Modelling the biogeochemistry of a tidal flat ecosystem with EcoTiM

The ecological tidal model simulates the cycling of carbon, nitrogen, phosphate, and silicate and describes the tidal, diurnal, and annual dynamics of the back barrier area of the island Spiekeroog in the German Bight. The region is characterized by strong tidal currents and extensive tidal flats. It is strongly influenced by the conditions in the southern part of the German Bight. This model study investigates the dependence of the model behavior on the boundary conditions and the forcing. The effect of short- and long-term sea level rise on nutrient and plankton dynamics is analyzed. As the model is set up as semi-Lagrangian with only a coarse approximation of the hydrodynamics, the seasonal and intratidal variability in the biogeochemical cycling can only be reproduced qualitatively. By varying the boundary conditions, the intrinsic dynamics of the back barrier area can be separated from boundary condition effects. This study shows that any agreement between model results and field data cannot be expected without correct boundary conditions. The seasonal variability is of major importance, while higher-frequency variability only plays a minor role.