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| This picture shows a cross section of a dead zone over time http://blog.nola.com/graphics/deadzone_how061007.gif |
Chemicals such as nitrogen and phosphorous are key catalysts in fertilizers because nitrogen is an essential building block in plan growth and phosphorous is important for the storage and movement of energy throughout the plant (Herself's Houston Garden 2014). These chemicals are dumped into the Gulf within the fresh water that runs out from the Mississippi River and induce spikes in algal population (dubbed “algal blooms”); algae are closely related to plants evolutionarily, and the fertilizers act the same way towards them (National Geographic 2014). Although the algal population is typically limited by algal feed/resources, the nitrogen and phosphorous rich water breaks this glass ceiling. Since algae have a short lifespan, the result is water full with dead and decaying algae. The decomposition process of algae consumes all of the oxygen dissolved in the water, and creates a dead zone (Silverman 2014).
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| Here you can see the proportion of algal population in an algal bloom as compared to normal conditions. http://www.islandbreath.org/2010Year/08/100806deadzone.png |
Dead zones expand and recede depending on the time of year. During the spring, snow melts, which increases nutrient-rich water levels, fostering algal blooms (which cause the dead zone to reach it’s zenith during august (Silverman 2014). During the fall, decreased temperature results in less algal growth, which decreases the size of algal blooms, causing a recession in a dead zone’s size (Silverman 2014). Dead zones do not fade and re-oxygenate because of stratification, which prevents waters of different densities from mixing (in this case, the fresh water which is less dense sits on top of the de-oxygenated salt water, preventing the salt water from oxygenating via contact with the air) (Wikipedia 2014a). A dead zone’s impact on the biology of a region is obviously negative. Less habitable waters result in a lower marine life population that is essentially “cramped” within the smaller oxygen-rich zones. Additionally, those unable to escape the dead zone die, and their decomposition also adds to that of algal blooms. Lower oxygen levels in other areas lead to mutations among aquatic life; in the gulf killifish, decreased size of reproductive organs and low egg counts has been observed (Wikipedia 2014b). Over the last 20 years, the Gulf of Mexico’s dead zone has been fluctuating in a somewhat random fashion (figure below); though, the average size of the dead zone itself has been steadily increasing.
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| The average size of the dead zone itself has been steadily increasing over the past 20 years. http://www.noaanews.noaa.gov/stories2013/images/2013hypoxiagraph2.png |
National Geographic: Education. (2014) Dead Zone. National
Geographic. (Date accessed: February 16, 2014.)
http://education.nationalgeographic.com/education/encyclopedia/dead-zone/?ar_a=1.
http://education.nationalgeographic.com/education/encyclopedia/dead-zone/?ar_a=1.
Silverman, J. (2014) Should we be worried about the dead zone in the Gulf of Mexico?. How Stuff Works. (Date accessed: February 16, 2014.)
http://science.howstuffworks.com/environmental/earth/oceanography/dead-zone.htm
Herself's Houston Garden. (2014) Nitrogen, Phosphorous, and Potassium are primary nutrients your plant requires. Herself's Houston Garden. (Date accessed: February 26, 2014.) http://herselfshoustongarden.com/2008/02/nitrogen-phosphorus-and-potassium-what-do-they-do-for-your-plants.html
http://science.howstuffworks.com/environmental/earth/oceanography/dead-zone.htm
Herself's Houston Garden. (2014) Nitrogen, Phosphorous, and Potassium are primary nutrients your plant requires. Herself's Houston Garden. (Date accessed: February 26, 2014.) http://herselfshoustongarden.com/2008/02/nitrogen-phosphorus-and-potassium-what-do-they-do-for-your-plants.html
Wikipedia. (2014a) Stratification (Water). Wikipedia, the free encyclopedia. (Date accessed: February 16, 2014.) http://en.wikipedia.org/wiki/Stratification_(water)
Wikipedia. (2014b) Dead Zone (Ecology). Wikipedia, the free
encyclopedia. (Date accessed: February 16, 2014.) http://en.wikipedia.org/wiki/Dead_zone_(ecology)#Effects