL) gene were amplified and partially sequenced from environmental DNA or from isolated cells. The sequences showed little variability among the assemblages and nominal species. Although general congruence of molecular and morphometric separation supports the species level separation of C. ocellata/trichonidea from the probably conspecific C. comensis/pseudocomensis/costei, sequence divergences between the groups are in the same range as within them, so that a conspecificity of all four taxa cannot be unequivocally excluded. © 2015 The International Society for Diatom Research.

Skeletonema potamos is a poorly known freshwater species in the ancestrally and predominantly marine genus Skeletonema. With phylogenetic analysis of two nuclear {partial SSU (18S) and partial LSU (28S) rDNA)} and two chloroplast (rbcL and psbC) genes, we verified its placement within the genus Skeletonema and identified the mostly brackish species, Skeletonema subsalsum, as its closest known relative. Comparisons of SSU and LSU rRNA genes from S. potamos populations from Europe and North America revealed no intraspecific variation. Skeletonema potamos can be a dominant element of the phytoplankton community in various ecosystems, including the River Danube. We tracked phytoplankton composition in the River Danube weekly from 1979 to 2 012, and throughout this period, S. potamos exhibited a strong increase in proportion of total phytoplankton abundance and biomass - an increase that was correlated with increasing water temperature over the same time period. Current records indicate a temperate distribution of S. potamos, but ecological data predict possible expansion of its geographic range and increase in seasonal duration within existing habitats in response to the warming of surface waters.

Stephanodiscus triporus was described in 1978, based on a study from the phytoplankton of Volgograd Reservoir that used transmission electron microscopy. This species is small, diameter 3.7–10.6 µm, with 14–30 striae and 30–60 areolae in 10 µm, and differs from other Stephanodiscus species by the presence of three satellite pores in the single central fultoportula. Later a new species similar in morphology to S. triporus, was described from Iowa, USA, namely S. vestibulis. A large population of S. vestibulis was found in Lake Balaton and the species also occurs in different Hungarian and French waters. Detailed comparison of S. triporus and S. vestibulis, based on our results and literature, showed they are very similar. Therefore we reinvestigated the type material of both and compared them with the Hungarian and French specimens. Conventional and geometric morphometric analyses were carried out, also including comparisons with the morphologically closest taxon, S. minutulus. There is a continuum of vari...

We investigated the diel vertical distribution patterns of microcrustacean zooplankton (Cladocera, Copepoda) in a shallow pond (max. depth: 70 cm) of the Oreg-turjan peatland (Ocsa, Central Hungary) during three 24-h periods in July (19-20th), August (17-18th) and September (11-12th) 2011. Environmental variables showed remarkable vertical stratification. Oxygen concentration was close to zero in the entire water column from night until sunrise, while the lower strata (from 20 cm below the surface) were close to anoxic during all three diel cycles. It proved to be the main determinant of the vertical distribu- tion of microcrustaceans. Accordingly, the highest proportion of individuals was present in the surface layer. Chlorophyll-a concentration and phytoplankton biomass were inversely distributed compared to zoo- plankton. Microcrustaceans (mainly Daphnia curvirostris) migrated to the middle layer only in August, which could be explained by a trade-off between food resources, dissolved oxygen (DO) and competition with littor- al zooplankters. The diurnal density patterns of microcrustaceans suggested horizontal migration into the aquatic macrophytes during night, which could be a strategy to avoid Chaoborus predation. Our results show that strong vertical gradients of abiotic and biotic factors occur even in such shallow waterbodies. Among them, DO can maintain constant vertical aggregation of zooplankters by limiting their occurrence to the surface layers.

Seasonal dynamics of cladoceran and copepod zooplankton were studied over a one-year period in five permanent ponds of a cutaway peatland, situated in the Danube−Tisza Interfluve, Central Hungary. 17 cladoceran, 11 cyclopoid copepod and 6 harpacticoid copepod species were identified and most of them were typical of small lowland ponds. Nevertheless, some taxa like Cyclops insignis, Ceriodaphnia setosa and Macrocyclops distinctus are considered to be rare in Hungary. The microcrustacean assemblages exhibited apparent seasonal succession with typical seasonal species. There appears to be at least two main successional patterns in the five ponds. After general cyclopoid copepod dominance in winter (Cyclops strenuus and Cyclops insignis), at sites with higher proportion of open water and submerged vegetation, spring was characterized by the dominance of the large cladoceran Daphnia curvirostris, which declined during summer, when microcrustacean assemblages composed mainly of smaller, littoral cladocerans. At these sites, species richness and diversity reached their maximum in autumn. In the case of duckweed covered ponds, succession led to less diverse autumn assemblages with fewer species, dominated by Simocephalus exspinosus. Our results draw the attention to the importance of long-term investigations and the often neglected winter sampling in the accurate evaluation of species richness (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Results of an ecological quality ratio-based qualification system, developed on the basis of the analysis of 1,161 benthic diatom dataset of the Hungarian national database, are presented herein. Using Kohonen’s Self Organising Map technique, the 25 Hungarian physiographic river types were pooled into six larger distinct categories (diatom river groups). Diatom metrics were tested for their sensitivity to the targeted stressors (nutrients, COD hydromorphological alteration) in each group. The strongest relationships were found in the case of the IPS, SI and TI indices; therefore the average of these metrics (IPSITI) was proposed as a national multimetric index for Hungarian streams. Based on IPSITI values, the ratio of moderate to worse quality water was the highest in those groups containing small rivers. In the case of large, lowland and mid-altitude rivers with fine sediment, the good and moderate ecological status was more characteristic. Applicability of the IPSITI seems to be very useful in case of small- and medium-sized rivers. For these rivers, the index showed a significant relationship with nutrients and organic pollutants. In the case of very large rivers, the stressor–index relationships were not significant because of the insufficient number of samples and the small range of stressors.

