“Dead zone (ecology)”的意思、由来-开放百科全书

Dead zones are hypoxic (low-oxygen) areas in the world's oceans and large lakes, caused by "excessive nutrient pollution from human activities coupled with other factors that deplete the oxygen required to support most marine life in bottom and near-bottom water. (NOAA)".^[2] Historically, many of these sites were naturally occurring. However, in the 1970s, oceanographers began noting increased instances and expanses of dead zones. These occur near inhabited coastlines, where aquatic life is most concentrated. (The vast middle portions of the oceans, which naturally have little life, are not considered "dead zones".)

In March 2004, when the recently established UN Environment Programme published its first Global Environment Outlook Year Book (GEO Year Book 2003), it reported 146 dead zones in the world's oceans where marine life could not be supported due to depleted oxygen levels. Some of these were as small as a square kilometre (0.4 mi²), but the largest dead zone covered 70,000 square kilometres (27,000 mi²). A 2008 study counted 405 dead zones worldwide.^[3]^[4]

Causes

Aquatic and marine dead zones can be caused by an increase in nutrients (particularly nitrogen and phosphorus) in the water, known as eutrophication. These chemicals are the fundamental building blocks of single-celled, plant-like organisms that live in the water column, and whose growth is limited in part by the availability of these materials. Eutrophication can lead to rapid increases in the density of certain types of these phytoplankton, a phenomenon known as an algal bloom.{{citation needed|date=March 2017}}

The major groups of algae are Cyanobacteria, green algae, Dinoflagellates, Coccolithophores and Diatom algae. Increase in input of nitrogen and phosphorus generally causes Cyanobacteria to bloom. Other algae are consumed and thus do not accumulate to the same extent as Cyanobacteria.^[5] Cyanobacteria are not good food for zooplankton and fish and hence accumulate in water, die, and then decompose. The bacterial degradation of their biomass consumes the oxygen in the water, thereby creating the state of hypoxia. Dead zones can be caused by natural and by anthropogenic factors. Natural causes include coastal upwelling and changes in wind and water circulation patterns. Use of chemical fertilizers is considered the major human-related cause of dead zones around the world. Runoff from sewage, urban land use, and fertilizers can also contribute to eutrophication.^[6]

Notable dead zones in the United States include the northern Gulf of Mexico region,^[3] surrounding the outfall of the Mississippi River, the coastal regions of the Pacific Northwest, and the Elizabeth River in Virginia Beach, all of which have been shown to be recurring events over the last several years.

Additionally, natural oceanographic phenomena can cause deoxygenation of parts of the water column. For example, enclosed bodies of water, such as fjords or the Black Sea, have shallow sills at their entrances, causing water to be stagnant there for a long time.{{citation needed|date=March 2017}} The eastern tropical Pacific Ocean and northern Indian Ocean have lowered oxygen concentrations which are thought to be in regions where there is minimal circulation to replace the oxygen that is consumed.^[7] These areas are also known as oxygen minimum zones (OMZ). In many cases, OMZs are permanent or semipermanent areas.{{citation needed|date=March 2017}}

Remains of organisms found within sediment layers near the mouth of the Mississippi River indicate four hypoxic events before the advent of synthetic fertilizer. In these sediment layers, anoxia-tolerant species are the most prevalent remains found. The periods indicated by the sediment record correspond to historic records of high river flow recorded by instruments at Vicksburg, Mississippi.{{citation needed|date=March 2017}}

Changes in ocean circulation triggered by ongoing climate change could also add or magnify other causes of oxygen reductions in the ocean.^[8]

In August 2017, a report suggested that the US meat industry and agroeconomic system are predominantly responsible for the largest-ever dead zone in the Gulf of Mexico^[9]. Soil runoff and leached nitrate, exacerbated by agricultural land management and tillage practices as well as manure and synthetic fertilizer usage, contaminated water from the Heartland to the Gulf of Mexico. A large portion of the crops grown in this region are used as major feed components in the production of meat animals for agribusiness companies, like Tyson and Smithfield Foods.^[10]

Effects

Low oxygen levels recorded along the Gulf Coast of North America have led to reproductive problems in fish involving decreased size of reproductive organs, low egg counts and lack of spawning.

