Forty years of a salt marsh formation in the Wadden Sea: surface elevation, sediments, vegetation and bottom fauna

Abstract

In order to counteract heavy foreland losses in the lower reaches of the Weser estuary, a system of sedimentation fields surrounded by brushwood groynes was constructed in 1958. Over the next forty years, the land accretion process was monitored by surveys of bottom-surface elevation, sedimentology, development of vegetation cover and changes in bottom-fauna composition. From the viewpoint of coastal protection, the sedimentation fields achieved a continuous growth of half a metre within forty years and successfully reduced the regression of the eroding shoreline. The ecological results represent a documentation comprising all succession stages from a bare tidal flat to a vegetated salt marsh. However, though the larger parts of the fields had already exceeded mean high-water level at the final survey of 1997, aquatic elements were still present in the vegetation as well as in the bottom fauna. The lack of a seaward inclination was most likely the reason, why saline water from spring tides and storm surges remained enriched in the soil. With growing elevation and condensing vegetation, each of the fields had developed a branched creek system and a varied geomorphological relief. Their habitat and species diversity proved to be equal to naturally grown mainland salt marshes.