Nitrogen uptake and the importance of internal nitrogen loading in Lake Balaton

1. The importance of various forms of nitrogen to the nitrogen supply of phytoplankton has been investigated in the mesotrophic eastern and eutrophic western basin of Lake Balaton.<br /> 2. Uptake rates of ammonium, urea, nitrate and carbon were measured simultaneously. The uptake rates were determined using N-15 and C-14 methodologies, and N-2-fixation was measured using the acetylene-reduction method. The light dependence of uptake was described with an exponential saturation equation and used to calculate surface-related (areal) daily uptake. <br /> 3. The contribution of ammonium, urea and nitrate to the daily nitrogen supply of phytoplankton varied between 11 and 80%, 17 and 73% and 1 and 15%, respectively. N- 2-fixation was negligible in the eastern basin and varied between 5 and 30% in the western region of the lake. The annual external nitrogen load was only 10% of that utilized by algae.<br /> 4. The predominant process supplying nitrogen to the phytoplankton in the lake is the rapid recycling of ammonium and urea in the water column, The importance of the internal nutrient loading is emphasized

Review and Evaluation of Research on the Eutrophication of Lake Balaton -- A Background Report for Modeling

A consistent management of the cultural eutrophication of lakes requires systematic analysis based on the joint and coordinated effort of a variety of disciplines. This notion led the Hungarian Academy of Sciences to the foundation of the Coordinating Council for the Environmental Research on Lake Balaton, as an answer to the growing concern about the slow deterioration of the water quality of the lake, one of the primary touristic resorts of Hungary. The same idea made IIASA's Resources and Environment Area adopt the problem of eutrophication of waterbodies as one of its study objects. Mutual contacts awoke mutual interest in each others work, and in April 1978 IIASA and the Coordinating Council signed an Agreement to establish cooperative links aimed at the further development of ecological models and their practical application in the case of Lake Balaton. For IIASA the existing data and research material promised to be an excellent basis for a case study that could help to realize the objectives of the REN Area Task on Models for Environmental Management and Control. For the Hungarian partner, the cooperation gave access to IIASA's international scientific network and the ready availability of IIASA's computer facilities was also highly appreciated. From the outset of the collaboration, a principal concern of the partners was the collection of the relevant data. In performing this activity it appeared that a broadening of the spectrum of research covered by the Hungarian partner was desirable. A solution was found in the formation of a subcommittee of the Hungarian Bureau of Systems Analysis for the Environmental Research of the Balaton in January 1979. Apart from the representation of the Computer and Automation Institute (MTA SZTAKI) and the Biological Research Institute (MTA BKI) of the first initiator, the Hungarian Academy of Sciences (MTA), the official involvement of the National Water Authority (OVH) and its Research Institute for Water Resources Development (VITUKI) could be welcomed. Now, a rapid disclosure of the vital data followed soon after, thus enabling the setup of the IIASA computer data base, appended to this report in a graphical form. The realization of this data base, though not complete yet, is one of the first concrete achievements of the collaborative project. The publication of this background report can perhaps be seen as the second major achievement of the cooperation. An overview and appraisal of relevant research and data material on Lake Balaton as presented in this report is of paramount importance for a comprehensive modeling effort, and it can only be said that it has been lacking for too long a time. The authors are aware of the fact that there may be different interpretations than their own, and they are, therefore, open to criticism that could improve the picture of the problem of the eutrophication of the Balaton. The authors wish to express the hope that this report will be a stimulus for further ecological modeling research, in the interest of the international community, but even more so, in the interest of the actual protection of the "Hungarian Sea" itself

Eutrophication of Shallow Lakes: Modeling and Management. The Lake Balaton Case Study

The phenomenon of eutrophication is more irregular in character and less satisfactorily understood for shallow water bodies than for deep lakes. Research, initiated by IIASA, focussed of Lake Balaton, Hungary, as the subject of a case study. Three main considerations promoted the selection of Lake Balaton: 1) a large amount of data was available, due to Hungarian research activities; 2) the lake possesses the "typical" properties of shallow lakes; and 3) serious economic interests are associated to the solution of the eutrophication problem of Lake Balaton and so several "practical" questions had to be answered in addition to the pure "scientific" issues. The structure of the research was based on a systems analytical approach which allowed the joint study of scientific and practical issues covering a wide range of different disciplines such as biology, chemistry, physics, hydrology, mathematics, economics, etc. The mathematical models developed in harmony and interaction with data collection and experimental work played a significant role in the project. Several existing methods were adopted for modeling the ecological and hydrophysical processes as well as water quality management in parallel with establishing new methodologies. At the completion of the research an expert committee was established in Hungary to elaborate recommendations for the government concerning the revision and modification of existing measures on water quality control and regional development. In January 1983, the Council of Ministers approved the recommendations and made the relevant decisions. Thus, the research results were transferred to decision makers within a very short period, allowing them to bring in scientifically well established new decisions

