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Dead zone (ecology)
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This article is about the oceanic phenomenon. For other uses, see Dead zone (disambiguation).
Red circles show the location and size of many dead zones.
Black dots show dead zones of unknown size.
The size and number of marine dead zones—areas where the deep water is so low in dissolved oxygen that sea creatures can't survive—have grown explosively in the past half-century. – NASA Earth Observatory (2008)[1]
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] In the 1970s oceanographers began noting increased instances 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]
Contents
[hide]
1 Causes
2 Effects
3 Locations
3.1 Baltic Sea
3.2 Elizabeth River, Virginia
3.3 Lake Erie
3.4 Lower St. Lawrence Estuary
3.5 Oregon
3.6 Gulf of Mexico 'dead zone'
3.6.1 Size
3.6.2 Economic impact
3.6.3 History
4 Energy Independence and Security Act of 2007
5 Reversal
6 See also
7 Notes
8 References
9 Further reading
10 External links
Causes[edit]
Dead zones are often caused by the decay of algae during algal blooms, like this one off the coast of La Jolla, San Diego, California.
Climate has a significant impact on the growth and decline of ecological dead zones. During spring months, as rainfall increases, more nutrient-rich water flows down the mouth of the Mississippi River.[5] At the same time, as sunlight increases during the spring, algal growth in the dead zones increases dramatically. In fall months, tropical storms begin to enter the Gulf of Mexico and break up the dead zones, and the cycle repeats again in the spring.
Aquatic and marine dead zones can be caused by an increase in chemical 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]
Limnologist Dr. David Schindler, whose research at the Experimental Lakes Area led to the banning of harmful phosphates in detergents, warned about algal blooms and dead zones,
"The fish-killing blooms that devastated the Great Lakes in the 1960s and 1970s haven't gone away; they've moved west into an arid world in which people, industry, and agriculture are increasingly taxing the quality of what little freshwater there is to be had here....This isn't just a prairie problem. Global expansion of dead zones caused by algal blooms is rising rapidly."[6]
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 and this causes dead zones. Cyanobacteria are no good food for zooplankton and fish and hence accumulate in water, die, and then decompose. Other algae are consumed and hence do not accumulate to the same extent as Cyanobacteria.[7] Dead zones can be caused by natural and by anthropogenic factors. Use of chemical fertilizers is considered the major human-related cause of dead zones around the world. Natural causes include coastal upwelling and changes in wind and water circulation patterns. Runoff from sewage, urban land use, and fertilizers can also contribute to eutrophication.[8]
Notable dead zones in the United States include the northern Gulf of Mexico region,[5] 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] 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.[9] These areas are also known as oxygen minimum zones (OMZ). In many cases, OMZs are permanent or semipermanent areas.[citation needed]
Remains of organisms found within sediment layers near the mouth of the Mississippi River indicate four hypoxic events before the advent of artificial 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]
Changes in ocean circulation triggered by ongoing climate change could also add or magnify other causes of oxygen reductions in the ocean.[10]
In August 2017, a report found that the US meat industry is responsible for the largest-ever dead zone in the Gulf of Mexico[11]. Runoff from widespread manure and fertilizer pollution contaminated water from the Heartland to the Gulf. Much of this pollution comes from the vast quantities of corn and soy used to raise meat animals for agribusiness companies, like Tyson.[12]
Effects[edit]
Underwater video frame of the sea floor in the western Baltic covered with dead or dying crabs, fish and clams killed by oxygen depletion
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.[13]
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.[14]
It might be expected that fish would flee the potential suffocation, but they are often quickly rendered unconscious and doomed.[citation needed] 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]
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.[10]
Locations[edit]
Dead zone in the Gulf of Mexico
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.[15]
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.[3][4][16]
Baltic Sea[edit]
Main article: Baltic Sea hypoxia
This section needs expansion. You can help by adding to it. (August 2013)
Elizabeth River, Virginia[edit]
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 largest coal export facility, refineries, loading docks, container-repair facilities and others, so fish had been "offlimits since the 1920´s". 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 shown fish to return, the wetland to recover[17]
Lake Erie[edit]
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.[18] 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[edit]
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 275 metres (902 ft) and noticed since the 1930s.[19] The main concerns for Canadian scientists is the impact of fish found in the area.
Oregon[edit]
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] 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.[20][page needed]
Gulf of Mexico 'dead zone'[edit]
The area of temporary hypoxic bottom water that occurs most summers off the coast of Louisiana in the Gulf of Mexico[21] is the largest recurring hypoxic zone in the United States.[22] 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".[23] 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.[23] 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.[24] 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.[25][26]
Size[edit]
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).[27][21][28] The 2015 dead zone measured 16,760 square kilometers (6,474 square miles).[29] Nancy Rabalais of the Louisiana Universities Marine Consortium in Cocodrie predicted the dead zone or hypoxic zone in 2012 will cover an area of 17,353 sq kilometers (6,700 square miles) which is larger than Connecticut; however, when the measurements were completed, the area of hypoxic bottom water in 2012 only totaled 7,480 sq kilometers. The models using the nitrogen flux from the Mississippi River to predict the "dead zone" areas have been criticized for being systematically high from 2006 to 2014, having predicted record areas in 2007, 2008, 2009, 2011, and 2013 that were never realized.[30]
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 5,000 km (3,107 mi) larger than the previous year".[31]
Economic impact[edit]
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."[32][full citation needed] 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.[33] Courtney et al. hypothesize, that nutrient loading may have contributed to the increases in red snapper in the northern and western Gulf of Mexico.[34]
History[edit]
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.[35]
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." [35]
In July 2007, a dead zone was discovered off the coast of Texas where the Brazos River empties into the Gulf.[36]
Energy Independence and Security Act of 2007[edit]
The Energy Independence and Security Act of 2007 calls for the production of 36 billion US gallons (140,000,000 m3) of renewable fuels by 2022, including 15 billion US gallons (57,000,000 m3) of corn-based ethanol, a tripling of current production that would require a similar increase in corn production.[37] 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 inertial gas, it has more reactive forms, one of which is used to make fertilizer.[38]
According to 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 15-billion-US-gallon (57,000,000 m3) 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 has 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.[37]
Reversal[edit]
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.[39]
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.[39] 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[40] and San Francisco Bay.[3]
The chemical aluminium sulfate can be used to reduce phosphates in water.[41]
See also[edit]
Algal bloom
Anoxic event
Anoxic waters
Cultural eutrophication
Eutrophication
Fish kill
Hypoxia
Marine pollution
Ocean deoxygenation
Oxygen minimum zone
Shutdown of thermohaline circulation
Notes[edit]
Jump up ^ Aquatic Dead Zones NASA Earth Observatory. Revised 17 July 2010. Retrieved 17 January 2010.
