István Tátrai

The role of the Kis-Balaton Water Protection System in the control of water quality of Lake Balaton

Abstract Since the 1960s the nutrient load of Lake Balaton has increased significantly, causing a clear decline in water quality. To retain the nutrients from the lake, the Kis (small)-Balaton Water Protection System (KBWPS) was designed on the lower part of the main inflow, the River Zala. The first part of the KBWPS started to function in July 1985. After a few years the system became hypertrophic. According to our results, approximately 80 000 t of suspended solids, 300 t of total phosphorus (TP), 250 t of phosphate-P, 850 t of total nitrogen (TN), and 2450 t of nitrate-N were retained between 1986 and 1997 by the first part of the system. At present, the KBWPS retains about half of the suspended solids, more than one-third of TP, more than two-thirds of phosphate-P, only one-tenth of TN, but more than half of nitrate. A 16 km 2 area of the second part has been operating experimentally since 1992. This part retains approximately 75% of suspended solids (mostly of phytoplankton origin) coming from the first phase, but the phosphorus retention is low due to release of phosphorus from sediments. Until 1991 there were no significant differences in monthly means of the chlorophyll-a content from the western part of Lake Balaton. Since that time the chlorophyll-a content has been decreasing in the lake. This decrease could have been the result of the combined effects of weather conditions (temperature, rainfall) and nutrient availability.

Biomass dependent interactions in pond ecosystems: responses of lower trophic levels to fish manipulations

The effects of mature benthivorous cyprinid fish and theirrecruitment on sediment resuspension, turbidity, phyto- andzooplankton, and benthic macroinvertebrates were studied in fourexperimental ponds. The ponds were stocked with bream (Abramisbrama L.), white bream (Blicca bjoerkna L.), roach (Rutilus rutilus L.) and wild carp (Cyprinus carpio L.) of3+–5+ age classes at standing crop biomass varying from 0 to500 kg ha-1. Cyprinids caused an increase in sedimentresuspension and in turbidity, in proportion to their biomass. Meancrustacean biomass did not significantly affect phytoplanktonbiomass due to intense grazing by fish during spring. Ponds withhigh fish stocks showed reduced midge biomass and vegetation coverand increased biomass of predatory invertebrates.

Diurnal pattern of the ammonia and urea excretion of feeding and starved bream, Abramis brama L

Abstract 1. 1. Measurements of the rate of ammonia, urea and total nitrogen excretion of young bream (Abramis brama) were made (av. wt: from 8.1 ± 1.2−40.3 ± 6.3 g) at 15 ± 1 and 20 ± 1°C. 2. 2. Fish were fed daily on Zooplankton and Tubifex from 5–10% of their body weight. After completion of the experiments on feeding, fish measurements were carried out on bream starved for 30 days. Excreted ammonia and urea nitrogen were determined four times, while excreted total nitrogen once a day. 3. 3. About 50–60% of the nitrogen consumed with food was excreted as soluble compounds (NH4-N, urea-N) and faecal nitrogen. 4. 4. Ammonia was the chief end product of protein metabolism as about 45–60% of the total excreted nitrogen was NH4-N. 5. 5. Daily fluctuations in the proportion of ammonia excretion of feeding bream were observed, while urea showed a continuous rate of production. No diurnal response to feeding was observed. 6. 6. The daily pattern of ammonia excretion of starved bream fell in a manner comparable to the diurnal pulse of the 24 hr cycle of the feeding fish. The rate of urea excretion was also without any considerable changes during the starvation period.

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.

Feeding experiments with silver carp (Hypophthalmichthys molitrix Val.) Fry

Abstract Feeding experiments were carried out with fry of silver carp fed on cultured algae, Scenedesmus ellipsoideus, Anacystis nidulans, Anabaena flos-aquae , and on phytoplankton collected in Lake Balaton. Analyses of the intestinal contents of silver carp showed that blue-green algae and diatoms were ingested and digested to the greatest extent. Colonies of blue-greens and big forms of greens were ingested, but poorly digested. Fish were not able to ingest algae smaller than 10 μm in size. Silver carp fed on blue-greens consumed 11–13% of their body weight (wet wt) in a 40 mg l −1 algal suspension. Filtration rate, at the same food density, ranged between 2.6 and 3.3 l g −1 (body weight) 4 h −1 . Algae labeled with 14 C passed through the alimentary canals in an average time of 3.2 h. Feeding of silver carp was most intense in the afternoon and lowest at night. Fecal algae ( Scenedesmus ) did not increase either the biomass or the primary production at a fecal concentration of 1 mg l −1 . At a fecal concentration of 3 mg l −1 , however, there was a slight increase in both the biomass and the primary produciton. At 10 mg l −1 fecal concentration the biomass and primary production of living cells almost doubled. Fecal algae ( Anabaena ) increased the primary production at 10 mg l −1 , but at 50 mg l −1 the biomass was three times and the primary production four times higher as compared with the control.