Sudden and gradual responses of phytoplankton to global climate change: case studies from two large, shallow lakes (Balaton, Hungary and the Neusiedlersee Austria/Hungary)

This paper analyses two phytoplankton long-term datasets; both are from large, temperate shallow lakes. The main difference between them is that phytoplankton growth in Lake Balaton remained severely P-limited despite P-driven eutrophication during the last 30 years, whereas extremely high turbidity causes a permanent light limitation in Neusiedlersee and therefore an increase in P-loadings did not result in a similar increase in phytoplankton biomass. Neusiedlersee is a (slightly) saline inland lake. In Lake Balaton, the blue-green alga Cylindrospermopsis raciborskii blooms invariably if the July-august temperature deviates positively from a 30-year average by ca. 2 °C. A supposed global warming is predicted to cause a higher frequency (but not intensity!) of these blooms. Neusiedlersee is very shallow and therefore regulation techniques cannot prevent water levels sinking in successive dry years. Annual averages of phytoplankton seem to follow quite a regular, wave-like cyclicity. Such cycles can be recognised in the population records of the characteristic species. Similar changes were seen in changes of water level, conductivity, inorganic-P, inorganic N-forms and nutrient ratios. How phytoplankton species can follow a climatic cycle that covers 200 to 500 generations has not yet become clear. Because of reasons discussed in the paper, neither of the two cases can be generalised; each is quite individual

Environmental factors shaping the distribution of common wintering waterbirds in a lake ecosystem with developed shoreline

In this study, we tested whether the spatial distribution of waterbirds is influenced by shoreline urbanization or other habitat characteristics. We conducted monthly censuses along shoreline sections of a continental lake (Lake Balaton, Hungary) to assess the abundance of 11 common species that use this lake as a feeding and staging area during migration and winter. We estimated the degree of urbanization of the same shoreline sections and also measured other habitat characteristics (water depth, extent of reed cover, biomass of zebra mussels, distances to waste dumps and to other wetlands). We applied linear models and model averaging to identify habitat variables with high relative importance for predicting bird distributions. Bird abundance and urbanization were strongly related only in one species. Other habitat variables exhibited stronger relationships with bird distribution: (1) diving ducks and coots preferred shoreline sections with high zebra mussel biomass, (2) gulls preferred sites close to waste dumps, and (3) the abundances of several species were higher on shoreline sections close to other wetlands. Our findings suggest that the distribution of waterbirds on Lake Balaton is largely independent of shoreline urbanization and influenced by food availability and connectivity between wetlands

Impact of Dreissena fouling on the physiological condition of native and invasive bivalves : interspecific and temporal variations

The impact of Dreissena fouling on unionids has hardly been studied in Europe, despite the fact that in some ecosystems (e.g. Lake Balaton, Hungary) infestations of several hundreds to a thousand individuals per unionid have been observed. At present, the zebra mussel Dreissena polymorpha is a dominant species in Lake Balaton and in the last decade three other invasive bivalves were introduced, potentially increasing the pressure on native unionid survival. We examined whether the fouling of dreissenids (zebra and quagga (D. rostriformis bugensis) mussels) has a negative impact on native (Anodonta anatina, Unio pictorum and U. tumidus) and invasive (Corbicula fluminea and Sinanodonta woodiana) bivalves and whether there are any interspecific and temporal variations in fouling intensity and physiological condition measured by standard condition index and glycogen content. A significant negative impact was detected on native unionids only in July and September (no impact was detected in May), when the fouling rate was high. For invasive species, a significant negative impact was detected on S. woodiana with a high level of dressenid infestation; whereas no significant impact was detected on C. fluminea. Overall, this study confirms that Dreissena may threaten unionid species including the invasive S. woodiana, although high interspecific and temporal variations were observed. This situation should be taken into account in future ecological and conservational assessments because species respond differently to Dreissena fouling and effects seem to be more pronounced in late summer/early autumn. In addition, this study provides the first evidence that the invasive C. fluminea appear to be less vulnerable to dressenid fouling.The study was supported by the Hungarian Scientific Fund (KTIA-OTKA) under the contract No. CNK80140