Relating erosion shear stress to tidal flat surface colour

Abstract: The relationships between erosion shear stress and bio-geochemical parameters, and between the optical reflectance spectra and bio-geochemical parameters ofdifferent idal fiats were investigated in the North Frisian part of the Wadden Sea. Erosion shear stress shows clear dependencies both on fine-grain fraction <63 #m and on the benthic diatom chlorophyll a concentration present in the uppermost 1mm sediment layer. The strongest dependence of erosion shear stress on the benthic diatom chlorophyll a surface concentra-tion was found for muddy areas. This dependence vanishes for andy surface sediments. The reflectance spectra show two main classes. The first class contains information on the fine-grain fraction <63 #m of areas not covered by phytobenthos. The second class corresponds to the phytobenthos which can be subdivided into benthic diatoms and other macrophytes. A significant correlation was found between reflectance spectra and the amount of the fine-grain fraction <63 #m present and also between reflectance spectra and he benthic diatom chlorophyll a concentration. Thus, erosion shear stress can be related to tidal flat surface colour yielding a basis to map the erodibility of tidal fiats using optical remote sensing. Change in seabed morphology is regarded as one of the most critical issues for the development of coastal areas. Movements of seabed structures, changes in the average water depth, steady loss of bed material or changes in its composition have significant consequences for coastal protec-tion measures and ecosystem properties. Recen