A population of Amphora micrometra Giffen, collected in September 2002 from different habitats in Laguna Blanca in the Bolivian Altiplano, South America, has been examined using light transmission and scanning electron microscopy. The original description of this species is incomplete and insufficient to characterize the taxon in the light of the newly collected ultrastructural data. The holotype of A. micrometra was examined during the present study and compared to Bolivian specimens. An emended diagnosis of A. micrometra using all available information is provided. A taxonomic discussion based on available literature and the ecology of the taxon is also presented herein.

Epilithon and epiphyton samples collected from Lake Balaton (Hungary) in 2006 and 2007 contained, as dominant, specimens similar to those described in 1902 by Pantocsek as Fragilaria hungarica. Since Pantocsek had previously used the name F. hungarica in 1892 for a fossil taxon from Demend (Slovakia), the Lake Balaton specimens required a new name. Additionally, information collected during this study, using light (LM) and scanning electron microscopy (SEM), supports the transfer of the specimens from Lake Balaton to the genus Staurosira Ehrenberg. The nomenclatural consequences from Pantocsek’s dual use of the name F. hungarica, are solved herein by the proposal of the new name Staurosira grigorszkyi nom. nov.

Summary 1. An artificial glass substratum was incubated in the River Danube for a period of 28 days in order to detect the sequential colonization of microorganisms. 2. Light and fluorescent microscopy showed that microalgae and the picoalgal fraction on the slides increased rapidly over the first 2 weeks of colonization. Diatoms were numerically the most abundant component of the periphyton and their species richness and diversity increased rapidly in the early phase of colonization whereas diversity subsequently increased moderately. 3. Evenness of the diatom community was initially high, lower in the intermediate phase and again higher later on. Succession involving early, intermediate and late colonizer species was observed. Community composition during the first 5 days of colonization was very different from later stages whereas there were only minor changes subsequently. 4. Molecular community analysis by means of terminal restriction fragment length polymorphism analysis of PCR amplified 16S rRNA and 18S rRNA genes pointed to even larger differences between the composition of samples obtained early and late in the period. 5. The number of 18S rRNA and 16S rRNA terminal restriction fragments (T-RF-s) was variable over the colonization period and the fragment patterns of both the bacterial and eukaryotic portion of the microbial community were variable, with most T-RF-s unique to a single sample, suggesting a wide diversity and dynamic properties of periphytic organisms.

Benthic diatom flora of the River Danube was investigated along the river from the source streams to the end of the Hungarian stretch during a four-year period. Characteristic diatom community assemblages were established using KOHONEN Self-Organizing Map (SOM) algorithm. We found five sample clusters, arranged according to the location. The first three groups are located in the German-Austrian stretch, while the fourth and fifth groups are located in the Slovakian-Hungarian stretch. Characteristic species of the clusters 1 and 2 are Achnanthidium minutisimum (KUTZ.) CZARNECKI, Denticula tenuis KUTZ., Nitzschia fonticola GRUN., Psammothidium bioretii (GERMAIN) BUKHT. & ROUND, Melosira varians AG., Planothidium subatomoides (HUST.) BUKHT. & ROUND, character species of cluster 3 is Amphora pediculus (KUTZ.) GRUN., while character species of the clusters 4 and 5 are Nitzschia dissipata (KUTZ.) GRUN., Navicula cryptotenella LANGE-BERT., Cocconeis placentula var. euglypta (EHR.) GRUN., Rhoicosphenia abbreviata (AG.) LANGE-BERT., Nitzschia inconspicua GRUN. This arrangement is also well in agreement with the poorer water quality of the lower, and the better water quality of the upper stretch.

