MATHEMATICAL-MODELING AS A TOOL FOR MANAGEMENT IN EUTROPHICATION CONTROL OF SHALLOW LAKES

The eutrophication model DELWAQ-BLOOM-SWITCH is developed to be a func tional tool for water management. Therefore it includes nutrients, alg al biomass and composition as well as water transparency. A module des cribing the interaction between water and bottom gives the model the f lexibility to deal with measures, such as a decrease of the external p hosphorus loading and flushing with water differing in composition fro m the lake water. This paper focuses on the functional aspects of the model, the results of an application on Lake Veluwe, The Netherlands, and the implications for water management. With one set of coefficient s DBS reproduces the most important characteristics of Lake Veluwe for a period of two years before measures (reduction of the external load ing and flushing during the winter months) and eight years after the m easures. The phosphorus concentration decreased and became growth limi ting for algae instead of nitrogen and light. Both in measurements and modelling results, the algal composition changed from blue-green alga e dominance to green algae and diatom dominance. Lake Veluwe had a rel atively short transient phase after reduction of external loading, bec ause high nitrate concentrations in the flushing water inhibited a lon g period with high phosphorus releases from the bottom. Model calculat ions were carried out to investigate the effects of fish stock managem ent and optimization of flushing. Both measures are promising.