Modeling the impact of river discharge and wind

1. National Marine Environmental Forecasting Center, Beijing 100081, China 4 2. State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, China 5 3. Key Laboratory of Research on Marine Hazards Forecasting, National Marine Environmental Forecasting 6 Center , Beijing 100081, China 7 8 Abstract: The phenomenon of low dissolved oxygen (known as hypoxia) in coastal ocean system is closely 9 related to a combination of anthropogenic and natural factors. Marine hypoxic occurs in the Yangtze Estuary, 10 China with high frequency and long persistence. It‘s known that it related primarily to organic and nutrient 11 enrichment influenced by river discharges and physical factors, such as water mixing. In this paper, a 12 three-dimensional hydrodynamic model was coupled to a biological model to simulate and analyze the ecological 13 system of the East China Sea. By comparing with the observation data, the model results can reasonably capture 14 the physical and biochemical dynamics of the Yangtze Estuary. In addition, the sensitive experiments were also 15 used to examine the role of physical forcing (river discharge, wind speed, wind direction) in controlling hypoxia 16 in waters adjacent to the Yangtze Estuary. The results showed that the wind field and river discharge have 17 significant impact on the hypoxia off the Yangtze Estuary. The seasonal cycle of hypoxia was relatively insensitive 18 to synoptic variability in the river discharge, but integrated hypoxic areas were sensitive to the whole magnitude 19 of river discharge. Increasing the river discharge was shown to increase hypoxic areas, while decreasing the river 20 discharge was tended to decrease hypoxic areas. And the variations of wind speed and direction had great impact 21 on the seasonal variability of hypoxia and the integrated hypoxic areas. 22 Key word: Yangtze Estuary, wind, river discharge, hypoxia 23 24 25 26 Fundation item: The National Natural Science Foundation of China under contract No. 41222038, 41076011, 27 41206023 ; from the National Basic Research Program of China (―973‖ Program) under contract No. 28 2011CB403606;and.the "Strategic Priority Research Program" of the Chinese Academy of Sciences Grant No. X 29 DA1102010403. 30