In a study of the Gulf killifish by the Southeastern Louisiana University done in three bays along the Gulf Coast, fish living in bays where the oxygen levels in the water dropped to 1 to 2 parts per million (ppm) for three or more hours per day were found to have smaller reproductive organs. The male gonads were 34% to 50% as large as males of similar size in bays where the oxygen levels were normal (6 to 8 ppm). Females were found to have ovaries that were half as large as those in normal oxygen levels. The number of eggs in females living in hypoxic waters were only one-seventh the number of eggs in fish living in normal oxygen levels.^[11]

Fish raised in laboratory-created hypoxic conditions showed extremely low sex hormone concentrations and increased elevation of activity in two genes triggered by the hypoxia-inductile factor (HIF) protein. Under hypoxic conditions, HIF pairs with another protein, ARNT. The two then bind to DNA in cells, activating genes in those plant cells.

Under normal oxygen conditions, ARNT combines with estrogen to activate genes. Hypoxic cells in vitro did not react to estrogen placed in the tube. HIF appears to render ARNT unavailable to interact with estrogen, providing a mechanism by which hypoxic conditions alter reproduction in fish.^[12]

It might be expected that fish would flee the potential suffocation, but they are often quickly rendered unconscious and doomed.{{citation needed|date=March 2017}} Slow moving bottom-dwelling creatures like clams, lobsters and oysters are unable to escape. All colonial animals are extinguished. The normal re-mineralization and recycling that occurs among benthic life-forms is stifled.{{citation needed|date=March 2017}}

Despite most other life forms being killed by the lack of oxygen, jellyfish can thrive and are sometimes present in dead zones in vast numbers. These jellyfish blooms produce mucus and waste, leading to major changes in food webs in the ocean. The organic carbon is metabolised by bacteria which return it to the atmosphere in the form of carbon dioxide in what has been termed a "jelly carbon shunt".^[13]

It has been shown that future changes in oxygen could affect most marine ecosystems and have socio-economic ramifications due to human dependency on marine goods and services.^[8]

Locations

In the 1970s, marine dead zones were first noted in settled areas where intensive economic use stimulated scientific scrutiny: in the U.S. East Coast's Chesapeake Bay, in Scandinavia's strait called the Kattegat, which is the mouth of the Baltic Sea and in other important Baltic Sea fishing grounds, in the Black Sea, and in the northern Adriatic.^[14]

Other marine dead zones have appeared in coastal waters of South America, China, Japan, and New Zealand. A 2008 study counted 405 dead zones worldwide.^[15]^[16]^[17]

Baltic Sea

Researchers from Baltic Nest Institute published in one of PNAS issues reports that the dead zones in the Baltic Sea have grown from approximately 5,000 km2 to more than 60,000 km2 in recent years.

Some of the causes behind the elevated increase of dead zones can be attributed to the use of fertilizers, large animal farms, the burning of fossil fuels, and effluents from municipal wastewater treatment plants.^[18]

Elizabeth River, Virginia

The Elizabeth River estuary is important for Norfolk, Virginia, Chesapeake, Virginia, Virginia Beach, Virginia and Portsmouth, Virginia. It has been polluted by nitrogen and phosphorus, but also toxic deposits from the shipbuilding industry, the military, the world's largest coal export facility, refineries, loading docks, container-repair facilities and others, so fish had been "offlimits since the 1920s". In 1993, a group formed to clean it up, adopting the mummichog as a mascot, and has removed thousands of tons of contaminated sediment. In 2006, a 35-acre biological dead zone called Money Point was dredged out, and this let fish return, and the wetland recover^[19]

Lake Erie

A dead zone exists in the central part of Lake Erie from east of Point Pelee to Long Point and stretches to shores in Canada and the United States.^[20] The zone has been noticed since the 1950s to 1960s, but efforts since the 1970s have been made by Canada and the US to reduce runoff pollution into the lake as means to reverse the dead zone growth. Overall the lake's oxygen level is poor with only a small area to the east of Long Point that has better levels. The biggest impact of the poor oxygen levels is to lacustrine life and fisheries industry.

