Mud depocenters in shelf seas serve as a key element in the source-to-sink system of sediment transport on the Earth surface. Despite their undoubtful importance, physical mechanisms for their formation and functioning, sediment budgeting and cycling of localized depocenters remain largely unknown. This study aims to investigate the development of a spatially confined mud depocenter (“Helgoland Mud Area”) in the southern North Sea characterized by energetic hydrodynamics. By combining field observation with 3-dimensional numerical simulations, we analysed hydrodynamics and sediment dynamics over 2012–2014. Our results indicate a persistent transport of fine-grained sediments toward the depocenter and subsequent trapping resulting in accumulation, with distinct seasonal and spatial variations in the net depositional rate. The interaction of wind-driven coastal circulation with two distinct frontal systems—a salinity front and a tidal mixing front—emerges as a key mechanism of sediment dynamics. While the salinity front remains persistently over the HMA, promoting sediment deposition year-round, the tidal mixing front appears primarily in summer, limiting sediment deposition. Sediment inflows particularly from the paleo-Elbe valley and southwest coasts, dominate sediment supply to the HMA, while contemporary Elbe River sediment outflows contribute marginally due to a net landward transport. Southwesterly winds enhancing erosion and northerly winds promoting deposition. Additionally, short-term extreme events significantly contribute to annual net sedimentation. Our work highlights the influence of persistent tidal and wind forcing, sediment sources, and extreme events on mud depocenter development and underscores the need for further research into anthropogenic impacts on future fate of depocenters.

Seagrass meadows fulfil many essential ecological functions of which an important one is to stabilize sediment. Therefore, they are perceived as a nature-based alternative or addition to conventional rigid coastal protection. The magnitude of the impact by seagrass meadows depends on their morphology such as canopy height, stem density and spatial extent. However, deciduous, intertidal seagrass species are often simplified in modelling studies by adopting their annual mean height and density. This can lead to an erroneous estimate of their impact on hydro-morphodynamics and misconceptions about their contribution to coastal protection. Here, we assess the importance of seasonal change of seagrass properties for morphological development of a tidal basin in the Wadden Sea as an exemplary study. We applied numerical modeling to simulate the annual growth cycle of seagrass meadows and their interaction with hydro-morphodynamics. Based on validated seasonal change of seagrass properties by field surveys and comparison between scenarios of seagrass growth, our results show that adopting static seagrass parameters in modeling can lead to over- or underestimation of morphological changes induced by the seagrass meadows and even predict contrary results to simulations considering seasonal change of seagrass properties for the net sediment volume change in the intertidal zone. This points out the essential necessity of considering natural growth and decline cycles of seagrass meadows when assessing their role in coastal protection, especially in temperate zones where seasonal change of seagrass properties is distinct.