Modeling mussel bed influence on fine sediment dynamics on a Wadden Sea intertidal flat

Mussel beds are coherent colonies of mussels and are widespread in the Dutch Wadden Sea and the Eastern Scheldt estuary. Mussel beds are known to be an important factor in biogeomorphological processes, primarily because of the influence on fine sediment dynamics. Ongoing research to explore the use of mussels as bio-tools makes predictive modeling desirable. In this study a process-based model of the interaction between a young mussel bed and fine sediment was set up for use in Delft3D-FLOW. The model encompasses the hydraulic roughness of the mussel bed, active capture of suspended sediment by filter feeding and changed properties of sediment inside the mussel bed to account for the presence of biodeposited matter. The mussel bed implementation in Delft3D-FLOW was tested in a Wadden Sea intertidal mudflat model. Two current dominated summer months were simulated. The effects of different patterns, known to occur in young mussel beds, were evaluated. It was concluded that roughness and filtration rate of mussel beds are important factors in mussel bed influence on fine sediment. A combination of active deposition via filtration and slow down of the flow due to increased roughness leads to high net deposition in the mussel bed. In addition, the ability of young mussels to quickly climb on top of deposited material results in rapid trapping of large amounts of fine sediment. In the wakes of the mussel bed deposition is also high because of reduced flow velocities. Patchiness and specifically striped patterns cause mussel beds to experience less sedimentation than uniformly covered beds of the same size.