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One of the main threats of our time is the increasing water demand not only globally, but also locally. These are often met at the expense of ecological water demand, jeopardizing the structural and operational conditions necessary to maintain good ecological status in aquatic and wetland habitats. This is why it is of great importance to explore possible water retention options. In 2019, based on the long-term data series on the water level of River Tisza, we studied the frequency and extent of flooding in the floodplain between Tiszabercel and Gávavencsellő, where there are valuable wetlands, including a ‘sanctuary’-type backwater. This was necessary because recently the floodplains have undergone negative changes. Their water volume has gradually decreased, their valuable wildlife has become rarer, some of them have completely dried out in the autumn and even one of them has burned out. From the analysis of the examined 48-years data, it could be concluded that flooding was relatively frequent in the sampled area, but the extent of water coverage had no significant effect either in space or time. It was also found that only water levels above 700 cm (based on the water meter of Tiszabercel, 98.36 mBf) could adequately ensure that the water bodies are filled up and flushed out. However, there is little chance of this, because of four reasons: (1) water levels of this height are becoming rare; (2) the duration and height of high water levels are mostly short in time; (3) water levels of several water bodies are artificially decreased; (4) the drainage effect of the River Tisza – which has been significantly incised after the river regulation – prevails in the area. Due to all, in the future, there would be a great need to maintain the water levels in the floodplain wetlands as efficiently as possible after the floods – for which we have made specific proposals for the places and methods to preserve the ecologically necessary amount of water.

Cladocerans are biological indicators of environmental changes. Their remains provide information on past changes in lake environments. We studied the correspondence between contemporary Cladocera assemblages and their subfossil remains from an oxbow lake. We sought to demonstrate that there were differences among the various sites of an oxbow lake with different utilization based on contemporary and subfossil Cladocera assemblages and physical–chemical variables. The oxbow lake’s two sides are used as fishing sites, where angling is the main activity. The middle site of the lake is under nature protection with high macrovegetation coverage. Contemporary and subfossil Cladocera assemblages were sampled from 21 sampling sites along the oxbow lake. Our research showed that the subfossil Cladocera assemblages had higher species richness and densities (36 taxa) than the contemporary species (29 taxa). We found one species of the Polyphemidae family only in the contemporary assemblage. Among the sites, Cladocera assemblages differed in their species composition and density. The highest densities were found in the second fishing site due to the appearance of the small-sized Bosmids. The relationship between Cladocerans and the physical–chemical variables showed that some variables, such as chlorophyll-a, biological oxygen demand, dissolved oxygen, copper, phosphide, and organic matter content, significantly affected Cladocera composition. We found that the subfossil Cladocera assemblage was significantly more diverse and abundant than the contemporary one, indicating that an integrated sampling may be sufficient to provide better results on the total species composition of the water body.

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.

Here we report the results of our decades-long study on epiphytic communities from two tributary systems of the Szigetk&ouml, z section of the Danube River. The main goal of the investigation was to detect changes in the epiphytic communities at structural (core species, changes in the relative abundance of common species) and functional (trait changes) levels as a result of the most important anthropogenic effects on Szigetk&ouml, z, i.e., hydro-morphological modifications. We also examined the impact of rehabilitation on the tributary systems in terms of ecological potential. We discovered that mainly motile diatom species characterized the epiphyton due to reduced water volume were introduced into the tributary system after the diversion of the Danube. The ecosystem stabilized in the rehabilitated section, while the non-rehabilitated section showed a worsening tendency, mainly in the parapotamic branches. Our long-term data sets may provide a good basis for comparisons of different aquatic ecosystems, to define changes in the abundance of core species and in the structure of community in response to different anthropogenic pressures. It is fundamental to determine adaptive traits in assessing the impact of global warming stressors on biodiversity.

