Dead zones are hypoxic areas,
which are low-oxygen areas in the world’s oceans. This is usually caused by
excessive nutrient pollution from human activities. The wastes that go into the
water are primarily nitrogen and phosphorous from agricultural runoff, sewage
and even industrial emissions (McLamb 2008). Thus, oxygen needed for marine
life is depleted in these areas of high concentrated discharge, generally along
coastlines. Dead zones started to suddenly increase in the 1970s and
oceanographers started to notice a decrease in marine life. According to
scientists, the number of dead zones has doubled every 10 years since 1960
(Murray 2006). This is attributed to the tremendous increasing conversion of
forests and wetlands to agricultural and urban developments that took place in
1950, resulting in more waste and nutrients released into the water.
The major cause of dead zones is an
increase in chemical nutrients in water called eutrophication (Steer 1982).
These nutrients act as fundamental building block for single-celled organisms
named phytoplankton, which lead to a rapid increase in density in water.
Increase of nitrogen and phosphorous in water cause cyanobacteria, a type of
algae, to increase. As the algae die, bacteria decompose the dead algae
and consume huge amounts oxygen. Since the bacteria are consuming oxygen in
such large numbers, this eventually leads to extremely low levels of oxygen in
the bodies of water. Also, natural phenomena can cause lack of oxygen in water
like enclosed bodies of water. Dead zones occur in many areas of the country,
especially along the East Coast, the Gulf of Mexico and the Great Lakes. UN
Environment program published Global Environment Outlook Year Book, which
reported that 146 dead zones exist in the word with various sizes (UNEP 2004).
The Gulf of Mexico dead zone is an area of
hypoxic water at the mouth of the Mississippi River. It usually covers up to
6000 to 7000 square miles. The Gulf of Mexico is a major source for the seafood
industry, but because dead zones are killing marine life, these industries
are having trouble making business.
