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.     

Post-embryonic development of cyclopoid copepods in various seasons at Lake Balaton (Hungary)

The development, generation number and diapausing state of threeCyclops species dominant in the open water of Lake Balaton werestudied by means of vials placed back into the lake, in naturalfeeding conditions. The males of all three species turned intoadults earlier than the females. The copepodite V stage wasof the longest duration. Three generations of Cyclops vicinusdeveloped yearly; in spring, autumn and winter. About 50% ofthe copepodite stage IV of the spring generation entered activediapause at the end of May, beginning of June, then entereddormancy between the middle of June and middle of July. Consideringthe literary data as well, it seems that the generation numberof the species is the function of temperature and of the water'strophic state. The Acanthocydops robustus f. limnetica is fondof warm water (> 14°C). Seven generations of this speciesdeveloped completely yearly, during an average of 2-week intervalsbetween May and September. The eightli generation died in thenaupliar stage. The generation number of A. robustus f. limneticadepends on the average temperature of the lake. Inactive diapausecould not be observed for this species. Only one generationof Mesocyclops latckarti developed in autumn. The copepoditeV of the winter generation entered active diapause below a watertemperature of 10°C, and inactive diapause from the endof January, which state ended in March.     

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)     

Occurrence of gentamicin-producing micromonosporae in Lake Balaton (W. Hungary)

The total number of platable bacteria in the wet mud material characterized by the predominant occurrence of high-magnesian calcite and protodolomite of the Lake Balaton fluctuates between 3.5 X 10(4) and 2.3 X 10(5) g-1. Actinomycetes constitute about 25-30 per cent of this mud-community and not more than half of them belong to the genus Micromonospora. The presence of 10 species of this genus was detected among the isolated and studied strains identified by means of conventional methods and computer aided numerical analysis in which 20 authentic, mostly type strains of Micromonospora spp. were also involved. All of the three species of gentamicin-producing Micromonospora (M. echinospora, M. purpurea and M. sagamiensis) known so far were found in mud samples. These three species form stable but less numerous populations (less than 0.5 per cent of the total platable microflora) in the Balaton's mud, the members of which are capable to produce gentamicins at about 40-50 micrograms ml-1 level at most.     

Primary production of epipsammic algal communities in Lake Balaton (Hungary)

Benthic algal communities can play an important role in matter and energy flux of shallow lakes. Their contribution to total primary production of lakes has been largely unexplored. The aim of this study was to estimate the primary production of the epipsammic algal communities at different water depths in Lake Balaton (Hungary) with photosynthetic measurements performed in laboratory. The photosynthesis of the benthic algae of different origin was studied at nine different irradiance levels, in three replicates. The maximum photosynthetic rate (P _max) was always higher in samples from the shallow parts than those from the deeper regions of the lake. Along the west–east longitudinal axis of the lake P _max decreased in the southern part and increased in the middle of the lake as a consequence of differences in the chlorophyll-a concentrations. Knowing P _max, I _k, global radiation and extinction coefficient, the primary production (mg C m⁻² day⁻¹) of the epipsammic algal community was calculated at different water depths. In the shallow regions at 0.5 and 1 m water depth 75–95% and 60–85% of the production was attributable to the epipsammon. The percentage contribution of epipsammon was at 2 m water depth 20–65%. In the deeper pelagic region (>3 m) more than 85% of the primary production originated from the phytoplankton.     

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.     

Spatial distribution and short-term changes of benthic macrofauna in Lake Balaton (Hungary)

Spatial and short-term changes in the composition and density of the macrobenthic fauna were studied in Lake Balaton, a large shallow lake in Central Europe (Hungary). Spatial differences were examined along five transects and short-term changes at two stations of different trophic state. The macrobenthos consisted almost exclusively of Tubificidae and Chironomidae of the species Chironomus gr. plumosus, Procladius choreus, Tanypus punctipennis, Microchironomus tener and Cladotanytarsus sp. The Oligochaeta biomass showed a significant short-term decrease from 1995 to 1998, and their average biomass proved to be 0.86 and 0.79 g WFW (wet formalin weight) m-2 in 1996 and 1997, respectively. Chironomidae showed significant spatial and short-term differences following variations in primary production. Higher primary production resulted in higher biomass (up to 153.4 g WFW m-2 and 9785 ind. m-2 in 1995) of Chironomus-Procladius community, while lower primary production resulted in a very low biomass and abundance of the predatory Procladius-Tanypus-Microchironomus community (average: 3.16 g WFW m-2 and 1311 ind. m-2 in 1997). As compared to other lakes of similar climatic conditions, the total production of oligohaetes and chironomids proved to be very low in 1996 and 1997 (49.2 and 54.1 KJ m-2 yr-1, respectively). The 90% of the average chironomid production of Lake Balaton in 1996 and 1997 belonged to Ch. gr. plumosus (5.63 and 5.13 g m-2 yr-1), P. choreus (4.3 and 3.47 g m-2 yr-1) and T. punctipennis (0.27 and 2.21 g m-2 yr-1). This revised version was published online in July 2006 with corrections to the Cover Date.     

