István Grigorszky

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

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.

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 WS from W2 for Synura dominated lakes is suggested. It seemed also necessary to raise a group (YPh) for lakes dominated by Phacotus. Sorting of Dinophyta species into different already described functional groups is desirable.

Microcystin-LR alters the growth, anthocyanin content and single-stranded DNase enzyme activities in Sinapis alba L. seedlings

Seedlings of the white mustard (Sinapis alba L.) are sensitive to the cell-free extracts of a toxigenic strain of Microcystis aeruginosa and to microcystin-LR. Fresh mass of plants, plant length, including hypocotyl and root length and lateral root formation is inhibited in microcystin-LR treated seedlings. The decrease of anthocyanin content is obtained in microcystin treated mustard cotyledons. The tissue necrosis of cotyledons is a characteristic consequence of microcystin treatment. Microcystin-LR induces an increase in single stranded deoxyribonucleases (ssDNases) activity of S. alba seedlings as shown by spectrophotometric assays and by ssDNase activity polyacrylamide gels. The significance of this phenomenon is discussed in relation to general stress responses in plants. We conclude that microcystin-LR affects the whole physiology and the growth of plants.

Phytoplankton associations in a small hypertrophic fishpond in East Hungary during a change from bottom-up to top-down control

Phytoplankton species composition and abundance of a shallow hypertrophic fishpond (Mézeshegyi-tó, East Hungary) was studied for the period 1992–1995. The pond showed a pronounced algal periodicity. High-diversity phytoplankton assemblages occurred in spring and autumn. During the winter period, low diversity values were related either to stable community states, when K-strategist species dominated the plankton, or to a large bloom of r-strategist species. In summer, the stable environment led to low-diversity, high-biomass phytoplankton assemblages, dominated by Cylindrospermopsis raciborskii. At this time, the growth conditions for Cylindrospermopsiswere akin to those prevailing in a continuous fermentor. The overwhelming dominance of this species lasted for more than four months, during which time, the phytoplankton resembled that of one in the tropics. In August, 1993, an unsuccessful chemical treatment for reducing the algal bloom succeeded in killing the ponds entire population of fish. The large fish-stock comprised the planktivorous silver carp. Although the summer of 1994 was one of the warmest summers of this century, the expected Cylindrospermopsis bloom failed to develop probably because of a higher grazing pressure by large zooplankton. In spite of the fact that the temporal and spatial pattern of the phytoplankton is influenced principally by bottom-up effects, changes in cascading trophic interactions may also considerably influence the species composition and biomass.

Algal assemblage types of bog-lakes in Hungary and their relation to water chemistry, hydrological conditions and habitat diversity

Algal flora of 12 bog lakes was investigated during the period of March 1995 to August 1999 in Hungary. Of the 129 samples, 624 taxa of algae were identified. Species richness of individual samples ranged between 8 and 107 except the extraordinarily species rich Baláta-tó where 533 algal taxa were observed. Ordination of the samples resulted in five groups: (1) assemblages dominated by chlorococcalean algae and planktonic Cyanoprokaryota; (2) assemblages dominated by flagellates (Dinophyta, Cryptophyta, Euglenophyta, Chrysophyceae, Raphidophyceae); (3) chlorococcalean algae and cyanoprokaryotic assemblages with desmids, cryptophytes, dinoflagellates or euglenophytes as subdominants; (4) assemblages dominated by diatoms and (5) a group of samples where other taxa belonging to Xanthophyta and filamentous green algae dominated. The bogs were typically rich in inorganic N and P, moreover, their water chemical characteristics (including pH and conductivity) were rather uniform. Therefore, other factors than chemical properties were responsible for different flora. The above groups were characteristic to certain types of habitats. In the first group, plankton samples from relatively large pools with considerable open water can be found. The second group included samples taken from small bog pools. The third group contained the periphyton samples from macrophytes, living in bogs with constantly reliable water supply. Samples of group four and five comprised small bogs that occasionally dry up. Periphyton of lakes with Sphagnum belonged exclusively to the fifth group. This study has shown that small bog-pools are often inhabited by different species of flagellates and desmids are not as important as it has been widely believed. Hydrological properties and habitat diversity are the major factors influencing species richness of Hungarian bog-lakes.

Phytoplankton succession in the oligotrophic Lake Stechlin (Germany) in 1994 and 1995

Phytoplankton samples were taken weekly from January to December of 1994 (epilimnion) and 1995 (0–25 m, euphotic zone) from the deep, stratified, alkaline, oligotrophic Lake Stechlin, Baltic Lake District, Germany. The purpose of the study was to gain detailed information about phytoplankton changes including those of picophytoplankton, to relate these changes to stratification patterns and nutrient chemistry of the lake and to compare them to results from other lakes of similar character.During 1994–1995, a total of 142 phytoplankton taxa was encountered in quantitative samples, most being common in deep, oligotrophic lakes. Seasonal development of phytoplankton is characterized by a definite spring peak followed by a moderate summer peak. Autotrophic picophytoplankton made the largest contribution to the annual total biomass. This is probably true for other, temperate, non-acidic, oligotrophic lakes.Development of the spring assemblage (autotrophic picophytoplankton and centric diatoms) starts in February–March and is terminated by the onset of stratification when diatoms sink to the hypolimnion. Picophytoplankton, especially Synechococcus sp., assembles in a narrow deep-layer maximum in the upper hypolimnion.Our data show that neither deep circulations nor decreased incident radiation under winter ice and snow cover prevent the development of some specially adapted low-light – high-nutrient species. Our views about the length of vegetation period for phytoplankton need to be revised with respect to winter and isothermal conditions.

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

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 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.

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.

Improvement of the ecological water qualification system of rivers based on the first results of the Hungarian phytobenthos surveillance monitoring

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.

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.