Jump up ^ "NOAA: Gulf of Mexico 'dead zone' predictions feature uncertainty". National Oceanic and Atmospheric Administration (NOAA). June 21, 2012. Retrieved June 23, 2012.
^ Jump up to: a b c David Perlman, Chronicle Science Editor (2008-08-15). "Scientists alarmed by ocean dead-zone growth". Sfgate.com. Retrieved 2010-08-03. CS1 maint: Extra text: authors list (link)
^ Jump up to: a b Diaz, R. J.; Rosenberg, R. (2008-08-15). "Spreading Dead Zones and Consequences for Marine Ecosystems". Science. 321 (5891): 926–9. PMID 18703733. doi:10.1126/science.1156401.
^ Jump up to: a b "Blooming horrible: Nutrient pollution is a growing problem all along the Mississippi". The Economist. Retrieved June 23, 2012.
Jump up ^ David W. Schindler; John R. Vallentyne (2008). The Algal Bowl: Overfertilization of the World's Freshwaters and Estuaries. Edmonton, Alberta: University of Alberta Press. Retrieved June 23, 2012.
Jump up ^ "Whole Lake Experiment, Ford Lake, Prof Lehman"[permanent dead link], www.cees.iupui.edu, 2010-06-17
Jump up ^ Corn boom could expand 'dead zone' in Gulf msnbc.msn.com
Jump up ^ Pickard, G.L. and Emery, W.J. 1982. Description Physical Oceanography: An Introduction. Pergamon Press, Oxford, page 47.
^ Jump up to: a b Mora, C.; et al. (2013). "Biotic and Human Vulnerability to Projected Changes in Ocean Biogeochemistry over the 21st Century". PLOS Biology. 11: e1001682. PMC 3797030  . PMID 24143135. doi:10.1371/journal.pbio.1001682.
Jump up ^ Milman, Oliver (2017-08-01). "Meat industry blamed for largest-ever 'dead zone' in Gulf of Mexico". The Guardian. ISSN 0261-3077. Retrieved 2017-08-04.
Jump up ^ von Reusner, Lucia (August 1, 2017). "Mystery Meat II: The Industry Behind the Quiet Destruction of the American Heartland" (PDF). Mighty Earth. Retrieved August 4, 2017.
Jump up ^ 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.
Jump up ^ 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.
Jump up ^ Karleskint; Turner; and Small (2013). Introduction to Marine Biology (4 ed.). Brooks/Cole. p. 4. ISBN 978-1133364467. CS1 maint: Multiple names: authors list (link)
Jump up ^ Diaz, R. J.; Rutger Rosenberg (August 15, 2008). "Supporting Online Material for Spreading Dead Zones and Consequences for Marine Ecosystems" (PDF). Science. 321 (926): 926–9. PMID 18703733. doi:10.1126/science.1156401. Retrieved 2010-08-13.
Jump up ^ 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
Jump up ^ "Dead Zones".
Jump up ^ "Will "Dead Zones" Spread in the St. Lawrence River?". Archived from the original on 2013-06-26.
Jump up ^ 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
^ Jump up to: a b "NOAA: Gulf of Mexico 'Dead Zone' Predictions Feature Uncertainty". U.S. Geological Survey (USGS). June 21, 2012. Archived from the original on 2016-04-11. Retrieved June 23, 2012.
Jump up ^ "What is hypoxia?". Louisiana Universities Marine Consortium (LUMCON). Archived from the original on June 12, 2013. Retrieved May 18, 2013.
^ Jump up to: a b "Dead Zone: Hypoxia in the Gulf of Mexico" (PDF). NOAA. 2009. Retrieved June 23, 2012.
Jump up ^ 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
Jump up ^ D.A. Goolsby; W.A, Battaglin; B.T. Aulenbach; R.P. Hooper. (2001). "Nitrogen input to the Gulf of Mexico.". J.Environ Quality. 30: 329–336.
Jump up ^ "Board of Water Works Trustees of the City of Des Moines, Iowa, Plaintiff vs. Sac County Board of Supervisors et al." (PDF). United States District Court for The Northern District of Iowa, Western Division. March 16, 2015. Retrieved March 9, 2017. This article incorporates text from this source, which is in the public domain.
Jump up ^ "NOAA: Gulf of Mexico ‘dead zone’ is the largest ever measured". National Oceanic and Atmospheric Administration (NOAA). August 3, 2017. Archived from the original on August 2, 2017. Retrieved August 3, 2017.
Jump up ^ Lochhead, Carolyn (2010-07-06). "Dead zone in gulf linked to ethanol production". San Francisco Chronicle. Retrieved 2010-07-28.
Jump up ^ 2015 Gulf of Mexico Hypoxic Zone Size, Mississippi River/Gulf of Mexico Hypoxia Task Force, EPA, n.d.
Jump up ^ Courtney et al. Predictions Wrong Again on Dead Zone Area – Gulf of Mexico Gaining Resistance to Nutrient Loading. http://arxiv.org/ftp/arxiv/papers/1307/1307.8064.pdf
Jump up ^ Lisa M. Fairchild (2005). The influence of stakeholder groups on the decision making process regarding the dead zone associated with the Mississippi river discharge (Master of Science). University of South Florida (USF). p. 14. |access-date= requires |url= (help)
Jump up ^ "Archived copy". Archived from the original on 2016-04-11. Retrieved 2012-06-23.
Jump up ^ Grimes, C. B. Fishery production and the Mississippi River discharge. Fisheries (2001) 26(8), 17–26.
Jump up ^ 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
^ Jump up to: a b Jennie Biewald; Annie Rossetti; Joseph Stevens; Wei Cheih Wong. The Gulf of Mexico's Hypoxic Zone (Report). |access-date= requires |url= (help)
Jump up ^ Cox, Tony (2007-07-23). "Exclusive". Bloomberg. Archived from the original on 2010-06-09. Retrieved 2010-08-03.