Alga consumption of four dominant planktonic crustaceans in Lake Balaton (Hungary)

Between 1981–83 the gut contents ofDaphnia galeata, D. cucullata, Eudiaptomus gracilis, andCyclops vicinus were examined with light and scanning electron microscope to obtain information on the feeding of these species in Lake Balaton. The twoDaphnia species feed mainly on abioseston, and it is assumed that their primary nutrient source was organic matter adsorbed onto the surfaces of the abioseston granules plus bacteria and detritus.E. gracilis feeds on algae, showing a preference for green algae and diatoms.C. vicinus is also a prodigious consumer of algae in Lake Balaton, utilizing the whole size spectrum of phytoplankton. Concerning the trophic relationships between phytoplankton and zooplankton in Lake Balaton, that between diatoms and bothE. gracilis andC. vicinus is the most conspicouos. Convincing evidence for an extensive utilization of blue-green algae was not found. Though there is no firm evidence yet, it is likely that theDaphnia are dependent on organic matter adsorbed on the abioseston.     

Biological monitoring of heavy metal pollution in the region of Lake Balaton, (Hungary)

The concentrations of toxic heavy metals (Hg, Cd, Cr, Cu, Zn and Pb) were measured by atomic absorption spectrophotometry in the gills of mussels (Unio pictorum L.) both living in Lake Balaton as well as transferred to various parts of tributaries of the Lake. The measurements were performed separately with two-week intervals during the course of several months. It was found that (1) the concentration of the studied metals varied with time at each location, less variation occurred in the mussels living in the Lake itself. (2) There were both increases and decreases in the heavy metal concentration of the gills, presumably reflecting the changing level of pollution of the water. It is concluded that mussels can be used as biological indicators for detecting temporal variations in the degree of toxic heavy metal contamination in surface waters, and are good objects for signalizing local events of pollution.     

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.     

Terminal electron transport system (ETS)-activity in the sediment of Lake Balaton,Hungary

Terminal electron transport system (ETS)-activity of the sediment and plankton of Lake Balaton, the largest shallow lake of Central Europe was measured by tetrazolium-reduction biweekly during 1989–1990 and in the spring of 1991. Sediment proved to be enzymatically active to 30-35 cm down in the hypertrophic Keszthely Bay and to 15–20 cm down in the meso-eutrophic Siófok Basin. Sediment ETS-activity exceeded planktonic activity 15 to 24 fold.The total activity m^–2 showed one or two order of magnitude higher respiratory potential in Lake Balaton than needed for complete oxidation of the planktonic primary production; most of this potential was detected in the upper 3–5 cm sediment layer in springs. Incubations of cell-free homogenates of sediment bacteria showed that ETS remains active days after death of organisms at low temperature. Accumulated postmortem ETS-activity derived from the benthic diatoms, bacteria, plankton deposit and dead summer macrophytes seems to be responsible for the high ETS-activity of the sediment in the warming periods in springs. These enzyme fractions may contribute to the rapid oxidation of the alkaline, well-aerated lake.     

Population dynamics and food of bleak (Alburnus alburnus L.) in the littoral zone of Lake Balaton,Hungary

Intra- and interspecific effects together with changing environmental conditions regulate the dynamics of the fragile bleak populations in Lake Balaton. Size- and age-structures, length-weight relationships and mortality were studied on 1493 individuals and growth history were determined using scales from 703 specimens. The population growth rate was slow and the basic population parameters showed area variations along the longitudinal axis of the lake. Gut contents were analyzed in 224 individuals. The bleak stocks are trophically strongly related to the littoral zooplankton and benthos; and they play a significant energy-mediating role in the food-webs between the periphytic communities and fish assemblages in the littoral zone of Lake Balaton.     

