L. Somlyody

Updating water quality targets for shallow Lake Balaton (Hungary), recovering from eutrophication

The paper presents an overview about recovery of shallow Lake Balaton from eutrophication by assessing quantitative and qualitative changes in phytoplankton, zooplankton, and chironomids as a function of load reduction. The aim was to update the present water quality targets. The proposed targeting scheme supplements the existing one with a range of lake-specific ecological criteria. We conclude that simple targets (desired phytoplankton biomass and permissible load) are the best choice during the initial stage of eutrophication management, but more complex schemes including ecological criteria are needed to trace recovery when re-organization of the ecosystem takes place.

Stochastic Optimization Models for Lake Eutrophication Management

We develop a general framework for the study and the control of the eutrophication process of shallow lakes. The randomness of the environment variability in hydrological and meteorological conditions is an intrinsic characteristic of such systems that cannot be ignored in the analysis of the process or by management in the design of control measures.

Global urbanization and urban water: Can sustainability be afforded?

Urbanization is definitely one of the most characteristic global changes of today and of the coming few decades. Whereas the world population grows with almost one billion per decade, around four fifths of this growth is in urban areas. The challenges due to the development of urban centers, especially great urban agglomerations in developing countries in a sustainable way are huge. Water is one of the key figures in this equation. It has many roles; this paper discusses sustainable urban water infrastructure. First, solutions and experiences from the industrialized countries are summarized, and possibilities and difficulties to adapt them to large urban areas of the Third World are discussed. A particular focus in the affordability issue is taken. Various development indicators and their applicability are discussed. A summary and discussion on technical, economical, financial, and institutional alternatives follows.

Factors influencing lake recovery from eutrophication : The case of Basin 1 of Lake Balaton

Lake Balaton is a large, shallow, and calcareous lake that was subject to a rapid eutrophication during the 1970s. Management measures taken from the mid-1980s decreased the phosphorus load to the lake from 0.5 to 0.3 g P m-2 yr-1. Using long-term load and water quality data, we analyse the response of the formerly hypertrophic Basin 1 of the lake by the means of simple empirical models. Several factors that are commonly neglected during studies of lake recovery modified the apparent settling velocity of total P and consequently, the biomass of the phytoplankton. These factors included the loads of calcium and suspended solids, the loading ratio of the dissolved to particulate phosphorus, and blooming of the dominant cyanobacterium, Cylindrospermopsis raciborskii. Due to the rapid immobilisation of the mobile phosphorus in the surface sediments, moderate reduction (45-50%) in the external load resulted in a surprisingly fast and significant improvement of the water quality in the hypertrophic southwestern basins of the lake.

Water resources management in the face of climatic/hydrologic uncertainties

The text is the first international and comprehensive discussion of the impacts of climatic fluctuations and climate change on water resources management. The book presents an overview of the impacts of climatic change and fluctuations on a wide variety of water resources sectors including river runoff, water quality, water temperature, water use and demand, reservoir management, and water resources planning and management. The book is unique in that it then presents a series of case studies to both demonstrate the application of climate change impact assessment methodologies and to provide insights into catchment-, river basin-, national-scale impacts of climate change and fluctuations on the water resources of Africa, Europe, and North America.

Cyanobacteria-mediated internal eutrophication in shallow Lake Balaton after load reduction

Nutrient loads to large, shallow Lake Balaton have been reduced by 45-50% since mid-1980s. While a delayed, but still surprisingly fast recovery was observed in the hypertrophic western areas of the lake, eutrophication followed sewage diversion from the mesotrophic northern basins. We assessed factors that could lead to this unusual response. The prime reason of the observed biomass increase might be a trend of increasing mean water temperature during late summers and the concurrent invasion of the subtropical cyanobacterium, Cylindrospermopsis raciborskii with superior light and nutrient utilisation capabilities. In the mesotrophic areas, the prerequisite of the unforeseen success of C. raciborskii was the exceptionally high potential of this species to generate internal P load. Specific morphometric features of the lake rather than nutrient loads might substantiate the increasing dominance of the cyanobacterium in these areas. Our results stress the need to consider individual characteristics of aquatic ecosystems during eutrophication management.

