Trophic relationships between primary producers and fish yields in Lake Balaton

Relationships between chlorophyll a content of the water, the shoreline-length: water area ratio and the annual total fish yield as catch per unit effort (CUE: kg ha^–1 100 h^–1 as annual mean values) have been calculated by multivariable regression. The determination coefficient (r² = 0.913) showed a significant dependence of fish yield on morphometry of different lake areas. Accordingly, fish carrying capacity of the open water areas, calculated from chlorophyll a content and S/A, ranged from 12 to 34%, but that of the littoral zone between 66 and 88%. These findings have also been supported by echo-sounding records of the horizontal distribution of fish.Bream (Abramis brama L.) contributes the majority (70–80%) of fish stock and yield. Its food mainly consists of zooplankton and benthic invertebrates in ratios that are widely variable with season and depend on the age of fish. Average daily food consumption of individuals (age group 3 + and over) varies between 2 and 5 g. Bream consumes two- to three-times more food in the SW basin than in the NE one. This means that the present stocks inhabiting areas from NE to SW consume annually 13249–20085 t yr^–1 of food. According to estimated calorific values, the annual energy consumption of local populations along the longitudinal axis of the lake varies between 93 and 141 kJ m^–2 yr^–1. The efficiency of energy transfer from primary producers to fish is low and varies from 0.04 to 0.1%.     

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.     

Orthophosphate uptake of planktonic microorganisms in Lake Balaton

Seasonal orthophosphate uptake of natural plankton has been studied in hypertrophic and mesotrophic basins of Lake Balaton. Initial uptake of carrier-free labelled phosphoric acid followed first order kinetics in accordance with a single two-compartment model. In isotope equilibrium from 1.2 to 9.7 per cent of radioactivity was found in the filtrate. Turnover times of orthophosphate in water were some minutes in summer and two orders of magnitude longer in winter and April. Turnover time of phosphorus in microorganisms has been estimated on the basis of equilibrium isotope distribution between water and particular phases and turnover time in water. It ranged from 28 to over 1 000 min. The shortest times were found in summer, and the longest in winter. Turnover time of orthophosphate in water increased in relation to phosphate additions according to Michaelis-Menten kinetics. The values of Michaelis-constant plus the ambient orthophosphate concentration (K + S_n) suggested an overestimation of real phosphate concentrations by chemical measurements, being much lower than soluble reactive phosphorus contents in most cases, as it is well-known in many other lakes. Both K + S_n values and maximum uptake velocities (V) were significantly higher in the hypertrophic basin than in the mesotrophic one, in contrast to essentially similar values of turnover times. Maximum uptake velocity per unit chlorophyll-a P _opt:V ratio showed extreme to moderate phosphorus deficiency for Lake Balaton plankton, which seemed to decrease somewhat in the course of eutrophication.     

Biomass of planktonic crustaceans and the food of young cyprinids in the littoral zone of Lake Balaton

The littoral zone of Lake Balaton and its periphyton-zooplankton-fish communities have been investigated intensively in recent years. Total average number of crustacean plankton varied from 36 to 126 ind l^–1, their biomass from 0.49 to 1.86 mg ww l^–1 month^–1 at different areas of the littoral zone. In general, these values for the above parameters were higher in hypertrophic areas. 23 fish species occurred in the littoral zone with cyprinids dominating. The seasonal food spectra of Y-O-Y roach (Rutilus rutilus), white bream (Blicca bjoerkna) and bream (Abramis brema) were based mainly on planktonic crustaceans and benthic/periphytic invertebrates. According to the frequency of occurrence of crustaceans and other invertebrates, the food composition of young cyprinids differed significantly in the NE and SW-basins of the lake.     

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.     

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.     

Determination of the Limiting Plant Nutrient in the Water of Lake Balaton by Algal Assay Procedure

Algal assays were performed on water samples taken from different sites in Lake Balaton. Selenastrum capricornutum was used in the test to determine the primarily limiting plant nutrient. The results of supplementary nutrient additions to the bottle tests were evaluated by cell counts. The tests have indicated phosphorus as growth rate limiting, and in two cases as biomass limiting plant nutrient, but periodic occurrences of nitrogen limitation cannot be excluded.     

