Dead Zones
For as long as I can remember we have always had a fish tank in our home. I remember one day noticing green slime growing on the glass inside the tank. I asked my dad what is was and he told me it was algae build up. I asked him why did it grow and he didn’t know but said he knew how to get rid of it. Later that day we went to the pet store and he bought a new fish. It was a Pleco fish. It was a weird looking brown fish with a suction cup type of mouth that was apparently good for eating algae. A couple days later I watched as the fish stuck itself to the glass and ate the algae. I was amazed. Watching the Pleco fish made me wonder what happens when algae builds up in the ocean and what could cause it. Growing up we have all learned about how the effects of our pollution affects the planet. I remember being taught all about the hole in the ozone layer, and about how important it is to recycle our glass, plastics and paper products. But the only thing I can even remember learning that pertained to pollution in the ocean was the obvious toxic waste from nuclear power plants, and to make sure you cut the plastic rings that come attached to soda cans so sea turtles won’t get caught in them and choke to death. So I decided to find out what really causes pollution in our oceans, and I found a major issue that affects our seas but is rarely talked about. That is our oceans’ dead zones. The phrase “dead zone” refers to coastal waters that are too low in oxygen to sustain life. The lack of oxygen is called hypoxia. Phytoplankton are microscopic plants that grow in the sunlit surface waters of the ocean. They play a large role in sustaining ocean ecosystems and global climate. These plants are the base of the marine food chain. Dead zones are sparked by phytoplankton blooms that consume available oxygen and create these oxygen-starved zones where aquatic life cannot survive.
The chain of events that cause these dead zones begins on land. “Farmers often over fertilize their fields. The excess fertilizer, laden with nutrients like nitrogen, washes into creeks and rivers, where it’s eventually carried into coastal bays and the open sea” (Dybas, 2005) . Other sources include discharge of untreated sewage, animal waste from farms, and rising emissions from vehicles and factories. Nitrogen-fixing bacteria convert atmospheric nitrogen into nitrogen compounds that some organisms can use as food which in turn triggers the proliferation of phytoplankton blooms that deplete oxygen in the water. As a result there may be more phytoplankton in the water but it is less nutritious for the marine animals that feed on it. “When the phytoplankton die, they fall to the sea floor and are digested by microorganisms. The process removes oxygen from the bottom water and creates low-oxygen zones” (Dybas, 2005) . Most marine life cannot survive these conditions. While fish might flee this suffocation; slow moving, bottom dwelling creatures like clams, lobsters, and oysters are less able to escape. The hypoxic water appears normal on the surface, but on the bottom they are covered with dead and distressed animals, and in extreme cases, layers of sulfur-oxidizing bacteria which cause the sediment in these areas to turn black.
“Dead zones range in size, from small areas of coastal bays and estuaries to huge areas of the open sea, where they can reach tens of thousands of square kilometers. Most are found in temperate waters, off the eastern coast of the United States and in the seas of Europe” (Dybas, 2005) . They usually occur in the spring and summer months because that is when fertilizer runoff from farms is at its highest levels. Mix that with the warm ocean waters and it fuels the plankton blooms. There are over 400 dead zones in the world. The world’s two largest dead zones are located in the Baltic Sea and the Gulf of Mexico. Dead zones can trigger alarming and sometimes irreversible effects on the waters that they occur in. Hypoxic conditions found in dead zones cause food chain alterations, loss of biodiversity and in some cases high aquatic species mortality.
The realization of the situation is that we really have to be aware of the fact that what we do on land affects everything in the ocean as well. I almost feel like this is a problem that will never go away because farmers will probably never under fertilize their crops because the objective is to yield more crops in order to make more money, so for them it may not be cost effective to consider the danger they are causing in the oceans. The driving force of this planet is water. Human indifference is the ocean’s biggest threat. As humans we must strive to remember that our careless actions affect everything in nature, even at the bottom of the deep blue sea.
Works Cited
Dybas, C. L. (2005, July). Dead zones spreading in world oceans. BioScience, pp. 552-557.Retrieved February 15,2012, from the Environment Complete Database.
