Hypoxia over the Past Two Decades in the Ariake Sea

Dissolved oxygen (DO) plays a critical role in the marine ecosystem. However, in recent years, there have been reports from around the world of declining levels of DO, primarily occurring in the summer and caused by increased freshwater and nutrient input. Climate change has been causing an increase in both the duration and extent of precipitation, resulting in a substantial influx of effluents that has emerged as a primary contributor to the deterioration of water quality. In this study, A long-term pattern of hypoxia (from 2001 to 2020) in the Ariake Sea is described using a hydrodynamic model and a lower-trophic ecosystem model by Delft3D-Flow module and Delft3D-WAQ module. The freshwater inflow during the rainy season in the early summer is also evaluated to identify its relationship to the development of hypoxia and its effect at the interannual scales. From 2001 to 2020, there has been a significant increase in the area of hypoxia at the bottom sea layer after the summer effluent, indicating an upward trend that is positively correlated with the volume of effluent (R=0.67).