Growth of Bream,Abramis brama L., in Two Outside Basins of Different Trophic State of Lake Balaton

Age-composition, size-distribution, length/weight relationships and growth both in length and weight of bream stocks were studied on fishes collected in NE and SW basins of Lake Balaton during 1982/83. Stocks consisting of 10 to 12 age-groups were observed at the two lake areas. The linear growth and weight-gain in the SW-basin were annually faster than in the NE-basin, however, the growth of bream in Lake Balaton was slow as compared to that observed 10 years ago. Parallel with progressive eutrophication, the density of bream stocks increased by some 5–10 % especially at hypertrophic lake areas (SW) and consequently their growth was transformed to densitydependent. In the appearance of strong year-classes some cyclicism could be observed especially in the SW-basin.     

Lake Muzahi,Rwanda: limnological features and phytoplankton production

Lake Muhazi, a small lake of Rwanda (East Africa) was studied from 1986 to 1990. A dramatic decrease of the catch of Oreochromis niloticus (350 T y⁻¹ in the fifties vs 30 T y⁻¹ in 1982) suggested a loss of productivity or overfishing. In the same period, other ecological changes occurred: the submerged macrophytes regressed and there was a decrease in Secchi depth (0.65 m in 1987 vs 1.5 m in the fifties). Compared to other lakes of the same area, the plankton production seemed low. The results of the present study characterize lake Muhazi as a shallow lake with a rather unstable diurnal stratification and with slight differences in mixing regime between its eastern, deepest part and its western, shallowest part. Secchi disk depth does not vary seasonally to a large extent. The water has a rather high mineral content (conductivity of about 500 μS cm⁻¹ at 25 °C) and low concentrations of dissolved N and P, except in the hypolimnion, where NH _inf4 ^sup+ -N can be high. Two species, Microcystis aeruginosa and Ceratium hirundinella, account for most of the phytoplankton biomass, which is about 50–80 mg chlorophyll a m⁻² in the euphotic zone, usually with little seasonal variation. Daily gross production estimates amount to about 6 to 9.5 g O₂ m⁻² d⁻¹ with a significant difference between the two parts of the lake. Data on C:N and C:P ratio in the phytoplankton suggest that some N deficiency might occur in the eastern part. Moreover, the Zm:Zc ratio could also lead to rather low net production rates (0.21–0.25 d⁻¹ for a mixed layer of 4 m) In conclusion, the primary production of lake Muhazi is medium for African lakes and the hypothesis that decreased planktonic production could account for a reduced fish production should be discarded. Whereas the present yield of the fishery is only 20 kg ha⁻¹ y⁻¹, the yield estimated from primary production ranges between 46 and 64 kg ha⁻¹ y⁻¹. This could be reached through proper management. Finally, some hypotheses are given to explain the ecological changes which occurred in the lake.     

Phytoplankton community structure and environment in the Kenyan waters of Lake Victoria

• 1 Phytoplankton species composition, numerical abundance, spatial distribution and total biomass measured as chlorophyll a concentration were studied in relation to environmental factors in September 1994 (dry season) and March 1995 (rainy season), respectively, in the Kenyan waters of Lake Victoria; 103 species were recorded.
• 2 Blue‐green algae (Cyanophyceae) were most diverse, followed by diatoms (Bacillariophyceae), green algae (Chlorophyceae) and dinoflagellates (Dinophyceae).
• 3 Twinspan separated the phytoplankton communities in the Nyanza Gulf and those in the open lake during both seasons. During the dry season, the Nyanza Gulf was strongly dominated by blue‐greens, while diatoms dominated in the open lake. During the rainy season, blue‐greens remained dominant in the Nyanza Gulf although the number of species found was lower than during the dry season; in the open lake, blue‐greens replaced diatoms as the dominant group and there were more species than in the dry season.
• 4 Canonical correspondence analysis indicated that the phytoplankton species distribution was significantly correlated with turbidity during the dry season and with SiO₂ during the rainy season. Chlorophyll a concentrations ranging from 2.0 to 71.5 mg m^‐3 in the dry season and 2.0–17.2 mg m^‐3 in the rainy season confirm earlier reports of increasing phytoplankton biomass in Lake Victoria since the 1960s.

     

Mobility of phosphorus fractions in the sediments of Lake Balaton

Sediment phosporus was studied by a combination of the fractionation procedure of Hieltjes & Lijklema and the isotopic dilution technique in a mesotrophic (Tihany) and a hypertrophic (Keszthely) basin of Lake Balaton.In the calcareous sediments the largest part of phosphorus was bound to calcium. Iron-bound and residual P showed higher concentrations at Keszthely than at Tihany. There was little loosely adsorbed P at both locations. Vertical differences in P fractions of the sediments were more pronounced at Keszthely than at Tihany. Exchangeability of the fractions decreased in the following sequence: iron-bound > loosely adsorbed > calcium-bound > residual. Phosphorus, particularly in the calcium-bound fraction, was more mobile at Keszthely, and its exchangeability decreased rapidly downwards at both stations. Four times more potentially mobile phosphorus has been accumulated by the upper sediment layer at Keszthely than at Tihany.     

