The dead zone is a region of hypoxia (low oxygen) in the oceans and large lakes of the world, caused by "excessive nutritional contamination of human activity plus other factors that deplete the oxygen necessary to support most marine life under and near water. (NOAA) ". In the 1970s marine experts began to record an increase in dead zones. This happens near the inhabited coastline, where the aquatic life is most concentrated. (The vast central part of the ocean, which naturally has little life, is not considered a "dead zone".)
In March 2004, when the recently published United Nations Environment Program published the GEO Year Book 2003 (GEO Year Book 2003), it reports 146 dead zones in the oceans of the world where marine life can not supported due to the low oxygen levels. Some of them are as small as square kilometers (0.4 miles), but the largest dead zone covers 70,000 square kilometers (27,000m²). A 2008 study calculated 405 dead zones around the world.
Video Dead zone (ecology)
Cause
Dead water and marine zones can be caused by increased chemical nutrients (especially nitrogen and phosphorus) in the water, known as eutrophication. This chemical is the basic building blocks of single-celled organisms such as plants that live in the water column, and whose growth is limited in part by the availability of these materials. Eutrophication can lead to a rapid increase in the density of this particular type of phytoplankton, a phenomenon known as algal bloom.
Dr. Limnologis. David Schindler, whose research in the Experimental Lake Area led to the prohibition of harmful phosphates in detergents, warns of algae and dead zones,
"The blooms of the destructive fish that destroyed the Great Lakes in the 1960s and 1970s have not disappeared: they have moved west into the arid world where people, industries, and agriculture are increasingly weighing on the small freshwater quality there to be had at here.... This is not just a matter of grasslands The global expansion of dead zones caused by algae blooms is increasing rapidly. "
The main groups of algae are Cyanobacteria, green algae, Dinoflagellate, Coccolithophores, and Diatoms algae. Increased nitrogen and phosphorus inputs generally cause Cyanobacteria to bloom. Cyanobacteria are not good foods for zooplankton and fish and therefore accumulate in water, die, and then rot. Degradation of their biomass bacteria consumes oxygen in water, thus creating a hypoxic state. Other algae are consumed and therefore do not accumulate at the same level as Cyanobacteria. The dead zone can be caused by nature and by anthropogenic factors. Natural causes include coastal upwelling and changes in wind and water circulation patterns. The use of chemical fertilizers is considered the main cause of humans in dead zones around the world. Runoff from waste, urban land use, and fertilizer can also contribute to eutrophication.
The famous dead zones of the United States include the northern Gulf of Mexico region, around the fall of the Mississippi River, the Northwest Pacific coastal area, and the Elizabeth River in Virginia Beach, all of which have been proven to be repeated events over the past few years.
In addition, natural oceanographic phenomena can lead to deoxygenation of parts of the water column. For example, a closed water body, such as a fjord or the Black Sea, has a shallow sill at its entrance, causing water to become stagnant there for a long time. The eastern Pacific Ocean and the northern Indian Ocean have lowered the oxygen concentration thought to be in an area where there is minimal circulation to replace the oxygen consumed. These areas are also known as the minimum oxygen zone (OMZ). In many cases, OMZ is a permanent or semi-permanent area.
Remnants of organisms found in sediment layers near the mouth of the Mississippi River show four hypoxic events before the advent of artificial fertilizers. In this sedimentary layer, species of tolerant anoxia are the most common. The periods indicated by the sedimentary record correspond to the high flow history records recorded by the instrument in Vicksburg, Mississippi.
Changes in ocean circulation triggered by ongoing climate change can also increase or magnify other causes of oxygen depletion in the oceans.
In August 2017, a report found that the US meat industry was responsible for the largest ever dead zone in the Gulf of Mexico. Runoff from scattered debris and pollution of fertilizer contaminate water from Heartland to the Gulf. Most of this pollution comes from the large amount of corn and soybeans used to raise meat animals for agribusiness companies, such as Tyson.
Maps Dead zone (ecology)
Effects
The low oxygen levels recorded along the Gulf Coast of North America have led to reproductive problems in fish that involve decreased reproductive organ size, low egg count and lack of spawning.
In a study of Killifish Bay by Southeastern Louisiana University conducted in three bays along the Gulf Coast, fish live in a bay where the oxygen content in the water drops to 1 to 2 parts per million (ppm) for three hours or more per day. found to have smaller reproductive organs. Male gonads are 34% to 50% of men of similar size at bay where normal oxygen levels (6-8 ppm). Women were found to have ovaries half that larger than those in normal oxygen levels. The number of eggs in women living in hypoxic waters is only one-seventh the number of eggs in fish living in normal oxygen levels.
Fish raised in laboratory hypoxia conditions exhibit very low concentrations of sex hormones and increased activity in two genes triggered by the hypoxia-induced factor protein (HIF). Under hypoxic conditions, HIF is paired with another protein, ARNT. Both then bind the DNA in the cell, activating the genes in the plant cells.