Lower St. Lawrence Estuary

A dead zone exists in the Lower St. Lawrence River area from east the Saguenay River to east of Baie Comeau, greatest at depths over {{convert|275|m|ft}} and noticed since the 1930s.^[21] The main concerns for Canadian scientists is the impact of fish found in the area.

Oregon

Off the coast of Cape Perpetua, Oregon, there is also a dead zone with a 2006 reported size of 300 square miles (780 km²).{{citation needed|date=August 2014}} This dead zone only exists during the summer, perhaps due to wind patterns. The Oregon coast has also seen hypoxic water transporting itself from the continental shelf to the coastal embayments. This has seemed to cause intensity in several areas of Oregon's climate such as upwelled water containing oxygen concentration and upwelled winds.^[22]{{page needed|date=March 2017}}

Gulf of Mexico 'dead zone'

The area of temporary hypoxic bottom water that occurs most summers off the coast of Louisiana in the Gulf of Mexico^[23] is the largest recurring hypoxic zone in the United States.^[24] The Mississippi River, which is the drainage area for 41% of the continental United States, dumps high-nutrient runoff such as nitrogen and phosphorus into the Gulf of Mexico. According to a 2009 fact sheet created by NOAA, "seventy percent of nutrient loads that cause hypoxia are a result of this vast drainage basin".^[25] which includes the heart of U.S. agribusiness, the Midwest. The discharge of treated sewage from urban areas (pop. c 12 million in 2009) combined with agricultural runoff deliver c. 1.7 million tons of phosphorus and nitrogen into the Gulf of Mexico every year.^[25] Even though Iowa occupies less than 5% of the Mississippi River drainage basin, average annual nitrate discharge from surface water in Iowa is about 204,000 to 222,000 metric tonnes, or 25% of all the nitrate which the Mississippi River delivers to the Gulf of Mexico.^[26] Export from the Raccoon River Watershed is among the highest in the United States with annual yields at 26.1 kg/ha/year which ranked as the highest loss of nitrate out of 42 Mississippi subwatersheds evaluated for a Gulf of Mexico hypoxia report.^[27]^[28] In 2012, Iowa introduced the Iowa Nutrient Reduction Strategy which, "The Iowa Nutrient Reduction Strategy is a science and technology-based framework to assess and reduce nutrients to Iowa waters and the Gulf of Mexico. It is designed to direct efforts to reduce nutrients in surface water from both point and nonpoint sources in a scientific, reasonable and cost effective manner."^[29] The strategy continues to evolve, using voluntary methods to reduce Iowa's negative contributions through outreach, research, and implementation of nutrient holding practices. In order to help reduce agricultural runoff into the Mississippi Basin, Minnesota passed [https://www.revisor.mn.gov/statutes/cite/103F.48 MN Statute 103F.48] in 2015, also known as the "Buffer Law", which was designed to implement mandatory riparian buffers between farmland and public waterways across the State of Minnesota. The Minnesota Board of Water and Soil Resources (BWSR) issued a January 2019 report stating that compliance with the 'Buffer Law' has reached 99%.

Size

The area of hypoxic bottom water that occurs for several weeks each summer in the Gulf of Mexico has been mapped most years from 1985 through 2017. The size varies annually from a record high in 2017 when it encompassed more than 22,730 sq kilometers (8,776 square miles) to a record low in 1988 of 39 sq kilometers (15 square miles).^[30]^[23]^[31] The 2015 dead zone measured 16,760 square kilometers (6,474 square miles).^[32]

In late summer 1988 the dead zone disappeared as the great drought caused the flow of Mississippi to fall to its lowest level since 1933. During times of heavy flooding in the Mississippi River Basin, as in 1993, ""the "dead zone"

dramatically increased in size, approximately {{convert|5000|km|0|abbr=on}} larger than the previous year".^[34]

