Monday, February 13, 2012
It's where areas of the sea floor are hypoxic, meaning they have very low or completely zero, concentrations of dissolved oxygen. These dead zones are caused by an increase in chemical nutrients in the water. These chemical nutrients are produced by excess nitrogen from farm fertilizers, emissions from vehicles and factories, and from the sewage. These chemical nutrients spur the growth of thick algae, and underneath this algae the oxygen slowly vanishes and causes fish, crabs and other marine animals to suffocate and die. This is becoming a big problem today because it's spreading over the sea floors rapidly and is covering nearly the entire east and south coasts of the U.S as well as several west coast river outlets. Today 405 dead zones are known worldwide, compared to only 49 in the 1960's.