Dead Zones

If you had to imagine running out of oxygen, how would you describe the feeling? Your throat becomes tighter and tighter while you struggle to breath in, sucking in the non-existent breath for life and then your lungs feel as if they are empty. That is what fish are going through at the bottom of the ocean. The causes of dead zones can be fixed as to what is harming our environment.

  • Excess Nitrogen and other nutrients leads to dead zones
  • Human cause most of the excess nutrients to be present
  • Farming leads to wastes flowing into waters

Less oxygen dissolved in the water is often referred to as a “dead zone” because most marine life either dies, or, if they are mobile such as fish, leave the area. The cause of such “hypoxic” (lacking oxygen) conditions is usually eutrophication, an increase in chemical nutrients in the water, leading to excessive blooms of algae that deplete underwater oxygen levels.


Nitrogen is necessary to increase crop yields, but plants are inefficient at taking it up, and often more fertilizers and animal wastes are added than the plants need.

  • too much for plants to absorb
  • creates algae growth
  • destroys oxygen

Only a fraction of the nitrogen applied to soils actually ends up in the crops. The extra nitrogen leaches from the soil via water from rain and snow run-off ends up in crops, which changes the chemical make-up of the water thereby changing what is able to live in the water. Algal blooms usually die soon after they appear. The ecosystem simply cannot support the huge number of cyanobacteria. The organisms compete with one another for the remaining oxygen and nutrients.

Human Pollutants

Worldwide, humans create about 160 million metric tons of nitrogen each year, nitrogen is fast accumulating in the environment.

  • overuse of fertilizers
  • discharge of untreated sewage
  • rising emissions from vehicles and factories

From the causes listed above, nitrogen and phosphorus is being discharged into rivers and the coastal environment or being deposited from the atmosphere which triggers alarming and sometimes irreversible effects.

Image result for pollution of cars

Farming wastes

Farming wastes are flowing into the waters which is causing damage.

  • large amounts of manure
  • no place to dispose wastes/manure
  • too much fertilizer is being used

Cheryl Dybas states in the article “Dead Zones spreading in World Oceans”, that scientists believe that the gulf’s dead zone is the result of excess nutrients from agriculture in the large Mississippi River drainage basin. The Mississippi drains 31 states and 40 percent of the contiguous United States. More than 55 percent of agricultural lands and 33 percent of US farm-related jobs are found in the river’s drainage area (Dybas, 2005). Bacteria removes excess fertilizer from water, which enables them to convert nitrate to nitrogen that is then released into the atmosphere as a gas.


  • Dybas, C.L. (2005). Dead zones spreading in world oceans. BioScience, 55(7), 552-557.

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