Economic impact

Some assert that the dead zone threatens lucrative commercial and recreational fisheries in the Gulf of Mexico. "In 2009, the dockside value of commercial fisheries in the Gulf was $629 million. Nearly three million recreational fishers further contributed about $10 billion to the Gulf economy, taking 22 million fishing trips."^[35]{{full citation needed|date=March 2017}} Scientists are not in universal agreement that nutrient loading has a negative impact on fisheries. Grimes makes a case that nutrient loading enhances the fisheries in the Gulf of Mexico.^[36] Courtney et al. hypothesize, that nutrient loading may have contributed to the increases in red snapper in the northern and western Gulf of Mexico.^[37]

History

Shrimp trawlers first reported a 'dead zone' in the Gulf of Mexico in 1950, but it was not until 1970 when the size of the hypoxic zone had increased that scientists began to investigate.^[38]

After 1950, the conversion of forests and wetlands for agricultural and urban developments accelerated. "Missouri River Basin has had hundreds of thousands of acres of forests and wetlands (66,000,000 acres) replaced with agriculture activity [. . .] In the Lower Mississippi one-third of the valley's forests were converted to agriculture between 1950 and 1976." ^[38]

In July 2007, a dead zone was discovered off the coast of Texas where the Brazos River empties into the Gulf.^[39]

Energy Independence and Security Act of 2007

The Energy Independence and Security Act of 2007 calls for the production of {{convert|36|e9USgal|m3}} of renewable fuels by 2022, including {{convert|15|e9USgal|m3}} of corn-based ethanol, a tripling of current production that would require a similar increase in corn production.^[40] Unfortunately, the plan poses a new problem; the increase in demand for corn production results in a proportional increase in nitrogen runoff. Although nitrogen, which makes up 78% of the Earth's atmosphere, is an inert gas, it has more reactive forms, two of which (nitrate and ammonia) are used to make fertilizer.^[41]

According to {{Citation/make link|http://cropsci.illinois.edu/faculty/below/|Fred Below}}, a professor of crop physiology at the University of Illinois at Urbana-Champaign, corn requires more nitrogen-based fertilizer because it produces a higher grain per unit area than other crops and, unlike other crops, corn is completely dependent on available nitrogen in soil. The results, reported 18 March 2008 in Proceedings of the National Academy of Sciences, showed that scaling up corn production to meet the {{convert|15|e9USgal|m3|adj=on}} goal would increase nitrogen loading in the Dead Zone by 10–18%. This would boost nitrogen levels to twice the level recommended by the Mississippi Basin/Gulf of Mexico Water Nutrient Task Force (Mississippi River Watershed Conservation Programs), a coalition of federal, state, and tribal agencies that have monitored the dead zone since 1997. The task force says a 30% reduction of nitrogen runoff is needed if the dead zone is to shrink.^[40]

Reversal

Dead zones are reversible, though the extinction of organisms that are lost due to its appearance is not. The Black Sea dead zone, previously the largest in the world, largely disappeared between 1991 and 2001 after fertilizers became too costly to use following the collapse of the Soviet Union and the demise of centrally planned economies in Eastern and Central Europe. Fishing has again become a major economic activity in the region.^[42]

While the Black Sea "cleanup" was largely unintentional and involved a drop in hard-to-control fertilizer usage, the U.N. has advocated other cleanups by reducing large industrial emissions.^[42] From 1985 to 2000, the North Sea dead zone had nitrogen reduced by 37% when policy efforts by countries on the Rhine River reduced sewage and industrial emissions of nitrogen into the water. Other cleanups have taken place along the Hudson River^[43] and San Francisco Bay.^[15]

