The number and diversity of benthic, or bottom-dwelling, species are especially reduced. By depriving organisms of sunlight and oxygen, algal blooms negatively impact a variety of species that live below the water’s surface. Oxygen is necessary for almost all aquatic life, from sea grasses to fish. Sunlight is necessary for plants and organisms like phytoplankton and algae, which manufacture their own nutrients from sunlight, water, and carbon dioxide. They also prevent oxygen from being absorbed by organisms beneath them. Algal blooms prevent light from penetrating the water’s surface. Algal blooms can create dead zones beneath them. This rapid development of algae and phytoplankton is called an algal bloom. Organisms such as phytoplankton, algae, and seaweeds will grow quickly and excessively on the water’s surface. Algal Blooms Phosphorous, nitrogen, and other nutrients increase the productivity or fertility of marine ecosystems. Dead zones result from these impacts, which include algal blooms and hypoxia. Eutrophication and the Environment The eutrophication process has severe environmental impacts. The Chesapeake still has a dead zone, whose size varies with the season and weather. Since 1967, the Chesapeake Bay Foundation has led a number of programs that aim to improve the bay’s water quality and curb pollution runoff. 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. Atmospheric sources of nitrogen also contribute to eutrophication in some areas of the world. 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. 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. 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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