This paper presents the formulation, structure, and governing equations of an ecosystem model developed for the Scheldt estuary and the tidal river network. The model has twelve state variables: nitrate, ammonium, phosphate, dissolved silica, freshwater and marine phytoplankton (chlorophytes and diatoms), freshwater zooplankton (ciliates, rotifers, and copepods), and benthic detritus. The ecological model is coupled to the 1-D tidal resolving version of the Second-generation Louvain-la-neuve ice-ocean Model (SLIM) (http://www.climate.be/SLIM). The model successfully simulates the observed longitudinal and seasonal variation of plankton in the Scheldt estuary. The phytoplankton production in the estuary is governed by temperature, underwater available light, turbidity, nutrients, and discharge. Of all these factors, discharge seems to be dominant. High discharge increases the turbidity in the water column and thus reduces the underwater light, while low discharge means decreased nutrients. The marine phytoplankton species were present as far to the upstream limits of the brackish waters, with diatoms dominating in the spring and chlorophytes in early summer. The freshwater phytoplankton are seen from late spring to summer. Freshwater zooplankton followed the evolution of freshwater phytoplankton. |