Under normal oxygen conditions, ARNT joins the estrogen to activate the gene. Hypoxic cell in vitro does not react to the estrogen placed in the tube. HIF appears to make ARNT unavailable for interacting with estrogen, providing a mechanism in which the hypoxic state alters reproduction in fish.
It may be expected that the fish will escape from the possibility of suffocation, but they often quickly become unconscious and destroyed. Animals that live underground are slow like clams, lobsters, and oysters can not escape. All colonial animals were put out. The normal re-mineralization and recycling that occurs between benticic life forms is rigid.
It has been shown that future changes in oxygen can affect most marine ecosystems and have socio-economic consequences due to human dependence on marine goods and services.
Location
In the 1970s, dead sea zones were first recorded in residential areas where intensive economic use stimulated scientific scrutiny: in the US Gulf of Chesapeake Bay, in the Scandinavian strait called Kattegat, which is the mouth of the Baltic Sea and in other important Baltic Sea. fishing spots, the Black Sea, and the north Adriatic.
Other dead sea zones have appeared in the coastal waters of South America, China, Japan, and New Zealand. A 2008 study calculated 405 dead zones around the world.
Baltic Sea
High levels of hypoxia contribute to the collapse of Norwegian lobster fisheries.
Researchers from the Baltic Nest Institute published in one of the editions of PNAS reported that dead zones in the Baltic Sea have grown from about 5,000 km2 to more than 60,000 km2 in recent years.
Some of the causes behind the increased increase in dead zones can be attributed to the use of fertilizers, large animal farms, burning of fossil fuels, and waste from municipal wastewater treatment plants.
Elizabeth River, Virginia
The Elizabeth River Estuary is important for Norfolk, Virginia, Chesapeake, Virginia, Virginia Beach, Virginia and Portsmouth, Virginia. It has been contaminated by nitrogen and phosphorus, but also the toxic deposits of the shipbuilding industry, the military, the world's largest coal export facility, refineries, loading docks, container repair facilities and so on, so the fish have "disappeared since the 1920s ". s ".In 1993, a group was formed to clean it up, adopt mummichog as a mascot, and have transferred thousands of tons of contaminated sediment.In 2006, a biological 35-acre dead zone called Money Point was dredged out, and showed fish to return, wet to recover
Lake Erie
The dead zone is in the middle of Lake Erie from east of Point Pelee to Long Point and stretches to shore in Canada and the United States. This zone has been noticed since the 1950s to the 1960s, but efforts since the 1970s have been made by Canada and the US to reduce pollution of runoff into the lake as a means to reverse the growth of dead zones. Overall the oxygen level of the lake is bad with only a small area east of Long Point that has a better rate. The greatest impact of poor oxygen levels is the lacustrine life and the fishing industry.
Downstream St. Lawrence Estuary
A dead zone exists in the Lower St Lawrence River area east of the Saguenay River to the east of Baie Comeau, the largest at a depth of more than 275 meters (902 feet) and noticed since the 1930s. The main concern for Canadian scientists is the impact of fish found in the area.
Oregon
Offshore Cape Perpetua, Oregon, there is also a dead zone with 2006 reporting the size of 300 square miles (780 km2 ²). This dead zone exists only during the summer, probably due to wind patterns. The Oregon coast has also seen hypoxic water transporting itself from the continental shelf to coastal embays. This appears to cause intensity in some areas of Oregon's climate such as water containing oxygen and upwelled winds.
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The undersea area of ​​temporary hypoxia that occurs most of the summer off the coast of Louisiana in the Gulf of Mexico is the largest recurrent hypoxic zone in the United States. The Mississippi River, which is a drainage area for 41% of the US continent, removes high nutrient runoffs such as nitrogen and phosphorus into the Gulf of Mexico. According to a fact sheet 2009 made by NOAA, "seventy percent of the nutritional burden that causes hypoxia is the result of this vast drainage basin". which includes the heart of US agribusiness, the Midwest. Disposal of treated wastes from urban areas (pop C 12 million in 2009) combined with agricultural runoff yields c. 1.7 million tons of phosphorus and nitrogen to the Gulf of Mexico each year. Although Iowa occupies less than 5% of the Mississippi River basin, the average annual nitrous discharge from surface water in Iowa is about 204,000 to 222,000 metric tons, or 25% of all nitrate that the Mississippi River delivers to the Gulf of Mexico. The exports of the Raccoon River watershed were the highest in the United States with an annual yield of 26.1 kg/ha/year ranking as the highest nitrate loss of 42 subwatershed Mississippi evaluated for the Gulf of Mexico hypoxia report.
