Unusual links between inherent and apparent optical properties in shallow lakes, the case of Taihu Lake

The spectral distribution of downwelling solar irradiance is an important factor in the radiative balance, primary productivity and biogeochemistry in most lakes. In the present study, we show the relative importance of different inherent and apparent optical properties in controlling the spectral attenuation of diffuse downwelling irradiance in a large shallow lake in eastern China. Most importantly, we show how elevated concentrations of suspended matter not only increase attenuation but are linked to a “spectral shift” in major attenuation peaks, with important consequences on biogeochemical processes and remote sensing. The analysis of the lake optical properties in relation to the geographical distribution of submersed macrophytes indicates how heterogenic optical conditions play a role in controlling benthic primary production.