Ocean Dead Zones
Marine life needs to have a certain amount of oxygen in their environment- the water- in order to survive. When there isn’t enough oxygen, and marine life starts dying off, dead zones occur. This happens in large bodies of water and sometimes in lakes and rivers too. (1).
Dead zones are typically found in shallow waters, and are prevalent around the world along the sea coasts.
Eutrophication: an increase in chemical nutrients in the water, leading to excessive blooms of algae that deplete underwater oxygen levels. (1).
Dead zones happen because of eutrophication. Agricultural runoff, vehicular/ industrial emissions, sewage, and natural factors are the big ways in which dead zones are created. There’s 146 known dead zones around the world. (2).
“Experts believe the spread of dead zones caused an increase in water temperature resulting because of global warming. From 1960 to 2008, the number of dead zones is nearly doubling every decade.” (2).
These zones are all over the world; they occur especially in regions with lots of agricultural and industrial activity occur. “A 2008 study found more than 400 dead zones worldwide, including in South America, China, Japan, southeast Australia and elsewhere.” (1).
Dead zones were originally found in the 1970’s in a few areas: Chesapeake Bay off Maryland, Scandinavia’s Kattegat Strait, the mouth of the Baltic Sea, the Black Sea and the northern Adriatic. (1).
The Mississippi River is packed with nutrients and pollution, and is linked to the Gulf of Mexico. Because of this, the most well-known dead zone was created. It’s 8,500 square miles, which is almost the size of the state of New Jersey. (1). The area used to be filled with shrimp, but a decrease in oxygen results in reproductive issues for fish. The costs of Oregon and Virginia also have some well-known dead zones as well.
If the reasons of these zones are eradicated or reduced, the zones can be undone and oxygen can be in the region again. “A huge dead zone in the Black Sea largely disappeared in the 1990s following the fall of the Soviet Union, after which there was a huge spike in the cost of chemical fertilizers throughout the region.” (1). The United States has been working to lower the amount of industrial emissions in the areas where dead zones are problematic. “Efforts by countries along the Rhine River to reduce sewage and industrial emissions have reduced nitrogen levels in the North Sea’s dead zone by upwards of 35%.” (1).
Minnesota and Illinois’s agricultural flooding has washed nitrogen fertilizers into the Gulf of Mexico. This has a negative outcome because they cause a huge growth of algae that feed on them. (2).
Cleaning efforts have led to the reduction of the dead zones in the Hudson River and San Francisco Bay. Hurricane Katrina and the BP spill has made the pollution in the Gulf of Mexico worse, along with the increase of corn production in the Midwest due to the increase of algae-inducing nutrients being put into the water. The Mississippi Basin/Gulf of Mexico Water Nutrient Task Force has been working to reduce the dead zone’s size, since the discovery in 1997. But natural causes, paired with the agricultural industry booming throughout the Midwestern states, the force will face a difficult task in their efforts to reduce this zone. (1).
Resources
1: “What Causes Ocean ‘Dead Zones’?” Scientific American, www.scientificamerican.com/article/ocean-dead-zones/.
2: “Facts About Dead Zones In The Ocean.” Some Interesting Facts, 16 Nov. 2016, someinterestingfacts.net/facts-dead-zones-ocean/.