The phytoplankton database of the Middle Danube Basin was analysed and evaluated in order to describe the characteristic algal assemblages of the rivers. The dataset were extracted from the database of the Hungarian monitoring network and academic institutions. We implemented the Kohonen Self Organizing Map (SOM) method by which we can visualize the assemblages in topology-preserving projection of two-dimensional space. The method is capable of evaluating large datasets (more than 1800 samples in the present investigation). As a result, we can identify the different algal communities which characterize different river types. The algal communities were described as different ratios of algal functional groups. Since some of the groups are in close relation with certain types of environmental pressure it is also possible to highlight those rivers or river sections (or those periods) which are far from the expected good ecological status.

Water quality monitoring based on microscopical analysis of periphytic algae is fundamental to the European Water Framework Directive. However, the outcome of this kind of monitoring is often dependent on the experience of the operating taxonomist and the availability of an electron microscope for fine-scale taxonomic analysis. Furthermore, it is hampered by the insufficiencies of the morphology-based diatom taxonomy. Molecular fingerprinting methods have the potential to evade these problems and serve as a complementary tool in biomonitoring studies. To test this concept, periphyton of the River Danube was monitored for a period of six months using microscopical and molecular fingerprinting (terminal restriction fragment length polymorphism) methods in parallel. We identified 120 diatom taxa by light and electron microscopy, and diatom-based water quality using Omnidia Version 4 software was found to be good or moderate (IPS value between 12 and 16). The number of operational taxonomic units identified by terminal restriction fragment length polymorphism analysis of the 18S rRNA gene ranged from 7 to 29 for individual samples, and was in total 88 in the Mspl digest and 33 in the Rsal digest. The results of both analyses were compared by hierarchical classification and we found good correlation between the two methods. We propose, that after further development of molecular databases and methodology, molecular fingerprinting may have the potential to be implemented for routine biomonitoring purposes.

Based on the phytoplankton associations described for lakes (REYNOLDS, 2002), an assessment method has been elaborated for rivers. All phytoplankton associations were evaluated and scored by a number between 0-5. As many rivers can be defined as shallow, turbid, mesotrophic ecosystems of short residence time, those associations that prefer this type of environment were given high factor numbers, and those that are typical of stable hypertrophic lakes have got the lowest values. Highest values were given to those assemblages that contain mainly periphytic diatoms. To achieve an index, each species in the sample must be assigned to the appropriate functional group. Then the relative share of each functional groups are calculated. Relative shares are then multiplied by the factor number. The sum of these scores is the index. The reference values of the upper river sections are close to 5, while those of the lower river stretches are approximately 4. The method has been tested with hundreds of phytoplankton samples, it is simple, and after applying to a phytoplankton database can be computerised easily. Another advantage of the method that it is not restricted to a specific geographic region.

Two Cyclotella species were found during the electron microscopic investigation of core samples from Lake La Cruz. Cyclotella distinguenda Hustedt was subdominant in the layers 80-110 cms and C. delicatula Hustedt was frequent and abundant in the layers 20-180 cms. SEM studies revealed an interesting variation in their valve structure elements. Analyses of the morphological characteristics of these species on the basis of SEM micrographs (55 photos were taken from C. distinguenda and 95 from C. delicatula) was made it possible to complete their description. In this paper, the similarities and differences between Cyclotella distinguenda, C. delicatula and related taxa (Cyclotella azigzensis Flower, Gasse et Hakansson, C. costei Druart et Straub, C. cyclopuncta Hakansson et Carter, C. granulata Kulumbaeva et Genkal, C. plitvicensis Hustedt, C. wuethrichiana Druart et Straub) are discussed.

Navicula novaesiberica Lange-Bertalot was recorded for the first time on the Hungarian stretch of the Danube River. The species was found in low relative abundance values in the epilithon at God (riv.km. 1669). N. novaesiberica was described more than ten years ago, it is a relatively large and conspicuous species. However, there are only a few records of it in the literature. Some additional details on the morphology and autoecology of this species are provided here.

According to the European Water Framework Directives, benthic diatoms of lakes are a tool for ecological status assessment. In this study, we followed an integrative sample analysis approach, in order to find an appropriate substratum for the water qualification-oriented biomonitoring of a shallow soda lake, Lake Velencei. Six types of substrata (five artificial and one natural), i.e., andesite, granite, polycarbonate, old reed stems, Plexiglass discs and green reed, were sampled in May and in November. We analysed total alga and diatom composition, chlorophyll a content of the periphyton, surface tension and roughness of the substrata and carbon source utilisation of microbial communities. Water quality index was calculated based on diatom composition. Moreover, using a novel statistical tool, a self-organising map, we related algal composition to substratum types. Biofilms on plastic substrates deviated to a great extent from the stone and reed substrata, with regard to the parameters measured, whereas the biofilms developing on reed and stone substrata were quite similar. We conclude that for water quality monitoring purposes, sampling from green reed during springtime is not recommended, since this is the colonization time of periphyton on the newly growing reed, but it may be appropriate from the second half of the vegetation period. Stone and artificially placed old reed substrata may be appropriate for biomonitoring of shallow soda lakes in both spring and autumn since they showed in both seasons similar results regarding all measured features.

