Dead zone (ecology)
Dead zones are
Coastal regions, such as the Baltic Sea, the northern Gulf of Mexico, and the Chesapeake Bay, as well as large enclosed water bodies like Lake Erie, have been affected by deoxygenation due to eutrophication. Excess nutrients are input into these systems by rivers, ultimately from urban and agricultural runoff and exacerbated by deforestation. These nutrients lead to high productivity that produces organic material that sinks to the bottom and is respired. The respiration of that organic material uses up the oxygen and causes hypoxia or anoxia.
The
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 nutrients 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. With more available nutrients, single-celled aquatic organisms (such as algae and cyanobacteria) have the resources necessary to exceed their previous growth limit and begin to multiply at an exponential rate. Exponential growth leads to rapid increases in the density of certain types of these phytoplankton, a phenomenon known as an algal bloom.[6]
"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."[7]
The major groups of algae are
Dead zones can be caused by natural and by anthropogenic factors. Natural causes include coastal upwelling, changes in wind, and water circulation patterns. Other environmental factors that determine the occurrence or intensity of a dead zone include long water residence times, high temperatures, and high levels of sunlight penetration through the water column.[8]
Additionally, natural oceanographic phenomena can cause deoxygenation of parts of the water column. For example, enclosed bodies of water, such as
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]
Changes in ocean circulation triggered by ongoing climate change could also add or magnify other causes of oxygen reductions in the ocean.[11]
Anthropogenic causes include use of chemical fertilizers and their subsequent presence in water runoff and groundwater, direct sewage discharge into rivers and lakes, and nutrient discharge into groundwater from large, accumulated quantities of animal waste. Use of chemical fertilizers is considered the major human-related cause of dead zones around the world. However, runoff from sewage, urban land use, and fertilizers can also contribute to eutrophication.[12]
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.[13] 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 plant matter by-products from 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.[14] Over 86% of the livestock feed is inedible for humans.[15]
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. Around the world, dead zones have developed in continental seas, such as the Baltic Sea, Kattegat, Black Sea, Gulf of Mexico, and East China Sea, all of which are major fishery areas.[2]
Types
Dead zones can be classified by type, and are identified by the length of their occurrence:[16]
- Permanent dead zones are deep water occurrences that rarely exceed 2 milligrams per liter.
- Temporary dead zones are short lived dead zones lasting hours or days.
- Seasonal dead zones are annually occurring, typically in warm months of summer and autumn.
- Diel cycling hypoxia is a specific seasonal dead zone that only becomes hypoxic during the night
The type of dead zone can, in some ways, be categorized by the time required for the water to return to full health. This time frame depends on the intensity of eutrophication and level of oxygen depletion. A water body that sinks to anoxic conditions and experiences extreme reduction in community diversity will have to travel a much longer path to return to full health. A water body that only experiences mild hypoxia and maintains community diversity and maturity will require a much shorter path length to return to full health.[2]
Effects
The most notable effects of eutrophication are vegetal blooms, sometimes toxic,
Due to the hypoxic conditions present in dead zones, marine life within these areas tends to be scarce. Most fish and motile organisms tend to emigrate out of the zone as oxygen concentrations fall, and benthic populations may experience severe losses when oxygen concentrations are below 0.5 mg l−1 O2.[17] In severe anoxic conditions, microbial life may experience dramatic shifts in community identity as well, resulting in an increased abundance of anaerobic organisms as aerobic microbes decrease in number and switch energy sources for oxidation such as nitrate, sulfate, or iron reduction. Sulfur reduction is a particular concern as Hydrogen sulfide is toxic and stresses most organisms within the zone further, exacerbating mortality risks.[18]
Low oxygen levels can have severe effects on survivability of organisms inside the area while above lethal anoxic conditions. Studies conducted along the
Community composition in benthic communities is dramatically disrupted by periodic oxygen depletion events, such as those of seasonal dead zones and occurring as a result of Diel cycles. The longterm effects of such hypoxic conditions result in a shift in communities, most commonly manifest as a decrease in species diversity through mass mortality events. Reestablishment of benthic communities depend upon composition of adjacent communities for larval recruitment.[17] This results in a shift towards faster establishing colonizers with shorter and more opportunistic life strategies, potentially disrupting historic benthic compositions.[citation needed]
