Introduction
The Dynamic Ecosystem Model Oosterschelde (DEMO) is a dynamic simulation model that describes the spatial and temporal nutrient dynamics within the Oosterschelde Ecosystem. The Oosterschelde is a macrotidal basin in the south-west of The Netherlands. The tidal basin is a nature conservation area that is extensively used for mussel and oyster culture. The Oosterschelde is connected to the North Sea by a storm-surge barrier in the west, and water is exchanged between the North Sea and Oosterschelde by tidal currents. Due to the Delta works, there are no rivers discharging into the former estuary anymore. Some freshwater from the Volkerak-Zoommeer is leaking into the Oosterschelde through the Krammersluizen in the north and the Bergse Diepsluis in the east.
Location of the Oosterschelde in the south-western part of the Netherlands
Conceptual model
The model is based on a standard NPZ (Nutrients, Phytoplankton, Zooplankton) model. The model has 9 state variables:
- Dissolved inorganic nitrogen (DIN)
- Phytoplankton (Phyto)
- Zooplankton (Zoo)
- Detritus (Det)
- Mussels (Mus)
- Oysters (Oys)
- Cockles (Coc)
- Microphytobenthos (MPB)
- Bottom detritus (Bot_Det)
Four state variables (DIN, Phyto, Zoo and Det) are present in the water column and 5 state variables (Mus, Coc, Oys, MPB and Bot_Det) are present in the bottom. The units of the state variables of the state variables in the water phase are in mmol-N m-3 and the units of the state variable in the bottom are in mmol-N m-2. The state variables in the water phase are transported by tidal currents.
The state variables influence each other. For example DIN decreases by primary production (DINuptake) which will increase the amount of N in phytoplankton (Phyto). All dependencies are indicated in the following scheme using the labelled arrows. The label of the arrow indicates the process. The color of the labelled arrow corresponds to the color of the state variable from where the arrow originates.
Schematic representation of the DEMO model. State variables (large labels) are DIN (dissolved inorganic nitrogen), Phyto (phytoplankton), Zoo (zooplankton), Det (detritus), Mus (mussels), Coc (cockles), Oys (oysters), MPB (microphytobenthos), Bot_Det (bottom detritus). The processes are indicated by labelled arrows, where the color of the arrow corresponds to the color of the state variable where the arrow originates
The conceptual NPZ model applies for each of the model compartment. Exchange of state variables in the water column is based on a transport model.