The eastern part of the bay is a center of poultry farming, which produces large amounts of manure. Atmospheric nitrogen accounts for about a third of the nitrogen that enters the bay. The western part of the bay is full of factories and urban centers that emit nitrogen into the air. The Chesapeake’s high levels of nitrogen are caused by two factors: urbanization and agriculture. The Chesapeake Bay, on the East Coast of the United States, has one of the first dead zones ever identified, in the 1970s. This atmospheric nitrogen is then redeposited on land and water through the water cycle-rain and snow. Fossil fuels and fertilizers release nitrogen into the atmosphere. Factories and sewage facilities are less regulated than they are in developed countries, and sometimes wastewater is simply dumped into creeks, rivers, lakes, or the ocean.Ītmospheric sources of nitrogen also contribute to eutrophication in some areas of the world. In developing countries of Latin America, Asia, and Africa, untreated wastewater from sewage and industry mainly contribute to eutrophication. Runoff from large agricultural fields enters creeks and bays because of rain or irrigation practices. In developed countries, such as the United States and nations in the European Union, heavy use of animal manure and commercial fertilizers in agriculture are the main contributors to eutrophication. Human activities have emitted nearly twice as much nitrogen and three times as much phosphorus as natural emissions.ĭifferent regions of the world emit different levels of these nutrients.
These nutrients enter our air, soil, and water. These three processes emit large amounts of nitrogen and phosphorous. Understanding the eutrophication process provides the clearest picture of how and why dead zones develop.Įutrophic events have increased because of the rapid rise in intensive agricultural practices, industrial activities, and population growth. For this reason, dead zones are often located near inhabited coastlines.
Human activities are the main cause of these excess nutrients being washed into the ocean. With too many nutrients, however, cyanobacteria grows out of control, which can be harmful. At normal levels, these nutrients feed the growth of an organism called cyanobacteria, or blue-green algae. That is why these areas are called dead zones.ĭead zones occur because of a process called eutrophication, which happens when a body of water gets too many nutrients, such as phosphorus and nitrogen. Because most organisms need oxygen to live, few organisms can survive in hypoxic conditions. Dead zones are low-oxygen, or hypoxic, areas in the world’s oceans and lakes.
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