Microbial food web in a large shallow lake (Lake Balaton, Hungary)

Seasonal variations of phyto-, bacterio- and colourless flagellate plankton were followed across a year in the large shallow Lake Balaton (Hungary). Yearly average chlorophyll-a concentration was 11 µg 1^–1, while the corresponding values of bacterioplankton and heterotrophic nanoflagellate (HNF) plankton biomass (fresh weight) were 0.24 mg 1^–1 and 0.35 mg 1^–1, respectively. About half of planktonic primary production was channelled through bacterioplankton on the yearly basis. However, there was no significant correlation between phytoplankton biomass and bacterial abundance. Bacterial specific growth rates were in the range of 0.009 and 0.09 h^–1, and ended to follow the seasonal changes in water temperature. In some periods of the year, predator-prey relationships between the HNF and bacterial abundance were obvious. The estimated HNF grazing on bacteria varied between 3% and 227% of the daily bacterial production. On an annual basis, 87% of bacterial cell production was grazed by HNF plankton.     

Stir-up effect of wind on a more-or-less stratified shallow lake phytoplankton community,Lake Balaton,Hungary

Microstratification of phytoplankton in the large shallow Lake Balaton (Hungary) was studied during a 24 h period. Dissolved O₂ showed biological stratification; flagellates exhibited a definite circadian rhythm. In the middle of the investigation a heavy storm broke out which was followed by the disappearance of differences between different layers of water. Storm-induced destratification is described by cluster-analysis. Abundances of dominant species changed differently in connection with the storm. Numbers of Nitzschia sp. increased due to stirring up from the sediment surface. Numbers of single-celled or colony-forming species (Cyclotella comta, Crucigenia quadrata, Coelosphaerium kuetzingianum) practically did not change. Numbers of all the three dominant filamentous species (Aphanizomenon fos-aquae f. klebahnii, Lyngbya limnetica, Planctonema lauterbornii) significantly decreased, which might be attributed to an unknown loss process and was followed by a competitive displacement by algae of small cell size.     

The role of storms in the summer succession of the phytoplankton community in a shallow lake (Lake Balaton, Hungary)

The authors carried out day-to-day studies on the phytoplanktonof the largest shallow lake of Central Europe in the summerof 1976, 1977 and 1978. Data were analysed with diversity andcluster analyses. (i) Wind-induced stirring-up of the sedimentplays important role in the summer phytoplankton successionof the shallow lake. (ii) After storms algae with very smallcell sizes show synchronous development. In long calm periodsalgae with larger cell sizes exhibit organised population dynamics.(iii) In calm periods a shift from r-selection to predominantK-selection can be suspected. After the next storm importanceof r-selectionists again increases. (iv) Effect of changinggrowth- and loss rates on the population dynamics of the mostabundant species is discussed based on measured generation timesand calculated elimination. The phenomena discussed in the papercan appear to different extents in the summer phytoplanktonsuccession of other shallow, polimictic lakes.     

Stability and change of phytoplankton communities in a highly dynamic environment—the case of large,shallow Lake Balaton (Hungary)

Time series data of key environmental variables (water temperature, global radiation, vertical light attenuation, internal P load) and biomass of four colour classes of photosynthetically active algae were collected during 2003 and 2004 with daily resolution. Using these data, seasonal patterns of phytoplankton were analyzed as a function of the dynamic environment. Abstraction of the environmental state as a point in multi-dimensional space was used to identify habitat templates of bloom-forming groups and derive an indicator of environmental stability/physical disturbance. These templates were synthesized into a simple threshold model that sufficiently simulated development and collapse of various blooms. Blooms were, however, rare events related to specific environments with strong, unidirectional forcing. Tentative quantification of disturbance and compositional stability/community change allowed discriminating disturbance-driven changes and autogenic succession with reasonable success. The two processes were found to be equally important in shaping the composition and biomass of phytoplankton.     

Distribution of submerged macrophytes along environmental gradients in large,shallow Lake Balaton (Hungary)

Distribution of submerged macrophytes was assessed at 15 littoral sites in large, shallow Lake Balaton using the echo sounding technique. Sites represented the conspicuous longitudinal and transverse environmental gradients. Absence/presence of plants, water depth, bottom consistency and distance from the shore have been derived from echo sounding data. Turbidity and meteorological variables were recorded at a single site from 2004 to 2006. Site-specific variability in underwater light conditions (an indicator of stress) and exposure to breaking waves (an indicator of disturbance) were estimated by simple models.     

