ABSTRACT

Phytoplankton pigments in the sediment of Lake Kasumigaura were analyzed by HPLC. The depth profiles of echinenone and myxoxanthophyll, which are characteristic carotenoids of blue-green algae, showed an increase after the lock gate (Hitachigawa-suimon) was constructed 30 years ago to prevent seawater coming into the lake. The depth profile of β-carotene suggests that the algal biomass in the lake decreased 30 years ago, being consistent with the period of the construction of the lock gate, and then increased with the increase of freshwater phytoplankton such as blue-green algae.