Modelling nitrate and ammonium uptake by phytoplankton. Influence of the formulation in an ecosystem model
1998
Andersen, V. (Station zoologique, Villefranche-sur-Mer (France). Observatoire oceanologique) | Heibig, A.
We examine the response and behaviour of an ecosystem model subjected to five different formulations proposed in the literature for expressing nitrate and ammonium uptake by phytoplankton. The formulations all take into account the inhibition of nitrate uptake in the presence of ammonium. Eight state variables are considered in the model, developed for an enclosed water column with selective nutrient additions. The results of 70-day simulations of food web dynamics show that the results of the five formulations differ not only in the amplitude of the peaks but also in the number of peaks, their relative importance and their timing. Apparent effects increase with the trophic level. To obtain the same simulated evolution of the ecosystem with the five formulations, the parameter values have to be largely modified from those given by the original authors, and to vary greatly from one formulation to another. These results underline the differences of results between the formulations. They also show that care must be taken in the choice of functions, and corresponding parameter values, used in models of systems with periodic external nutrient inputs.
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