The aim of our study was to verify the effectiveness of passive nature conservation with regard to the preservation of species, by examining a typical mesozooplankton community. We investigated five oxbow lakes which were similar to each other in terms of size, depth and close-to-each, but which differed markedly from one to another in terms of lake management. One is under passive protection, the others are under different forms of management. Based on the NMDS (Non-metric Dimensional Scaling) analysis, we identified the variable (transparency) which is responsible for the segregation. In the case of rare species IndVal (Indicator Value) analysis was used to evaluate the occurrence and significance of indicator species. We also found marked differences in the species composition; seven species showed indicator values for the protected oxbow lake, five of which were significant (p

In our work, we sought to answer whether we find differences among the various zones of an oxbow lake with different land uses based on physico-chemical variables and dominant algal plankton species. The two ends of the oxbow lake are bordered by settlements, and near them there are open water areas where fishing is the major utilization form. Between the two open water areas we find a protected area with a large aquatic plant coverage and two transition zones towards the open water areas. The oxbow lake receives periodic water replenishment only at one end from one of the open water areas. During summer—due to the lack of rain—the water of the oxbow lake is used for irrigation in the surrounding arable land, so the water level fluctuation can be significant in the riverbed. Our study was performed within a vegetation period of spring, early summer, mid-summer, and fall. In connection with the ecological classification of a smaller water body, studies on the physical and chemical properties of the water and the composition of the algal plankton are usually carried out in few places and relatively infrequently. The characteristics of a water body are also influenced by seasonal changes, which can be the changes in the extent of vegetation coverage, the way land is used and the possibility of water replenishment, to which the algal community usually responds with changes. Based on our study, it can be said that even in a relatively small water body, we found a large differences based on the chemical and physical properties of the water and the characteristic algal species. Open water zones, areas with large macrovegetation coverage, and the transition zones were separated from each other.

During our work, we investigated the physical and chemical variables of a small surface watercourse to investigate how different anthropogenic effects affect its water quality. Along this small watercourse, there are well-separated areas that are affected by various anthropogenic effects. In addition to its origin and branches, in many places it is surrounded by agricultural land with insufficient buffer zones, which burdens the small watercourse with nitrogen and phosphorus forms. In the lower stages, artificial damming inhibits the natural flow of the T&oacute, c&oacute, Canal, thereby creating eutrophicated stagnant water areas. This is further strengthened by, in many cases, illegal communal and used water intake that further burdens the small watercourse. Considering the experience of our investigation, it can be stated that the examined small watercourse could barely suffer human impacts, and it could be described with great heterogeneity using physical and chemical variables. We experienced that this heterogeneity caused by anthropogenic effects appeared in all hydrologic states and seasons. Furthermore, our research showed that these small watercourses had such high heterogeneity that their monitoring and examination should be taken just as seriously as when it comes to larger watercourses.

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.

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.

Distribution of algae was studied in a series of water bodies ranging from 10−2 to ~109 m2 in the lowland region of the Carpathian basin in a late summer period. It has been demonstrated that lake size has pronounced impact on the morphological and chemical properties of the water bodies, and acting through these variables it shapes the distribution of the various algal groups in the water bodies of different sizes. Changes of the relative abundance of the various algal groups along the spatial scale showed four apparently distinct patterns. We found increasing relative abundance of heterocytic cyanobacteria, dinoflagellates and those taxa which have no capability of active locomotion and are characterised by high sinking rate in the large water bodies. The flagellated algae (Chlamydomonas spp., euglenophytes, Synura spp.) and the tichoplanktonic elements were characteristic for small-sized water bodies. Most of the chrysophytes and several other flagellated taxa showed hump-shaped distribution along the size scale of water bodies. The group of large colonial flagellated chlorophytes, non-heterocytic filamentous cyanobacteria and filamentous chlorophytes occasionally occurred in high relative abundance both in small and large-sized water bodies. Our findings suggest that water body size has pronounced impact on the composition of algal assemblages.

