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The causes of nutrient pollution, specifically of nitrogen and phosphorus nutrients, include agricultural runoff, fossil-fuel burning, and wastewater treatment effluent. Hypoxia occurs most often, however, as a consequence of human-induced factors, especially nutrient pollution (also known as eutrophication). Limited vertical mixing between the water "layers" restricts the supply of oxygen from surface waters to more saline bottom waters, leading to hypoxic conditions in bottom habitats. Stratification in the water column, which occurs when less dense freshwater from an estuary mixes with heavier seawater, is one natural cause of hypoxia. This occurs due to a balance between oxygen input from the atmosphere and certain biological and chemical processes, some of which produce oxygen while others consume it. The amount of oxygen in any water body varies naturally, both seasonally and over time.
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Since 1985, NOAA-sponsored research has monitored the largest dead zone in the United States, which forms every spring in the northern Gulf of Mexico. Unable to sustain life, these areas, called dead zones, may cause die-offs of fish, shellfish, corals, and aquatic plants. In some cases, vast stretches of open water become hypoxic. Hypoxia is often associated with the overgrowth of certain species of algae, which can lead to oxygen depletion when they die, sink to the bottom, and decompose. In ocean and freshwater environments, the term "hypoxia" refers to low or depleted oxygen in a water body. Graphic credit: Louisiana Universities Marine Consortium
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(Bottom panel) Long-term measured size of the hypoxic zone (green bars) measured during the ship surveys since 1985, including the target goal established by the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force and the 5-year average measured size (black dashed lines). Red area denotes 2 milligrams per liter of oxygen or lower, the level which is considered hypoxic, at the bottom of the seafloor.
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#HYPOXIA TREMULOUS SKIN#
Discoloration of the skin and eventual ulceration that sometimes accompany varicose veins are a result of hypoxia of the involved tissues. The localized pain of angina pectoris due to hypoxia occurs because of impaired oxygenation of the myocardium. cyanosis is not always present and in some cases is not evident until the hypoxia is far advanced. Generally they include dyspnea, rapid pulse, syncope, and mental disturbances such as delirium or euphoria. Signs and symptoms vary according to the cause. Diminished availability of oxygen to the body tissues its causes are many and varied and includes a deficiency of oxygen in the atmosphere, as in altitude sickness pulmonary disorders that interfere with adequate ventilation of the lungs anemia or circulatory deficiencies, leading to inadequate transport and delivery of oxygen to the tissues and finally, edema or other abnormal conditions of the tissues themselves that impair the exchange of oxygen and carbon dioxide between capillaries and tissues.