A basis for mapping the erodibility of tidal flats by optical remote sensing

A means of monitoring surface sediment stability of tidal flats with optica l remote sensing has been developed. Erosion shear stress and corresponding bio-geo-chemical parameters of tidal flats were measured over five years i n the Sylt/Romo Eight, Germany. Ground-based optical reflectance spectra we re measured during one year. A significant dependence of erosion shear stre ss on the benthic diatom chlorophyll a concentration in the uppermost l-mm layer was found for muddy areas but decreased with decreasing proportion of fine particles (< 63 mu m). With a low phytobenthic coverage there was a w eak dependence of erosion shear stress on the proportion of fine particles. There were two main classes of the reflectance spectra: containing informa tion on sediment type i.e. proportion of fine particles, and containing inf ormation on benthic diatoms and other phytobenthic species. There was a sig nificant correlation between the reflectance spectra and proportion of fine particles and also between reflectance spectra and benthic diatom chloroph yll a concentration. Hence, the erodibility of tidal flats can be mapped by optical remote sensing when benthic chlorophyll a concentration and propor tion of fine particles are used for estimation of the erosion shear stress.