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An aquatic system lacking dissolved oxygen (0% saturation) is termed anaerobic, reducing, or anoxic. In water, oxygen levels are approximately 7 ppm or 0.0007% in good quality water, but fluctuate. [5] Many organisms require hypoxic conditions. Oxygen is poisonous to anaerobic bacteria for example. [3]
Dissolved oxygen levels required by various species in the Chesapeake Bay (US). In aquatic environments, oxygen saturation is a ratio of the concentration of "dissolved oxygen" (DO, O 2), to the maximum amount of oxygen that will dissolve in that water body, at the temperature and pressure which constitute stable equilibrium conditions.
The temperature of a body of water directly affects the amount of dissolved oxygen it can hold. Following Henry's law, as water becomes warmer, oxygen becomes less soluble in it. This property leads to daily anoxic cycles on small geographic scales and seasonal cycles of anoxia on larger scales.
Hypoxia occurs when dissolved oxygen (DO) concentration falls to or below 2 ml of O 2 /liter. [2] When a body of water experiences hypoxic conditions, aquatic flora and fauna begin to change behavior in order to reach sections of water with higher oxygen levels. Once DO declines below 0.5 ml O 2 /liter in a body of water, mass mortality occurs.
Decreased levels of dissolved oxygen (DO) is a major contributor to poor water quality. Not only do fish and most other aquatic animals need oxygen, aerobic bacteria help decompose organic matter. When oxygen concentrations become low, anoxic conditions may develop which can decrease the ability of the water body to support life.
Equatorward winds drive the upwelling of low dissolved oxygen (DO), high nutrient, and high dissolved inorganic carbon (DIC) water from above the oxygen minimum zone. Cross-shelf gradients in productivity and bottom water residence times drive the strength of DO (DIC) decrease (increase) as water transits across a productive continental shelf.
In OMZs oxygen concentration drops to levels <10 nM at the base of the oxycline and can remain anoxic for over 700 m depth. [7] This lack of oxygen can be reinforced or increased due to physical processes changing oxygen supply such as eddy-driven advection, [7] sluggish ventilation, [8] increases in ocean stratification, and increases in ocean temperature which reduces oxygen solubility.
Pacific Ocean sections of dissolved oxygen and apparent oxygen utilization. Data from the World Ocean Atlas 2009 . In freshwater or marine systems apparent oxygen utilization ( AOU ) is the difference between oxygen gas solubility (i.e. the concentration at saturation) and the measured oxygen concentration in water with the same physical and ...