A Simulation Model for Phytoplankton Growth and Nutrient Cycling in Eutrophic, Shallow Lakes

Abstract A simulation model has been developed for phytoplankton growth and phosphorus and nitrogen cycling in eutrophic, shallow lakes. The model describes a seasonal cycle in a lake which, on a 1-year time scale, is assumed to be in equilibrium with respect to the inputs of nutrients, and forecasts made using the model of the effects of altered inputs predict new future equilibria. The model is rather simple and oriented towards practical applications. It is intended to describe average conditions only and the time scale resolution is of the order of several days. The model has been used to simulate 12 different lakes in Denmark, some of which have been described by two or more boxes. Most parameter values in the model were common to all simulations, while a few key parameters were allowed to vary somewhat from lake to lake. These parameters, however, could generally be chosen within quite a narrow range and if deviations from this range were necessary a qualitative explanation could usually be given. For lakes with short hydraulic retention times the simulations generally gave reasonably good results, and forecasts made with the model were in qualitative agreement with “educated guesses”. The paper describes the concepts and the structure of the model. Further, parameter values and selected numerical results, such as annual primary production, are listed for all simulations performed. Finally, a few examples are discussed in more detail.

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