Eutrophication is an increase in chemical nutrients — typically compounds containing nitrogen or phosphorus — in an ecosystem. It may occur on land or in fresh or salt water. The nutrients primarily come from sewage and fertilizer run off.
The two most acute symptoms of eutrophication are hypoxia (or oxygen depletion) and harmful algal blooms, which among other things can destroy aquatic life in affected areas. An algal bloom is a rapid increase in the population of algae in an aquatic ecosystem. Algal blooms may occur in freshwater as well as marine environments.
As more algae and plants grow, others die. This dead organic matter becomes food for bacteria that decomposes it. With more food available, the bacteria increase in number and use up the dissolved oxygen in the water. When the dissolved oxygen content decreases, many fish and aquatic insects cannot survive. This results in a dead area. Perhaps the best known example of a dead zone in the U.S. is found off the coast of New Orleans where the mighty Mississippi River drains in the Gulf of Mexico.
The Mississippi River originates as a tiny outlet stream from Lake Itasca in northern Minnesota. This tiny stream goes on to become one of the world’s greatest river systems, draining all or parts of 31 states and 2,350 square miles (6,086 sq. km) before it finally reaches the Gulf of Mexico. As a record-breaking volume of floodwater laden with sewage and fertilizers rolls down the waterways of the Mississippi Basin towards the Gulf of Mexico, a joint federal-state task force released an updated action plan to reduce low oxygen levels that cause a dead zone each summer in the Gulf of Mexico. Researchers say this year’s dead zone may be the largest ever recorded due to increased fertilizer use in the Midwest and flooding along the Mississippi River dumping even more water than usual into the Gulf of Mexico
The dead zone in the Gulf of Mexico is caused by eutrophication. Eutrophication threatens and degrades many coastal ecosystems around the world. Eutrophication leads to hypoxia or the absence of oxygen in the ecosystem reaching living tissues. Without oxygen, the ecosystem dies.