^ Jump up to: a b Potera, Carol (June 2008). "Corn Ethanol Goal Revives Dead Zone Concerns". Environmental Health Prospectives.
Jump up ^ "Dead Water". Economist. May 2008.
^ Jump up to: a b Mee, Laurence (November 2006). "Reviving Dead Zones". Scientific American.
Jump up ^ 'Dead Zones' Multiplying In World's Oceans by John Nielsen. 15 Aug 2008, Morning Edition, NPR.
Jump up ^ "Wisconsin Department of Natural Resources" (PDF). Archived from the original (PDF) on 2009-11-28. Retrieved 2010-08-03.
References[edit]
Diaz, R.J.; Rosenberg, R. (2008). "Spreading dead zones and consequences for marine ecosystems". Science. 321 (5891): 926–929. PMID 18703733. doi:10.1126/science.1156401.
Osterman, L.E., et al. 2004. Reconstructing an 180-yr record of natural and anthropogenic induced hypoxia from the sediments of the Louisiana Continental Shelf. Geological Society of America meeting. Nov. 7–10. Denver. Abstract.
Taylor, F.J.; Taylor, N.J.; Walsby, J.R. (1985). "A bloom of planktonic diatom Ceratulina pelagica off the coastal northeastern New Zealand in 1983, and its contribution to an associated mortality of fish and benthic fauna". Intertional Revue ges. Hydrobiol. 70: 773–795. doi:10.1002/iroh.19850700602.
Morrisey, D.J. (2000). "Predicting impacts and recovery of marine farm sites in Stewart Island New Zealand, from the Findlay-Watling model". Aquaculture. 185: 257–271. doi:10.1016/s0044-8486(99)00360-9.
Potera, C (2008). "Corn Ethanol Goal Revives Dead Zone Concerns". Environmental Health Perspectives. 116 (6): A242–A243. doi:10.1289/ehp.116-a242.
Further reading[edit]
Hendy, Ian (August 2017), Gulf of Mexico ‘dead zone’ is already a disaster – but it could get worse, The Conversation
Bryant, Lee (April 2015), Ocean ‘dead zones’ are spreading – and that spells disaster for fish, The Conversation
David Stauth (Oregon State University), "Hypoxic "dead zone" growing off the Oregon Coast" July 31, 2006
Suzie Greenhalgh and Amanda Sauer (WRI), "Awakening the 'Dead Zone': An investment for agriculture, water quality, and climate change" 2003
Reyes Tirado (July 2008) Dead Zones: How Agricultural Fertilizers are Killing our Rivers, Lakes and Oceans. Greenpeace publications. See also: "Dead Zones: How Agricultural Fertilizers are Killing our Rivers, Lakes and Oceans". Greenpeace Canada. 2008-07-07. Retrieved 2010-08-03.
MSNBC report on dead zones, March 29, 2004
Joel Achenbach, "A 'Dead Zone' in The Gulf of Mexico: Scientists Say Area That Cannot Support Some Marine Life Is Near Record Size", Washington Post, July 31, 2008
Joel Achenbach, "'Dead Zones' Appear In Waters Worldwide: New Study Estimates More Than 400", Washington Post, August 15, 2008
External links[edit]
Louisiana Universities Marine Consortium
UN Geo Yearbook 2003 report on nitrogen and dead zones
NASA on dead zones (Satellite pictures)
Gulf of Mexico Dead Zone – multimedia
Gulf of Mexico Hypoxia Watch, NOAA Joel Achenbach
NutrientNet, an online nutrient trading tool developed by the World Resources Institute, designed to address issues of eutrophication. See also the PA NutrientNet website designed for Pennsylvania's nutrient trading program.
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Key signature
From Wikipedia, the free encyclopedia
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For use in cryptography, see Key signature (cryptography).
Key signature A major / F♯ minor with three sharps placed after the clef.
In musical notation, a key signature is a set of sharp (♯), flat (♭), and rarely, natural (♮) symbols placed together on the staff. Key signatures are generally written immediately after the clef at the beginning of a line of musical notation, although they can appear in other parts of a score, notably after a double barline.
A key signature designates notes that are to be played higher or lower than the corresponding natural notes and applies through to the end of the piece or up to the next key signature. A sharp symbol on a line or space in the key signature raises the notes on that line or space one semitone above the natural, and a flat lowers such notes one semitone. Further, a symbol in the key signature affects all the notes of one letter: for instance, a sharp on the top line of the treble staff applies to Fs not only on that line, but also to Fs in the bottom space of the staff, and to any other Fs. This convention was not universal until the late Baroque and early Classical period, however; music published in the 1720s and 1730s, for example, uses key signatures showing sharps or flats on both octaves for notes which fall within the staff.[citation needed]
An accidental is an exception to the key signature, applying only in the measure in which it appears.
Although a key signature may be written using any combination of sharp and flat symbols, a series of thirteen homogeneous key signatures, ranging from between six flats to six sharps and each flat or sharp being on notes separated by a perfect fifth from each other, are by far the most commonly used; their use is assumed in much of this article. A piece scored using a single diatonic key signature and no accidentals contains notes of at most seven of the twelve pitch classes, which seven being determined by the particular key signature.
Each major and minor key has an associated key signature that sharpens or flattens the notes which are used in its scale. However, it is not uncommon for a piece to be written with a key signature that does not match its key, for example, in some Baroque pieces,[1] or in transcriptions of traditional modal folk tunes.[2]
Later on, this use of a key signature that is theoretically incorrect for a piece as a whole or a self-contained section of a piece became less common (in contrast to brief passages within a piece, which, as they modulate from key to key often temporarily disagree with the key signature); but it can be found at least as late as one of Beethoven's very late piano sonatas. For example, in his Sonata No. 31 in A♭ major, Op. 110, the first appearance of the Arioso section in the final movement is notated throughout in six flats; but it both begins and ends in A♭ minor and has a significant modulation to C♭ major, and both these keys theoretically require seven flats in their key signature. (The second appearance later in the movement of this same section, a semitone lower, in G minor, uses the correct key signature of two flats.)
