The largest “Dead Zone” off the coast of North America occurs in the Gulf of Mexico. The area varies in size but can cover anywhere from 6,000 to 7,000 square miles. The “Dead Zone” begins at the Mississippi River delta and occurs between the inner and mid-continental shelf extending westward towards the upper Texas coast.
Dead Zones are known as “hypoxic” (having less than two parts per million-dissolved oxygen) regions that cannot support marine life. They are the result of pollutants distributed into the ocean from nitrogen rich fertilizer from the farm areas of the Mid Western United States.
The nutrient rich fertilizer is carried from the Mississippi River into the ocean where it creates Algal Blooms. The result of the artificially enhanced Algal growth is depletion of the dissolved oxygen in the water. This creates a “hypoxic” environment in which no marine life can survive.
Two significant results of the algal growth contribute to this problem, one, is the lack of sunlight being transmitted into the ocean depths and two, the death of the algae creates bacteria which rapidly consume the dissolved oxygen depleting the supply.
Dead Zones are not permanent and typically return year after year in the warmer months. Studies have shown that the condition is reversible with the reduction of fertilizer being distributed in the water column. The Baltic Sea dead zone receded from 1991 to 2001 due to the lack of fertilizer being dumped into it from Russia.
The results of “eutrophication” (definition of Dead Zone) have been shown to reduce the number of “benthic” organisms (definition of oxygen breathing marine life). Hypoxic water supports fewer organisms causing massive deaths of fish in regions where dead zones occur.
The Gulf of Mexico is the source of major seafood in the region. Continuing progression of the hypoxic region will adversely affect the regions ability to sustain commercial seafood production. Ways to mitigate the dead zone eutrophication start by attacking the problem at the source.
Solutions include the reduction of fertilizer distribution into the river by using less fertilizer and timing it to occur when it will not be carried into the waterway by runoff. Controlling animal wastes so they are not carried into the river also improves the situation.
Closely monitoring sewage systems and septic tanks to reduce groundwater discharge as well as changing industrial practices to prevent elimination of waste products by way of river discharge are also ways to improve the problem.
Funding efforts to restore, improve, and replace wetlands in regions adjacent to the river will also mitigate the condition. Wetlands have been shown to filter and dramatically reduce the amount of nitrates and phosphates (nutrients contributing to the algal growth) being discharged into the ocean.
Adopting proactive methods in which to reduce the amount of fertilizer being distributed into the ocean and increasing public awareness about the problem are ways we can continue to promote a sustainable environment for future generations.
http://serc.carleton.edu/microbelife/topics/deadzone/
http://www.gulfhypoxia.net/
http://www.ccnmag.com/article/dean_zone_off_gulf_of_mexico_largest_ever