Phytoplankton nitrogen demand and the significance of internal and external nitrogen sources in a large shallow lake (Lake Balaton,Hungary)

Since the middle of 1990s the trend of Lake Balaton towards an increasingly trophic status has been reversed, but N₂-fixing cyanobacteria are occasionally dominant, endangering water quality in summer. The sources of nitrogen and its uptake by growing phytoplankton were therefore studied. Experiments were carried out on samples collected from the middle of the Eastern (Siófok) and Western (Keszthely) basins between February and October 2001. Ammonium, urea and nitrate uptake and ammonium regeneration were measured in the upper 5-cm layer of sediment using the ¹⁵N-technique. Ammonium was determined by an improved microdiffusion assay. N₂ fixation rates were measured by the acetylene-reduction method. Ammonium regeneration rates in the sediment were similar in the two basins. They were relatively low in winter (0.13 and 0.16 μg N cm^?3 day^?1 in the Eastern and Western basin, respectively), increased slowly in the spring (0.38 and 0.45 μg N cm^?3 day^?1) and peaked in late summer (0.82 and 1.29 μg N cm^?3 day^?1, respectively). Ammonium uptake was predominant in spring in the Eastern basin and in summer in the Western basin, coincident with the cyanobacterial bloom. The amount of N₂ fixed was less than one third of the internal load during summer when external N loading was insignificant. Potentially, the phytoplankton N demand could be supported entirely by the internal N load via ammonium regeneration in the water column and sediment. However, the quantity of N from ammonium regeneration in the upper layer of sediment combined with that from the water column would limit the standing phytoplankton crop in spring in both basins and in late summer in the Western basin, especially when the algal biomass increases suddenly.     

Paleolimnological reconstruction of the trophic state in Lake Balaton (Hungary) using Cladocera remains

The sediment of Lake Balaton (Hungary) provides important information about the lake’s history, particularly with regard to eutrophication. In this study, we used fossil pigment analysis and subfossil Cladocera remains preserved in a dated sediment core to identify trophic stages from ~250 bc to present. Dates of the most recent eutrophic events are in good agreement with previously published data. In general, the abundance and diversity of the Cladocera community increased with eutrophication and decreased with oligotrophication. The sediments of Lake Balaton were characterised by Chydoridae remains, of which Alona species were the most abundant. Of these, Alona quadrangularis and Alona affinis accounted for 40 and 20% of the total Cladocera remains, respectively. The trophic state of Lake Balaton varied between mesotrophic and eutrophic regimes. Seven different trophic periods were identified in Lake Balaton on the basis of Sedimentary Pigment Degradation Unit (SPDU) content of the sediment. Eutrophic states were (1) from ~250 to ~30 bc, (3) between ~300 and ~590 ad, (5) between 1834 and 1944 and (7) from the 1960s until present. Mesotrophic states were (2) ~30 bc to ~300 ad, (4) 590–1834, (6) 1944–1960s. Discriminant analysis of the cladoceran data confirmed these historic events, except for the short mesotrophic episode between 1944 and 1960. The first stage of eutrophication of Lake Balaton (~250 to ~30 bc) was characterised by extensive macrophyte vegetation, as indicated by the increasing abundance of vegetation-associated Cladocera species (Eurycercus lamellatus, Sida crystallina, Pleuroxus sp.). Intensification of eutrophication was identified since the 1980s, reflected by a high abundance of Bosmina species. The most significant planktivorous fish of Lake Balaton was the Sabre carp (Pelecus cultratus), and when its number decreased, the abundance of Bosmina species increased. This study shows that Cladocera are responsive to trophic state changes, underlining their importance as a tool for the assessment of lake eutrophication.     