Fisheries
The influence of dead zones on fisheries and other marine commercial activities varies by the length of occurrence and location. Dead zones are often accompanied by a decrease in biodiversity and collapse in benthic populations, lowering the diversity of yield in commercial fishing operations, but in cases of eutrophication-related dead zone formations, the increase in nutrient availability can lead to temporary rises in select yields among pelagic populations, such as anchovies.[17] However, studies estimate that the increased production in the surrounding areas do not offset the net decrease in productivity resulting from the dead zone. For instance, an estimated 17,000 MT of carbon in the form of prey for fisheries has been lost as a result of dead zones in the Gulf of Mexico.[2] Additionally, many stressors in fisheries are worsened by hypoxic conditions. Indirect factors such as increased success by invasive species and increased pandemic intensity in stressed species such as oysters both lead to losses in revenue and ecological stability in affected regions.[19]
Coral reefs
There has been a severe increase in mass mortality events associated with low oxygen causing mass hypoxia with the majority having been in the last 2 decades. The rise in water temperature leads to an increase in oxygen demand and the increase for ocean deoxygenation which causes these large coral reef dead zones. For many
Around six million people, the majority who live in developing countries, depend on coral reef fisheries. These mass die-offs due to extreme hypoxic events can have severe impacts on reef fish populations. Coral reef ecosystems offer a variety of essential ecosystem services including shoreline protection, nitrogen fixation, and waste assimilation, and tourism opportunities. The continued decline of oxygen in oceans on coral reefs is concerning because it takes many years (decades) to repair and regrow corals.[20]
Jellyfish blooms
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. Jellyfish blooms produce large quantities of mucus, leading to major changes in food webs in the ocean since few organisms feed on them. The organic carbon in mucus is metabolized by bacteria which return it to the atmosphere in the form of carbon dioxide in what has been termed a "jelly carbon shunt".[23] The potential worsening of jellyfish blooms as a result of human activities has driven new research into the influence of dead zones on jelly populations. The primary concern is the potential for dead zones to serve as breeding grounds for jelly populations as a result of the hypoxic conditions driving away competition for resources and common predators of jellyfish.[24] The increased population of jellyfish could have high commercial costs with loss of fisheries, destruction and contamination of trawling nets and fishing vessels, and lowered tourism revenue in coastal systems.[24]
Seagrass beds
Globally, seagrass has been declining rapidly. It is estimated that 21% of the 71 known seagrass species have decreasing population trends and 11% of those species have been designated as threatened on the ICUN Red List. Hypoxia that leads to eutrophication caused form ocean deoxygenation is one of the main underlying factors of these die-offs. Eutrophication causes enhanced nutrient enrichment which can result in seagrass productivity, but with continual nutrient enrichment in seagrass meadows, it can cause excessive growth of microalgae, epiphytes and phytoplankton resulting in hypoxic conditions.[20]
Seagrass is both a source and a sink for oxygen in the surrounding water column and sediments. At night, the inner part of seagrass oxygen pressure is linearly related to the oxygen concentration in the water column, so low water column oxygen concentrations often result in hypoxic seagrass tissues, which can eventually kill off the seagrass. Normally, seagrass sediments must supply oxygen to the below-ground tissue through either photosynthesis or by diffusing oxygen from the water column through leaves to
Because hypoxia increases the invasion of sulfides in seagrass, this negatively affects seagrass through photosynthesis, metabolism and growth. Generally, seagrass is able to combat the sulfides by supplying enough oxygen to the roots. However, deoxygenation causes the seagrass to be unable to supply this oxygen, thus killing it off.[20]
Deoxygenation reduces the diversity of organisms inhabiting
Seagrass also provides many ecosystem services including water purification, coastal protection, erosion control, sequestration and delivery of trophic subsidies to adjacent marine and terrestrial habitats. Continued deoxygenation causes the effects of hypoxia to be compounded by climate change which will increase the decline in seagrass populations.[25][20]
Mangrove forests
Compared to seagrass beds and coral reefs, hypoxia is more common on a regular basis in mangrove ecosystems, though ocean deoxygenation is compounding the negative effects by anthropogenic nutrient inputs and land use modification.[20]
