Modelling Mesocosm Experiments

In this report, an integrated model including fate of and effects of contaminants on an ecological model is presented. The aim is to simulate the dynamic behaviour of the mesocosm experiments carried out at NERI (see D431-D433) to elucidate the combined effects of nutrients and contaminants at ecosystem level. The outcome of the simulation highlighted some strengths and weaknesses of the methodology. On the one hand it is shown that it is possible to represent the main dynamics observed in a mesocosm experiment over a relatively short time (11 days) with a rather simplified food-web model. This confirms that the model contains the features necessary to represent the system correctly even on a small scale. On the other hand some of the parameters, e.g. the shape of the dose-response curve for phytoplankton and zooplankton, had to be fitted with a very limited amount of experimental data. More research would be necessary to elucidate this part of the model. The difference between the enriched and non enriched communities was not that obvious to represent in the model, since the data NO¯3 + NO¯2 and NH+4 concentrations in the enriched and non-enriched systems are similar.