Influence of cyanobacterial bloom accumulation and dissipation on underwater light attenuation in a large and shallow lake

Abstract

Cyanobacterial bloom accumulation and dissipation frequently occur in Lake Taihu, a typically shallow, eutrophic lake due to wind wave disturbance. However, knowledge of the driving mechanisms of cyanobacterial blooms on underwater light attenuation is still limited. In this study, we collected a high-frequency in situ monitoring of the wind field, underwater light environment, and surface water quality to elucidate how cyanobacterial bloom accumulation and dissipation affect the variations in underwater light attenuation in the littoral zone of Lake Taihu. Results showed that cyanobacterial blooms significantly increased the diffuse attenuation coefficient of ultraviolet-B (K_d(313)), ultraviolet-A (K_d(340)), and photosynthetically active radiation (K_d(PAR)); the scattering of total suspended matter (b_bp(λ)); and the absorption of phytoplankton (a_ph(λ)) and chromophoric dissolved organic matter (CDOM, a_g(λ)) (p < 0.01). The K_d(PAR) decreased quickly during the processes of bloom dissipation, but the decrease of K_d(313) and K_d(340) lagged 0.5 day. Our results suggested that cyanobacterial blooms could increase particle matters and elevated the production of autochthonous CDOM, resulting in underwater light attenuation increase. Ultraviolet radiation (UVR) and PAR attenuation both have significant responses to cyanobacterial blooms, but the response processes were distinct due to the different changes of particle and dissolved organic matters. Our study unravels the driving mechanisms of cyanobacterial blooms on underwater light attenuation, improving lake ecosystem management and protection.

Keywords: Cyanobacterial blooms; Diffuse attenuation coefficient; Lake Taihu; Photosynthetically active radiation; Ultraviolet.