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Paper Topic:

Dead Zones

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Dead Zones

Dead zones are areas near the sea floor , the bottom water , wherein the level of dissolved oxygen present has become very low , hypoxic , or even completely absent , anoxic . These areas are caused by an increase in phytoplankton productivity (Dybas , 553 ) The academic community studying dead zones has come to the conclusion that an increase in the use of fertilizer near the dead zones causes the said increase in phytoplankton activity . The use of fertilizers increases the nitrogen

concentration in the water on which algae thrive . When the huge number of alga involved in the blooms die , the bodies sink to the bottom and are fed on by bacteria . These bacteria are the primary cause of the dead zones . The bacteria increase and thrive on the dead algae and thus consume massive amounts of oxygen . Other marine life forms in the vicinity are thus affected (Dybas , 555 Weir , 10

In an article , Creeping Dead Zones , by the National Aeronautics and Space Administration (NASA , It is shown that Dead Zones are not only caused by agriculture but also by natural catastrophes and a restricted flow of water . Natural catastrophes can cause a large bulk of organic material to be deposited in nearby bodies of water . The effects of this organic deposit are similar to that of fertilizer deposit . Restriction in water flow does not allow a replenishment of oxic water , water with normal levels of oxygen , and thus cause anoxia . Restriction in water flow may come about naturally but may also be a result of agriculture and natural catastrophes

The problem posed by dead zones is clear . With lower levels of oxygen in these areas , the water is no longer able to support life forms previously existing there . All aerobic life in the specific zone is brought to an end with a reduction of oxygen concentration to zero (Dybas , 554 ) The marine life capable of fleeing the dead zone escape and try to live in an environment less able to support the lifestyle of these organisms . Reproduction rate may be lowered and an eventual crash in the population of these organisms may be witnessed (Weir , 11

The rate at which the dead zones are spreading around the world is alarming . There are an estimated 146 dead zones (Dybas , 553 ) around the world . The most popular is the one found in the Gulf of Mexico , a seasonal dead zone that is relieved of by oxic water during the fall (Weir , 10 ) Other areas documented by NASA include the Mississippi River Delta , Pearl River mouths in China , Baltic Sea , Black Sea , and the Saanich Inlet in Canada . The fertilizer-caused dead zones are relatively young areas however areas such as the Saanich Inlet caused by restriction in water flow have evidence of being 12000 years old in existence . This shows that dead zones could prove to have long-lasting negative effects on marine life

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