ECOLOGICAL MODELING IN COASTAL WATERS - TOWARDS PREDICTIVE PHYSICAL-CHEMICAL-BIOLOGICAL SIMULATION-MODELS

A simple, but general, simulation model is specified according to the state-of-the-art within phytoplankton modelling: Process representatio ns are based upon prevailing theoretical and empirical representations given in the literature, and a set of earlier published values of mod el coefficients that have demonstrated good fit to reliable observatio ns was selected. The emerging phytoplankton model was then validated a gainst data obtained from enclosure experiments with light-, N-, P- an d Si-limitations. We applied no tuning of the coefficients as the purp ose of this test was to estimate the predictive power of the proposed model. The general standard deviations between model predictions and o bservations were on the range 0.04-0.36 and 0.13-0.42 for the nutrient and phytoplankton state variables respectively. Not surprisingly, the se values are higher than those obtained in tuned simulations. Neverth eless, several characteristics, such as the balance between diatoms an d flagellates, were predicted by the model. The phytoplankton model wa s set up and driven by a 3-dimensional physical model for the North Se a. The period February-June 1988 was simulated and forced with realist ic topography, meteorological data, riverine freshwater and nutrient i nput. Simulated developments in nutrients, diatoms and flagellates are presented with references to actual observations and the Chrysochromu lina polylepis bloom in 1988. Several important characteristics, such as the timing of two diatom blooms in March and April and one flagella te bloom in May together with vertical and horizontal distributions of nutrients, were simulated without tuning of the model to the actual o bservations. The present simulations support the general idea that fla gellates in the coastal areas of the North Sea are stimulated by anthr opogenic nutrients, but more specifically that a strong flagellate blo om in the Kattegat-Skagerrak area, corresponding to the C. polylepis b loom, was stimulated by such nutrients in May 1988. Although the model should be improved before it is applied in a management context, the great potential of using such models in environmental management is de monstrated.