Parameterization of chlorophyll a-specific absorption coefficients and effects of their variations in a highly eutrophic lake: a case study at Lake Kasumigaura, Japan

Abstract

The chlorophyll a-specific absorption coefficient ($a_{\text{ph}}^{*} \left( \lambda \right)$) in a highly eutrophic lake can show characteristics distinct from that in the ocean due to the differences in the structure and composition of phytoplankton. In this study, investigated the variation of $a_{\text{ph}}^{*} \left( \lambda \right)$ in Lake Kasumigaura, a highly eutrophic lake in Japan, in association with the package effect and the effect of accessory pigments, and carried out the parameterization of $a_{\text{ph}}^{*} \left( \lambda \right)$. Although $a_{\text{ph}}^{*} \left( \lambda \right)$ did not vary spatially, it did show significant temporal variation, with a particularly high value after spring-bloom. This high $a_{\text{ph}}^{*} \left( \lambda \right)$ in spring was attributed to a lower package effect and a higher proportion of carotenoid than the other samples. Although the value of $a_{\text{ph}}^{*} \left( \lambda \right)$ was correlated with the concentration of chlorophyll-a (Chl-a), the correlation coefficient was lower than those reported in the ocean. Some lake-water samples showed variations of the package effect and the effect of accessory pigments that were independent of the concentration of Chl-a, and these independent variations resulted in the weak correlation between $a_{\text{ph}}^{*} \left( \lambda \right)$ and the concentration of Chl-a. Together, these results suggest that the factors controlling $a_{\text{ph}}^{*} \left( \lambda \right)$ in highly eutrophic lakes are distinct from that in ocean samples.