Tracing the green-tide outbreaks using in situ, AUV, satellite and model data in Shinyang Bay, Korea

Abstract

Shinyang Bay, located on the eastern coast of Jeju Island, Korea, is semi-closed bay. Shinyang Bay has a wide sandy beach along the north to east coast, and has a shallow water depth that is greatly affected by tidal changes. Submarine groundwater is discharged from Shinyang Port and land-based aquaculture farms that started commercial flatfish farming for the first time in Korea are located along the west coast. The green-tide outbreak began after the mid-90s and has continued to occur until now. The purpose of this study is to analyze the cause of the green-macroalgae bloom using big-data. The hydrographic observation conducted monthly CTD observation and sample analysis (nutrient, POC, seaweed) on 9 points in the bay and 12 coastal points, and measured ocean currents using small-GPS drift from 2019 to 2021. The occurrence area of green-tide was calculated to use the drone, aerial photo, Sentinel images. Each image was performed during monthly low tide, and individual images were synthesized and masked out, and classified object. A numerical model simulated the circulation in the bay. The occurrence area of green-tide was the lowest in March and the highest in June. During 2020, the cumulative occurrence area of green-tide is about 2 million m2. The continuous occurrence area of green-tide is the eastern and western coast and the middle part of the bay. First reason is the rising of the sea surface temperature during winter. Second is changing the circulation pattern due to the artificial structure in the bay. It causes the accumulating seaweed on the beach and investigates that the supply of nutrients for growth discharges from aquaculture farms and submarine ground water. The results of the numercal model and drift measurement showed that the port construction at the western entrance in the late 1990s increased the duration time compared to before construction and increased the number of particles flowing into the beach rather than into the outside.