Contents
[hide]
1 Conventions
1.1 Notational conventions
1.2 Variants of standard conventions
2 Major scale structure
2.1 Scales with sharp key signatures
2.2 Scales with flat key signatures
3 Relationship between key signature and key
3.1 Additional terminology
4 Exceptions
4.1 Unusual signatures
5 History
6 Table
7 See also
8 References
Conventions[edit]
1. B major scale: no key signature; accidentals required throughout
2. B major scale: key signature; accidentals not needed
In principle, any piece can be written with any key signature, using accidentals to correct the pattern of whole and half steps. The purpose of the key signature is to minimize the number of such accidentals required to notate the music. The sequence of sharps or flats in key signatures is generally rigid in modern music notation. This allows musicians to identify the key simply by the number of sharps or flats (which is the same in any clef), rather than their position on the staff. For example, if a key signature has only one sharp, it must be an F-sharp,[3] which corresponds to a G major or an E minor key.
However, in 20th-century music, there are occasional exceptions to this, where a piece uses an unorthodox or synthetic scale, where a key signature may be invented to reflect this. This may consist of a number of sharps or flats that are not the normal ones (such as a signature of just C♯ or E♭), or it may consist of one or more sharps combined with one or more flats (such as a signature containing both F♯ and B♭). Key signatures of this kind can be found in the music of Béla Bartók, for example.
The effect of a key signature continues throughout a piece or movement, unless explicitly cancelled by another key signature. For example, if a five-sharp key signature is placed at the beginning of a piece, every A in the piece in any octave will be played as A sharp, unless preceded by an accidental (for instance, the A in scale 2 illustrated – the next-to-last note – is played as an A♯ even though the A♯ in the key signature (the last sharp sign) is written an octave lower).[3]
In a score containing more than one instrument, all the instruments are usually written with the same key signature. Exceptions include:
If an instrument is a transposing instrument.
If an instrument is a percussion instrument with indeterminate pitch.
Composers usually omit the key signature for timpani parts. Besides not using a key signature, timpani parts were early on also treated often as transposing instrument parts, the pitch of the high drum being written as C and, as timpani were almost always tuned a perfect fourth apart (dominant on the low drum and tonic on the high drum), the pitch of the low drum being written as G, with the actual pitches indicated at the beginning of the part, e.g. "timpani in D–A", if they were tuned A (low drum) and D (high drum).
Composers may omit the key signature for horn and occasionally trumpet parts. This is perhaps reminiscent of the early days of brass instruments, when crooks would be added to them, in order to change the length of the tubing and allow playing in different keys.[citation needed]
On occasion, in more modern works, instruments may be notated in different keys even when they are not transposing instruments, because the music is polytonal and the different parts are actually in different keys which sound together.
Circle of fifths showing major and minor keys and their signatures
Notational conventions[edit]
The convention for the notation of key signatures follows the circle of fifths. Starting from C major (or equivalently A minor) which has no sharps or flats, successively raising the key by a fifth adds a sharp, going clockwise round the circle of fifths. The new sharp is placed on the new key's leading note (seventh degree) for major keys or supertonic (second degree) for minor keys. Thus G major (E minor) has one sharp which is on the F; then D major (B minor) has two sharps on F and C and so on.
Similarly successively lowering the key by a fifth adds a flat, going counterclockwise around the circle of fifths. The new flat is placed on the subdominant (fourth degree) for major keys or submediant (sixth degree) for minor keys. Thus F major (D minor) has one flat which is on the B; then B♭ major (G minor) has two flats (on B and E) and so on.
Put another way: for key signatures with sharps, the first sharp is placed on F with subsequent sharps on C, G, D, A, E and B; for key signatures with flats, the first flat is placed on B with subsequent flats on E, A, D, G, C and F. There are thus 15 conventional key signatures, with up to seven sharps or flats and including the empty signature of C major (A minor).
Corollaries:
Starting from a key with flats in its key signature: raising by fifths successively reduces the flats to zero at C major (A minor). Further such raising adds sharps as described above.
Starting from a key with sharps: lowering by fifths successively reduces those sharps to zero. Further such lowering adds flats as described above.
When the process of raising by a fifth (adding a sharp) produces more than five or six sharps, successive such raising generally involves changing to the enharmonic equivalent key using a flat-based signature. Typically this is at F♯ = G♭, but may also be at C♯ = D♭ or B = C♭. The same principle applies to the process of successive lowering by a fifth.
The relative minor is a minor third down from the major, regardless of whether it is a flat or a sharp key signature.
The key signatures with seven flats (♭) and seven sharps (♯) are rarely used because they have simpler enharmonic equivalents. For example, the key of C♯ major (seven sharps) is more simply represented as D♭ major (five flats). For modern practical purposes these keys are (in twelve tone equal temperament) the same, because C♯ and D♭ are enharmonically the same note. Pieces are written in these extreme sharp or flat keys, however: for example, Bach's Prelude and Fugue No. 3 from Book 1 of The Well-Tempered Clavier BWV 848 is in C♯ major. The modern musical Seussical by Flaherty and Ahrens also has several songs written in these extreme keys.
Key signatures can be further extended through double sharps and double flats (for example, a piece in the key of G♯ major can be expressed with a double sharp on F and six sharps on the other six pitches). As with the seven-sharp and seven-flat examples, it is rarely necessary to express music in such keys when simpler enharmonic examples can instead be used (in the case of G♯, the same passage could be expressed in A♭ with only four flats).
Natural key signature: a key signature with seven naturals (♮) used to cancel the seven sharps (♯) of the previous signature.
The key signature may be changed at any time in a piece, usually at the beginning of a measure, simply by notating the new signature, although if the new signature has no sharps or flats, a signature of naturals, as shown, is needed to cancel the preceding signature. If a change in signature occurs at the start of a new line on the page, where a signature would normally appear anyway, the new signature is customarily repeated at the end of the previous line to make the change more conspicuous.
Variants of standard conventions[edit]
In traditional use, when the key signature change goes from sharps to flats or vice versa, the old key signature is cancelled with the appropriate number of naturals before the new one is inserted; but many more recent publications (whether of newer music or newer editions of older music) dispense with the naturals and simply insert the new signature.
Similarly, when a signature with either flats or sharps in it changes to a smaller signature of the same type, strict application of tradition or convention would require that naturals first be used to cancel just those flats or sharps that are being subtracted in the new signature before the new signature itself is written; but, again, more modern usage often dispenses with these naturals.
