Judit Padisák

Selection of phytoplankton associations in Lake Balaton, Hungary, in response to eutrophication and restoration measures, with special reference to the cyanoprokaryotes

Restoration of shallow lakes degraded by eutrophication has often been protracted as a consequence of the accumulation and subsequent releases of phosphorus in their sediments (internal load). Balaton, the largest shallow lake in Central Europe, underwent rapid eutrophication during the 1960s–1970s, during which a west-east gradient of trophic state developed. Measures to reverse the eutrophication and to restore the lake to its historic quality were initiated in the mid-1980s. The external phosphorus load has been decreased considerably but the responses of the phytoplankton have been slight and sometimes counterintuitive. At the level of total biomass, the erstwhile distinctiveness of the down-lake trophic gradient has weakened. The eukaryotic plankton flora has altered little but floristic changes in the dominant cyanoprokaryota are consistent with environmental changes attributable to the eutrophication and subsequent restoration. The dominant species are shown to have been consistently related to variables including sediment-water interactions, physical disturbances and the specific biotic adaptations of the organisms but the phytoplankton development in given years and in given parts of the lake has fluctuated with the stochasticity of the weather. In some years, hypertrophic conditions have continued to develop, marked by the development of prolific cyanoprokaryote blooms; in other years, phytoplankton biomass scarcely exceeded a mesotrophic level, with a species composition resembling that which obtained prior to the recent eutrophication. The species associations represented are believed to be consistent with the responses of groups of species observed elsewhere, suggesting that the patterns of community assembly in the phytoplankton are potentially predictable.

Hutchinson´s heritage: the diversity-disturbance relationship in phytoplankton

This paper introduces a collection of contributions presented at the 8th Workshop of the International Association of Phytoplankton Taxonomy and Ecology. It compares the substance of with what to limnologists is the more familiar ‘paradox of the plankton’ posed by G. E. Hutchinson. The utility of Connells Intermediate Disturbance Hypothesis in plankton ecology is, potentially, more instructive but inherent difficulties in relating response to stimulus have to be overcome. A copy of the brief distributed to contributors before the workshop is appended.

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.

Are phytoplankton dynamics in rivers so different from those in shallow lakes

This paper introduces a series of contributions to the ninth meeting of the International Association of Phytoplankton Taxonomy and Ecology, held in Belgium during July, 1993. It draws from the original papers a synthesis which supports the view that the successful species in rivers and turbid shallow lakes are selected primarily on their ability to survive high-frequency irradiance fluctuations as they are circulated through steep light gradients. The selective distinction is less than that which discriminates between plankton of deep lakes and shallow lakes or even between clear and turbid shallow ones. River plankton is, however, dependent on fast growth rates but its survival in rivers is aided by a suite of water-retentive mechanisms. The ecology of turbid systems is dominated by physical interactions, those biotic interactions traditionally believed to regulate limnetic communities being suppressed and rarely well-expressed.

Intermediate disturbance in the ecology of phytoplankton and the maintenance of species diversity: a synthesis

This paper concludes a collection of contributions presented at the 8th Workshop of the International Association of Phytoplankton Taxonomy and Ecology. It derives a consensus as to the virtues and strengths of J. H. Connells Intermediate Disturbance Hypothesis (IDH), its applicability to phytoplankton ecology and its theoretical and practical weaknesses. The view is expressed that the IDH is too useful a concept to reject and that, as a word model, it provides a powerful link between diversity and disturbance. The more robust investigations that are necessary to consolidate the tenancy of IDH need to concentrate upon the separation and quantification of the stimulus- and response-components of disturbance.

Morpho-functional groups and phytoplankton development in two deep lakes (Lake Garda, Italy and Lake Stechlin, Germany)

Phylogenetic classifications of plants often do not reflect their ecological functions. In fact, the functional mechanisms of biological communities may be better understood if species are pooled into groups having similar characteristics. The objective of this work is to evaluate, with the use of multivariate methods, classifications based on the morphological and functional characteristics (size and form, mobility, potential mixotrophy, nutrient requirements, presence of gelatinous envelopes) of cyanobacteria and eukaryotic algae to explain the seasonal dynamic of the phytoplankton community. The analyses involve data from two deep lakes: Lake Garda, southern Alps, zmax = 350 m; biennium 2002–2003) and Lake Stechlin (north-east Germany, zmax = 67 m; 1995, 1998 and 2001). In both lakes, the temporal evolution of the phytoplankton communities within individual years followed a regular annual cycle, with the exception of Lake Stechlin in 1998, when an irregular phytoplankton pattern was caused by a sudden mass appearance of Planktothrix rubescens in the spring and summer months, resulting in a collapse of the whole community in autumn. Overall, the temporal developments of the phytoplankton communities obtained on the basis of patterns of the morpho-functional groups appeared highly comparable with those obtained, in the single years, on the basis of the original phytoplankton species matrices. The comparison of the morpho-functional groups of the lakes Garda and Stechlin showed important differences in the abundance and seasonality of the dominant phytoplankton types. The results obtained in this study underline that the use of classifications based on the adaptive strategies of the single species may represent a useful tool to investigate the community evolution and to compare phytoplankton assemblages of different lakes, overcoming problems related to possible differences of taxonomic accuracy and identification.

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.

The influence of different disturbance frequencies on the species richness, diversity and equitability of phytoplankton in shallow lakes

The relationships between the species richness, diversity and equitability of phytoplankton is discussed in the context of Connells (1978, Science 199: 1304–1310) Intermediate Disturbance Hypothesis (IDH). The records of 759 vertical phytoplankton samples, which were obtained from four shallow central European lakes (Balaton, Neusiedlersee, and two small artificial ponds) at daily to weekly intervals were analysed.

Shape and size in phytoplankton ecology: do they matter?

This paper summarises the outcomes of the 14th Workshop of the International Association of Phytoplankton Taxonomy and Ecology (IAP). The authors mostly addressed their contributions on the following topics: morphological and morpho-functional descriptors of phytoplankton, size and shape structure of phytoplankton related to different kinds of environmental variables and the role of morphological and physiological plasticity of phytoplankton in maintaining the (apparently) same populations under different environmental conditions. Case studies from different kinds of aquatic environments (deep and shallow lakes, reservoirs with different age, purpose and trophic state, floodplain wetlands mostly in the temperate region but also from subtropical and tropical ones) have shown that similar environmental forcing calls for similar morpho-functional properties even though the corresponding associations can be markedly different on species level.

Equilibrium/steady-state concept in phytoplankton ecology

This paper summarises the outcomes of the 13th Workshop of the International Association of Phytoplankton Taxonomy and Ecology (IAP). The authors mostly addressed their contributions on the following topics: the effect of trophic state on the attainment of a steady-state; the establishment of equilibria in deep and shallow lakes; the role of spatial heterogeneity, disturbance, and stress in the establishment of equilibrium assemblages; the mechanisms leading to the steady state; the frequency and longevity of equilibrium phases, and the role of morphological and physiological plasticity of phytoplankton in maintaining the (apparently) same populations under different environmental conditions. The composition of steady-state assemblages is compared to that of phytoplankton functional groups (coda). Those functional associations recognised as steady-state assemblages appear to be strongly K-determined in many instances.