Hydrophysical and Ecological Models of Shallow Lakes and Reservoirs: A Summary Report of an IIASA Workshop

An important subtask within the Resources and Environment Area (REN) of the International Institute for Applied Systems Analysis (IIASA) is the development and application of models for environmental quality control and management. The initial objectives of this task are to assess existing models, to develop improved hydrophysical and ecological models as tools for the analysis of water quality problems, and to apply these models to lakes, reservoirs, and river systems. On September 13-16, 1977, a workshop on the general aspects of water quality modeling (IIASA CP-78-10) was held at IIASA. The most recent theoretical developments in the field of Water Quality were discussed at this meeting. At the same time the application of hydrophysical and ecological models to various water bodies was considered. As a result of this workshop it was decided that attention should be focussed on the water quality problems of natural lakes and man-made impoundments (reservoirs). In addition, it was felt that IIASA could make an important contribution to the use of models for water quality control and management purposes by attempting to bridge the gap between the hydrophysical and ecological modeling disciplines. Accordingly, it was decided to convene two specialized workshops. The first of these was on Hydrophysical and Ecological Modelling of Deep Lakes and Reservoirs (IIASA CP-78-7) held on December 12-15, 1977, in Laxenburg. The second of these was on hydrological and ecological modeling of shallow lakes and reservoirs, and was held on April 11-14, 1978, in Laxenburg. The subject of deep lakes and reservoirs chosen for the December workshop implies a basic concern with stratification and interactions at the free surface boundary rather than with conditions of full vertical mixing and bottom sediment interactions. The subject of shallow lakes and reservoirs chosen for the April workshop implies a basic concern with the condition of full vertical mixing and bottom sediment interactions. This report summarizes the results of this second workshop, which was attended by 28 people representing 14 countries and by 13 IIASA staff members from 5 countries. Prior to the workshop, a set of questions related to ecological and hydrophysical modeling problems were formulated by the IIASA staff and sent to the participants with the request to indicate on which questions they would like to give a short presentation as a start to the discussion of the questions. Topics discussed at the workshop included: -- Characteristic Features of Shallow Lakes and Reservoirs: influence of wind and wave action, longitudinal and vertical mass transport processes, exchange of nutrients between the water body and the sediments, influence of sediment types on the transformation processes of chemical compounds -- Hydrophysical Models: horizontal and vertical transport and diffusion processes, interaction across the water/sediment interface -- Ecological Models: evaluation of available data by simple models, sensitivity analysis, improvement in the quantity of data, further development of ecological models of shallow lakes taking into account the binding and mobilization of nutrients in the sediments -- Water Quality Models: limiting nutrients/carbon, nitrogen, phosphorus, element-cycle models/simple and complex models -- Field Data Collection and Model Verification Techniques: coordination of chemical and biological field measurements with water quality models, choice of parameters -- Possible Case Studies These discussions are summarized in the Introduction. In addition, some of the participants presented original papers at the discussion of the ecological and hydrophysical questions. These papers are included in the second part of this Proceedings following the Discussion. It should be noted that a paper by H.A. Tsvetova on Numerical Modeling of the Dynamics of Lake Baikal was presented at the workshop. It is not included in these proceedings but will be published separately in IIASA's Professional Paper Series. The paper was originally intended for presentation at the workshop on Hydrophysical and Ecological Modelling of Deep Lakes and Reservoirs. This workshop was an excellent opportunity for experienced modelers from both the ecological and hydrophysical areas to come together for a discussion of problems of mutual interest and to exchange ideas and viewpoints