Like seagrass, mangrove trees transport oxygen to roots of rhizomes, reduce sulfide concentrations, and alter microbial communities. Dissolved oxygen is more readily consumed in the interior of the mangrove forest. Anthropogenic inputs may push the limits of survival in many mangrove microhabitats. For example, shrimp ponds constructed in mangrove forests are considered the greatest anthropogenic threat to mangrove ecosystems. These shrimp ponds reduce
Due to these frequent hypoxic conditions, the water does not provide habitats to fish. When exposed to extreme hypoxia, ecosystem function can completely collapse. Extreme deoxygenation will affect the local fish populations, which are an essential food source. The environmental costs of shrimp farms in the mangrove forests grossly outweigh their economic benefits. Cessation of shrimp production and restoration of these areas and reduce eutrophication and anthropogenic hypoxia.[20]
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
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.[4][2]
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.[citation needed]
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
With its massive size, the Baltic Sea is best analyzed in sub-areas rather than as a whole. In a paper published in 2004, researchers specifically divided the Baltic Sea into 9 sub-areas, each having its own specific characteristics.[29] The 9 sub-areas are discerned as follows: Gulf of Bothnia, Archipelago region, Gulf of Finland, Gulf of Riga, Gulf of Gdansk, Swedish East-coast, Central Baltic, Belt Sea region, and Kattegat.[29] Each sub-area has responded differently to nutrient additions and eutrophication; however, there are a few general patterns and measures for the Baltic Sea as a whole.[29] As the researchers Rönnberg and Bonsdorff state,
"Irrespective of the area-specific effects of the increased loads of nutrients to the Baltic Sea, the sources are more or less similar in the whole region. The extent and the severity of the discharges may differ, however. As is seen in e.g. HELCOM (1996) and Rönnberg (2001), the major sources in the input of nutrients are derived from agriculture, industry, municipal sewage and transports. Nitrogen emissions in form of atmospheric depositions are also important, as well as local point sources, such as aquaculture and leakage from forestry."[29]
In general, each area of the Baltic Sea is experiencing similar anthropogenic effects. As Rönnberg and Bonsdorff state, "Eutrophication is a serious problem in the Baltic Sea area."[29] However, when it comes to implementation of water revival programs, each area likely will need to be handled on a local level.[citation needed]
Virginia
Chesapeake Bay
According to the National Geographic, the Chesapeake Bay was one of the first hypoxic zones to be identified in the 1970s.[30] The Chesapeake Bay experiences seasonal hypoxia due to high nitrogen levels.[31] These nitrogen levels are caused by urbanization, there are multiple factories that pollute the atmosphere with nitrogen, and agriculture, the opposite side of the bay is used for poultry farming, which produces a lot of manure that ends up running off into the Chesapeake Bay.[32][33]
From 1985 - 2019, there were efforts from the caretakers of Chesapeake Bay to reduce the annual hypoxic volumes. There was significant improvement in 2016-2017 that gave assurance to the caretakers that the efforts were successful, however recent data has shown that further efforts are needed to continuously curb the effects of global warming.[34]
Elizabeth River, Virginia
The Elizabeth River estuary is used for commercial and military use and is one of the most commonly used ports on the East Coast of the USA.[35] From 2015-2019, 11 different conditions were measured in various areas of the Elizabeth River. Throughout the river, there were consistently high levels of nitrogen and phosphorus, along with high levels of other contaminants contributing to the poor quality of life for bottom feeders along the river. [36] The main cause of the pollution to the Elizabeth river has been the military and industrial activities through the 1990s.[37] In 1993, the Elizabeth River Project was started in attempt to do a restoration project on the river. Adopting one of the fish whose species had been largely impacted by the pollution, the Fundulus heteroclitus (Mummichog), the group was able to gain traction and carry out multiple projects and has removed thousands of tons of contaminated sediment. [38] In 2006, Maersk-APM, a major shipping company, wanted to build a new port on the Elizabeth River.[39] As part of the environmental mitigation they worked with the Elizabeth River Project to create the Money Point Project, which was an effort to restore Money Point, which had been deemed biologically depleted due to a black tar like substance called creosote laying at the bottom. Maersk-APM gave $5 million to help get the project up and running.[40] By 2012, they were able to restore over 7 acres of tidal marsh, 3 acres of oyster reef and created a new shoreline.[41] In 2019, the Money Point Project received the "Best Restored Shore" award from the American Shore and Beach Preservation Association.[42]