Ecological water quality problems are frequently connected to increment of phytoplankton productivity and overdominance of some phytoplankton species. Metrics that show monotonously increasing or decreasing tendencies along stressor gradients is recommended for ecological state assessment. Diversity metrics are influenced by various physical disturbances and show high within-year variability; thus, there is no agreement on the usefulness of these metrics as state indicators. To test the usefulness of phytoplankton diversity in ecological state assessment we investigated the productivity–diversity relationships for lakes and rivers in the Carpathian Basin (Hungary). We demonstrated that the shape of productivity–diversity relationship depends on the investigated water body type. Regarding lakes, hump-shaped relationship was found for all computed metrics. Parallel with the increase in phytoplankton productivity values, diversity metrics showed monotonously increasing tendencies in rhithral and decreasing tendencies in large potamal rivers. We found no systematic relationship in the case of small lowland rivers. Changes of diversity metrics calculated for species and functional groups showed similar tendencies within the types, only the slopes of regression lines differ each other. The use of diversity metrics as ecological state indicators should be restricted to water body types where diversity decreases or increases monotonously with phytoplankton biomass. Regarding the lakes the use of diversity metrics is not recommended for ecological state assessment. In rhithral and large potamal river assessment, application of diversity metrics should be strongly considered. We demonstrated that diversity metrics can be useful components of multimetric indices proposed to use by the Water Framework Directive.

Effects of zinc on growth, cell morphology, oxidative stress responses and zinc removal activity of two common phytoplankton species, Monoraphidium pusillum (Printz) Komarkova-Legnerova and Monoraphidium griffithii (Berkeley) Komarkova-Legnerova were investigated at a concentration range of 0.2–160 mg l−1 zinc. Cell densities and chlorophyll content decreased compared with controls in cultures of both species, effective concentrations causing 50 % growth inhibition within 72 h on the basis of cell numbers were 33.69 and 25.63 mg l−1 zinc for M. pusillum and M. griffithii, respectively. Changes in cell morphology and elevated lipid peroxidation levels appeared in zinc-treated cultures of both species, but only at higher (>10 mg l−1) zinc concentrations. The most effective zinc removal appeared at 20 and 10 mg l−1 zinc concentration for M. pusillum and M. griffithii, respectively. Removed zinc is mainly bound on the cell surface in the case of both species. This study provides new data for the zinc tolerance and zinc removal ability of the green algae M. pusillum and M. griffithii and shows that green algal species common in surface waters could have zinc tolerance and zinc-binding abilities, which makes them feasible in treatment of waters contaminated with 10–20 mg l−1 zinc.

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.

The restoration and management of shallow, pond-like systems are hindered by limitations in the applicability of the well-known models describing the relationship between nutrients and lake phytoplankton biomass in higher ranges of nutrient concentration. Trophic models for naturally eutrophic small, shallow, endorheic lakes have not yet been developed, even though these are the most frequent standing waters in continental lowlands. The aim of this study was to identify variables that can be considered as main drivers of phytoplankton biomass and to build a predictive model. The influence of potential drivers of phytoplankton biomass (nutrients, other chemical variables, land use, lake use and lake depth) from 24 shallow eutrophic lakes was tested using data in the Pannonian ecoregion (Hungary and Romania). By incorporating lake depth, TP, TN and lake use as independent and Chl-a as dependent variables into different models (multiple regression model, GLM and multilayer perception model) predictive models were built. These models explained >50% of the variance. Although phytoplankton biomass in small, shallow, enriched lakes is strongly influenced by stochastic effects, our results suggest that phytoplankton biomass can be predicted by applying a multiple stressor approach, and that the model results can be used for management purposes.

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.

The inhibitory effects of cyanobacterial compounds as possible explanation of the lack of stable Cyanobacteria–Cryptophyta coexistence in steady-state phytoplankton assemblages were studied. The possible interactions between two phytoplankton species, a toxic Microcystis aeruginosa (cyanobacteria) and a non-toxic Cryptomonas ovata (Cryptophyta) were investigated (i) in mixed cultures (containing C. ovata and M. aeruginosa cells); (ii) in M. aeruginosa crude extract-treated C. ovata cultures and (iii) in purified microcystin-LR (MC-LR) treated C. ovata cultures. The results of experiments proved that the presence of living M. aeruginosa cells have more inhibitory effects on C. ovata cultures than the crude extract of the M. aeruginosa cells; or the presence of the purified MC-LR. These results suggest that MCs does not play as important role in cyanobacteria–Cryptophyta interaction as it was presumed; hence more complex effects (allelopathy among them) can be significant in shallow lakes ecosystems.

