Dominant species, functional assemblages and frequency of equilibrium phases in late summer phytoplankton assemblages in Hungarian small shallow lakes

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 W _S from W2 for Synura 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.     

Cladocerans as indicators in the importance of passive nature conservation

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 <?0.001). In contrast, in the case of the other four oxbow lakes, a total of one species showed an indicator value. Finally, regression tree analysis was used to distinguish the oxbow lakes from each other for both common and mass-occurring species. Among the mass-occurring species, the protected oxbow lake is characterized by a large number of Acropreus harpae (Baird, 1835), while in case of the other, non-protected, oxbow lakes Alona guttata (Sars, 1862) and Alonella excisa (Fischer, 1854) are the basis for the separate classification. There is a positive effect of passive protection regarding the quantitative and qualitative occurrence of the zooplankton community. Our study highlights the importance of this kind of passive protection in the life of a particular water body and advocates that their protection should be maintained.     

Redefinition of Peridinium lomnickii Wołoszynska (Dinophyta) by scanning electronmicroscopical survey

Peridinium lomnickii Wo?oszynska was investigated by scanning electron microscopy with special attention to the importance of development of thecal plate during the life cycle. Different life cycle stages (gymnodinoid-, glenodinoid-, peridinioid) are described on the basis of development of cell wall, presence and development of sutures, appearance of pore and the change of the cell shape. Differences and possible relationships between the three existing varieties of the species are discussed. We suggest that the three varieties of P. lomnickii, P. lomnickii var. lomnickii, P. lomnickii var. wierzejskii and P. lomnickii var. splendida,represent the different life cycle stages of the species. These results and the known ontogenic cycle of dinophyta taxa should be taken into consideration, when a phylogenic tree of the dinophytes is constructed.     

Use of Phytoplankton Assemblages for Monitoring Ecological Status of Lakes within the Water Framework Directive: The Assemblage Index

The ingress of an urban stream carrying high contaminant loads into a large coastal river originates a “dispersion plume” subject to the hydrological conditions of a river affected by tidal influences. In the present study 21 sites within the “contaminant plume” of the Riachuelo River in the Rio de la Plata were analysed on the same date in order to evaluate the biological status of the area which receives this strong environmental impact, and to examine its effect on the zoobenthic communities. Diversity, taxonomic richness, abundance, physico-chemical parameters and a biological index (IMRP) were used to assess the responses of the macroinvertebrates. The correlation between exposure and effect was calculated by means of the exposure index (IEX). The relationship between the macroinvertebrate communities and environmental variables was examined using CCA analysis. Conductivity, Cr, BOD and COD, were most strongly correlated with Axis 1, suggesting the existence of a gradient of environmental degradation. The most severely contaminated sites (IMRP= 1.1–2.5; IEX = 100–78%) were all characterized by a reduced community dominated by Nematoda and Oligochaeta. A moderate response was observed between 1400 and 1600 m from the coast (IMRP = 2.6–3.9; IEX = 36%) largely owing to the physico-chemical characteristics of the recipient river which contributed to moderating the effect of the anthopogenic perturbation. For statistical validation, this area was compared with historical physico-chemical and biological data, where OD and COD showed the same tendency throughout the 10-year period.     

The Effects of Temperature, Nitrogen, and Phosphorus on the Encystment of Peridinium cinctum, Stein (Dinophyta)

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.     

Alteration of cylindrospermopsin production in sulfate- or phosphate-starved cyanobacterium Aphanizomenon ovalisporum

The effect of sulfate and phosphate deprivation on cell growth and cylindrospermopsin level was studied in Aphanizomenon ovalisporum ILC-164. Sulfate starvation induced a characteristic reduction of cylindrospermopsin pool size on the basis of cell number and unit of dry mass of culture. Phosphorous starvation of A. ovalisporum cultures induced a lesser reduction of cylindrospermopsin pool size. This divergence in the pool size of cylindrospermopsin may be the consequence of different growth rate. To show the metabolic changes concomitant with reduction of cylindrospermopsin pool size were obtained by measurement of ATP sulfurylase and alkaline phosphatase activity. The present study is the first concerning the cylindrospermopsin content under sulfate starvation and discusses it in relation to phosphorous starvation.     

Which factors affect phytoplankton biomass in shallow eutrophic lakes?

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.     

Deep chlorophyll maximum by Ceratium hirundinella (O. F. Müller) Bergh in a shallow oxbow in Hungary

Hydrobiologia - The stability of the water column permitted stable stratification of the shallow (maximum depth: 3.75 m) oxbow, Kecskészugi-Holt Körös in summer 2000. During the...     

The relationship between phytoplankton species dominance and environmental variables in a shallow lake (Lake Vrana,Croatia)

The shallow Lake Vrana was studied over a 1-year period, special attention being paid to the phytoplankton. Phytoplankton was investigated monthly with respect to temporal variability of selected environmental factors. The regular annual development observed was in species contribution to total biomass rather than in seasonal changes in species composition. The assemblage was dominated by Cosmarium tenue Arch. and Synedra sp. In winter and in spring the phytoplankton assemblage was dominated by Cosmarium tenue and high contribution of Synedra sp. was observed during the summer and autumn. Results suggest that concentrations of inorganic nitrogen and phosphorus were critical in regulating phytoplankton biomass and species dominance.