Size
The underwater hypoxic area that occurs for several weeks each summer in the Gulf of Mexico has been mapped for most of the year from 1985 to 2017. Size varies each year from a record high by 2017 when it covers over 22,730 sq km (8,776 sq mi) to record lows in 1988 from 39 square kilometers (15 square miles). The 2015 dead zone measures 16,760 square kilometers (6,474 square miles). Nancy Rabalais of the University of Louisiana Marine Consortium in Cocodrie, Louisiana estimates dead zones or hypoxic zones in 2012 will cover an area of ​​17,353 square kilometers (6,700 square miles) larger than Connecticut; However, when the measurement is complete, the lower water area of ​​hypoxia in 2012 amounts to only 7,480 square kilometers. Models using the nitrogen flow from the Mississippi River to predict "dead zone" areas have been criticized for being systematically high from 2006 to 2014, after forecasting record areas in 2007, 2008, 2009, 2011 and 2013 that were never realized.
By the end of the summer of 1988, the death zones disappeared due to severe drought causing the flow of Mississippi to fall to its lowest level since 1933. During the period of the great floods in the Mississippi River Basin, as in 1993, "" dead zones "increased dramatically, in size, around 5,000 km (3,107 mi) larger than the previous year ".
Economic impact
Some claim that dead zones threaten the lucrative commercial and recreational fisheries in the Gulf of Mexico. "In 2009, the value of the commercial fishing dock in the Gulf was $ 629 million.Almost three million recreational fishermen further contributed about $ 10 billion to the Gulf economy, taking 22 million fishing trips." Scientists are not in universal agreement that nutrient loading has a negative impact on fisheries. Grimes made the case that nutrient loading increased fisheries in the Gulf of Mexico. Courtney et al. hypothesized that nutrient loading might have contributed to the increase in red snapper in the Gulf of Mexico north and west.
History
Shrimp trawling ships first reported 'dead zone' in the Gulf of Mexico in 1950, but it was not until 1970 when the size of the hypoxia zone had increased so the scientists began to investigate.
After 1950, forest and wetland conversion for agricultural and urban development was accelerated. "The Missouri River Valley has hundreds of thousands of hectares of forest and wetlands (66,000,000 hectares) replaced by agricultural activity [...] In Lower Mississippi, a third of the valley forest was converted to agricultural land between 1950 and 1976."
In July 2007, the dead zone was found off the coast of Texas where the Brazos River was in the Gulf.
The Gulf of Oman
In 2018, scientists confirmed that the Gulf of Oman includes one of the largest and most severe sea dead zones in the world. The dead zone covers nearly 63,700 square miles of Gulf of Oman. The dead zone is completely composed of anoxic conditions, which means no oxygen, or suboxic conditions, with low oxygen levels. The cause is a combination of increased ocean warming with increased runoff of nitrogen and phosphorus from fertilizers. The previous dead zone was not researched because of geopolitical factors.
Energy Independence and Security Act of 2007
The Energy Independence and Security Act of 2007 calls for the production of 36 billion billion US (140,000,000 m 3 ) of renewable fuels by 2022, including 15 billion US gallons (57 million m 3 ) from corn-based ethanol, three times that of current production that would require a similar increase in corn production. Unfortunately, the plan poses a new problem; increased demand for corn production yields a proportional increase in nitrogen runoff. Although nitrogen, which makes up about 78% of Earth's atmosphere, is an inert gas, it has a more reactive form, two of which (nitrate and ammonia) are used to make fertilizer.
According to Fred Under, a professor of plant physiology at the University of Illinois at Urbana-Champaign, corn needs more nitrogen-based fertilizer because it produces higher grains per unit area than other crops and, unlike other plants, maize is entirely dependent on available nitrogen in the soil. The results, reported on March 18, 2008 in the Proceedings of the National Academy of Sciences, show that an increase in corn production to meet the 15 billion-US gallon target (57,000,000 m 3 ) will increase nitrogen loading in the Dead Zone by 10-18%. This will increase levels of nitrogen up to twice the level recommended by the Mississippi River Watershed Conservation Programs, a coalition of federal, state, and tribal agencies that have been monitoring dead zones since 1997. the task force says a 30% reduction in nitrogen runoff is needed if the dead zone shrinks.
Inversion
The dead zone is reversible, despite the extinction of an organism lost by its emergence. The Black Sea death zone, formerly the largest in the world, was largely lost between 1991 and 2001 after fertilizers became too expensive to use after the collapse of the Soviet Union and the collapse of a planned economy centered in Eastern and Central Europe. Fisheries have again become the main economic activity in the region.
While the Black Sea "cleansing" is largely unintentional and involves a decline in the use of uncontrollable fertilizers, the US has advocated other purge by reducing large industrial emissions. From 1985 to 2000, the North Sea dead zone had nitrogen reduced by 37% when policy efforts by countries on the Rhine River reduced the waste and emissions of the nitrogen industry into water. Other cleansing has occurred along the Hudson River and San Francisco Bay.
Source of the article : Wikipedia
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