Epilithic algae of the River Danube were investigated alongside the river from the source streams Breg and Brigach up to the end of the Hungarian stretch. Beside the data acquisition about the species composition of epilithic algae, diatom-based water quality analysis was performed with the aid of the widely used European software OMNIDIA. Additional samplings were carried out with monthly frequency at God (river-km 1669) in order to investigate the impact of a dry period on the water quality. We found that the diatoms Achnanthidium minutissimum and Amphora pediculus, furthermore the Chlorophyta species Protoderma viride gained an overall strong dominance on most parts of the Danube. However, species composition was very different in the source streams Breg and Brigach and on a short upper stretch of the Danube. Thus, two well-defined parts could be distinguished on the basis of epilithic algal composition: the source area and the lower stretch including the total length of the Austrian, Slovakian and Hungarian stretches. We concluded that the differences between the upper stretch and the middle stretch of the Danube have practically vanished which is the result of the large-scale dam constructions on the river. Two invasive diatom species were found in the Danube: Didymosphenia geminata and Reimeria uniseriata. Using OMNIDIA program we found that the indices IPS, IBD and CEE gave reliable water quality assessment in the River Danube. According to these, the water quality of the Danube is good or excellent around the sources and, through gradual deterioration, it becomes moderate or partly bad in Slovakia and Hungary. In August 2003, unusually low phytoplankton abundances were found at God, which did not correspond with the low water discharge. At the same time epilithic diatoms showed unexpectedly vigorous multiplication and produced large masses of gelatinous matrix. The diatom-based water quality turned out to be poor (polluted). The peculiar phenomenon could only partly be explained; however, it draws the attention to the necessity of water quality analysis based on several (monthly) sampling per year.

1 , GY. TABA 3 and K. T. KISS 1 The suitability of benthic diatoms in the biological monitoring program of the water quality of Lake Velence was tested. Diatom indices were calculated with the aid of the software Omnidia based on reed periphyton samples collected between 1988 and 1990, and 1999 to 2004. We have pointed out which indices are appropriate for indicating the water quality changes of Lake Velence. The correlation between the indices IBD, IPS, IDG, and the total nitrogen, total phosphorus content of the water and chlorophyll-a content of the periphyton was calculated. Significant negative correlation was found between the indices and the total phosphorus content of the water. Moreover, we concluded that the chlorophyll-a content of the periphyton related to surface area can also provide information about the water quality. Based on these results the index IBD seems to be the most suitable for the water quality analysis of Lake Velence. Recommendations are provided here concerning the ecological status classification of Lake Velence based on epiphytic diatoms; unaccounted questions and future assignments are also outlined in connection with this.

Plankton samples collected from a yellow watered bog pool of the mesotrophic “Calaţele Padurii” peat bog (Romanian Western Mountains, Transylvania), exhibited an outstandingly rich Mallomonas population. The observations carried out by light and scanning electron microscopy revealed that the population belongs to Mallomonas intermedia Kisselev. Based on the presence of lance head bristles, distributed all over the cell armour (except few anterior collar, unilaterally serrated ones), it became evident that the population belong to the nominate variety (var. intermedia). Mallomonas intermedia var. saliceaensis formerly described from Transylvania differs by the type variety by the presence of exclusively serrated bristles. The present finding proved that Mallomonas intermedia could not be properly identified at infraspecific level solely based on the ultra structure of scales, without knowing the structure of bristles, too.

Benthic diatom investigations of some Hungarian streams have been carried out in order to find reference sites in assistance to the ecological quality analysis of the different river types according to the Hungarian river typology. On the basis of the coevaluation of biological and chemical parameters, among the investigated streams, some part of Kemence stream seems to be the appropriate reference site for the classification of the highland, siliceous rivers of Hungary. However, further invastigations are needed for the selection of reference sites for the other types of Hungarian river typology. This is the most difficult in the case of lowland rivers, which are exposed to more severe anthropogenic impacts. Important is the question which biological parameters should be investigated and considered when assessing the ecological condition of our waters. In the United States, e.g. the assessment of the relative abundance of Achnanthidium minutissimum is quite widespread (Stevenson and Bahls 1999), the exte...