Lake Erie
A seasonal dead zone exists in the central part of
Lower St. Lawrence Estuary
A dead zone exists in the Lower
Oregon
There is a hypoxic zone covers the coasts of Oregon and Washington[52] that reached peak size in 2006 at an area of over 1,158 square miles.[53] Strong surface winds between April and September cause frequent upwelling that results in an increase of algae blooms, rendering the hypoxia a seasonal occurrence.[54] The upwelling has contributed to lower temperatures within the zone.[55] The dead zone has resulted in sea organisms such as crabs and fish relocating and an interference of commercial fishing.[52] Organisms that cannot relocate have been found to suffocate, leaving them unable to be used by fishermen.[56] In 2009, one scientist described "thousands and thousands" of suffocated, crabs, worms, and sea stars along the seafloor of the hypoxic zone.[57] In 2021, 1.9 million dollars were put into monitoring and continuing to study the hypoxic conditions in the area that the dead zone occurs in.[56]
Gulf of Mexico 'dead zone'
The area of temporary hypoxic bottom water that occurs most summers off the coast of
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 square kilometers (8,776 square miles) to a record low in 1988 of 39 square kilometers (15 square miles).[67][58][68] The 2015 dead zone measured 16,760 square kilometers (6,474 square miles).[69]
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".[71]
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."[72] 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.[73] Courtney et al. hypothesize, that nutrient loading may have contributed to the increases in red snapper in the northern and western Gulf of Mexico.[74]
In 2017, Tulane University offered a $1 million challenge grant for growing crops with less fertilizer.[75]
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.[76]
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."[76]
In July 2007, a dead zone was discovered off the coast of Texas where the Brazos River empties into the Gulf.[77]
Korea
Jinhae Bay
Jinhae Bay is the first of Korea's two major dead zones. Hypoxia was first reported in Jinhae Bay in September 1974. In 2011, a joint study was done to observe and record causes, effects, and what can be done about Korea's hypoxic zones. It was discovered that Jinhae Bay exhibits a seasonal dead zone from early June to late September. This dead zone is caused by "domestic and land use waste and thermal stratification". Jinhae Bay experiences hypoxia largely at the bottom of its bay. The ratio of phosphorus to nitrogen is imbalanced at the bottom, where it is otherwise balanced at the top, with the exception of early June to late September where the Bay experiences eutrophication as a whole. The effects of Jinhae Bay's hypoxia is seen in the marine system surrounding Korea, with a loss of biological diversity, particularly of the calcareous shelled organisms.[78]
Shihwa Bay
Shihwa Bay is a coastal reservoir created in 1994 to supply surrounding agricultural lands with water, and act as a run-off lake for nearby industrial plants. The Bay was made without much environmental consideration, and by 1999, water quality had a significant drop. This drop in water quality is attributed to the bay not having enough circulation or new water flow to accommodate the domestic and industrial waste being dumped. In response, the Korean government set up a pollution management system within the bay, and has a gate system that allows the Bay to mix with water in the sea. Shihwa Bay is also experiencing an imbalance of phosphorus to nitrogen, but also large sources of ammonium.[79]
Energy Independence and Security Act of 2007
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.[80] 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.[81]
According to Fred Below, a professor of crop physiology at the
Reversal
The recovery of benthic communities is primarily dependent upon the length and severity of hypoxic conditions inside the hypoxic zone. Less severe conditions and temporary depletion of oxygen allow rapid recovery of benthic communities in the area due to reestablishment by benthic larvae from adjacent areas, with longer conditions of hypoxia and more severe oxygen depletion leading to longer reestablishment periods.
Small scale hypoxic systems with rich surrounding communities are the most likely to recover after nutrient influxes leading to eutrophication stop. However, depending on the extent of damage and characteristics of the zone, large scale hypoxic condition could also potentially recover after a period of a decade. For example, 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.[82]
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.[82] 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[83] and San Francisco Bay.[4]
See also
- Algal bloom
- Anoxic event
- Anoxic waters
- Cultural eutrophication
- Desert
- Eutrophication
- Fish kill
- Hypoxia
- Marine pollution
- Ocean deoxygenation
- Oxygen minimum zone
- Shutdown of thermohaline circulation
Notes
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- Bibcode:2013arXiv1306.5114C. Archivedfrom the original on February 24, 2015. Retrieved June 21, 2013.
