10:45 AM - 12:15 PM
[ACG42-P11] Mixing and hypoxia influenced by global warming in Lake Kasumigaura
Keywords:stratification, hypoxia, climate change
Recent global warming due to climate change significantly influences lake circulations and ecosystems. Especially in the summer season, stratification is strengthen by increasing in temperature, which results in hypoxia in the bottom boundary layer. It has also reported in Lake Kasumigaura that hypoxic water masses upwelling near the surface by strong winds cause acid deprivation deaths of plants and animals, resulting in severe damage to fishing and aquaculture industries. Investigating effects of global warming is important to solve water environment problems. In this study, we analyzed long-term water quality data between 2005 and 2022 (18 yearlong) observed at the Kamaya Monitoring Station located in Lake Kitaura that is a part of the Lake Kasumigaura system. Water temperature of Lake Kitaura significantly increases with a ratio of approximately 0.04 degrees per year due to global warming. The ratio between surface wind stress and the surface incoming buoyancy flux explains the intensity of stratification. This implies that the wind stress and solar radiation are attributed to mixing conditions. Each summer season was divided into hot summer or cool summer by time averaged air temperature. Hypoxia events tend to frequently occur during the hot summers. The ratio of 42% in the hottest summer season, July, 2018, was occupied by hypoxic events in the bottom layer. In contract, any hypoxic events were not observed in the coolest summer season, July, 2007. Daytime stratification was significantly enhanced in hot summers by comparing with cool summers. Our results suggest that global warming have a significant impact on mixing conditions in shallow lakes.