Crustaceans as biological indicators of heavy metal pollution in Lake Balaton (Hungary)

Hydrobiologia - Trace metals (Cd, Cu, Pb, Zn) were measured in mixed zooplankton samples collected from the open water of Lake Balaton (Hungary) in order to assess spatial and seasonal changes in...     

Biological availability and humic properties of dissolved organic carbon in Lake Balaton (Hungary)

The nursery role of the Mondego estuary for marine fish species was studied between June 2003 and May 2004. The spatial and temporal distribution and abundance patterns of 0-group Dicentrarchus labrax (Linnaeus, 1758), Platichthys flesus (Linnaeus, 1758) and Solea solea (Linnaeus, 1758) were analyzed based on monthly sampling surveys in five stations along the estuarine gradient. Fishing took place during the night at low water of spring tides, using a 2 m beam trawl. The spatial patterns of estuarine colonization were different according to species. D. labrax showed a wider distribution, but the main nursery ground was the same as for S. solea. Highest densities of S. solea juveniles were found in oligohaline areas, with muddy bottoms and high benthic invertebrates availability, while P. flesus occurred mainly in the sandy uppermost areas. D. labrax was found in both these areas. Fish abundance in the estuary mainly reflected seasonal changes.     

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.     

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.     

A five-year study of autotrophic winter picoplankton in Lake Balaton,Hungary

Picoeukaryotes dominate the phytoplankton of Lake Balaton—the largest shallow lake in Central Europe—in the winter period. We examined the annual dynamics of picoplankton abundance and composition in the lake in order to establish if the picoeukaryotes merely survive the harsher winter conditions or they are able to grow in the ice-covered lake when the entire phytoplankton is limited by low light and temperature. Lake Balaton has an annual temperature range of 1–29°C, and it is usually frozen between December and February for 30–60 days. In the spring-autumn period phycocyanin and phycoerythrin rich Cyanobacteria are the dominant picoplankters, and picoeukaryotes are negligible. Our five-year study shows the presence of three types of picophytoplankton assemblages in Lake Balaton: (1) Phycoerythrin-rich Cyanobacteria—the dominant summer picoplankters in the mesotrophic lake area; (2) Phycocyanin-rich Cyanobacteria—the most abundant summer picoplankters in the eutrophic lake area and; (3) Picoeukaryotes—the dominant winter picoplankters in the whole lake. The observed winter abundance of picoeukaryotes was high (up to 3 × 10⁵ cells ml⁻¹), their highest biomass (520 μg l⁻¹) exceeded the maximum summer biomass of picocyanobacteria (500 μg l⁻¹). Our results indicate that the winter predominance of picoeukaryotes is a regular phenomenon in Lake Balaton, irrespective of the absence or presence of the ice cover. Picoeukaryotes are able to grow at as low as 1–2°C water temperature, while the total phytoplankton biomass show the lowest annual values in the winter period. In agreement with earlier findings, the contribution of picocyanobacteria to the total phytoplankton biomass in Lake Balaton is inversely related to the total phytoplankton biomass, whereas no such relationship was observable in the case of picoeukaryotes.     

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...     

Amphipoda (Crustacea) in the Littoral Zone of Lake Balaton (Hungary). Qualitative and Quantitative Studies

Species composition, size distribution, egg number and biomass of different amphipod species on littoral submerged aquatic vegetation (Myriophyllum, spicatum and Potamogeton perfoliatus stands) and on the stony shores of Lake Balaton at Tihany were estimated in August 1983 and 1985. Three species occurred in the material: Corophium curvispinum, Dikerogammarus haemobaphes and Dikerogammarus villosus. The bulk was formed by C. curvispinum. The mean number of eggs per female of the three investigated species showed differences at the different sampling stations and ranged between the following values: C. curvispinum from 3.3 to 8.8, D. haemobaphes from 16.4 to 22.8 and D. villosus from 8.0 to 17.5. The total biomass of amphipods was 1.8 and 3.5 mg dry weight/g fresh weight of macrophytes in 1983 and 1985 respectively, and 4.7 mg animal per dm² stone surface in the stony littoral zone in 1983.     

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.