Parameterization of chlorophyll-specific phytoplankton absorption coefficients for productive lake waters

We examined and parameterized chlorophyll-specific phytoplankton absorption coefficients (a^*_ph(λ)) for three turbid productive Estonian lakes on the basis of bio-optical measurements in 2005-2013. A new model parameterization was created that enables to reconstruct the spectra of a^*_ph(λ) for turbid productive waters with the higher reliability than previous parameterizations for ocean and coastal waters. The coefficients A(λ) and B(λ) of our model differ from those found in seas, coastal waters and other types of lakes. For any water type separately the increase of total chlorophyll concentration accompanied with the decrease of a^*_ph. Our results showed significant seasonal differences between the model parameters due to diversity of the phytoplankton assemblages. This suggests that season-specific models should be developed and validated. Improving the modelling of chlorophyll-specific phytoplankton absorption spectra for hypertrophic lakes is still pending on the availability of a larger dataset, which includes simultaneous measurements of chlorophyll concentrations, phytoplankton absorption coefficients and phytoplankton species composition. Our results implied that total chlorophyll concentration is not a universal predictor of the magnitude of chlorophyll-specific phytoplankton absorption coefficient. The a_ph(λ) models are also likely site and season dependent. Further research is needed for quantifying the role of accessory pigments and other optical constituents as well as the cell size of dominant algal species for considering their influence on the modelling outputs.