Correlation of a lake eutrophication model to field experiments

Abstract

A vertical box interaction model is applied to a bay of the highly eutrophic Lake Lugano on the Italian-Swiss border, in order to interprete the experimental framework developed by sampling activity and field research during 1981. This bay receives the greatest part of the effluent put into Lake Lugano, after passing through a waste water treatment plant and being discharged into the bay through one of its tributaries. Particular attention is devoted to the phosphorus cycle in the epilimnion during summer stratification, and to the role played by the organic phosphorus components (dissolved and particulate) in the regeneration process. In fact the operation of the waste water treatment plant has increased the concentration significance of the organic dissolved phosphorus form in the bay, raising the problem of its biological availability. The procedure consists of assessing the transfer coefficients among the various phosphorus forms by means of comparisons between calculated evolution and measured average summer value of the related epilimnetic concentrations. The proposed correlation allows an evaluation of the mean residence time of phosphorus in the various compartments and the total phosphorus turnover time in the ecosystem. A predictive use of the model simulating a reduction of phosphorus loading is also presented.