2025 Volume 45 Issue 1 Pages 12-28
In recent years, excessive overgrowth of floating aquatic plants has become an issue in a number of inland lakes in Japan. However, the relationship between this overgrowth and meteorological and water quality factors remains unclear. In this study, we used PlanetScope, which is provided by a commercial optical satellite constellation with high temporal and spatial resolution, to extract the activity level of floating aquatic plants in Lake Inbanuma in Chiba Prefecture and Lake Suwako in Nagano Prefecture, which are representative eutrophic lakes in Japan where floating aquatic plants are overgrown. We conducted correlation and causal analyses using meteorological data from the Japan Meteorological Agency (JMA) and water quality observation data for public water bodies, and examined the relationship between plant overgrowth and the monthly median of the normalized aquatic vegetation index (NDAVI) of floating aquatic plants. The results showed that in both lakes, there was a statistically significant relationship between temperature and the growth of floating aquatic plants, and that dissolved oxygen concentrations decreased when the plants were rooting. In Lake Inbanuma, there was a positive relationship between water quality indicators related to organic matter, such as chemical oxygen demand (COD) and suspended solids (SS), and the growth of floating aquatic plants, but this relationship was not found in Lake Suwako.
