Dissolved and suspended matter variability in coastal waters: photosynthetic available light

To assess an effect of optically active components (OAC) on water transparency and the spectral features of downwelling irradiance (E-d (lambda)) in coastal waters several scenarios have been simulated: blooms of planktonic microalgae (with the exception of coccolithophore blooms), resuspension of sediments, incoming of suspended and dissolved organic matter with river/coastal run off. General and specific effects of OAC variability on (E-d (lambda) have been revealed. The general effects are: the OAC increase resulted in decrease of water transparency and narrowing of euphotic layer, which in turn led to decreasing in photosynthetic available radiation (PAR) averaged within the mixed layer from the surface down to the bottom altering the light condition of plankton and benthic algae. Specific effects caused by the differences in the shape of light absorption coefficient spectrum of the OAC are: in the scale of optical depths, the spectral features of (E-d (lambda) varied depending on the relative content of OAC; shift of penetrating irradiance to the longer wavelengths was amplified from phytoplankton to non-algal particles, to colored dissolved organic matter. Values of chlorophyll a concentration and K-d at particular wavelength or spectrally average K-d are not sufficient for correct assessment of underwater light. An additional indicator characterizing the ratio between OAC is required.