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Dead zones are hypoxic (low-
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
) areas in the world's
ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wor ...
s and large lakes. Hypoxia occurs when dissolved oxygen (DO) concentration falls to or below 2 mg of O2/liter. When a body of water experiences hypoxic conditions, aquatic flora and fauna begin to change behavior in order to reach sections of water with higher oxygen levels. Once DO declines below 0.5 ml O2/liter in a body of water, mass mortality occurs. With such a low concentration of DO, these bodies of water fail to support the aquatic life living there. Historically, many of these sites were naturally occurring. However, in the 1970s,
oceanographer Oceanography (), also known as oceanology and ocean science, is the scientific study of the oceans. It is an Earth science, which covers a wide range of topics, including ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamic ...
s began noting increased instances and expanses of dead zones. These occur near inhabited
coastline The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in ...
s, where
aquatic life An aquatic ecosystem is an ecosystem formed by surrounding a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms that are dependent on each other and on their environment. The tw ...
is most concentrated. 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 Marine life, sea life, or ocean life is the plants, animals and other organisms that live in the salt water of seas or oceans, or the brackish water of coastal estuaries. At a fundamental level, marine life affects the nature of the planet. ...
could not be supported due to depleted oxygen levels. Some of these were as small as a square kilometer (0.4 mi2), but the largest dead zone covered 70,000 square kilometers (27,000 mi2). A 2008 study counted 405 dead zones worldwide.


Causes

Aquatic and marine dead zones can be caused by an increase in nutrients (particularly nitrogen and phosphorus) in the water, known as
eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phyt ...
. 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 Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. ...
, a phenomenon known as an
algal bloom An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term ''algae'' encompass ...
.
Limnologist Limnology ( ; from Greek λίμνη, ''limne'', "lake" and λόγος, ''logos'', "knowledge") is the study of inland aquatic ecosystems. The study of limnology includes aspects of the biological, chemical, physical, and geological characteris ...
Dr.
David Schindler David William Schindler, , (August 3, 1940 – March 4, 2021) was an American/Canadian limnologist. He held the Killam Memorial Chair and was Professor of Ecology in the Department of Biological Sciences at the University of Alberta in Edmonton, A ...
, whose research at the
Experimental Lakes Area IISD Experimental Lakes Area (IISD-ELA, known as ELA before 2014) is an internationally unique research station encompassing 58 formerly pristine freshwater lakes in Kenora District Ontario, Canada. Previously run by Fisheries and Oceans Canada, ...
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."
The major groups of algae are
Cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...
,
green algae The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/ Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga ...
,
Dinoflagellates The dinoflagellates ( Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates ...
,
Coccolithophore Coccolithophores, or coccolithophorids, are single celled organisms which are part of the phytoplankton, the autotrophic (self-feeding) component of the plankton community. They form a group of about 200 species, and belong either to the king ...
s and Diatom algae. An increase in the input of nitrogen and phosphorus generally causes Cyanobacteria to bloom. Other algae are consumed and thus do not accumulate to the same extent as Cyanobacteria. Cyanobacteria are not good food for zooplankton and fish and hence accumulate in water, die, and then decompose. The bacterial degradation of their biomass consumes the oxygen in the water, thereby creating the state of hypoxia. Dead zones can be caused by natural and by
anthropogenic Anthropogenic ("human" + "generating") is an adjective that may refer to: * Anthropogeny, the study of the origins of humanity Counterintuitively, anthropogenic may also refer to things that have been generated by humans, as follows: * Human i ...
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.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''.'' Additionally, natural oceanographic phenomena can cause deoxygenation of parts of the water column. For example, enclosed bodies of water, such as
fjords In physical geography, a fjord or fiord () is a long, narrow inlet with steep sides or cliffs, created by a glacier. Fjords exist on the coasts of Alaska, Antarctica, British Columbia, Chile, Denmark, Germany, Greenland, the Faroe Islands, Icela ...
or the
Black Sea The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Rom ...
, have shallow sills at their entrances,Gregg, M. C., and E. O¨ zsoy (2002), Flow, water mass changes, and hydraulics in the Bosporus, ''J. Geophys. Res.'', 107(C3), 3016, causing water to be trapped there for a long time. 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. These areas are also known as oxygen minimum zones (OMZ). In many cases, OMZs are permanent or semi-permanent areas. Remains of organisms found within
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand ...
layers near the mouth of the
Mississippi River The Mississippi River is the List of longest rivers of the United States (by main stem), second-longest river and chief river of the second-largest Drainage system (geomorphology), drainage system in North America, second only to the Hudson B ...
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 Vicksburg is a historic city in Warren County, Mississippi, United States. It is the county seat, and the population at the 2010 census was 23,856. Located on a high bluff on the east bank of the Mississippi River across from Louisiana, Vi ...
. Changes in ocean circulation triggered by ongoing
climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
could also add or magnify other causes of oxygen reductions in the ocean. 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
fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
s 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.Corn boom could expand 'dead zone' in Gulf
NBC News.msn.com
In August 2017, a report suggested that the US
meat industry The meat industry are the people and companies engaged in modern industrialized livestock agriculture for the production, packing, preservation and marketing of meat (in contrast to dairy products, wool, etc.). In economics, the meat industry is ...
and agroeconomic system are predominantly responsible for the largest-ever dead zone in the
Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United ...
. Soil
runoff Runoff, run-off or RUNOFF may refer to: * RUNOFF, the first computer text-formatting program * Runoff or run-off, another name for bleed, printing that lies beyond the edges to which a printed sheet is trimmed * Runoff or run-off, a stock marke ...
and leached
nitrate Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insolu ...
, exacerbated by agricultural land management and tillage practices as well as manure and synthetic
fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
usage, contaminated water from the Heartland to the Gulf of Mexico. A large portion of the crops grown in this region are used as major feed components in the production of meat animals for agribusiness companies, like
Tyson Tyson is a male given name of old French origin meaning 'high-spirited', 'fire'. It is from this that a surname arose 'son of Tyson'. Surname *Alan Tyson (1926–2000), British musicologist *Barbara Tyson (born 1964), Canadian actress *Bill Tyso ...
and Smithfield Foods. Notable dead zones in the United States include the northern Gulf of Mexico region, 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, Kattegat, Black Sea, Gulf of Mexico, and East China Sea, all of which are major fishery areas.


