Spatial clustering and temporal analysis of bio-optical properties in the Wadden Sea

Titelangaben

Moradi, Masoud ; Hommersom, Annelies ; Arabi, Behnaz:
Spatial clustering and temporal analysis of bio-optical properties in the Wadden Sea.
In: Estuarine, Coastal and Shelf Science. Bd. 325 (2025) . - 109488.
ISSN 0272-7714
DOI: https://doi.org/10.1016/j.ecss.2025.109488

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Abstract

The inherent optical properties (IOPs), remote sensing reflectance (Rrs), and optically significant water constituent concentrations (WCCs) were investigated in the optically complex Wadden Sea, the world's largest tidal flat. Field data were collected during four cruises covering the entire study area from 1998 to 2023, at discrete time intervals. These data included the absorption coefficients of three optically significant constituents—phytoplankton pigments (ap(λ), m−1), non-algal particles (aNAP(λ), m−1), and colored dissolved organic matter (aCDOM(λ), m−1)— as well as above-water Rrs(λ) (sr−1), backscattering coefficients (bbp(λ), m−1), total particle absorption (ap(λ), m−1), beam attenuation, chlorophyll-a concentrations (Chla, mg m−3), suspended particulate matter concentrations (SPM, g m−3), and the percentage of organic matter (POM, %). A multivariate spatial clustering analysis of selected IOPs identified six clusters: one representing the North Sea and five representing distinct regions of the Wadden Sea. The results demonstrated significant spatial and temporal variability in all IOPs and Rrs(λ) spectra. Most IOPs spanned two orders of magnitude and exhibited strong co-variations with WCCs. The findings highlighted that mineral and organic particles primarily influenced the Rrs(λ) spectra and backscattering coefficients in the tidal channels and phytoplankton-rich intertidal flats, respectively. The effect of river discharge and tidal patterns on the variabilities of IOPs and WCCs was analyzed in detail. Overall, sediment resuspension, biological activity, tidal cycles, and river runoff were identified as the primary factors driving the variability of IOPs and WCCs across different areas of the Wadden Sea.