Indirect effect of different fish communities on nutrient chlorophyll relationship in shallow hypertrophic water quality reservoirs

Effects of different fish communities on the proportion of different nitrogen and phosphorous forms and the amount of phytoplankton (chlorophyll a) were examined in two consecutive years (1992–1993) in three Hungarian shallow water reservoirs (Cassette and outer reservoir of the Kis–Balaton Water Protection System, and Marcali reservoir). Possible interactions between nutrient concentrations and the amount of phytoplankton in these reservoirs were also examined. Considerable differences in the proportions of different nutrient forms were observed between the three test sites, which could be explained by the presence of different fish stocks in these reservoirs. In the Cassette, the fish biomass necessary for a water quality improvement was around 50 kg ha−1. Phytoplankton biomass was controlled by the zooplankton, consequently chlorophyll a concentrations decreased considerably, while those of dissolved nutrients significantly increased. In the outer reservoir, phytoplankton was controlled bottom-up, since the 250 kg ha−1 fish biomass was larger than the critical value due to the high proportion of planktivorous species. Chlorophyll a concentrations were high, and nutrients were mainly in particulate form (in algal cells). In the Marcali reservoir, the recently introduced silver carp population could not control fully the phytoplankton. The biomass of phytoplankton decreased only slightly, while its composition changed considerably. Although biomanipulation with silver carp is suitable for ceasing cyanobacterial blooms, reduction of the amount of planktivorous fish seems to be a more adequate method for increasing water transparency, rather than introduction of phytoplankton feeding fish.

Seasonal and spatial variability of sediment bacterial communities inhabiting the large shallow Lake Balaton

Seasonal studies of surface sediment bacterial communities, from two basins with differing trophic states within Lake Balaton (Hungary), were carried out using molecular (denaturing gradient gel electrophoresis, DGGE) and cultivation-based techniques. The presence of polyphosphate accumulates was tested using Neisser staining, and phosphatase activity was investigated on organic phosphorus (P) compound. Aerobic viable cell counts were significantly higher in the eutrophic than mesotrophic basin in each season. The lowest viable counts were observed in the autumn and the highest in spring and summer month in both basins. The DGGE fingerprints of the samples reflected that the composition of sediment bacterial communities in the two basins were distinct in spring and summer, and similar in autumn, but similarly diverse in all seasons. On the basis of partial 16S rDNA sequences, the 216 strains were affiliated with six major bacterial lineages: Firmicutes; Actinobacteria, Bacteroidetes, Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria. Common species characterized from both basins constituted up to 66% of all identified phylotypes. Strains related to Bacillus sp. were dominant in all but one sample. Isolates affiliated with Aeromonas sp. prevailed in the sample taken from the mesotrophic basin in spring. The majority of the strains showed excess poly-P accumulation. Association of Neisser staining and phosphatase activity test results suggested that excess poly-P accumulation serves as P storage for sediment bacteria. Our study implied the importance of Firmicutes, Actinobacteria, Alphaproteobacteria, and Aeromonas species in benthic bacterial P retention.

Management measures and long-term water quality changes in Lake Balaton (Hungary)

A reduction in the external and internal P loadings along with the removal of benthivorous cyprinids resulted in a significant improvement of the water quality in the hypertrophic western part of Lake Balaton by 1996, some ten years following first management measure. Enhanced internal P loading after the reduction in external nutrient load is clearly an important factor explaining the duration of recovery in shallow lakes. Phytoplankton responded quite rapidly to reductions in nutrient loading and fish stock, whereas the effect on both the structure and abundance of the crustacean plankton was less pronounced. The role of top-down control of phytoplankton by crustaceans following nutrient reduction is not clearly understood in shallow lakes. Grazing did not play a significant role in the overall reduction of algal biomass in Lake Balaton. Since high concentration of suspended mineral particles from both sediment resuspension and lime precipitation causes permanent food limitation of daphnids, the top-down effects were negligible in Lake Balaton following fish stock reduction. Fish community structure did not respond to the lower external and internal TP loads cyprinids being dominant in both the pre- and post-management periods.

Contribution of bream, Abramis brama (L.), to the nutrient dynamics of Lake Balaton

Dry matter, total carbon (C), nitrogen (N) and phosphorus (P) content of mature bream from Lake Balaton were investigated and the quantities of N and P stored in the bream population and their possible removal by fishery were estimated. Carbon made up 43.3–44.8% of dry weight, N made up on average 10.6% of the dry weight of bream and P accounted for a further 2.7%. About 3.3 kg N ha−1 and 0.9 kg P ha−l are stored in the bream population. Approximately 0.5 kg N ha−1 and 0.1 kg P ha−1 are removed from the lake by bream harvest. Taking into account the total fish yield, the N removal is 2.1% and P removal 3.4% of the amount entering the lake.

Oxygen consumption and ammonia excretion of herbivorous chironomid larvae in Lake Balaton

The oxygen consumption and ammonia excretion of a herbivorous midge larva,Chironomus sp., inhabiting Lake Balaton was measured at two different temperatures. The loss of energy through respiration and that through ammonia excretion were calculated. The daily respiratory energy loss amounted to 655.5 ± 123.8 J g−1 at 17 °C and to 1 160.0 ± 168.4 J g−1 (dry weight) at 25 °C. Mean energy loss through ammonia excretion was about 40% less than through respiration.