The future of the Wadden Sea sediment fluxes: still keeping pace with sea level rise?

In the light of regional relative sea level rise due to global sea level rise, postglacial rebounce, polder drainage and gas exploitation in the Wadden Sea, a mean rise of the Wadden Sea bottom due to net sediment flux into the Wadden Sea is believed to be the only process counteracting future drowning of the intertidal areas in the Wadden Sea. This process has been largely balancing the sea level rise in recent centuries, and it is a major societal concern, if its efficiency will remain strong enough under possibly accelerated climate change.

The processes driving sediment accumulation in the Wadden Sea are highly complex. The susceptibility of Wadden Sea sediment fluxes to climate change depends on a variety of factors. The major physical factors are changed net precipitation patterns (with impacts on estuarine circulation) and changed wind patterns (with impacts on wave stirring and sediment transport). Other important mechanisms are changed functions and distributions of benthic filter feeders, also due to invasions of new species. Biogeochemical processes further modulate fluxes of cohesive sediments (aggregation and bio-stabilisation). Accompanying shifts in water turbidity will have ecosystem wide effects.

We have therefore proposed to systematically investigate the susceptibility of sediment accumulation in the Wadden Sea to changed external forcing by merging available data, and knowledge (guiding hypotheses) and by developing a comprehensive physical, geological, ecological and biogeochemical model for the entire Wadden Sea area. The integrated model system will quantitatively reproduce the major processes driving sediment accumulation in the Wadden Sea.

To carry out this study, a consortium of seven institutes from The Netherlands, Germany and Denmark had been established.

A Wadden Sea numerical model system carefully calibrated to observational data sets of sediment concentrations and other key parameters has been set up. The system consists of various models (e.g. GETM, Delft3D) which interact which each other on a modular basis, coupling abiotic processes to biotic processes.