Characteristics of dissolved oxygen and its affecting factors in the Yangtze estuary

The cruises on hypoxia research were carried out in the Yangtze Estuary and adjacent area of the East China Sea on June, August and October, 2006. DO, stability and the concentration of nitrate and phosphate in the section B were analyzed. The result indicates that there is distinct difference among the concentration of DO in the section B of the three cruises. The DO distribution is higher in surface water but lower in bottom. The oxygen minimum value (1.1 mg · L^-1) is found at the bottom in August, and the apparent oxygen utilization (AOU) is higher than 2.79 mg · L^-1 in the section B. The strong halocline above the hypoxic zone, as a result of affluent water from the coastwise, Taiwan Warm Current, and the high concentration of organic substance are major factors causing the formation of the hypoxia. The stability of the seawater goes down, the vertical mixing affect the DO through its effect on stratification, in October. Δ DO is primarily affected by the stability and the concentration of Δ NO₃^-, Δ DIP.