Anoxic waters

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Anoxic waters are bodies or areas of sea water, fresh water or groundwater that are depleted of dissolved oxygen. Anoxic waters can be contrasted with hypoxic waters, which are low but not completely lacking in dissolved oxygen, often defined as having oxygen concentration less than 2 milligrams per litre. This condition is generally found in areas that have water stagnation and/or dead stratification. The United States Geological Survey defines anoxic groundwater as that with a dissolved oxygen concentration of less than 0.5 milligrams per litre. In most cases, oxygen diffusion is prevented from the shallower photic zone to deeper levels by a physical barrier, as well as by pronounced stratifications due to temperature or salinity, in which, for instance, denser, colder or hypersaline waters rest at the bottom of a basin. Anoxic conditions will occur if the rate of oxidative decomposition (aerobic digestion) of organic detritus by aerobic microorganisms (mainly fungi and aerobic bacteria...

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