Composition,density and feeding of crustacean zooplankton community in a shallow,temperate lake (Lake Balaton,Hungary)

Composition density and filtering rates of crustacean zooplankton were studied in the open water and among the macrophytes of the oligo-mesotrophic part of Lake Balaton from 1981 to 1983. From the individual filtering rates of the different populations and the densities community grazing rates were derived.Copepoda made up 79–90% of crustacean plankton community in the open lake and 95–97% of it in littoral zone. Among them the nauplii dominated. At the end of summer 1982, when Anabaenopsis was in bloom, the filter-feeding species (Eudiaptomus, Daphnia) practically disappeared, being replaced by cyclopoids. Daphnia had the highest filtering rates followed by those of Eudiaptomus and Diaphanosoma. Among copepods, the filtering rates in decreasing order were: ovigerous > all adults > copepodites > nauplii. > . The filtering rates of the different species varied both seasonally as well as from year to year. In 1983, when the concentration of organic seston decreased, filtering rate increased compared with those in the earlier years. During the water bloom in 1982, the rates decreased by 70% on the average.The community grazing rate was very low (3% per day) in the open lake and among macrophytes, both in 1981 and 1982; also the share of crustacean zooplankton in grazing was very low. In 1983, together with the improving of water quality, the community grazing rate increased 4-fold. In 1981 and 1983 the rates were influenced by water temperature but in 1982 by seston concentration.     

An attempt to trace eutrophication in a shallow lake (Balaton,Hungary) using chironomids

Lake Balaton, the largest shallow lake in Central Europe, is about 20 000 years old. An enormous increase in tourism and the disproportionate building development of the last few decades has resulted in the acceleration of eutrophication in the lake. Widespread research to reveal the causes of water-quality deterioration and possible ways of protection against it have recently started. The investigation of the larvae of non-biting midges (Diptera: Chironomidae) in the sediment of the open-water zone has also begun. The contemporary faunal composition strongly correlates with the trophic gradient along the longitudinal axis of the lake. We therefore supposed that the eutrophication process should be identifiable from the analysis of subfossil chironomid head capsules from the upper (15 cm thick) layer of the sediment. We found that quantitative results could only be obtained when fragments as well as relatively intact head capsules are considered. Our data verify that the originally oligo-mesotrophic community has been gradually replaced by eutrophic species in a west to east direction. Large-bodied larvae belonging to the Chironomus plumosus group mix the sediment down to 15 cm as they build their tubes and consequently alter the original proportions of head capsules at the different levels. So the sequence of communities through the sediment-layers is not quite reliable.     

The food of bream (Abramis brama L.) in two basins of Lake Balaton of different trophic status

Contrary to earlier observations the food composition of bream (Abramis brama L.) in Lake Balaton has changed in parallel with eutrophication. These changes were probably caused by increased population density and connected with density dependent growth as well as sharpened inter- and intraspecific competition in the cyprinid community. According to the frequency of occurrence, zooplankton followed by benthic invertebrates comprised the majority of the bream's food. By weight, however, benthic food dominated in both basins. Size-related dietary changes were pronounced, but statistically not always significant, suggesting the overall importance of the most abundant and available prey types. Bream did not strongly select any of the zooplankton groups, however, seasonal changes in food composition alternated in parallel with the trophic gradient along the longitudinal axis of the lake.     

Changes of organic matter quality along the longitudinal axis of a large shallow lake (Lake Balaton)

Hydrobiologia - Dissolved organic matter (DOM) is quantitatively the most significant pool of organic matter in lakes. Within DOM, the pool of dissolved organic carbon (DOC) is dominated...     

Evaluation of the trophic state of Lake Pamvotis Greece,a shallow urban lake

The trophic state of the shallow Lake Pamvotis was evaluated in order to search for potential restoration strategies. During the last decades Lake Pamvotis has been influenced by many of man-made impacts, such as sewage discharge and water level fluctuation. Physicochemical and biological parameters were monitored during the period 1998–1999. Important relationships were found between physicochemical and biological parameters as elucidated by redundancy analysis. Moreover, habitat conditions and the distribution of the aquatic macrophytes were also considered. Lake Pamvotis is a eutrophic ecosystem exhibiting also, a serious decline of submerged vegetation. Restoration management strategy requires reduction of the external and internal organic load, control of non-point pollution sources, control of hydrological regime, and establishment of bio-manipulation techniques.