The Rakos-stream is a small stream near Budapest (Hungary). The water of the stream is considerably polluted with communal and industrial wastewaters. In May and September 2001 benthic diatom samples were collected along the stream, in May from the surface of available water plants and gravel. In September samples from the side of the concrete bed of the stream were also gathered. Diatoms were identified and their relative abundances were determined in each sample. The diatom indices SLA, L&M, IBD, IPS, EPI-D and CEE were calculated using the software ,,Omnidia", which has been developed in France for the purpose of water quality analysis with benthic diatoms. The Shannon-Weaver diversity values were calculated for each association and the data were clustered by Czekanowski and Jaccard indices. The aim of the study was to draw some conclusions on the water quality and to give a floristical overview of benthic diatom flora, since algological observations were previously not made on this stream. The quality of the water based on benthic diatoms is good near the source of the stream, moderate near the mouth and polluted on the middle reach. The diversity values increase from the source towards the mouth. The cluster dendrograms showed that the similarity of benthic diatom associations is firstly influenced by the sampling point, and then by the seasonality. The sampled substratum has less influence. Some very interesting species for Hungary were found. The planktic centric species Thalassiosira duostra was observed in our samples, in greater individual numbers on the most polluted reaches of the stream. Cyclotella distinguenda was noticed at several points (this is the first occurrence of this species in Hungary). Diadesmis confervacea was identified in some samples (it is the third occurrence of this species in Hungary). This species is supposed to be an invasive diatom, which has until recently been considered as a mainly tropical taxon. Finally, Navicula microrhombus was found in fairly great relative abundance at several points in the Rakos-stream (this is also the first occurrence of this species in Hungary).

In the shallow Lake Velencei (surface area 24.5 km2) reed communities (Scirpo-Phragmitetum) are of great significance due to extensive metabolic activity of algal-bacterial associations developing on their submerged surfaces. Samples for algological and bacteriological studies were taken in April 2000 and July 2001 at five sites of the lake and were analysed with traditional methods as well as with tools of molecular biology (16S rDNA sequencing). These investigations have shown that (i) The original mosaic structure of the lake disappeared; periphytic algae became spatially uniform both in terms of taxonomic composition and abundance. (ii) The biodiversity of the reed periphyton decreased. The dominance of the weed algal species Achnanthes minutissima Kutz. increased significantly. (iii) The most frequent bacteria were members of the genera Pseudomonas, Acinetobacter, Shewanella and Agrobacterium characterised by oxidative chemoorganotrophic heterotrophic- and Aeromonas and Bacillus species with fermentative metabolism. (iv) Among the studied bacterial strains both plant growth promoting bacteria, members of Pseudomonas fluorescens group, and potential plant pathogens (Agrobacterium, Aureobacterium, Curtobacterium) were present.

Since the description of Thalassiosira gessneri by HUSTEDT (1956) from the lake Maracaibo (Venezuela), only HASLE & LANGE (1989) published an important paper on this centric diatom from five rivers of USA. During the present study twenty-two centric diatom taxa were found in the phytoplanktron samples of the Luxembourgish stretch of the river Moselle. Several of them are relatively common in European rivers but some of them are rare or interesting in morphological and/or taxonomical point of view: Actino-cyclus normanii (GREGORY) HUSTEDT, Cyclotella scaldensis MUYLAERT et SABBE, Thalassiosira gessneri HUSTEDT, T. incerta MAKAROVA. The discovery of the brackish water species Thalassiosira gessneri in the phytoplankton of the River Moselle seems to be one of the first records from Europe. We also recently found it in periphyton samples of the rivers Rhone, Saone in France near Lyon and in the phytoplankton of River Danube in Hungary near Dunakiliti, of Main-Danube Channel in Germany at Kelheim. A morphological comparison was made, in light- and scanning electron microscope, of specimens from the lake Maracaibo, from North American rivers (HASLE & LANGE, 1989) and European rivers. A detailed morphological analysis of T. gessneri and T. lacustris is given, in comparison with related taxa: T. australiensis (GRUNOW) HASLE and T. bramaputrae (EHRENBERG) HAKANSSON. A discussion about the nomenclatural position of T. lacustris (GRUNOW) HASLE is also presented.

Cyclotella hispanica Kiss, HEGEWALD et Acs is described as a new taxon from three Spanish lakes. It is characterized by two unusual morphotypes. One morphotype has a plain valve face and a fine striation seems to be close to C. gracilis NIKITEEVA et LIKHOSH-WAY. The other morphotype has three remarkable depressions and elevations on the valve face and a well-developed striation, therefore resembling C. tripartita HAKANSSON. The existence of two morphotypes on one and the same cell affirms, that these are different features of one species only.

