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The Dead Zone in the Gulf of Mexico What is the Dead Zone? What is the Dead Zone? Every summer in the Gulf of Mexico an area becomes void of life due to severely depleted levels of oxygen in the Gulf's water, a state known as hypoxia. This condition kills every oxygen-dependent sea creature within its zone. The Dead Zone varies in size from year to year, but generally it has been growing since 1993. In 2005, researchers mapping the Dead Zone found that it covered 4,564 square miles, an area slightly smaller than the state of Connecticut. In some years it has covered up to roughly 7,000 square miles. The Dead Zone is caused by excess nitrogen and phosphorus that is washed into the Gulf from the Mississippi River. These nutrients ignite huge algae and phytoplankton blooms. As the blooms die, they drop to the ocean floor and decompose, using up the oxygen of the deeper water. The stratification of the water that occurs during the summer in the Gulf prevents the deepest water from becoming re-oxygenated. As a direct result, oxygen levels fall below 2 parts per million, a level at which most marine life, including all commercial fish, crab and shrimp species, cannot survive. The Dead Zone is now one of the largest hypoxic zones of water in the world. Where does the Dead Zone come from? Scientific research has indicated that the excess nutrients (nitrogen and phosphorus) result from human activities in the upstream Mississippi River watershed. The principal areas contributing nutrients to the Mississippi River, and ultimately to the Gulf, are streams draining the corn belt states, particularly Iowa, Illinois, Indiana, Ohio, and southern Minnesota.The average concentration of nitrate-nitrogen in the main stem of the Mississippi River has doubled since 1950. Commercial fertilizer is the single largest contributor. Others include animal manure, municipal and domestic waste and atmospheric deposition (from powerplants and vehicles). The present use of nitrogen fertilizer in the basin is estimated to be about 7 million metric tons per year and accounts for more than one-half of the annual nitrogen input to the river. A major, rapidly growing, source of nutrients in America's waterways comes from Concentrated Animal Feeding Operations (CAFOs). These corporate hog, chicken and cattle farms concentrate massive amounts of manure in small areas, often leading to egregious manure spills into rivers and streams or soils over-saturated with manure. Manure is sometimes used as fertilizer because it contains large amounts of nitrogen and phosphorus, the very same nutrients which are attributed with the creation of the Dead Zone, but over-saturated soils are not capable of absorbing the manure and, after a rain or irrigation, it runs off the land into rivers and streams. Municipal and domestic wastes include discharges from sewage treatment plants and stormwater runoff from city streets, both of which have a high concentration of nitrogen and phosphorus. Atmospheric deposition results when nutrients settle in the Mississippi waterways and the Gulf directly from the air after being released by sources such as automobiles and fossil-fueled power plants. The Growth of the Dead Zone As early as the 1950's and 1960's shrimp trawlers reported observing isolated areas where catches were abnormally low or as well as "dead" or "red" water, but it wasn't until the 1970's that hypoxia was scientifically documented off the Gulf Coast in several environmental assessment studies. Systematic survey of the size and timing of the Dead Zone began in 1985. These surveys show that from the years 1985 - 1992 (not including the low-flow years of 1988-89) the Dead Zone grew from slightly below 4000 sq. miles to just above 4000 sq. miles, or around the size of Massachusetts. Then, after the floods of 1993, the Dead Zone exploded to a size of 7000 sq. miles, a size comparable to the entire state of New Jersey. Why is the Dead Zone bad? The Dead Zone poses an enormous threat to the biodiversity, ecological integrity, and fishery productivity of the Gulf of Mexico. The magnitude of the devastation of the Dead Zone is huge. The environmental impacts of low oxygen levels in water, or hypoxia include: noxious algal blooms that choke out fish, shrimp and crabs; altered coastal phytoplankton food webs -- the lowest rung of the ocean food chain upon which most sea life depends; altered stream-side ecosystems. The direct impacts on fisheries is of note, particularly massive fish kills, altered migration patterns for species like shrimp, and loss of suitable habitat for the spawning of fish, shrimp and crabs. The Dead Zone also poses a very real threat to the economy of the Gulf region and the $4 billion a year seafood economy. Fishermen can no longer depend on the waters afflicted by the Dead Zone and must travel hundreds of miles around the Dead Zone to catch commercial fish, shrimp and crabs. The economic impacts could become more serious if the Dead Zone continues to grow. The Gulf Coast faces the risk of developing hypoxia severe enough to wipe out almost the entire commercial fishery. A loss such as this would devastate the economy of the Gulf region and be felt across the nation. The Gulf of Mexico produces almost 40 percent of the country's commercial fishing yield, and a large portion of the most valuable fishery, shrimp. The current ecological impacts of the Dead Zone are already significant and the potential for future catastrophic impacts -- ecological and economic -- clearly exists. What is being done? Cutting the flow of nutrients from the Mississippi River basin to the Gulf of Mexico is key to reducing the Dead Zone in the Gulf. States, with help and direction from the U.S. Environmental Protection Agency, are developing numeric water quality standards for nitrogen and phosphorus. These standards would specify the concentration of nutrients that would be allowed in the water. Development of numeric standards for nutrients is important because they are necessary to impose limits in polluters' discharge permits and to develop cleanup plans for waters impaired by for nitrogen and phosphorus. Although the EPA asked states to adopt nutrient standards by 2004, many states are still far behind in developing numeric standards, others are planning to develop numeric standards for phosphorus but not nitrogen, and many do not even have any plans to develop numeric nutrient water quality standards. Agribusiness and other special interests are pressuring states to delay setting nutrient standards. Since the EPA sees the development of these standards as voluntary for the states, public pressure is essential to encourage states to develop criteria and to ensure that states develop criteria that will protect water quality. What You Can Do Cleaning up the Dead Zone in the Gulf of Mexico will not be easy, but we must begin tackling this huge threat now. Some scientists believe that cutting nutrient inputs to the Gulf by almost half will be essential to make significant progress in reducing the Dead Zone. States need to take action to protect water quality in the Gulf. Even if your state is not contributing to the Dead Zone in the Gulf, excessive nutrients have caused pollution of lakes, rivers and coastal areas throughout the United States. Ask your state's Governor to establish numeric nutrient standards to protect waters from pollution. You could make the following points:
For More Information Read an assessment of hypoxia in the Gulf of Mexico by the National Ocean Service (an agency of the National Oceanic and Atmospheric Administration)
Visit the U.S. Geological Survey's website on Gulf hypoxia:
Visit the U.S. Environmental Protection Agency's website on the Mississippi River Basin and Gulf hypoxia:
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