Horizontal sampling within a lentic oxbow demonstrated the uneven distribution of algae at both large and small scales. An index of heterogeneity is proposed to characterize the fine-scale horizontal patchiness, which is defined as the ratio of the coefficient of variation among samples and the error in counting the algae. Applying a vertical grid sampling strategy, a distinct patchy distribution of several algal species was observed. Most of the patches were formed by those species that have good buoyancy-regulating mechanisms (blue―green algae, dinoflagellates). Atelomixis caused by surface cooling may be the explanation of the heterogeneity. We have shown that the anisotropic horizontal distribution of the phytoplankton could cause high uncertainty in lake quality assessment. Therefore, to improve accuracy composite sampling is needed.

A method recently proposed by Coesel that uses the desmid flora to assess the conservation value of aquatic habitats was applied to an alkaline and hypertrophic oxbow of the Upper Tisza river (NE Hungary). According to the macrophyte community the oxbow contains two distinct habitats, both of which provide suitable conditions for the development of a rich desmid flora. High temporal and spatial differences in the algal flora were observed in periphyton and plankton samples taken in June and August 2004. The sample of Utricularia vulgaris periphyton collected in August was characterised by the most species-rich desmid flora. The conservation value of this sample was the maximum according to Coesel’s method. The latter also proved to be useful for the assessment of the conservation value of plankton net samples taken from among the macrophytes. The use of modified rarity value calculations as recently proposed by Feher did not significantly affect the conservation value, but different enumeration methods to quantify the floristic diversity did result in different conservation values. We found that Coesel’s desmid based method is a useful tool for assessing the conservation value of the studied oxbow. Based our results the Coesel method’s applicability and usefulness depended on (i) the sampling location (open water or macrophytic region) samples were taken from open water or from macrophytic region; and (ii) species enumeration procedures (up to 400 specimens counted, or whole droplets counted).

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.

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.

(2006). The possibility of reconstruction of past hydrological changes in a Sphagnum bog by the use of testate amoebae (Rhizopoda: Testacea) in the Carpathian Basin. SIL Proceedings, 1922-2010: Vol. 29, No. 4, pp. 1751-1756.

Peatlands offer the potential for high resolution records of water balance over Holocene timescales, yet this potential is under-exploited in many areas of the world. Within Europe, peatlands are mostly confined to areas north of 55° N, but several areas of southern and eastern Europe contain small peatlands which may be suitable for palaeoclimatic reconstruction. In this paper we test the potential of peatlands in the Carpathian region for deriving quantified estimates of water table changes using testate amoebae analysis. A training set for palaeohydrological reconstruction from testate amoebae assemblages was obtained by collecting surface samples from 13 peatlands, including 9 from Hungary and 4 from Transylvania (Romania). Using a simple measure of mean annual water tables estimated from staining of PVC tape, we found that some peatlands were heavily influenced by runoff and groundwater, and were therefore not suitable as modern analogues of ombrotrophic climatically sensitive sites. The relationship between the testate amoebae assemblages in the modern samples and the environmental variables was explored using CCA. The CCA biplot showed that the most important variables are depth to water table and moisture content, confirming that hydrology is a key control on taxon distribution. pH was a secondary gradient. A transfer function for % moisture and depth to water table was established and applied to fossil assemblages from a sequence from Fenyves-tető, Transylvania, Romania. The reconstructed water table shows a number of variations which have parallels with other palaeoclimatic records from Europe and the North Atlantic prominent phases of higher water tables are associated with the periods 8000–8300 cal BP, 3000–2500 cal BP and after 600 cal BP. We suggest that these were periods of particular intensification of westerly airflow which affected eastern Europe as well as western and central Europe.