- ^ "Adapt-N Wins Tulane Nitrogen Reduction Challenge to Reduce Dead Zones: What's Next?" (Press release). December 19, 2017. Archived from the original on October 31, 2021. Retrieved January 25, 2021.
- ^ a b Jennie Biewald; Annie Rossetti; Joseph Stevens; Wei Cheih Wong. The Gulf of Mexico's Hypoxic Zone (Report). Archived from the original on September 25, 2019. Retrieved September 25, 2019.
- ^ Cox, Tony (July 23, 2007). "Exclusive". Bloomberg. Archived from the original on June 9, 2010. Retrieved August 3, 2010.
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- ^ PMID 18560496.
- ^ "Dead Water". Economist. May 2008.
- ^ a b Mee, Laurence (November 2006). "Reviving Dead Zones". Scientific American. Archived from the original on September 13, 2016. Retrieved September 25, 2019.
- ^ 'Dead Zones' Multiplying In World's Oceans Archived December 30, 2017, at the Wayback Machine by John Nielsen. August 15, 2008, Morning Edition, NPR.
References
- Diaz, R. J.; Rosenberg, R. (August 15, 2008). "Spreading Dead Zones and Consequences for Marine Ecosystems". Science. 321 (5891): 926–929. S2CID 32818786.
- Osterman, Lisa E.; Poore, Richard Z.; Swarzenski, Peter W.; Turner, R. Eugene (2005). "Reconstructing a 180 yr record of natural and anthropogenic induced low-oxygen conditions from Louisiana continental shelf sediments". Geology. 33 (4): 329. S2CID 55361042.
- Taylor, F. J.; Taylor, N. J.; Walsby, J. R. (1985). "A Bloom of the Planktonic Diatom,Cerataulina pelagica, off the Coast of Northeastern New Zealand in 1983, and its Contribution to an Associated Mortality of Fish and Benthic Fauna". Internationale Revue der gesamten Hydrobiologie und Hydrographie. 70 (6): 773–795. .
- Morrisey, D.J; Gibbs, M.M; Pickmere, S.E; Cole, R.G (May 2000). "Predicting impacts and recovery of marine-farm sites in Stewart Island, New Zealand, from the Findlay–Watling model". Aquaculture. 185 (3–4): 257–271. .
- Potera, Carol (June 2008). "Fuels: Corn Ethanol Goal Revives Dead Zone Concerns". Environmental Health Perspectives. 116 (6): A242-3. PMID 18560496.
- Minnesota Board of Water and Soil Resources (BWSR, 2018), Alternative Practices Introduction | MN Board of Water, Soil Resources
- Minnesota 'Buffer Law' statute: MN Statute 103F.48
- BWSR Update, January 2019: [1] Archived February 16, 2019, at the Wayback Machine
- Ronnberg, C., & Bonsdorff, E. (February 2004). Baltic Sea eutrophication: area-specific ecological consequences [Article; Proceedings Paper]. Hydrobiologia, 514(1–3), 227–241. https://doi.org/10.1023/B:HYDR.0000019238.84989.7f
- Le Moal, Morgane, Gascuel-Odoux, Chantal, Ménesguen, Alain, Souchon, Yves, Étrillard, Levain, Alix, ... Pinay, Gilles (2019). Eutrophication: A new wine in an old bottle? Elsevier, Science of the Total Environment 651:1–11.
Further reading
- Growing 'dead zone' Confirmed by Underwater Robots in the Gulf of Oman, phys.org, April 2018
- 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 at archive.today (archived January 29, 2013)
- 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. July 7, 2008. Archived from the originalon September 8, 2010. Retrieved August 3, 2010.
- 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", The Washington Post, July 31, 2008
- Joel Achenbach, "'Dead Zones' Appear In Waters Worldwide: New Study Estimates More Than 400", The Washington Post, August 15, 2008
External links
- Louisiana Universities Marine Consortium
- UN Geo Yearbook 2003 report on nitrogen and dead zones at the Library of Congress Web Archives (archived August 2, 2005)
- NASA on dead zones (Satellite pictures) Archived November 23, 2015, at the Wayback Machine
- Gulf of Mexico Dead Zone – multimedia
- Gulf of Mexico Hypoxia Watch, NOAA, Joel Achenbach at the Wayback Machine (archived October 9, 2007)
- NutrientNet at the Wayback Machine (archived July 11, 2010), 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.