11:00 AM - 1:00 PM
[AOS22-P02] The physical impact of the heavy rainfall and freshwater inflow on hypoxia in a semi-enclosed sea
Keywords:heavy rainfall, hypoxic water mass, semi-enclosed sea, coastal sea model, particle tracking
Climate change might increase the scale and frequency of heavy rainfall. Increased heavy rainfall can have a significant impact on the coastal environment, including hypoxia. In this study, we inversely estimated the coefficients of the water balance model for rivers in catchment area using the Green's function and the measured salinity in the bay, in order to obtain freshwater discharge into the bay during heavy rains. Then we investigated the changes in the flow and physical structure of the sea area and the amount of oxygen supplied to the lower layers of the bay during heavy rains.
The flow model (FVCOM) was applied to Nanao Bay, and the model parameters were optimized using the field observation results. Using this model, we reproduced the flow and physical structure during the period before and after the hypoxia was observed in field observations, and we placed the particles in the hypoxic region and conducted the particle tracking. The contribution of each physical factor was investigated by comparing the results with the results of particle tracking excluding the influences of freshwater inflow, wind, tides and their interactions.
Freshwater input often promotes seawater exchange in the bay and oxygen supply to oxygen-depleted lower layer in the bay, where a vertical circulation is developed in which low-salinity water flows out from the upper layer and high-salinity water around the mouth of the bay flows into the lower layer. In the study area, during heavy rains, however, the influence of freshwater inflow alone was not clear. On the other hand, the combined influences of wind and freshwater inflow promoted seawater exchange and possibly impacted on the amount of oxygen supplied to the lower layers.
The flow model (FVCOM) was applied to Nanao Bay, and the model parameters were optimized using the field observation results. Using this model, we reproduced the flow and physical structure during the period before and after the hypoxia was observed in field observations, and we placed the particles in the hypoxic region and conducted the particle tracking. The contribution of each physical factor was investigated by comparing the results with the results of particle tracking excluding the influences of freshwater inflow, wind, tides and their interactions.
Freshwater input often promotes seawater exchange in the bay and oxygen supply to oxygen-depleted lower layer in the bay, where a vertical circulation is developed in which low-salinity water flows out from the upper layer and high-salinity water around the mouth of the bay flows into the lower layer. In the study area, during heavy rains, however, the influence of freshwater inflow alone was not clear. On the other hand, the combined influences of wind and freshwater inflow promoted seawater exchange and possibly impacted on the amount of oxygen supplied to the lower layers.