For avoiding the unfavorable environmental conditions several aquatic microorganisms are capable of forming specialized resistance cells like akinets, hypnospores, statospores, etc. Recognition of the important role of cysts in the life cycles of dinoflagellates increased the need to study their role in the ecology of phytoplanktons, and this, combined with the knowledge of chemical and biological characteristics of the water, may lead to a better understanding of the spatial and temporal dynamics of dinoflagellates. This paper reports on the effects of temperature, nitrogen, and phosphorus on the percentage of encystment of the dinoflagellate Peridinum cinctum Stein. The phosphorus content of the medium affected encystment only at the highest temperature applied (22 °C). Nitrogen content and temperature were the most important factors controlling the encystment.

On basis of recent developments in phytoplankton ecology an assemblage index, Q, was developed to assess ecological status of different lake types established by the Water Framework Directive (WFD). Since 5 ≥ Q ≥ 0, the developed index can provide 5-grade qualification required by WFD. Case studies from very different lake types support the usefulness of the developed index. Straights and weaknesses of the Q index for monitoring purposes are discussed. Without arguing for the superiority of the assemblage index in comparison with any other measures of ecological status of lakes, we aim to open a discussion about its possible applications.

Characteristics of the algal flora and the water chemical parameters of some tropical lakes in the valley of the Rio Doce (Brazil, Minas Gerais State) were investigated. The collected samples included 9 species of the Dinophyta division. Besides the well known pantropical/temperate taxa two others, Peridinium baliense (considered earlier as narrowly endemic in the Indo-malayan region) and a previously undescribed species was found. These two latter taxa proved to be subdominant in the plankton samples. Both taxa are described and illustrated by drawings and light micrographs. The new species shares features with P. baliense, which belongs to the lomnickii section, but has completely different hypothecal plate structure and shows differences in its ecology as well. These differences allow us to conclude that this taxon is a new species, consequently the name P. brasiliense sp. nova is proposed. Although in the taxonomy of freshwater dinoflagellates the hypothecal plate arrangement is usually neglected, our results indicate that taxonomic weight of this feature sometimes might be remarkable. Quantitative analysis of the microvegetation suggests that the large sized dinoflagellates, owing to their capability of active locomotion can be important members of the phytoplankton in stratified tropical lakes. Selected physical and chemical environmental data are presented for the investigated localities.

Late summer phytoplankton associations were studied qualitatively and quantitatively in 80 Hungarian lakes altogether (mostly shallow salt lakes, reservoirs, oxbows, gravel pit lakes). Equilibrium phases sensu Sommer et al. (1993) were found only in 17 lakes. Most of them were under some kind (high salt content or very low level of nutrients) of stress factor. It is concluded that environmental stress forces phytoplankton communities towards equilibrium. No relationship between occurrence of equilibria and trophic state was found. Species number of non-equilibrated lakes was almost three times as high as those in equilibrium. Of the 31 recently described (Reynolds et al., 2002) phytoplankton assemblages most of those were recognized that are likely to occur in shallow lakes. Separation of a functional group Ws from W2 forSynura dominated lakes is suggested. It seemed also necessary to raise a group (Y Ph ) for lakes dominated by Phacotus. Sorting of Dinophyta species into different already described functional groups is desirable.

