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Hypoxic Waters 101

By Edited Nov 17, 2015 0 0

What is Hypoxia

Hypoxia can be defined as follows according to the US Geological Survey,

Hypoxia – “Hypoxia means low oxygen and is primarily a problem for estuaries and coastal waters. Hypoxic waters have dissolved oxygen concentrations of less than 2-3 ppm. Hypoxia can be caused by a variety of factors, including excess nutrients, primarily nitrogen and phosphorus, and water body stratification due to saline or temperature gradients. These excess nutrients, eutrophication, promote algal growth. As dead algae decompose, oxygen is consumed in the process, resulting in low levels of oxygen in the water.” - Mississippi River Basin Watershed Nutrient Task Force, 2010

 To sum it up, Hypoxia- low oxygen levels caused by decomposing algae in bodies of water. 


Hypoxia from Algae

So if decomposing algae is behind hypoxia the next thing would be to figure out where the algae is all coming from.  Well what happens is the algae is naturally present in the water but the amount of algae gets a boost by the addition of man made fertilizers such as ammonia, urea and potash.  These are common commercial fertilizers that are applied on crop fields and on front lawns all across America.  In addition to these nutrients, other hazardous materials are deposited by industrial waste water being dump back onto the landscape where some of it escapes into watersheds.  All  these chemicals and nutrients then combine in the water and cause the algae population to explode creating a huge algae bloom in the water.  This algae bloom goes through its normal life cycle and then dies.  Once the bloom dies it starts to decompose and decomposing bacteria will use the available oxygen, dropping the levels below 2 ppm which is below the threshold needed by most aquatic life.   


Gulf of Mexico

A example of this that hits close to home is the Gulf of M

Mississippi River Watershed
exico Hypoxic zone.  The hypoxic zone in the Gulf is located  off the Mississippi River delta in Louisiana.  While hypoxia does occur in other coastal waters around the country it is especially prevalent here, due to the large drainage area that the Mississippi river brings to this location.  Not only is the drainage area large (around 40% of the lower 48 states) it drains some of the most heavily used farmland in the country as well as a large part of the US urban and suburban population.  The combination of size of the watershed and the large amounts of fertilizer applications in urban and rural settings creates a perfect recipe that causes the large algae blooms off the coast.

This hypoxia is devastating both to local ecosystems and economies as it returns year after year and impacts the aquatic life and in turn the commercial fishing and tourism industries that depend on the aquatic life.  Fishermen are forced farther out to sea in the chase after reduced fish populations that used to be much richer closer to shore.  Tourism is effected in a similar fashion since it reduces sight seeing opportunities and private fishing success as well.

There are many public and private organizations dedicated to reducing the amount of hypoxia present in the Gulf of Mexico, such as the EPA and the Gulf of Mexico Alliance.

If you wish to personally help reduce the effects of man made hypoxia there are a few steps you can take.

  1. Reduce or stop any nutrient inputs of lawns or gardens
  2. Push for restoration of riparian zones and wetlands in your area.
  3. Properly dispose of all chemicals, oils and other hazardous wastes.
  4. Apply correct amounts of fertilizer to field crops.
  5. Establish filter strips at the edge of field to catch nutrient and water runoff from fields.
  6. Anything to stop nutrients from leaving where you apply them.


If we all do our part we can successfully reduce the impact we have on our nations water.  If you have any questions feel free to leave a comment on the article and I will get back to you as quick as I can.











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