2021 Volume 41 Issue 5 Pages 563-574
In the south basin of Lake Biwa, some environmental changes have currently become social issues, such as the occurrence of cyanobacterial bloom, the inflow of muddy or turbid water, and the overgrowth of submerged aquatic vegetation (SAV). Since such changes in ecosystems are highly dependent on meteorological conditions and often occur locally, unexpectedly, or intermittently, they can be difficult to detect by means of the current frequency and effort of water quality monitoring and biological surveys. Consequently, it hinders the progress of analysis of factors that cause the ecosystem changes. In this study, we set a fixed point and time-lapse camera on the roof of a lakeside building and investigated how the camera captured the ecosystem changes during April to December 2018. The camera detected the changes of weather, the occurrence of phytoplankton blooms, muddy or turbid water inflows, and the growth and decline of SAV. We found the peak of Red Ratio (RR) of the RGB was consistent with the muddy or turbid water of the photograph, and Green Ratio (GR) of the RGB tended to be high in response to the occurrence of phytoplankton blooms. In addition, the GR of SAV showed constant, and was significantly lower than that of phytoplankton blooms in the water. Thus, the time-lapse process of muddy water inflow immediately after torrential rain can be captured more clearly by mapping with RR, and the SAV cover can be shown with GR.
