Response of the Eastern Scheldt ecosystem to a changing environment: Functional or adaptive?

Abstract

A storm-surge barrier situated at the mouth of the Eastern Scheldt (Oosterschelde) estuary (S.W. Netherlands) and two secondary dams in the northern and eastern parts of the estuary were completed by 1987. The exchange between the Eastern Scheldt and the North Sea, the freshwater discharges into the estuary and the flow velocities decreased.

The results of an extensive ecological research programme in the Eastern Scheldt before and during the building of the storm-surge barrier were integrated into a dynamical ecosystem model. With this simulation model, the carbon and nutrient fluxes between the most dominant functional groups of the Eastern Scheldt ecosystem could be quantified.

Subsequent research (after completion of the storm-surge barrier) allowed a quantification of the impact of the engineering works on the ecosystem of the Eastern Scheldt, and therefore the ecosystem model was calibrated for the pre- and post-barrier periods.

Both calibrations resulted in a set of parameter vectors. Each set reflects the uncertainty in the calibration result for the variables and the period for which the model was calibrated. Results of the calibrations are compared with respect to the carbon flows of the ecosystem. By definition, adaptive responses take place within the functional groups of the model, while functional responses occur between the functional groups of the model. The simulation model is used to test whether the ecosystem response to the changing environment is functional or adaptive. It is shown that while the modelled ecosystem is superficially unchanged, adaptive responses still take place within the functional groups of phytoplankton and (probably) zooplankton.