Dynamics of fine-grained sediments and stratigraphic evolution of a back-barrier tidal basin of the German Wadden Sea (southern North Sea).

Abstract

As a result of land reclamation and dike construction over the last millennium, the size of many Wadden Sea tidal basins has been reduced by as much as 50%. As a consequence, average energy levels along the shoreline have increased and have prevented the formation of natural mud flats and salt marshes along much of the mainland shore. Sediment distribution patterns in the Wadden Sea show a progressive shoreward fining trend in sediment composition and hence in mean grain size, indicating the existance of a shore-normal energy gradient. At the mainland shore, this gradient is abruptly terminated by the dike, finer sediments than about 88 µm lacking appropriate accommodation space for its deposition. As a result, the modern Wadden Sea is largely a sand-dominated depositional system, both in a physical and a biological sense. The reduction in accommodation space for fine-grained sediments has resulted in severe physical and biological disturbances in the remaining backbarrier tidal basins.