A fine-grained sediment budget for a small tidal area, Königshafen, Sylt, Germany

A net budget for fine-grained sediment (<63 μm) has been computed for the Königshafen tidal area; a small tidal bay covering an area of some 4 km², located in the Wadden Sea at the north-eastern end of Sylt. The net budget for fine-grained sediment has been separated into the following sediment sources: (1) Supply from the North Sea, (2) Salt marsh erosion, (3) biological primary production and (4) atmospheric deposition. The total net accumulation within the area has been calculated by geomorphological mapping combined with estimates of fine-grained accumulation rates determined from ²¹⁰Pb core dating. The net accumulation was calculated to 1400 t/y based on ²¹⁰Pb dating. The salt marsh erosion is measured to supply 16% of this sediment, and from literature studies primary production and atmospheric deposition are estimated to supply 7% and 1%, respectively. The remaining 76% between the three above mentioned sediment sources and the total net accumulation originates from the North Sea and from fluvial input to the adjacent tidal area. A minimum of 70% of the total supply of fine-grained sediment accuinitiated in Königshafen originates from the North Sea. It is shown that on a yearly basis an average of 0.5 g/m³ is filtered out of the water exchanged between Königshafen and the North Sea. Although this is a small quantity compared to other tidal areas, the trapping efficiency is shown to be relatively high compared to other areas. It is suggested that this difference may be explained by the influence of benthic organisms on the aggregation of fine-grained suspended sediment.