Morphodynamic development of intertidal mudflats: consequences for the extension of the pioneer zone

Abstract

During the last two decades erosion of salt marshes has occurred in the Dutch Wadden Sea, mostly starting with a retreat of the pioneer vegetation in front of the marsh. Spatial variations in erosion of the pioneer zone was likely to the wash away processes of seeds and seedlings. During the winter a dramatic loss in seed numbers was found at shore normal transects. This loss increased from the pioneer zone to the intertidal mudflat. On the intertidal mudflat and in the pioneer zone the erodability of the soil was measured with an in situ erosion flume. Erosion of the bed was high at stations located on the intertidal mudflat, where the soil had a relative low mud content. Hydrodynamic measurements carried out at the border of the pioneer zone/intertidal mudflat showed erosion of the bed surface to take place predominantly during a sequence of storm conditions. In these situations bed load transport is expected to be the most important process which determined erosion of the bed. The optimalization of technical measures to prevent increased erosion of the area should be based on reduction of wind-induced waves and the increase of sedimentation of mud. Together these may result in a decrease of the mobility of the bed and facilitate the settlement and survival of the pioneer vegetation.