In early spring 2000, two incidents of bursting dams int he mines Baia Mare and Baia Borsa (Romania) produced peak amounts of cyanide (32 mg 1(-1)) and heavy metals (mostly lead [2.9 mg 1(-1) in April], copper [18 mg 1(-1) in February and 0.86 mg 1(-1) in April] and zinc [0.95 mg 1(-1) in February and 2.9 mg 1(-1) in April] – data at the Romanian-Hungarian border section). A major fish kill and severe damage of benthos populations resulted. The aim of this study was to investigate the impact of the accident on planktonic and periphytic algae. Apart from detailed taxonomic information, diversity, evenness and diatom indices, chlorophyll-a analysis, X-ray fluorescence spectroscopy (TXRF), spectral analysis and SEM were applied. While transient damage of periphyton, especially the sensitive Chladophora glomerata, could be detected in the River Tisza, the phytoplankton did not respond. Flooding may have prevented effects by dilution. The problems related to algae as suitable biota for immediate spill effects are discussed.

A detailed scanning electron microscopic investigation was carried out to clarify the taxonomic status of a small sigmoid Nitzschia species, a potential indicator of Central European soda waters. We found this taxon to be one of the dominant epiphytic diatoms collected from sodic bomb crater ponds at Apaj (Hungary). The large population allowed for a morphometric comparison based on frustule ultrastructure with the type material of the most similar species, Nitzschia austriaca Hustedt that was originally described from a soda pan in the region. The results clearly demonstrated an overlap between the Apaj population and the type material of N. austriaca (based on NMDS analysis), therefore we argue that they represent the same taxon. An emended diagnosis of N. austriaca is given. Total suspended solids and total phosphorous proved to be the most important factors predicting the occurrence of the species, with possible interactive effects of conductivity and pH. We then expanded the distribution of the species by revisiting data originating from previous large-scale surveys targeting sodic habitats in Hungary. On the basis of our results, N. austriaca is a characteristic species for Central European soda waters, including the protected astatic soda pans, indicating their typical chemical and physical characteristics.

The colonization, structure and composition of the periphyton which developed on the artificial substratum (sand-blasted matglass-slides) positioned into current line were studied in the main arm of the River Danube at God (1669 riv. km) in the summer of 1997, during a low water period. Five replicates were taken on the first day in the 3rd, 6th, 9th and 24th hour, after that every day for a week, then every three days for another two weeks. Phytoplankton samples were taken four times during the study (on the 1st, 6th, 13th and 20th day) to compare the composition of benthic and planktic algae. Altogether 222 taxa were identified 95 taxa from the phytoplankton and 176 from the periphyton. The number of common species was 50. after three hours from the immersion, only coccoid bacteria (mainly colineforms) were found on the substratum but after 6 hours the first algae. The first colonizer was Diatoma vulgaris, which adheres with on apical pad. In the first few hours only a few species formed the community and low diversity and low evenness was the consequence. After 24 hours the community was already diverse with a total of 35 species. During the first week of colonization the periphyton was composed almost exclusively of quick reproduction rate R (ruderal strategy) selected species, the evenness showed an increase parallel to species richness. The basal-layer of the Danube periphyton developed at that time, where diatoms attached to the substratum mainly with on apical pad. From the second week there was a small decrease in the evenness, when the rate of slower multiplying C, C-S (competitive strategy, stress tolerant strategy) selected species increased. In the second week stalk forming species formed an intermediate layer adhering with long, branching gelatinous stalk. The thick periphyton cover filtered out planktic species from the water like a net, and more and more euplanktic Centrales species were found in the samples.

Underwater light climate, phytoplankton composition and photosynthesis, bacterioplankton production and heterotrophic nanoflagellate abundance were studied in the River Danube near Budapest in 1991. During the winter months water transparency was high, the euphotic zone deep (3 m), but the phytoplankton biomass and the primary production were low as a consequence of low water temperature and reduced global radiation. An increase in phytoplankton abundance (chlorophyll-a concentration reaching 164 μg.l -1 ) during the spring low water period in April and May was observed. This large population was lost to the summer floods. The months of July and August experienced low chlorophyll-a concentrations even though water temperature increased to 20°C. This spring peak was superseded by a second peak in September. The abundance of phototrophic picoplankton in the river was low when compared to that of lakes (10 3 -10 5 cells.ml -1 ). These low concentrations suggest that their contribution towards primary production in the river is not important. The value of the vertical attenuation coefficient (Kd) was mainly influenced by the concentration of suspended solids. In winter the Z eu / Z avg ratio approached 1.0 suggesting that the algae were not light limited this period. The ratio ranged from 0.5-0.7 during the spring and autumn algal blooms and decreased to 0.2-0.3 during the summer floods. The P/R ratio of phytoplankton in the whole water column approached 1.0 in June and July and exceeded 2.0 during the rest of the period. This result supported the hypothesis that light limitation is solely sufficient to prevent algal growth during the summer floods. The mineral nutrients (N, P) do not limit algal growth in the River Danube. Bacterial production measured by 3 H-thymidine incorporation averaged 1.19 nmol.l -1 .d -1 in 1991. The annual average net bacterial production was found to be only 10% that of primary production. Bacterial production seasonal dynamics were found to be independent of phytoplankton production. Zooplankton grazing was considered unimportant in the River Danube. Heterotrophic nanoflagellates (HNF) attained high numbers and were considered to be the main consumer of bacterioplankton and so could play a determining role in the processes of the nutrient cycling in the River Danube.