Types

Dead zones can be classified by type, and are identified by the length of their occurrence: * 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.


Effects

The most notable effects of eutrophication are vegetal blooms, sometimes toxic,
loss of biodiversity Biodiversity loss includes the worldwide extinction of different species, as well as the local reduction or loss of species in a certain habitat, resulting in a loss of biological diversity. The latter phenomenon can be temporary or permanent, de ...
and anoxia, which can lead to the massive death of aquatic organisms. 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. 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 Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The under ...
is toxic and stresses most organisms within the zone further, exacerbating mortality risks. Low oxygen levels can have severe effects on survivability of organisms inside the area while above lethal anoxic conditions. Studies conducted along the
Gulf Coast The Gulf Coast of the United States, also known as the Gulf South, is the coast, coastline along the Southern United States where they meet the Gulf of Mexico. The list of U.S. states and territories by coastline, coastal states that have a shor ...
of
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...
have shown hypoxic conditions lead to reduction of reproductive rates and growth rates in a variety of organisms including fish and benthic invertebrates. Organisms able to leave the area typically do so when oxygen concentrations decrease to less than 2 mg l−1. At these oxygen concentrations and below, organisms that survive inside the oxygen deficient environment and are unable to escape the area will often exhibit progressively worsening stress behavior and die. Surviving organisms tolerant of hypoxic conditions often exhibit physiological adaptations appropriate for persisting within hypoxic environments. Examples of such adaptations include increased efficiency of oxygen intake and use, lowering required amount of oxygen intake through reduced growth rates or dormancy, and increasing the usage of anaerobic metabolic pathways. 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. This results in a shift towards faster establishing colonizers with shorter and more opportunistic life strategies, potentially disrupting historic benthic compositions. 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 An anchovy is a small, common forage fish of the family Engraulidae. Most species are found in marine waters, but several will enter brackish water, and some in South America are restricted to fresh water. More than 140 species are placed in 1 ...
. 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. 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. Despite most other life forms being killed by the lack of oxygen,
jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbre ...
can thrive and are sometimes present in dead zones in vast numbers.
Jellyfish bloom Jellyfish blooms are substantial growths in population of species under the phyla Cnidaria (including several types of jellyfish) and Ctenophora (comb jellies). Blooms may take place naturally as a result of ocean and wind patterns, ecosystem sh ...
s produce large quantities of mucus, leading to major changes in
food web A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Another name for food web is consumer-resource system. Ecologists can broadly lump all life forms into one o ...
s 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". 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. 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. In addition to environmental impacts, eutrophication also poses a threat to society and human health. In a review on eutrophication, researchers wrote, "Eutrophication poses a threat to the environment, the economy (e.g. impact on shellfish production, fishing, tourism), but also to human health (Von Blottnitz et al., 2006; Sutton et al., 2011). Attempts to evaluate the monetary impacts of eutrophication have been made over the last two decades, mainly in the United States and in the Baltic Sea (Dodds et al., 2009; Gren et al., 1997). These studies indicate a variety of impacts and costs which are quantifiable fairly directly, for instance when cities of hundreds of thousands of people are deprived of drinking water for several days. One example is the toxic algal bloom in the western Lake Erie basin in 2014, which led to disruption of water supplies to 400,000 people (Smith et al., 2015) On the other hand, integrating all the environmental, health and socio-economic impacts in the calculations of indirect effects, poses more of a challenge (Folke et al., 1994; Romstad, 2014)."


