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.