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. Different regions of the world emit different levels of these nutrients. Human activities have emitted nearly twice as much nitrogen and three times as much phosphorus as natural emissions. These nutrients enter our air, soil, and water. These three processes emit large amounts of nitrogen and phosphorous. Causes of Eutrophication Eutrophic events have increased because of the rapid rise in intensive agricultural practices, industrial activities, and population growth. Understanding the eutrophication process provides the clearest picture of how and why dead zones develop. 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, cyano bacteria 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. Dead zones occur because of a process called eutrophication, which happens when a body of water gets too many nutrients, such as phosphorus and nitrogen. That is why these areas are called dead zones. 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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