See also

Notes

1. ^Aquatic Dead Zones NASA Earth Observatory. Revised 17 July 2010. Retrieved 17 January 2010.
2. ^{{cite web|url=http://www.noaanews.noaa.gov/stories2012/20120621_deadzone.html|title=NOAA: Gulf of Mexico 'dead zone' predictions feature uncertainty|publisher=National Oceanic and Atmospheric Administration (NOAA)|location=|date=June 21, 2012|page=|accessdate=June 23, 2012}}
3. ^¹{{cite journal|journal=The Economist|title=Blooming horrible: Nutrient pollution is a growing problem all along the Mississippi|url=http://www.economist.com/node/21557365?fsrc=scn/tw/te/ar/bloominghorrible|accessdate=June 23, 2012}}
4. ^{{cite book|title=The Algal Bowl: Overfertilization of the World's Freshwaters and Estuaries|url=https://www.amazon.com/The-Algal-Bowl-Overfertilization-Freshwaters/dp/0888644841|publisher=University of Alberta Press|location=Edmonton, Alberta|author1=David W. Schindler|author2=John R. Vallentyne|year=2008|accessdate=June 23, 2012}}
5. ^https://sanjeebme.blogspot.com/2019/03/global-warming-and-health.html sanjeeb balmiki{{dead link|date=March 2019|bot=InternetArchiveBot |fix-attempted=yes }}, www.https://sanjeebme.blogspot.com/2019/03/global-warming-and-health.html, 2010-06-17
6. ^Corn boom could expand 'dead zone' in Gulf msnbc.msn.com
7. ^Pickard, G.L. and Emery, W.J. 1982. Description Physical Oceanography: An Introduction. Pergamon Press, Oxford, page 47.
8. ^¹{{cite journal |last1=Mora |first1=C. |title=Biotic and Human Vulnerability to Projected Changes in Ocean Biogeochemistry over the 21st Century |journal=PLOS Biology |volume=11 |pages=e1001682 |year=2013 |doi=10.1371/journal.pbio.1001682|display-authors=etal |pmid=24143135 |pmc=3797030}}
9. ^{{Cite news|url=https://www.theguardian.com/environment/2017/aug/01/meat-industry-dead-zone-gulf-of-mexico-environment-pollution|title=Meat industry blamed for largest-ever 'dead zone' in Gulf of Mexico|last=Milman|first=Oliver|date=2017-08-01|work=The Guardian|access-date=2017-08-04|language=en-GB|issn=0261-3077}}
10. ^{{Cite web|url=http://www.mightyearth.org/wp-content/uploads/2017/07/Meat-Pollution-in-America.pdf|title=Mystery Meat II: The Industry Behind the Quiet Destruction of the American Heartland|last=von Reusner|first=Lucia|date=August 1, 2017|website=Mighty Earth|access-date=August 4, 2017}}
11. ^Landry, C.A., S. Manning, and A.O. Cheek. 2004. Hypoxia suppresses reproduction in Gulf killifish, Fundulus grandis. e.hormone 2004 conference. Oct. 27–30. New Orleans.
12. ^Johanning, K., et al. 2004. Assessment of molecular interaction between low oxygen and estrogen in fish cell culture. Fourth SETAC World Congress, 25th Annual Meeting in North America. Nov. 14–18. Portland, Ore.
13. ^{{cite web |last1=Yong |first1=Ed |title=Jellyfish shift ocean food webs by feeding bacteria with mucus and excrement |url=http://blogs.discovermagazine.com/notrocketscience/2011/06/06/jellyfish-shift-ocean-food-webs-by-feeding-bacteria-with-mucus-and-excrement/ |publisher=Discover Magazine |accessdate=4 October 2018 |date=6 June 2011}}
14. ^{{cite book|title=Introduction to Marine Biology |author=Karleskint; Turner; and Small |publisher=Brooks/Cole |page=4|date=2013 |edition=4|isbn=978-1133364467}}
15. ^¹²{{cite news|author=David Perlman, Chronicle Science Editor |url=http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/08/15/MNLD12ADSN.DTL |title=Scientists alarmed by ocean dead-zone growth |publisher=Sfgate.com |date=2008-08-15 |accessdate=2010-08-03}}
