To understand how to efficiently observe the biomass and community of phytoplankton,
phytoplankton sampling was carried out from June to October 2019 at the Yeongju dam sediment control
reservoir (YJ) and Bohyeonsan dam reservoir (BH1 and BH2). The results derived from microscopic observation,
such as the conventional phytoplankton qualitative/quantitative analysis, and from the CHEMTAX method based
on the pigments, were compared. The relative contribution of phytoplankton, calculated by the microscopy and
CHEMTAX methods, showed a significant difference in all four classes: cryptophyta, chlorophyta, cyanobacteria,
and diatoms. In addition, the correlation between the two observation methods was poor. This might be caused
by methodological differences in microscopy that do not consider the varying cell sizes among phytoplankton
species. In this study, by converting the cells into carbon, the slope between both carbon biomasses based
on microscopy and CHEMTAX was improved close to the 1 : 1 line, and the y-intercept was closer to 0 for
cryptophyta and diatoms. For cyanobacteria, the slope increased, the y-intercept decreased, and the plot
approached 1:1 although the correlation coefficients were not improved in all classes. The present study suggests
that application of CHEMTAX based on pigment analysis could be a possible approach to efficiently determine
the relative carbon proportions of individual classes of phytoplankton community composition.