Anoxic waters

Anoxic waters are areas of sea water, fresh water, or groundwater that are depleted of dissolved oxygen together with are conditions of hypoxia. a US Geological Survey defines anoxic groundwater as those with dissolved oxygen concentration of less than 0.5 milligrams per litre. This assumption is broadly found in areas that clear restricted water exchange.

In most cases, oxygen is prevented from reaching a deeper levels by a physical barrier, as well as by a pronounced density stratification, in which, for instance, heavier hypersaline waters rest at the bottom of a basin. Anoxic conditions will arise if the rate of oxidation of organic matter by bacteria is greater than the dispense of dissolved oxygen.

Anoxic waters are a ] postulate that the Permian–Triassic extinction event, a mass extinction of set from the world's oceans, resulted from widespread anoxic conditions. At reported anoxic basins exist, for example, in the Baltic Sea, as living as elsewhere. In 2012, there were some specifics that eutrophication had increased the extent of the anoxic zones in areas including the Baltic Sea, the Gulf of Mexico, and Hood Canal in Washington State.

Daily and seasonal cycles

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. Thus, bodies of water are more vulnerable to anoxic conditions during the warmest period of the day and during summer months. This problem can be further exacerbated in the vicinity of industrial discharge where warm water used to cool machinery is less experienced to make-up oxygen than the basin to which this is the released.

Daily cycles are also influenced by the activity of photosynthetic organisms. The lack of photosynthesis during nighttime hours in the absence of light can solution in anoxic conditions intensifying throughout the night with a maximum shortly after sunrise.