(2000). Seasonal succession of phytoplankton in a small oligotrophic oxbow and some consideration to the PEG model. SIL Proceedings, 1922-2010: Vol. 27, No. 1, pp. 152-156.

Population dynamics of Cyclotella ocellata PANTOCSEK were examined from 1991 to 1993 in an oligo-mesotrophic, gravel-pit lake near Madrid (Spain). Monthly and daily sampling was carried out to track seasonal- and auxosporulation dynamics, respectively. This species was the most abundant planktonic diatom in the lake. The population increased steadily in spring until the seasonal peak (3.8.10 6 ind/ L in April) and then abundance declined slowly through late winter. Time series techniques showed that the seasonal dynamics were driven by exogenous factors: there was a relationship between Cyclotella abundance and the chemical environment, both TP (synchronic) and SRSi (with delay). Auxosporulation (studied on a daily scale) occurred in late summer, when 90 % of cells had a diameter of less than 10 μm. The smallest vegetative cells of C. ocellata (preauxospores) presented an endogenous dynamic: their dynamics had no relationship with environmental changes and the cell size dynamic seems to be the most important factor in inducing auxosporulation. The regenerated population (auxospores and initial cells) constituted the largest component of diatom biomass during thermal overturn, and followed the increase in nutrient concentration. The dynamic was also controlled by nutrients in the lake as influenced by mixing, hence it was driven by exogenous factors. The pattern of life history strategies followed by C. ocellata was that of synchronous sexuality under favourable conditions: vegetative growth throughout the year, a reduction in size when nutrients were decreasing until a critical size and a critical percentage of minor cells was reached and then, when more nitrogen became again available, the formation of auxospores for one month.

A strain of Cyclotella meneghiniana was isolated from the River Danube. The optimum irradiance and temperature for growth were determined in batch cultures. The optimum temperature for growth was 25 °C. The estimated saturated irradiance was near 125 µE m-2 s-1. The calculated Ik for growth and photosynthesis were 30 ± 3 and 44 ± 6 µE m-2 s-1 respectively. A continuous culture technique was used to test the growth and cell composition at the transition state between batch, nutrient sufficiency, and a low rate of nutrient supply. Algal response was characterized by high intracellular N and C with negative growth rate. At a low dilution rate (0.06 d-1), the continuous culture theory was not followed. This critical rate is characterized by low chlorophyll-a content per cell and may depend on the mode of nutrition.

The small, chain-forming centric diatom Skeletonema potamos (Weber) Hasle is one of the most important species of phytoplankton in the River Danube in Hungary. In low water periods from May to October, its abundance is high, contributing 10–20% of total biomass (its fresh weight is 3–6 mg 1−1). The first data about its occurrence in Hungary, in the southern Danube stretch, were published by Schmidt & Voros (1981). The presence of S. potamos was noted in Danube samples taken at the end of fifties near Budapest (Kiss, 1986). This species became abundant in the Hungarian stretch of River Danube at the end of sixties simultaneously with eutrophication.

Phosphatase enzymes are capable of releasing phosphate through cleavage of phosphoester bonds. The seasonal importance of this process was examined by using a model substrate paranitrophenylphosphate and the Michaelis-Menten equation to estimate the release rate of PO 4 -P from phosphomonoesters. The seasonal occurrence of phosphomonoesters and acid phosphatase activity was used to estimate the velocity of phosphate release from these compounds. Filter fractionation of phosphatase activity demonstrated that most activity (60%) was in size fractions less than 0.45 microm. The release rates were highest in May and June (15 to 25 nmol L -1 min -1 ) during the Gonyostomum semen (Raphidophyta) bloom and decreased to less than 2 nmol L -1 min -1 in two weeks and remained low throughout the summer and the fall. Fractionation of 32 P-H 3 PO 4 labelled dissolved organic phosphorus showed this fraction to vary considerably through the year. Potential phosphate release declined through the summer and into the fall. Significance of the co-occurrence of phosphomonoesters and acid phosphatase activity maxima and Gonyostomum semen (Raphidophyta) bloom is discussed.

