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The exaerobic zone is found at the boundary of anoxic and hypoxic zones. Hypoxia can occur throughout the water column and also at high altitudes as well as near sediments on the bottom. It usually extends throughout 20–50% of the water column, but depends on the water depth and location of pycnoclines (rapid changes in water density with depth).
Dead zones are hypoxic (low-oxygen) areas in the world's oceans and large lakes. 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.
Anaerobic ammonium oxidation with nitrite (anammox) is a major pathway of fixed nitrogen removal in the anoxic zones of the open ocean. [20] Anammox requires a source of ammonium, which under anoxic conditions could be supplied by the breakdown of sinking organic matter via heterotrophic denitrification.
Redox gradients form in water columns and their sediments. Varying levels of oxygen (oxic, suboxic, hypoxic) within the water column alter redox chemistry and which redox reactions can occur. [10] Development of oxygen minimum zones also contributes to formation of redox gradients.
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.
Dead zone (ecology) – Low-oxygen areas in coastal zones and lakes caused by eutrophication Hypoxia (environmental) – Low oxygen conditions or levels Meromictic – Permanently stratified lake with layers of water that do not intermix Pages displaying short descriptions of redirect targets
Ocean deoxygenation has led to suboxic, hypoxic, and anoxic conditions in both coastal waters and the open ocean. Since 1950, more than 500 sites in coastal waters have reported oxygen concentrations below 2 mg liter −1, which is generally accepted as the threshold of hypoxic conditions. [25]
Histotoxic hypoxia, the inability of cells to take up or use oxygen from the bloodstream; Anemic hypoxia, Blood is not able to take sufficient amount of oxygen due to Anemia; Hypoxemic hypoxia or hypoxemia, a deficiency of oxygen in arterial blood; Hypoxic hypoxia, a result of insufficient oxygen available to the lungs