Apparent oxygen utilisation
（重定向自Apparent oxygen utilization）
![Apparent oxygen utilization at 1000 m depth. Data from the World Ocean Atlas 2009.](/Images/godic/202412/21/WOA09_1000m_AOU_AYool2102.png")
![Pacific Ocean sections of dissolved oxygen and apparent oxygen utilization. Data from the World Ocean Atlas 2009.](/Images/godic/202412/21/WOA09_180E_AOU_AYool2102.png")
In freshwater or marine systems apparent oxygen utilisation (AOU) is the difference between the measured dissolved oxygen concentration and its equilibrium saturation concentration in water with the same physical and chemical properties. Such differences typically occur when biological activity acts to change the ambient concentration of oxygen. For example, primary production liberates oxygen and increases its concentration, while respiration consumes it and decreases its concentration.