Ecological background and importance of the change of chironomid fauna (Diptera: Chironomidae) in shallow Lake Balaton

The objectives of this research were to record the changes in composition of the open-water, bottom-dwelling chironomid fauna in Lake Balaton between 1978–1984, to examine the causes of these changes, and to discover their significance in the life of the lake.The spatio-temporal dispersion of larvae is compared with the water and sediment quality of each basin in the lake. It is established that, under present conditions, nutrient status can be regarded as the chief environmental factor.Studies of population dynamics show that chironomids play a highly important role in preserving sediment quality. Chironomids are an essential element in the organic matter circulation of the lake. They dominate a sub-system that retards water quality degradation, and thus they play a prominent role in the natural prevention of eutrophication.     

Field and Laboratory Studies on Nile Phytoplankton in Egypt IV. Phytoplankton of Aswan High Dam Lake (Lake Nasser)

Seasonal, local and monthly vertical variations in chlorophyll a concentration and in qualitative and quantitative counts in Aswan High Dam Lake (AHDL) phytoplankton were followed from March 1982 to February 1984. The chlorophyll a values correlated more or less with the total phytoplankton counts. Total algal counts exhibited considerable local variations in the different seasons and tended to decrease in the most southern part of AHDL, especially during the flood period. The temporal course of algal development showed an almost inverse trend to that of dissolved nitrate-nitrogen. The possibility of nitrogen limitation of algal growth was verified. Diatoms and blue-green algae alternated in the dominance of the phytoplankton community. The genera Cyclotella and Anabaenopsis respectively were the most predominant genera among the diatoms and blue-greens and consequently in the phytoplankton community.     

Bottom-up effects of bream (Abramis brama L.) in Lake Balaton

Enclosures (17 m³) were used in the mesotrophic area of Lake Balaton to determine the impact of benthivorous bream (Abramis brama L.) on the lower trophic levels during summers of 1984–86. In enclosures with a fish biomass similar to the biomass in the eutrophic area of the lake, the number of phytoplankton species was highest. In enclosures with a low fish biomass the phytoplankton was dominated by the greens. A high biomass of bream in the mesotrophic basin caused bacterial production corresponding to that of the eutrophic part of the lake. Crustaceans were dominated by copepods and were unable to control phytoplankton peaks. Bottom-up effects of bream were more obvious than top-down effects and seem to be more important in the possible control of water quality.     

Relations between planktivorous fish abundance,zooplankton and phytoplankton in three lakes of differing productivity

Hydrobiologia - Water chemistry, phytoplankton, zooplankton and fish populations werestudied over several years in three shallow, non-stratified lakes withdiffering nutrient loadings and fish...     

Life history of Corophium curvispinum G. O. Sars (Crustacea,Amphipoda) living on macrophytes in Lake Balaton

Samples of the amphipod Corophium curvispinum were collected from Myriophyllum spicatum twice a month during the vegetation period. The animals were sexed, their length measured and the eggs of females were counted. Length frequency histograms served to follow the life history of C. curvispinum.Reproduction lasts from May to October. The animals born in May–June reproduce in the same year while the summer-autumn generation reproduces the following year. The life span is about 1 year. The highest fecundity was found in June, the lowest in October.     

Correlation between algal species diversity index and phytoplankton community biomass in a mesotrophic lake (West Siberia, Russia)

The study deals with phytoplankton biodiversity in mesotrophic Sartlan Lake, a large natural saline water body in the south of West Siberia. Two different approaches are used: floristic and ecological cenotic. The former is good for determining and analyzing the phytoplankton species composition. The latter gives a quantitative estimation of the phytoplankton biodiversity from the equation of information theory: $ H_b = - \sum\limits_{i = 1}^n {\frac{{B_i }} {B}\log _2 \frac{{B_i }} {B}} The study deals with phytoplankton biodiversity in mesotrophic Sartlan Lake, a large natural saline water body in the south of West Siberia. Two different approaches are used: floristic and ecological cenotic. The former is good for determining and analyzing the phytoplankton species composition. The latter gives a quantitative estimation of the phytoplankton biodiversity from the equation of information theory: , where H _b is the biodiversity (bits); B _i is the population biomass of the species i; B is the entire phytoplankton community biomass (mg/l). A reliable stable negative correlation exists between the phytoplankton biomass and species diversity. Analytical equations and a diagram are given to illustrate the correlation between these values. Original Russian Text ? V.I. Ermolaev, 2009, published in Sibirskii Ekologicheskii Zhurnal, 2009, Vol. 16, No. 4, pp. 623–628.     