When the signature changes from a smaller to a larger signature of the same type, the new signature is simply written in by itself, in both traditional and newer styles.
At one time it was usual to precede the new signature with a double barline (provided the change occurred between bars and not inside a bar), even if it was not required by the structure of the music to mark sections within the movement; but more recently it has increasingly become usual to use just a single barline. The courtesy signature that appears at the end of a line immediately before a change is usually preceded by an additional barline; the line at the very end of the staff is omitted in this case.
If both naturals and a new key signature appear at a key signature change, there are also more recently variations about where a barline will be placed (in the case where the change occurs between bars). For example, in some scores by Debussy, in this situation the barline is placed after the naturals but before the new key signature. Hitherto, it would have been more usual to place all the symbols after the barline.
In key signatures of five or more sharps or of seven flats, one occasionally encounters variant positions of particular symbols in the key signatures, both of them in the bass clef.
The A♯ which is the fifth sharp in the sharp signatures may occasionally be notated on the top line of the bass staff, whereas it is more usually found in the lowest space on that staff. An example of this can be seen in the full score of Ottorino Respighi's Pines of Rome, in the third section, "Pines of the Janiculum" (which is in B major), in the bass-clef instrumental parts.
In the case of seven-flat key signatures, the final F♭ may occasionally be seen on the second-top line of the bass staff, whereas it would more usually appear below the bottom line. An example of this can be seen in Isaac Albéniz's Iberia: first movement, "Evocación", which is in A♭ minor.
Major scale structure[edit]
Except for C major, key signatures appear in two varieties, "sharp key signatures" ("sharp keys") and "flat key signatures" ("flat keys"), so called because they contain only one or other.[4]
Scales with sharp key signatures[edit]
Sharp key signatures consist of a number of sharps between one and seven, applied in this order: F C G D A E B.[5][6] A mnemonic device often used to remember this is "Father Charles Goes Down And Ends Battle."[4][not in citation given]Schonbrun indeed offers this mnemonic, but makes no claim whatever about frequency of use, or indeed whether it had ever been used before Schonbrun concocted it for his book.--> The key note or tonic of a piece in a major key is immediately above the last sharp in the signature.[7] For example, one sharp (F♯) in the key signature of a piece in a major key indicates the key of G major, the next note above F♯. (Six sharps, the last one being E♯ (an enharmonic spelling of F♮) indicate the key of F♯ major, since F has already been sharped in the key signature.)
Major key
Number
of sharps
Sharp notes
Minor key
Enharmonic
equivalent
C major 0 A minor None
G major 1 F♯ E minor None
D major 2 F♯, C♯ B minor None
A major 3 F♯, C♯, G♯ F♯ minor None
E major 4 F♯, C♯, G♯, D♯ C♯ minor None
B major 5 F♯, C♯, G♯, D♯, A♯ G♯ minor C♭ major/A♭ minor
F♯ major 6 F♯, C♯, G♯, D♯, A♯, E♯ D♯ minor G♭ major/E♭ minor
C♯ major 7 F♯, C♯, G♯, D♯, A♯, E♯, B♯ A♯ minor D♭ major/B♭ minor
This table shows that each scale starting on the fifth scale degree of the previous scale has one new sharp, added in the order given above.[6]
Scales with flat key signatures[edit]
"Flat key signatures" consist of one to seven flats, applied as: B E A D G C F[5][6] The mnemonic device is then reversed for use in the flat keys: "Battle Ends And Down Goes Charles' Father".[4] The major scale with one flat is F major. In all other "flat major scales", the tonic or key note of a piece in a major key is four notes below the last flat, which is the same as the second-to-last flat in the signature.[7] In the major key with four flats (B♭ E♭ A♭ D♭), for example, the penultimate flat is A♭, indicating a key of A♭ major.
Major key
Number
of flats
Flat notes
Minor key
Enharmonic
equivalent
C major 0 A minor None
F major 1 B♭ D minor None
B♭ major 2 B♭, E♭ G minor None
E♭ major 3 B♭, E♭, A♭ C minor None
A♭ major 4 B♭, E♭, A♭, D♭ F minor None
D♭ major 5 B♭, E♭, A♭, D♭, G♭ B♭ minor C♯ major/A♯ minor
G♭ major 6 B♭, E♭, A♭, D♭, G♭, C♭ E♭ minor F♯ major/D♯ minor
C♭ major 7 B♭, E♭, A♭, D♭, G♭, C♭, F♭ A♭ minor B major/G♯ minor
In this case each new scale starts a fifth below (or a fourth above) the previous one.
Relationship between key signature and key[edit]
A key signature is not the same as a key; key signatures are merely notational devices. They are convenient principally for diatonic or tonal music.
The key signature defines the diatonic scale that a piece of music uses without the need for accidentals. Most scales require that some notes be consistently sharped or flatted. For example, the only sharp in the G major scale is F sharp, so the key signature associated with the G major key is the one-sharp key signature. However, it is only a notational convenience; a piece with a one-sharp key signature is not necessarily in the key of G major, and likewise, a piece in G major may not always be written with a one-sharp key signature; this is particularly true in pre-Baroque music, when the concept of key had not yet evolved to its present state.
In any case, more extensive pieces often change key (modulate) during contrasting sections, and only sometimes is this change indicated with a change of key signature; if not, the passage in the second key will not have a matching key signature.
Bach Cantata 106 is almost entirely in E♭ major, but has only two flats, not three, in the key signature Play (help·info)
The Toccata and Fugue in D minor, BWV 538 by Bach has no key signature, leading it to be called the Dorian, but it is still in D minor; the B♭s that occur in the piece are written with accidentals.
Additional terminology[edit]
Keys which are associated with the same key signature are called relative keys.
When musical modes, such as Lydian or Dorian, are written using key signatures, they are called transposed modes.
Exceptions[edit]
D Freygish scale Play (help·info)
Exceptions to common-practice-period use may be found in Klezmer scales, such as Freygish (Phrygian). In the 20th century, composers such as Bartók and Rzewski (see below) began experimenting with unusual key signatures that departed from the standard order.
Because of the limitations of the traditional highland bagpipe scale, key signatures are often omitted from written pipe music, which otherwise would be written with two sharps, the usual F♯ and C♯.[8] (In this case the pipes are incapable of playing F♮ and C♮ so it is not necessary to specify the sharps.)