16. ^¹{{cite journal|title=Spreading Dead Zones and Consequences for Marine Ecosystems |doi=10.1126/science.1156401 |date=2008-08-15|last1=Diaz|first1=R. J.|last2=Rosenberg|first2=R.|journal=Science|volume=321|issue=5891|pages=926–9|pmid=18703733}}
17. ^{{cite journal|url=http://www.epa.gov/msbasin/pdf/diaz_data.pdf |title=Supporting Online Material for Spreading Dead Zones and Consequences for Marine Ecosystems |publisher= |date=August 15, 2008 |journal=Science | doi=10.1126/science.1156401 | issue=926 |accessdate=2010-08-13 |author2=Rutger Rosenberg | volume=321|last1=Diaz|first1=R. J.|pages=926–9 | pmid=18703733}}
18. ^{{Cite web|url=http://www.balticnest.org/balticnest/activities/news/news/deadzoneshaveincreasedbymorethan10foldinthelastcentury.5.3186f824143d05551ad52e7.html|title=Dead zones have increased by more than 10-fold in the last century - Baltic Nest Institute|date=2014-04-01|website=www.balticnest.org|language=en|access-date=2018-06-04}}
19. ^Rona Kobell Elizabeth River rises from the depths. Dedicated group is slowly bringing one of nation's most polluted rivers back to life. Bay Journal, July 01, 2011
20. ^{{cite web|url= http://www.loe.org/shows/segments.html?programID=05-P13-00040&segmentID=8|title= Dead Zones}}
21. ^{{cite web|url=http://www.dfo-mpo.gc.ca/science/Publications/article/2005/01-12-2005-eng.htm |title=Will "Dead Zones" Spread in the St. Lawrence River? |deadurl=yes |archiveurl=https://web.archive.org/web/20130626205148/http://www.dfo-mpo.gc.ca/science/Publications/article/2005/01-12-2005-eng.htm |archivedate=2013-06-26 |df= }}
22. ^Griffis, R. and Howard, J. [Eds.]. 2013. Oceans and Marine Resources in a Changing Climate: A Technical Input to the 2013 National Climate Assessment. Washingtonn, DC: Island Press
23. ^¹{{cite web|publisher=U.S. Geological Survey (USGS)|accessdate=June 23, 2012|date=June 21, 2012|title=NOAA: Gulf of Mexico 'Dead Zone' Predictions Feature Uncertainty|url=http://www.usgs.gov/newsroom/article_pf.asp?ID=3252|archiveurl=https://web.archive.org/web/20160411221020/http://www.usgs.gov/newsroom/article_pf.asp?ID=3252|archivedate=2016-04-11}}
24. ^{{cite web |publisher=Louisiana Universities Marine Consortium (LUMCON) |accessdate=May 18, 2013 |title=What is hypoxia? |url=http://www.gulfhypoxia.net/Overview/ |deadurl=yes |archiveurl=https://web.archive.org/web/20130612015526/http://www.gulfhypoxia.net/overview/ |archivedate=June 12, 2013 |df= }}
25. ^¹{{cite web|url=http://www.noaanews.noaa.gov/stories2009/pdfs/new%20fact%20sheet%20dead%20zones_final.pdf|format=PDF|title=Dead Zone: Hypoxia in the Gulf of Mexico|publisher=NOAA|location=|year=2009|page=|accessdate=June 23, 2012}}
26. ^K. E. Schilling & R.D. Libra. The relationship of nitrate concentrations in streams to row crop land use in Iowa. J.Environ. Qual, 2000 29, 1846–1851
27. ^{{Cite journal |author1=D.A. Goolsby|author2=W.A, Battaglin|author3=B.T. Aulenbach|author4=R.P. Hooper. |year= 2001 |title=Nitrogen input to the Gulf of Mexico. |url=https://www.academia.edu/10768141/Nitrogen_Input_to_the_Gulf_of_Mexico|journal=J.Environ Quality |volume=30 |pages=329–336}}
28. ^{{cite web|url=http://www.midwestagriculturallawguide.com/wp-content/uploads/2015/03/Des-Moines-Board-of-Water-Works-Trustees-Complaint.pdf|title=Board of Water Works Trustees of the City of Des Moines, Iowa, Plaintiff vs. Sac County Board of Supervisors et al.|date=March 16, 2015|publisher=United States District Court for The Northern District of Iowa, Western Division|accessdate=March 9, 2017}} {{PD-notice}}