     

Dynamics of phytoplankton detritus in a shallow,eutrophic lake (Lake Loosdrecht,The Netherlands)

A study was made of the mortality and aerobic decomposition of light- and phosphorus-limited cultures of Oscillatoria limnetica, a dominant phytoplankton species in shallow, eutrophic Lake Loosdrecht (The Netherlands). When placed in the dark at 20 °C, most cells died and lysed within twelve days. The labile organic matter was completely decomposed within three weeks. Absorbance spectra indicated that blue green algae may contributed significantly to the refractory dissolved substances in the lake. Refractory particulate matter constituted from 7 to 24% of the biomass of O. limnetica, depending on the growth rate before incubation in the dark. The decomposition rate of this fraction was 0.005 d^–1. On a basis of a steady-state model of the dynamics of phytoplankton detritus, the areal organic dry weight concentration of the detritus in the lake is ca. 60 g m^–2. This means the quantities of detritus in the seston and epipelon are about equal.     

Ingestion Rates of Some Daphnia Species in a Shallow Lake (Lake Balaton,Hungary)

Filtering rates of three species of Daphnia were studied in situ by the ¹⁴C technique during the summer in a lake with a water temperature of 20-25°C (Lake Balaton, Hungary). The renewal time of gut contents proved to be 3-5 min in each of the three species whether fed on natural or artificial food. From May to September, filtering rates of D. cucullata, D. hyalina and D. galeata averaged 7.8, 10.3 and 9.2 ml ind.⁻¹ day⁻¹, respectively. Identically long individuals of all three species had almost the same filtering rates in spring, whereas in summer animals of identical weights had similar filtering rates regardless of species because of the length variability of the helmets. The grazing rate of adult filter-feeding crustaceans is suggested to be approximately 7 % per day.     

Population dynamics of the freshwater dinoflagellate Ceratium hirundinella in the largest shallow lake of Central Europe, Lake Balaton, Hungary

SUMMARY.

• 1 Horizontal distribution, long-term (1933–82) and short-term (day-to-day) changes in abundance, vertical stratification and circadian rhythm of the freshwater dinoflagellate Ceratium hirtmdinella were studied in Lake Balaton, the largest shallow lake of Central Europe.
• 2 The lowest abundance was consistently found in those areas of the lake which had the strongest currents.
• 3 The density of C. hirundinella seemed to be, at least in those parts of the lake above the level of fertility considered oligotrophic, insensitive to changes in trophic conditions; only its relative contribution to total biomass decreased with increased enrichment.
• 4 During the day the bulk of the population stayed at a level in which the light intensity was between 126 and 440 μE m^-2 s^-1 PAR.

     

Diversity of fish species assemblages distributed in the drainage area of Lake Balaton (Hungary)

Hydrobiologia - Varying habitats of northern and southern inflows running into Lake Balaton provide appropriate living conditions for numerous fish species. Inflowing canals, creeks, and rivulets...     

Long-term dynamics of phytoplankton assemblages: Microcystis-domination in Lake Taihu, a large shallow lake in China

Long-term phytoplankton assemblages in a large shallow Chineselake, Lake Taihu, were presented using the monthly monitoringdata from October 1991 to December 1999. Earlier research results(1960, 1981 and 1988) were applied to discuss the differenttrophic stages of the lake. The species composition in the lakewas more closely related to eutrophication level than to lake-size,shallowness, or turbidity. Each summer, a single peak of phytoplanktonbiovolume appeared in Meiliang Bay. The results of principalcomponents analysis showed a distinct temporal shift in speciescomposition between summer and winter. A clear spatial differencein phytoplankton occurred between Meiliang Bay and the lakecentre. Wind speed and direction affected the horizontal distributionof phytoplankton, especially Microcystis, in the lake. Temperature,underwater light climate, nutrients and grazing by zooplanktonand by fish were discussed to explain the overwhelming dominanceof Microcystis. Four nutrient-phytoplankton stages were identifiedin the lake: an oligo-mesotrophic stage with low algal biomassuntil 1981, a eutrophic situation with blooms of Microcystisduring 1988–1995, hypertrophic conditions with the dominanceof Planctonema and total phosphorus up to 200 mg m^-3 from 1996to 1997 and the restoration period after 1997. The wax and waneof the phytoplankton assemblages were mainly controlled by temperature,wind and turbidity while long-term biomass dynamics were influencedby the level of nutrients.     