Variant key signatures in a Victoria motet. In the superius (soprano) part the E♭ appears first, and in two other parts a flat occurs in two octaves.
Unusual signatures[edit]
Further information: Anhemitonic scale § Modes of the ancohemitonic heptatonic scales and the key signature system
The above 15 key signatures only express diatonic scales and are therefore sometimes called standard key signatures. Other scales are written either with a standard key signature and use accidentals as required, or with a nonstandard key signature. Examples of the latter include the E♭ (right hand), and F♭ and G♭ (left hand) used for the E♭ diminished (E♭ octatonic) scale in Bartók's Crossed Hands (no. 99, vol. 4, Mikrokosmos), or the B♭, E♭ and F♯ used for the D Phrygian dominant scale in Frederic Rzewski's God to a Hungry Child.
The absence of a key signature does not always mean that the music is in the key of C major / A minor as each accidental may be notated explicitly as required, or the piece may be modal or atonal. An example is Bartók's Piano Sonata, which has no fixed key and is highly chromatic.
If not bound by common practice conventions, microtones can also be notated in a key signature; which microtonal symbols are used depends on the system.
The common practice period conventions are so firmly established that some musical notation programs have been unable to show nonstandard key signatures until recently.[9]
History[edit]
The use of a one-flat signature developed in the Medieval period, but signatures with more than one flat did not appear until the 16th century, and signatures with sharps not until the mid-17th century.[10]
When signatures with multiple flats first came in, the order of the flats was not standardized, and often a flat appeared in two different octaves, as shown at right. In the late 15th and early 16th centuries, it was common for different voice parts in the same composition to have different signatures, a situation called a partial signature or conflicting signature. This was actually more common than complete signatures in the 15th century.[11] The 16th-century motet Absolon fili mi attributed to Josquin des Prez features two voice parts with two flats, one part with three flats, and one part with four flats.
Baroque music written in minor keys often was written with a key signature with fewer flats than we now associate with their keys; for example, movements in C minor often had only two flats (because the A♭ would frequently have to be sharpened to A♮ in the ascending melodic minor scale, as would the B♭).
Table[edit]
Key signature
Major key
Minor key

no sharps or flats C major A minor
Key signature
Added ♯
Major key
Minor key
Key signature
Added ♭
Major key
Minor key

1 sharp F♯ G major E minor
1 flat B♭ F major D minor

2 sharps C♯ D major B minor
2 flats E♭ B♭ major G minor

3 sharps G♯ A major F♯ minor
3 flats A♭ E♭ major C minor

4 sharps D♯ E major C♯ minor
4 flats D♭ A♭ major F minor

5 sharps A♯ B major G♯ minor
5 flats G♭ D♭ major B♭ minor

6 sharps E♯ F♯ major D♯ minor
6 flats C♭ G♭ major E♭ minor

7 sharps B♯ C♯ major A♯ minor
7 flats F♭ C♭ major A♭ minor
See also[edit]
Key signature names and translations
Major and minor
Parallel key
Relative key
Theoretical key
Universal key
References[edit]
Jump up ^ Schulenberg, David. Music of the Baroque. New York: Oxford University Press, 2001. p. 72.. "(…) to determine the key of a Baroque work one must always analyze its tonal structure rather than rely on the key signature."
Jump up ^ Cooper, David. The Petrie Collection of the Ancient Music of Ireland. Cork: Cork University Press, 2005. p. 22. "In a few cases Petrie has given what is clearly a modal melody a key signature which suggests that it is actually in a minor key. For example, Banish Misfortune is presented in D minor, although it is clearly in the Dorian mode."
^ Jump up to: a b |url=http://www.dummies.com/how-to/content/how-to-read-key-signatures.html |title=How to Read Key Signatures|accessdate=29 January 2014
^ Jump up to: a b c Schonbrun, Marc (2005). The Everything Music Theory Book, p.68. ISBN 1-59337-652-9.
^ Jump up to: a b Bower, Michael. 2007. "All about Key Signatures". Modesto, CA: Capistrano School (K–12) website. (Accessed 17 March 2010).
^ Jump up to: a b c Jones, George Thaddeus. 1974. Music Theory: The Fundamental Concepts of Tonal Music Including Notation, Terminology, and Harmony, p.35. Barnes & Noble Outline Series 137. New York, Hagerstown, San Francisco, London: Barnes & Noble. ISBN 9780064601375.
^ Jump up to: a b Kennedy, Michael. 1994. "Key-Signature". Oxford Dictionary of Music, second edition, associate editor, Joyce Bourne. Oxford and New York: Oxford University Press. ISBN 0-19-869162-9.
Jump up ^ Nienhuys, Han-Wen; Nieuwenhuizen, Jan (2009). "GNU LilyPond — Notation Reference". 2.6.2 Bagpipes. Retrieved 2010-03-28. Bagpipe music nominally uses the key of D Major (even though that isn’t really true). However, since that is the only key that can be used, the key signature is normally not written out.
Jump up ^ One of the most popular musical notation programs, Finale, has only included the option to create a nonstandard key signature since their 2009 version: Finale 2009 User Manual for Windows. "Non-Standard Key Signature." http://www.finalemusic.com/UserManuals/Finale2009Win/Finale.htm (accessed February 17, 2011).
Jump up ^ "Key Signature", Harvard Dictionary of Music, 2nd ed.
Jump up ^ "Partial Signature", Harvard Dictionary of Music, 2nd ed.
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Prevalence of mental disorders
From Wikipedia, the free encyclopedia
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The prevalence of mental disorders has been studied around the world, providing estimates on how common mental disorders are. Different criteria or thresholds of severity have sometimes been used.
National and international figures are typically estimated by large-scale surveys of self-reported symptoms up to the time of assessment; sometimes a figure is calculated for the occurrence of disorder in the week, month or year prior to assessment–a point or period prevalence; sometimes the figure is for a person's lifetime prior to assessment–the so-called lifetime prevalence.
