Relating erosion shear stress to tidal flat surface colour

Abstract

Abstract The relationships between erosion shear stress and bio-geochemical parameters, and between the optical reflectance spectra and bio-geochemical parameters of different tidal flats were investigated in the North Frisian part of the Wadden Sea. Erosion shear stress shows clear dependencies both on fine-grain fraction <63 µm and on the benthic diatom chlorophyll a concentration present in the uppermost 1 mm sediment layer. The strongest dependence of erosion shear stress on the benthic diatom chlorophyll a surface concentration was found for muddy areas. This dependence vanishes for sandy surface sediments. The reflectance spectra show two main classes. The first class contains information on the fine-grain fraction <63 µm 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 µm present and also between reflectance spectra and the 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 flats using optical remote sensing.