Seasonal dynamics of all major protozoan groups were investigated in the plankton of the River Danube, upstream of Budapest (Hungary), by bi-weekly sampling over a 1-year long period. Sixty-one heterotrophic flagellate, 14 naked amoeba, 50 testate amoeba, 4 heliozoan and 83 ciliate morphospecies were identified. The estimated abundance ranges of major groups throughout the year were as follows: heterotrophic flagellates, 0.27-7.8 x 10(6)ind.l(-1); naked amoebae, max. 3300ind.l(-1); testaceans, max. 1600ind.l(-1); heliozoans, max. 8500ind.l(-1); ciliates, 132-34,000ind.l(-1). In terms of biovolume, heterotrophic flagellates dominated throughout the year (max. 0.58mm(3)l(-1)), and ciliates only exceeded their biovolume in summer (max. 0.76mm(3)l(-1)). Naked amoeba and heliozoan biovolume was about one, and testacean biovolume 1-3, orders of magnitude lower than that of ciliates. In winter, flagellates, mainly chrysomonads, had the highest biomass, whilst ciliates were dominated by peritrichs. In 2005 from April to July a long spring/summer peak occurred for all protozoan groups. Beside chrysomonads typical flagellates were choanoflagellates, bicosoecids and abundant microflagellates (large chrysomonads and Collodictyon). Most abundant ciliates were oligotrichs, while Phascolodon, Urotricha, Vorticella, haptorids, Suctoria, Climacostomum and Stokesia also contributed significantly to biovolume during rapid succession processes. In October and November a second high protozoan peak occurred, with flagellate dominance, and slightly different taxonomic composition.

The seasonal variation in primary production, individual numbers, and biomass of phyto- and zooplankton was studied in the River Danube in 1981. The secondary production of two dominant zooplankton species (Bosmina longirostris and Acanthocyclops robustus) was also estimated. In the growing season (April-Sept.) individual numbers dry weights and chlorophyll a contents of phytoplankton ranged between 30−90 × 106 individuals,1−1, 3–12 mg 1−1, and 50–170 μg 1−1, respectively. Species of Thalassiosiraceae (Bacillariophyta) dominated in the phytoplankton with a subdominance of Chlorococcales in summer. Individual numbers and dry weights of crustacean zooplankton ranged between 1400–6500 individuals m−3, and 1.2–12 mg m−3, respectively. The daily mean gross primary production was 970 mg C m−3 d−1, and the net production was 660 mg C m−3 d−1. Acanthocyclops robustus populations produced 0.2 mg C m−3 d−1 as an average, and Bosmina longirostris populations 0.07 mg C m−3 d−1. The ‘ecological efficiency’ between phytoplankton and crustacean zooplankton was 0.03%.

14.1 IntroductionA series of astrobiological high-altitude expeditions to the South AmericanAndean Mountains were initiated in 2002 to explore the highest perenniallakes on Earth, including several volcanic crater lakes at or above 6000 min elevation. During the next five years, they will provide the first integratedlong-term astrobiological characterization and monitoring of lacustrineenvironments and their biology at such an altitude. These extreme lakesare natural laboratories that provide the field data, currently missingabove 4000 m, to complete our understanding of terrestrial lakes and biota.Research is being performed on the effects of UV in low-altitude lakesand models of UV flux over time have been developed (Cockell, 2000). Thelakes showing a high content of dissolved organic material (DOM) shieldorganisms from UV effects (McKenzie et al., 1999; Rae et al., 2000). DOMacts as a natural sunscreen by influencing water transparency, and thereforeis a determinant of photic zone depth (Reche et al., 2000). In sparselyvegetated alpine areas, lakes tend to be clearer and offer less protectionfrom UV to organisms living in the water. Transparent water, combinedwith high UV irradiance may maximize the penetration and effect of UVradiation as shown for organisms in alpine lakes (e.g., Vincent et al., 1984;Vinebrook and Leavitt, 1996). Shallow-water benthic communities in theselakes are particularly sensitive to UV radiation. Periphyton, which definescommunities of microorganisms in bodies of water, can live on varioussusbtrates. While on rocks, they include immobile species that cannot seeklow UV refuges unlike sediment-dwelling periphyton (Happey-Wood, 1988;Vincent et al., 1993) or alpine phytoflagellates (Rott, 1988) which bothundergo vertical migration. Inhibition of algal photosynthesis by UV radia-tion has been documented in the laboratory (Ha ¬der, 1993) and it has beenshown that phytoplankton production is reduced by formation of nucleic acidlesions (Karentz et al., 1991) or production of peroxides and free oxygenradicals (Cooper et al., 1989). Most of the experiments that have demon-strated in situ suppression of algal growth by UV radiation have eitherused artificially enhanced UV irradiance (Worrest et al., 1978) or shallowsystems (