Seasonal Dynamics of Picocyanobacteria and Picoeukaryotes in a Large Shallow Lake (Lake Balaton,Hungary)

The abundance and composition of autotrophic picoplankton (APP) were studied between February 2003 and March 2004 in Lake Balaton. Water samples were taken fortnightly in the eutrophic western basin and mesotrophic eastern basin. Our study, which took more than one year, revealed pronounced seasonal pattern of the picoplankton abundance and composition. According to our results there were three types of picoplankton in Lake Balaton: 1. Phycoerythrin‐rich coccoid cyanobacteria (PE), dominant summer picoplankters in the mesotrophic lake area; 2. Phycocyanin‐rich cyanobacteria (PC), the most abundant summer picoplankters in the eutrophic lake area; 3. Picoeukaryotes, dominant winter picoplankters in the whole lake. The observed abundance of picoeukaryotes (3 × 10⁵ cells ml^–1) was one of the highest ever found. Our study confirms that in Lake Balaton the colonial autotrophic picoplankton (colonial APP) become dominant in summer in the nutrient limited period. We have found strong negative relationship between the concentrations of available nitrogen forms (NH₄–N, NO₃–N, urea‐N) and the colonial APP abundance. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Continuous monitoring of phytoplankton dynamics in Lake Balaton (Hungary) using on-line delayed fluorescence excitation spectroscopy

1. This study introduces delayed fluorescence (DF) excitation spectroscopy as an on‐line tool for in situ monitoring of the composition and biomass of various colour classes of phytoplankton when they are photosynthetically active (cyanobacteria, chlorophytes, chromophytes and cryptophytes). The DF data are validated by comparison with those from conventional methods (weekly microscopic counts and the measurement of chlorophyll concentration). 2. The composition of phytoplankton as assessed by DF agreed reasonably well with the results from microscopic counts, particularly when differences in chlorophyll‐specific DF integrals of the various colour classes were taken into account. 3. Integrals of DF spectra were converted into concentration of chlorophyll a using empirical factors derived from field data. The value of the conversion factor was nearly twice as high when the relative abundance of cyanobacteria was low (<15%) than when it was high. The converted DF‐chl time series agreed well with chlorophyll measurements particularly when blooms were developing. As the DF method is inherently free of the interference caused by pigment degradation products, the discrepancy between the two data sets increased during the collapse of blooms and when sediment resuspension was intense. 4. Fourier spectrum analysis of the time series of DF‐chl indicated that samples must be taken, at a minimum, every 2–3 days to capture the dynamics of phytoplankton. As a consequence, the dynamics of various algal blooms, including their timing, duration and net growth rate, could be estimated with greater confidence than by using conventional methods alone. 5. On‐line DF spectroscopy is an advanced technique for monitoring daily the biomass and composition of the photosynthetically active phytoplankton in aquatic environments, including turbid shallow lakes. At present, the detection limit is around 1 mg DF‐chl a m^?3 in terms of total biomass but confidence in estimates of phytoplankton composition declines sharply below about 5 mg chl a m^?3. 6. On‐line DF spectroscopy represents a promising approach for monitoring phytoplankton. It will be useful in water management where it can act as an early‐warning system of declines in water quality. In basic ecological research it can supplement manual methods. While default calibration spectra may be acceptable for routine monitoring, we suggest a careful individual calibration of the DF spectrometer for basic research. The statistical methods developed here help to assess the adequacy of various calibration sets.     

Coupling of phytoplankton and detritus in a shallow,eutrophic lake (Lake Loosdrecht,The Netherlands)

An oscillating steady state is described of phytoplankton, dominated by Prochlorothrix hollandica and Oscillatoria limnetica, and sestonic detritus in shallow, eutrophic Lake Loosdrecht (The Netherlands). A steady-state model for the coupling of the phytoplankton and detritus is discussed in relation to field and experimental data on phytoplankton growth and decomposition. According to model predictions, the phytoplankton to detritus ratio decreases hyperbolically at increasing phytoplankton growth rate and is independent of a lake's trophic state. The seston in L. Loosdrecht contains more detritus than phytoplankton as will apply to many other lakes. The model provides a basis for estimating the loss rate of the detritus, including decomposition, sedimentation and hydraulic loss. In a shallow lake like L. Loosdrecht detritus will continue to influence the water quality for years.