Winter phytoplankton communities of Utah Lake,Utah, USA

Phytoplankton samples were collected from ice-covered Utah Lake during February and March, 1979 in order to characterize the winter algal flora. These samples were analyzed for presence and abundance of diatoms and non-diatom algae as well as selected water chemical parameters. A total of 159 diatom taxa and 20 non-diatoms was found in the water column under the ice. The flagellates Carteria stellifera, Euglena gracilis and Chlamydomonas globosa dominated the winter non-diatom flora while Stephanodiscus cf. dubius, Cyclotella meneghiniana, Navicula minima, Fragilaria construens var. venter, and Melosira granulata var. angustissima dominated the winter diatom flora. Species richness and abundance were elevated in the major bays of the lake.     

Comparative seasonal changes,and inter-annual variability and stability,in a 26-year record of total phytoplankton biomass in four English lake basins

Long-term sequences of total phytoplankton biomass are described and analysed in relation to environmental conditions and species composition. They are based on largely weekly sampling of mean concentrations of chlorophyll a ([Chl]) in the euphotic zones of four English lake basins over 26 years. More restricted sampling is used to illustrate the regulation of vertical distribution, and a comparison with several chemical indices of seston abundance.The seasonal variation of [Chl] is predominantly constructed from two peaks in spring and summer-autumn. These are separated by a universal and light-limited winter minimum that is accentuated in the deeper basins and a more variable early summer minimum to which diatom sedimentation, species replacement and grazing by Cladocera contribute. In some years or year-sequences additional peaks of varied origin may be interpolated (frequency modulation), especially in the shallower basins. Some variability of maxima with nutrient enrichment and particular species-crop failure or success (e.g. Ceratium spp.), and of minima with growth limitation, loss modes and species replacement, exists within and between basins (amplitude modulation).Depth-colonization is primarily controlled by restrictions on vertical mixing associated with the seasonal temperature/density stratification. Relative timings can be important for areal biomass development. Though [Chl] is mainly epilimnetic in summer, metalimnetic and hypolimnetic accumulations can also arise by growth in situ, flagellate migration, or sedimentation. Variations in the content of Chl below unit area, for entire lake column or euphotic zone, are less sensitive to trophic state than are mean euphotic concentrations because of compensating influences of morphometry and light penetration.Correspondences exist between temporal sequences of [Chl] and some chemical components of seston (C, N, reducing capacity), but ratios to P show much variation.Comparison is made with other observations of seasonal phytoplankton biomass, with reference to latitudinal influence and to proposed generalisations regarding seasonal pattern.     

The trophic state of Lake Ladoga as indicated by late summer phytoplankton

As a part of the joint Russian-Finnish evaluation of human impact on Lake Ladoga, we studied the phytoplankton of the lake in order to find biological indicators for eutrophication. A second aim of the investigation was intercalibration of sampling and phytoplankton counting techniques between the Russian and Finnish laboratories. Phytoplankton samples were collected from 27 sampling stations in the lake and from the rivers Volkhov and Neva in 9–13 August 1993. In surface water samples the phytoplankton fresh weight biomass varied in the range 218–3575 mg m^–33. Highest biomass values were encountered in Sortavala Bay, and lowest ones in the western central part of the lake. Phytoplankton species composition varied considerably in the lake; blue-green and green algae predominated near-shore areas and Cryptophyceae in the offshore stations. Canonical correspondance analysis revealed close grouping of eutrophy indicating communities, dominated mainly by greens and blue-greens, in the most nutrient-rich parts of Lake Ladoga, the Volkhov and Svir Bays. Samples from the vicinity of the inflows of Vuoksi and Burnaya Rivers and off Pitkaranta formed a separate group, dominated by diatoms, most of which were typical to mesotrophic or eutrophy lakes. As judged by phytoplankton biomass values and chlorophyll a concentrations, Lake Ladoga may generally be classified as mesotrophic. Eutrophicated areas are found in the northern archipelago of the lake and in the areas influenced by large rivers.