What are Dead Zones?
According to the National Oceanic and Atmospheric Administration, the term "dead zone" is a more common name for hypoxia, which refers to a reduced level of oxygen in the water. Hypoxic zones are areas in ocean that have much lower oxygen concentration in which animal life suffocates and dies. One of the largest dead zones forms in the Gulf of Mexico every spring. When farmers prep their lands every spring with fertilization, the run off from the rainfall gathers in streams, rivers, and lakes and creates a disturbance of the animal life within the area. These hypoxia areas occur naturally throughout the world, but scientists are concerned about the areas that are created or enhanced by human activity. There are many factors that influence the contribution to a dead zone such as physical, chemical, and biological stressors, but the issue of nutrient pollution is considered the primary cause of dead zones created by humans. The excess nutrients that run off from the land or as piped wastewater are capable of stimulating the overgrowth of algae. When an overgrowth of algae occurs, the algae sinks to the bottom of the body of water and decomposes. This process of decomposition consumes the oxygen source and depletes the supply needed to sustain a healthy living environment for the animal life. These dead zones are usually located in many areas in the United States, but particularly along the East Coast, the Gulf of Mexico, and the Great Lakes. The NOAA states that there is not a specific country or area that is immune to producing a dead zone. The second largest dead zone is located within the United States, which is in the northern Gulf of Mexico.
Vast algae blooms in northern Europe's Baltic Sea fuels annual aquatic dead zones, where the oxygen levels are too low to support most animal life.
How Many/Where are They Located?
The Scientific American states that a new study has been reported in which there are 405 identified dead zones throughout the world. In the 1960's, there were 49 identified areas with animal life depletion due to the lack of oxygen. The largest identified dead zone lies in the Baltic Sea and it lacks oxygen year-round. The study also indicated that around 235,000 tons of food is lost to hypoxia in the Gulf of Mexico. This amount is enough to feed 75% of the average brown shrimp harvested from Louisiana gulf.
Satellite image of toxic algae bloom in Lake Erie in 2011.
Dead Zone's Impact on the Ecosystem?
According to The National Center for Biotechnology Information, hypoxia affects thousands of km2 of marine waters all over the world. This causes mass mortality of animals,bethic defaunation, and a decline in fishery production in many places. Due to the growth of the population and global warming, over the past few decades, the severity and frequency of hypoxia has increased dramatically and is likely to be an issue in the future. The effect of hypoxia on marine animals has an effect on reproduction, development, growing, and feeding. Some fish species and marine organisms are able to detect hypoxia and are able to actively avoid it.
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