We investigated the possibilities of reconstructing the hydrological history of an East Carpathian Sphagnum bog (Fenyves-tető, near Erzsebetbanya) based on the Testacea fauna and the humification. A Russian-type sampler was used to supply undisturbed cores of 400 cm in depth. The exotic marker method (Lycopodium clavatum as a marker) was used for quantitative estimation of the abundances. Humic acid concentration was measured by photometry. The age of the peat layers was determined by radiocarbon method. Altogether we identified 33 testate amoebae taxa; there were 10 taxa which were frequent in the samples and have remarkable faunistic and ecological significance. Based on the relative abundance of Testacea taxa, eight zones were identified. The following species were characteristic of dry conditions: Assulinamuscorum, Difflugiapulex, and Nebelamilitaris, while wet conditions were indicated by Amphitrema flavum and Hyalospheniapapilio. We found strong qualitative correlation between the humification and the relative frequencies of the testate amoebae. Major changes of the moisture conditions can be appropriately reconstructed from the quantitative and qualitative analysis of testate amoebae, and offer a good characterization for the rapid changes of the moisture conditions and the stable periods. We have demonstrated that the analysis of Testacea and the study of humification are useful for reconstructing hydrological changes.

A total of 512 samples collected from 86 Hungarian water bodies were analyzed for Dinophyta species and compared to common limnological characteristics. Temperature and organic matter content were the most important factors controlling the occurrence of Dinophyta species. Total phosphorus and conductivity were of lesser importance. On average, seven to eight taxa of Dinophyta were recorded in individual samples at a temperature of 12-18°C and a COD Mn than 10 mg l -1 . The most important genera were Peridiniopsis, Cleistoperidinium and Ceratium. A two-factor principal component model explained 72% of the total variance within the data set. The first principal component explained 75 and 85% of the total variance within the temperature and organic matter variables. A cluster analysis, using within-group linkages, resulted in five groups of organisms that differed primarily with respect to their distribution along a temperature gradient.

The stability of the water column permitted stable stratification of the shallow (maximum depth: 3.75 m) oxbow, Kecskeszugi-Holt Koros in summer 2000. During the stratified period a deep chlorophyll maximum (DCM) was found at depths getting 60–180 μmol m−2 s−1 photosynthetically active radiation (PAR). The phytoplankton was dominated by Ceratium hirundinella and it is concluded that the development of the DCM largely resulted from the behavioural aggregation of this motile flagellate.

Toxic cyanobacteria are known to produce cyanotoxins, toxic secondary metabolites. In recent years the cylindrospermopsin (tricyclic guanidinyl hydroxymethyluracil)-producing organisms Aphanizomenon ovalisporum, Cylindrospermopsis raciborskii, and Umezakia natans have been inhabiting polluted fresh waters. Cylindrospermopsin, a potent hepatotoxic cyanotoxin, has been implicated in cases of human poisoning as well. This study describes the isolation and purification of cylindrospermopsin from A. ovalisporum with the help of a slightly modified Blue-Green Sinapis Test, a plant test suitable for determining the cyanotoxin content of chromatographic fractions besides plankton samples. The recent modification, using microtiter plates for the assay, improves the method and reduces the amount of sample needed for the assay. This approach proved that plant growth and metabolism, at least in the case of etiolated Sinapis alba seedlings, are inhibited by cylindrospermopsin. The establishment of capillary electrophoresis of cylindrospermopsin and consideration of the results reported here lead us to the expectation that capillary electrophoresis of cylindrospermopsin may be a powerful and useful analytical method for investigating cyanobacterial blooms for potential cylindrospermopsin content and toxicity. Confirmation of chemical identity of the purified compound is performed by UV spectrophotometry, NMR, and MALDI-TOF.

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.

An unknown small naviculoid diatom was found in the epiphyton samples from Hungary (in Kanyari Holt-Tisza oxbow) and in the epilithon samples from France (Canal de Berry at Épineuil-le-Fleuriel). Detailed observations using light and scanning electron microscopy were used to describe Brevilinea kevei Ács & Ector sp. nov. It can be separated from Brevilinea pocosinensis Siver et al. (which was the only described species in the genus) by its size (smaller than B. pocosinensis), shape (elliptic valve, never capitate) and ecological requirements. Brevilinea pocosinensis lives in acidic conditions while B. kevei in neutral ones. Differential diagnostic criteria with respect to similar taxa, especially Fallacia indifferens (Hustedt) D.G. Mann, together with ecological implications of this finding are briefly discussed.