Contents
[hide]
1 Population studies
1.1 World Health Organization global study
1.2 US mental health studies
1.3 European population studies
2 Specific mental disorders
2.1 Anxiety disorders
2.2 Mood disorders
2.3 Schizophrenia
2.4 Personality disorders
2.5 Child psychiatric disorders
3 See also
4 References
5 External links
Population studies[edit]
Numerous large-scale surveys of the prevalence of mental disorders in adults in the general population have been carried out since the 1980s based on self-reported symptoms assessed by standardized structured interviews, usually carried out over the phone.
Mental disorders have been found to be common, with over a third of people in most countries reporting sufficient criteria to be diagnosed at some point in their life.[1] The World Health Organization (WHO) reported in 2001 that about 450 million people worldwide suffer from some form of mental disorder or brain condition, and that one in four people meet criteria at some point in their life.[2][3][4]
World Health Organization global study[edit]
The World Health Organization is currently undertaking a global survey of 26 countries in all regions of the world, based on ICD and DSM criteria.[5] The first published figures on the 14 country surveys completed to date, indicate that, of those disorders assessed, anxiety disorders are the most common in all but 1 country (prevalence in the prior 12-month period of 2.4% to 18.2%) and mood disorders next most common in all but 2 countries (12-month prevalence of 0.8% to 9.6%), while substance disorders (0.1%–6.4%) and impulse-control disorders (0.0%–6.8%) were consistently less prevalent.[6]
The United States, Colombia, the Netherlands and Ukraine tended to have higher prevalence estimates across most classes of disorder, while Nigeria, Shanghai and Italy were consistently low, and prevalence was lower in Asian countries in general. Cases of disorder were rated as mild (prevalence of 1.8%–9.7%), moderate (prevalence of 0.5%–9.4%) and serious (prevalence of 0.4%–7.7%).[6]
The World Health Organization has published worldwide incidence and prevalence estimates of individual disorders. Obsessive-compulsive disorder is two to three times as common in Latin America, Africa, and Europe as in Asia and Oceania.[7] Schizophrenia appears to be most common in Japan, Oceania, and Southeastern Europe and least common in Africa.[8] Bipolar disorder and panic disorder have very similar rates around the world.[9][10]
However, these are widely believed to be underestimates, due to poor diagnosis (especially in countries without affordable access to mental health services) and low reporting rates, in part because of the predominant use of self-report data, rather than semi-structured instruments such as the Structured Clinical Interview for DSM-IV (SCID); actual lifetime prevalence rates for mental disorders are estimated to be between 65% and 85%.[citation needed][8]
US mental health studies[edit]
Previous widely cited large-scale surveys in the US were the Epidemiological Catchment Area (ECA) survey and subsequent National Comorbidity Survey (NCS). The NCS was replicated and updated between 2000 and 2003 and indicated that, of those groups of disorders assessed, nearly half of Americans (46.4%) reported meeting criteria at some point in their life for either a DSM-IV anxiety disorder (28.8%), mood disorder (20.8%), impulse-control disorder (24.8%) or substance use disorders (14.6%). Half of all lifetime cases had started by age 14 and 3/4 by age 24.[11]
In the prior 12-month period only, around a quarter (26.2%) met criteria for any disorder—anxiety disorders 18.1%; mood disorders 9.5%; impulse control disorders 8.9%; and substance use disorders 3.8%. A substantial minority (23%) met criteria for more than two disorders. 22.3% of cases were classed as serious, 37.3% as moderate and 40.4% as mild.[12][13]
European population studies[edit]
A 2004 cross-European study found that approximately one in four people reported meeting criteria at some point in their life for one of the DSM-IV disorders assessed, which included mood disorders (13.9%), anxiety disorders (13.6%) or alcohol disorder (5.2%). Approximately one in ten met criteria within a 12-month period. Women and younger people of either gender showed more cases of disorder.[14]
A 2005 review of 27 studies have found that 27% of adult Europeans is or has been affected by at least one mental disorder in the past 12 months. It was also found that the most frequent disorders were anxiety disorders, depressive, somatoform and substance dependence disorders.[15]
Specific mental disorders[edit]
Anxiety disorders[edit]
A review that pooled surveys in different countries up to 2004 found overall average prevalence estimates for any anxiety disorder of 10.6% (in the 12 months prior to assessment) and 16.6% (in lifetime prior to assessment), but that rates for individual disorders varied widely. Women had generally higher prevalence rates than men, but the magnitude of the difference varied.[16]
Mood disorders[edit]
See also: Epidemiology of depression
A review that pooled surveys of mood disorders in different countries up to 2000 found 12-month prevalence rates of 4.1% for major depressive disorder (MDD), 2% for dysthymic disorder and 0.72% for bipolar 1 disorder. The average lifetime prevalence found was 6.7% for MDD (with a relatively low lifetime prevalence rate in higher-quality studies, compared to the rates typically highlighted of 5–12% for men and 10–25% for women), and rates of 3.6% for dysthymia and 0.8% for Bipolar 1.[17] Certain population subgroups, such as physicians in training, have 12-month prevalence rates as high as 21 to 43%.[18][19]
Schizophrenia[edit]
Further information: Epidemiology of schizophrenia
Further information: Sluggish schizophrenia § Statistics
A 2005 review of prior surveys in 46 countries on the prevalence of schizophrenic disorders, including a prior 10-country WHO survey, found an average (median) figure of 0.4% for lifetime prevalence up to the point of assessment and 0.3% in the 12-month period prior to assessment. A related figure not given in other studies (known as lifetime morbid risk), reported to be an accurate statement of how many people would theoretically develop schizophrenia at any point in life regardless of time of assessment, was found to be "about seven to eight individuals per 1,000" (0.7/0.8%). The prevalence of schizophrenia was consistently lower in poorer countries than in richer countries (though not the incidence), but the prevalence did not differ between urban/rural areas or men/women (although incidence did).[20]
Personality disorders[edit]
Studies of the prevalence of personality disorders (PDs) have been fewer and smaller-scale, but a broader Norwegian survey found a similar overall prevalence of almost 1 in 7 (13.4%), based on meeting personality criteria over the prior five-year period. Rates for specific disorders ranged from 0.8% to 2.8%, with rates differing across countries, and by gender, educational level and other factors.[21] A US survey that incidentally screened for personality disorder found an overall rate of 14.79%.[22]
Child psychiatric disorders[edit]
Further information: Epidemiology of child psychiatric disorders
Approximately 7% of a preschool pediatric sample were given a psychiatric diagnosis in one clinical study, and approximately 10% of 1- and 2-year-olds receiving developmental screening have been assessed as having significant emotional/behavioral problems based on parent and pediatrician reports.[23]
See also[edit]
Epidemiology of child psychiatric disorders
References[edit]
Jump up ^ "Cross-national comparisons of the prevalences and correlates of mental disorders. WHO International Consortium in Psychiatric Epidemiology". Bull. World Health Organ. 78 (4): 413–26. 2000. PMC 2560724  . PMID 10885160. doi:10.1590/S0042-96862000000400003.
