Geo-Environment Science

In the water environment evaluation of a eutrophic water body, it is important to conduct it from the viewpoint of seasonal change and how that affects the quantity and kind of algae in addition to its gross weight. In this study, consecutive observation of the Chl.alpha density according to the algae class was conducted, and the change of characteristics was examined by wavelet analysis. In this research, for In Vivo Chl.a, which is divided into blue-green algae, green algae, dinoflagellate genus/diatoms, and cryptophyte algae, total Chl.a and water temperature were measured by multiwavelength excitation spectrofluorometer (FluoroProbe). Additionally, the surface water was sampled about once a week, and algae were identified to the genus level with an optical microscope. Based on this observation, a lot of blue-green algae exist in the intended reservoir in summer, and as blue-green algae decreased, dinoflagellate genus/diatoms and cryptophyte algae also decreased. In the fluctuation component of the Chl.a density in each algae class, a slow frequency component from a few days to a week accelerated, and there was the contribution of a frequency component of about 1.2 × 10^(-5) (circadian rhythm) locally. The Chl.a density increased when the contribution of the fluctuation component of this circadian rhythm was high in all four kinds of algae. Furthermore, to examine the relevance between a change in the Chl.a density and the environmental factor, a cross-correlation coefficient of each Chl.a density for water temperature and amount of solar radiation was evaluated. As a result, because the correlation between each Chl.a density and the environmental factor could not be found, their fluctuation components were focused on, and the cross-correlation of the wavelet component interval for 24 hours was examined for both. In this way, good cross-correlation was accepted for blue-green algae and green algae, which should be considered mainly a result of eutrophication. From these, good responsiveness could be found by paying attention to the fluctuation component of a circadian rhythm when relevance of the quantity of the outbreak of algae and the environmental factor were examined.