Modelling the ecosystem dynamics and nutrient cycling of the Spiekeroog back barrier system with a coupled Euler–Lagrange model on the base of ERSEM

The here presented model EcoTiM (Ecological Tidal Model) simulates the cycling of carbon, nitrogen, phosphate, and silicate and describes the tidal, diurnal, and annual dynamics within the back barrier system of the East Frisian island Spiekeroog. The movement of the water has been realized by a Lagrangian approach. Finite water bodies move along a pre-calculated velocity field, each one representing a mesocosm, described by the pelagic part of the ERSEM ecosystem model. The consideration of finite water bodies allows the mass conserving coupling of the pelagic part of the model to the sediment model. The simulation studies demonstrate that the model reflects the observed characteristics of the real system as the diurnal tidal, and annual cycles of nutrients. The model also allows a budgeting of the net annual primary production which is in good accordance with observations in other shallow regions. The sensitivity analysis shows that the impact of the input from the floodgate into the Wadden Sea system plays a minor role, the system is mainly determined by the boundary conditions of the North Sea.