Jump up ^ WHO | The world health report
Jump up ^ Sherer R (January 2002). "Mental Health Care in the Developing World". Psychiatric Times. XIX (1).
Jump up ^ Mental problems 'hit one in four'
Jump up ^ The World Mental Health Survey Initiative
^ Jump up to: a b Demyttenaere K, Bruffaerts R, Posada-Villa J, et al. (June 2004). "Prevalence, severity, and unmet need for treatment of mental disorders in the World Health Organization World Mental Health Surveys". JAMA. 291 (21): 2581–90. PMID 15173149. doi:10.1001/jama.291.21.2581.
Jump up ^ Ayuso-Mateos, Jose Luis. "Global burden of obsessive-compulsive disorder in the year 2000" (PDF). World Health Organization. Retrieved February 27, 2013.
^ Jump up to: a b Ayuso-Mateos, Jose Luis. "Global burden of schizophrenia in the year 2000" (PDF). World Health Organization. Retrieved February 27, 2013.
Jump up ^ Ayuso-Mateos, Jose Luis. "Global burden of bipolar disorder in the year 2000" (PDF). World Health Organization. Retrieved December 9, 2012.
Jump up ^ Ayuso-Mateos, Jose Luis. "Global burden of panic disorder in the year 2000" (PDF). World Health Organization. Retrieved February 27, 2013.
Jump up ^ Kessler RC, Berglund P, Demler O, Jin R, Merikangas KR, Walters EE (June 2005). "Lifetime prevalence and age-of-onset distributions of DSM-IV disorders in the National Comorbidity Survey Replication". Arch. Gen. Psychiatry. 62 (6): 593–602. PMID 15939837. doi:10.1001/archpsyc.62.6.593.
Jump up ^ Kessler RC, Chiu WT, Demler O, Merikangas KR, Walters EE (June 2005). "Prevalence, severity, and comorbidity of 12-month DSM-IV disorders in the National Comorbidity Survey Replication". Arch. Gen. Psychiatry. 62 (6): 617–27. PMC 2847357  . PMID 15939839. doi:10.1001/archpsyc.62.6.617.
Jump up ^ US National Institute of Mental Health (2006) The Numbers Count: Mental Disorders in America Retrieved May 2007
Jump up ^ Alonso J, Angermeyer MC, Bernert S, et al. (2004). "Prevalence of mental disorders in Europe: results from the European Study of the Epidemiology of Mental Disorders (ESEMeD) project". Acta Psychiatr Scand Suppl. 109 (420): 21–7. PMID 15128384. doi:10.1111/j.1600-0047.2004.00327.x.
Jump up ^ Wittchen HU, Jacobi F (August 2005). "Size and burden of mental disorders in Europe--a critical review and appraisal of 27 studies". Eur Neuropsychopharmacol. 15 (4): 357–76. PMID 15961293. doi:10.1016/j.euroneuro.2005.04.012.
Jump up ^ Somers JM, Goldner EM, Waraich P, Hsu L (February 2006). "Prevalence and incidence studies of anxiety disorders: a systematic review of the literature". Can J Psychiatry. 51 (2): 100–13. PMID 16989109.
Jump up ^ Waraich P, Goldner EM, Somers JM, Hsu L (February 2004). "Prevalence and incidence studies of mood disorders: a systematic review of the literature". Can J Psychiatry. 49 (2): 124–38. PMID 15065747. Archived from the original on November 12, 2013.
Jump up ^ Rotenstein, Lisa S.; Ramos, Marco A.; Torre, Matthew; Segal, J. Bradley; Peluso, Michael J.; Guille, Constance; Sen, Srijan; Mata, Douglas A. (2016-12-06). "Prevalence of Depression, Depressive Symptoms, and Suicidal Ideation Among Medical Students: A Systematic Review and Meta-Analysis". JAMA. 316 (21): 2214–2236. ISSN 1538-3598. PMID 27923088. doi:10.1001/jama.2016.17324.
Jump up ^ Douglas A. Mata, Marco A. Ramos, Narinder Bansal, Rida Khan, Constance Guille, Emanuele Di Angelantonio & Srijan Sen (2015). "Prevalence of Depression and Depressive Symptoms Among Resident Physicians: A Systematic Review and Meta-analysis". JAMA. 314 (22): 2373–2383. PMC 4866499  . PMID 26647259. doi:10.1001/jama.2015.15845. CS1 maint: Multiple names: authors list (link)
Jump up ^ Saha S, Chant D, Welham J, McGrath J (May 2005). "A systematic review of the prevalence of schizophrenia". PLoS Med. 2 (5): e141. PMC 1140952  . PMID 15916472. doi:10.1371/journal.pmed.0020141.
Jump up ^ Torgersen S, Kringlen E, Cramer V (June 2001). "The prevalence of personality disorders in a community sample". Arch. Gen. Psychiatry. 58 (6): 590–6. PMID 11386989. doi:10.1001/archpsyc.58.6.590.
Jump up ^ Grant BF, Hasin DS, Stinson FS, et al. (July 2004). "Prevalence, correlates, and disability of personality disorders in the United States: results from the national epidemiologic survey on alcohol and related conditions". J Clin Psychiatry. 65 (7): 948–58. PMID 15291684. doi:10.4088/JCP.v65n0711.
Jump up ^ Carter AS, Briggs-Gowan MJ, Davis NO (January 2004). "Assessment of young children's social-emotional development and psychopathology: recent advances and recommendations for practice". J Child Psychol Psychiatry. 45 (1): 109–34. PMID 14959805. doi:10.1046/j.0021-9630.2003.00316.x.
External links[edit]
Prevalence of Mental Illness in the United States: Data Sources and Estimates Congressional Research Service
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