Dead zones have been around for years, some even occurring naturally, but it isn’t until recently that the rate of these areas have increased rapidly. Most of the human related dead zones are due to the use of chemical fertilizers that have leeched into water supplies. Nitrogen and phosphorous are the major players in creating these zones, though runoff from sewage, landfills and fossil fuel byproducts are also large contributors. From 1997-2007 the Virginia Institute of Marine Science has recorded that dead zones have increased from four to four hundred [Source: Wildlife Extra News]. According to a study from the Leibniz Institute of Marine Sciences in Germany, marine dead zones will increase 50 percent by 2050 [Source: MongoBay].
Dead zones are areas in oceans and large bodies of freshwater that have become so oxygen depleted that much aquatic life cannot survive. Most of these zones are located downriver from highly populated areas. Fertilizer and fossil fuel runoff washes into rivers and streams which then triggers extreme planktonic growth. The algae then dies, gets decomposed by bacterial microbes leading to oxygen use. Creation of a dead zone has led to mass deaths among aquatic creatures in those areas. NASA has identified 415 dead zones spanning 95,000 square miles in the world, half the size of California in 2008, with the number doubling every decade since 1960 [Source: NASA]. One of the largest in the US is located at the mouth of the Mississippi (Gulf of Mexico region) and is 8,500 square miles, around the size of New Jersey [Source: SFGate], though this number does not currently reflect the effects of the Deepwater Horizon incident. According to Michigan State University professor Nathaniel Ostrom, the oil spill could worsen hypoxia. Bacteria that feast on hydrocarbon would break down the oil and consume more oxygen (much like the microbes that decompose algae). On top of that the oil and dispersants could also reduce the flow of oxygen and nutrients for marine plant life, further reducing oxygen levels [Source: Physorg].
These dead zones are severe ecological concerns and while it has a major effect on marine life, it can also contribute to climate change. As oxygen level decreases, nitrous oxide production increases, a greenhouse gas 300 times more potent than carbon dioxide [Source: Inhabitat]. In water depth less than 300 feet the combination of high microbial respiration plus denitrification (a process of microbial nitrate dissolution) the N20 production rate can exceed 10,000 times normal ocean N20 levels. According to oceanographer Louis Codispoti, “As the volume of hypoxic waters move towards the sea surface and expands along our coasts, their ability to produce the greenhouse gas nitrous oxide increases. With low-oxygen waters currently producing about half of the ocean’s net nitrous oxide, we could see an additional significant atmospheric increase if these ‘dead zones’ continue to expand” [Source: Mother Jones]. Unfortunately, there is little research into the effects of these dead zones on the atmosphere, since most of these studies observe changes in aquatic ecology.
While these dead zones are expanding, it can be reversed as evidenced by the Black Sea. In the late 80s early 90s, the Black Sea was the largest dead zone in the world, however between 1991-2001, the process was reversed due partly because of the Soviet Union’s fall and high prices of fertilizer. Many industrial farms closed down due to high costs, and fertilizer usage dropped drastically, leading to less pollution. While this was largely unintentional, other cleanup efforts include San Francisco Bay, Hudson River and the North Sea.
Expanding dead zones, warming oceans and ocean acidification are all related problems and fortunately can be reversed possibly just by not polluting bodies of water. While the concept may seem simple enough, the actual clean up and reversal could take decades and may simply not be enough.