Water-Quality Modelling: A Comparison of Transport-Oriented and Ecology-Oriented Approaches

In water-quality modelling several different directions can be distinguished according to the strategy employed and the disciplinary background used for analysis. A precise classification would be difficult to make, but the manifest difference between transport-oriented and ecology-oriented water-quality models creates at least two obvious groups. In the first case, the description of biological and chemical processes is oversimplified, while in the second, the same applies to transport phenomena. Both approaches determine the level of involvement of the respectively less emphasised phenomena by a priori assumptions. This paper discusses this apparent gap and how to overcome it. No overall procedure is given; instead, a framework is suggested which is based on establishing the relative importances of the various subprocesses determining water quality and proceeding to the corresponding model structure. This should allow the proper combination of knowledge gained from theory and observations, and, furthermore, the elaboration of essential modelling steps such as parameter estimation and model identification. To illustrate, two examples are presented—one concerns heavy-metal pollution of a river, the second involves a lake for which the wind-induced interaction between water and sediment was analysed. In the first situation, a one-dimensional, coupled hydrodynamic-transport-water-quality model for three cadmium compartments was adopted. For the second problem, it was necessary to determine the unknown boundary condition at the lake bottom. This latter was achieved by simplifying the governing transport equation into an ordinary differential equation and introducing some simplifying hypotheses. Given data from regular, intensive observations, the calibration, identification and validation of this model were carried out using the extended Kalman filtering technique.

Modelling a complex environmental system: The lake Balaton study

Abstract A systems approach is introduced into eutrophication modelling and is illustrated by the example of Lake Balaton, Hungary, one of the worlds largest shallow lakes. One of the major features of the problem is its complexity. Many interrelated processes should be considered in the lake and in the corresponding watershed, both on the level of scientific understanding and policy making. The other essential feature is the presence of various kinds of uncertainties. The approach developed is off-line in character, which avoids the direct coupling of the detailed descriptions of all the subprocesses. The procedure starts with the decomposition of the entire model into smaller, tractable units, forming a hierarchial system. This step is followed by aggregation, the aim of which is to preserve and integrate only essentials in the higher stratum. The various levels involve the modelling of biological phenomena, the sediment-water interaction, hydrodynamic and transport processes and the nutrient loads, with the corresponding calibration and validation steps. The approach accounts also for the influence of natural and man-made influences, as well as for the propagation of uncertainties. The procedure can lead to a realistic but yet simple model on the higher level of the hierarchy, where an optimization problem should be solved (e.g., how the maximum water quality improvement can be achieved under given budget constraints). The various steps of the study are illustrated by examples.

Sediment and Its Interaction with Water

Lakes act as the dustbins of their watersheds. Major fractions of materials washed out of the soil or discharged to the rivers feeding a lake accumulate in the sediments, including undesirable substances, such as insecticides used in agriculture, lead from gasoline and washed off the streets, and nutrients discharged in agricultural, domestic, and industrial wastewater. Together with natural substances, such as organic decay products, silt, clay, sand, and salts, these substances form a complex mixture that settles on the lake bottom. During their transport in the watershed and residence in the lake and its sediment many physical, chemical, and biological transformations may change the amount and physicochemical nature of these compounds over varying time scales. Hence the lake sediments reflect the history of the watershed and the natural and cultural events over long periods of time.

Operation of the Kis-Balaton reservoir: evaluation of nutrient removal rates

As one of the major measures for controlling the man-made eutrophication of Lake Balaton, the Hidvég reservoir of 20 km2 surface area was built near the mouth of River Zala, draining half the watershed of the lake, and representing the largest nutrient source for the lake. The reservoir, as the first element of the expected total system of 70 km2 surface area (Kis-Balaton Control System), started to operate in June 1985, aiming at removing nutrients primarily through sedimentation, adsorption and uptake by macrophytes.Detailed investigations began with the operation. These cover the observation of upstream and downstream nutrient loads and the water quality in the reservoir, the study of major phosphorus removal processes, and analysis of the nitrogen cycle and of the behaviour of phytoplankton, zooplankton, fish and macrophytes. The research programme is completed by the evaluation of observations (including the use of phosphorus budget models), with special emphasis on future operation modes of the reservoir.The nutrient removal efficiencies in the reservoir came up to expectations. The removal rates for suspended solids, total-P, soluble reactive-P and nitrate-N exceeded 50 % in the first full year of operation (1986). As a result of reservoir operation, nutrient loads in the western basin of Lake Balaton have been significantly reduced. However, the improvement in water quality can be expected only with a lag time due to the internal P load of the basin.