Specific absorption coefficient and the phytoplankton package effect in Lake Taihu, China

In order to investigate variations of absorption and total chlorophyll-a (TChl-a)-specific absorption coefficient of phytoplankton in Lake Taihu, 57 water samples obtained from Lake Taihu during November 8-22, 2007 were used in this study. Package effect and accessory pigments' influences on the absorption spectra were also examined. Phytoplankton absorption was measured by quality filter technical, and TChl-a concentration was measured by hot ethanol method. Results yielded significant variations in phytoplankton absorption and TChl-a-specific absorption coefficient. Phytoplankton absorption coefficient at 675 nm is highly correlated to TChl-a concentration, while absorption at 440 nm is less correlated to TChl-a concentration because of great package effect and accessory pigments' influence. There was an inverse relationship between a (ph)*(lambda) and TChl-a concentration. Four types of absorption spectra are identified by normalizing a (ph)*(lambda) to a (ph)*(440). The a (ph)*(lambda) variation is mainly due to accessory pigments and package effect, whose influence at 675 nm ranges from 83.2% to 28%, with an average of 65.3%. Meanwhile, the wide varying ratio of a (ph)*(440) to a (ph)*(675) indicates a large variation range in the ratio of accessory pigment to TChl-a concentration. Those findings are significant to estimate Chl-a concentration based on bio-optical model, estimate primary production from remote sensing, and plan further ecological restoration measures for Lake Taihu.