Modeling study of a hypoxia event off the Yangtze Estuary

Many estuaries, influenced by large discharge and high nutrients load, periodically become hypoxia due to the stratification of water body and the consumption of oxygen by organic matters.

Yangtze river is the longest river in China and drains one-fifth of the land area of China. It brings huge amount of nutrients into the East China Sea (ECS) and contributes significantly to the eutrophication in the ECS. In the past twenty years, hypoxia water was reported several times off the Yangtze Estuary (YE). Recently measurements also indicated that hypoxia had increased over times off the YE. Study on the mechanism of hypoxia formation off the YE is still a big challenge because physical forcing and biogeochemical processes in this region are very complicate.

During an underway survey in August 2013, low dissolved oxygen (< 2 mg) were observed at bottom layer of couples of stations off the YE. To study this hypoxia event, the Regional Ocean Modeling System (ROMS) with a sediment transport module and a biological module was applied to the YE. The hydrodynamic part and biological part of the model were both well validated. With the model, we simulated the hypoxia event in August 2013. Undergoing work is to do numerical experiments to diagnose the contributions of physical forcing and biological processes to the hypoxia formation.