29. ^{{Cite web|url=http://www.nutrientstrategy.iastate.edu/|title=Iowa Nutrient Reduction Strategy {{!}} Iowa Nutrient Reduction Strategy|website=www.nutrientstrategy.iastate.edu|language=en-us|access-date=2018-10-16}}
30. ^{{cite web|url=http://www.noaa.gov/media-release/gulf-of-mexico-dead-zone-is-largest-ever-measured|title=NOAA: Gulf of Mexico ‘dead zone’ is the largest ever measured|publisher=National Oceanic and Atmospheric Administration (NOAA)|location=|date=August 3, 2017|page=|accessdate=August 3, 2017|archiveurl=https://web.archive.org/web/20170802173757/http://www.noaa.gov/media-release/gulf-of-mexico-dead-zone-is-largest-ever-measured|archivedate= August 2, 2017}}
31. ^{{cite news|url=http://articles.sfgate.com/2010-07-06/news/21939174_1_dead-zone-ethanol-production-oil-spill|title=Dead zone in gulf linked to ethanol production|publisher=San Francisco Chronicle|date=2010-07-06|accessdate=2010-07-28 | first=Carolyn | last=Lochhead}}
32. ^[https://www.epa.gov/ms-htf/northern-gulf-mexico-hypoxic-zone 2015 Gulf of Mexico Hypoxic Zone Size], Mississippi River/Gulf of Mexico Hypoxia Task Force, EPA, n.d.
33. ^Courtney et al. Predictions Wrong Again on Dead Zone Area – Gulf of Mexico Gaining Resistance to Nutrient Loading. https://arxiv.org/ftp/arxiv/papers/1307/1307.8064.pdf
34. ^{{cite thesis |type=Master of Science|author=Lisa M. Fairchild|title=The influence of stakeholder groups on the decision-making process regarding the dead zone associated with the Mississippi river discharge|publisher=University of South Florida (USF)|year=2005|page=14|accessdate=June 23, 2012}}
35. ^{{cite web |url=http://www.usgs.gov/newsroom/article_pf.asp?ID=3252 |title=Archived copy |accessdate=2012-06-23 |deadurl=yes |archiveurl=https://web.archive.org/web/20160411221020/http://www.usgs.gov/newsroom/article_pf.asp?ID=3252 |archivedate=2016-04-11 |df= }}
36. ^Grimes, C. B. Fishery production and the Mississippi River discharge. Fisheries (2001) 26(8), 17–26.
37. ^Joshua M Courtney, Amy Courtney, Michael W Courtney. Nutrient Loading Increases Red Snapper Production in the Gulf of Mexico. Hypotheses in the Life Sciences, 3, 1 pp 7–14. {{ISSN|2042-8960}}
38. ^¹{{cite report|title=The Gulf of Mexico's Hypoxic Zone|author1=Jennie Biewald|author2=Annie Rossetti|author3=Joseph Stevens|author4=Wei Cheih Wong|accessdate=June 23, 2012}}
39. ^{{cite web |last=Cox |first=Tony |url=https://www.bloomberg.com/apps/news?pid=newsarchive&sid=a4Tb2AFv6CRk&refer=home |title=Exclusive |publisher=Bloomberg |date=2007-07-23 |accessdate=2010-08-03 |deadurl=yes |archiveurl=https://web.archive.org/web/20100609030628/http://www.bloomberg.com/apps/news?pid=newsarchive |archivedate=2010-06-09 |df= }}
40. ^¹{{cite news | last = Potera | first = Carol | title = Corn Ethanol Goal Revives Dead Zone Concerns | work = Environmental Health Prospectives | date = June 2008}}
41. ^{{cite news | title = Dead Water | work = Economist | date = May 2008}}
42. ^¹{{cite news | last = Mee | first = Laurence | title = Reviving Dead Zones | work = Scientific American | date = November 2006}}
43. ^[https://www.npr.org/templates/story/story.php?storyId=93619388 'Dead Zones' Multiplying In World's Oceans] by John Nielsen. 15 Aug 2008, Morning Edition, NPR.