Locations

In the 1970s, marine dead zones were first noted in settled areas where intensive economic use stimulated scientific scrutiny: in the U.S. East Coast's
Chesapeake Bay The Chesapeake Bay ( ) is the largest estuary in the United States. The Bay is located in the Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula (including the parts: the Eastern Shore of Maryland / ...
, in Scandinavia's
strait A strait is an oceanic landform connecting two seas or two other large areas of water. The surface water generally flows at the same elevation on both sides and through the strait in either direction. Most commonly, it is a narrow ocean chan ...
called the
Kattegat The Kattegat (; sv, Kattegatt ) is a sea area bounded by the Jutlandic peninsula in the west, the Danish Straits islands of Denmark and the Baltic Sea to the south and the provinces of Bohuslän, Västergötland, Halland and Skåne in Sweden ...
, which is the mouth of the
Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and from ...
and in other important Baltic Sea fishing grounds, in the
Black Sea The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Rom ...
, and in the northern
Adriatic The Adriatic Sea () is a body of water separating the Italian Peninsula from the Balkan Peninsula. The Adriatic is the northernmost arm of the Mediterranean Sea, extending from the Strait of Otranto (where it connects to the Ionian Sea) to the ...
. Other marine dead zones have appeared in coastal waters of
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
,
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
, and
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island coun ...
. A 2008 study counted 405 dead zones worldwide.


Baltic Sea

Researchers from Baltic Nest Institute published in one of
PNAS ''Proceedings of the National Academy of Sciences of the United States of America'' (often abbreviated ''PNAS'' or ''PNAS USA'') is a peer-reviewed multidisciplinary scientific journal. It is the official journal of the National Academy of Scie ...
issues reports that the dead zones in the Baltic Sea have grown from approximately 5,000 km2 to more than 60,000 km2 in recent years. Some of the causes behind the elevated increase of dead zones can be attributed to the use of fertilizers, large animal farms, the burning of fossil fuels, and effluents from municipal wastewater treatment plants. 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.Ronnberg, C., & Bonsdorff, E. (2004, Feb). Baltic Sea eutrophication: area-specific ecological consequences rticle; Proceedings Paper ''Hydrobiologia, 514''(1-3), 227-241. https://doi.org/10.1023/B:HYDR.0000019238.84989.7f 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. 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. 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.” 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." However, when it comes to implementation of water revival programs, each area likely will need to be handled on a local level.


Chesapeake Bay

As reported by the National Geographic "The Chesapeake Bay, on the East Coast of the United States, has one of the first dead zones ever identified, in the 1970s. The Chesapeake's high levels of nitrogen are caused by two factors: urbanization and agriculture. The western part of the bay is full of factories and urban centers that emit nitrogen into the air. Atmospheric nitrogen accounts for about a third of the nitrogen that enters the bay. The eastern part of the bay is a center of poultry farming, which produces large amounts of manure." The National Geographic further stated "Since 1967, the Chesapeake Bay Foundation has led a number of programs that aim to improve the bay's water quality and curb pollution runoff. The Chesapeake still has a dead zone, whose size varies with the season and weather."


Elizabeth River, Virginia

The Elizabeth River estuary is important for
Norfolk, Virginia Norfolk ( ) is an independent city in the Commonwealth of Virginia in the United States. Incorporated in 1705, it had a population of 238,005 at the 2020 census, making it the third-most populous city in Virginia after neighboring Virginia B ...
,
Chesapeake, Virginia Chesapeake is an independent city in the Commonwealth of Virginia, United States. At the 2020 census, the population was 249,422, it is the second-most populous independent city in Virginia, tenth-largest in the Mid-Atlantic, and the 90th ...
,
Virginia Beach, Virginia Virginia Beach is an independent city located on the southeastern coast of the Commonwealth of Virginia in the United States. The population was 459,470 at the 2020 census. Although mostly suburban in character, it is the most populous city ...
and
Portsmouth, Virginia Portsmouth is an independent city in southeast Virginia and across the Elizabeth River from Norfolk. As of the 2020 census, the population was 97,915. It is part of the Hampton Roads metropolitan area. The Norfolk Naval Shipyard and Naval M ...
. It has been polluted by nitrogen and phosphorus, but also toxic deposits from the shipbuilding industry, the military, the world's largest coal export facility, refineries, loading docks, container-repair facilities and others, so fish had been "offlimits since the 1920s". In 1993, a group formed to clean it up, adopting the
mummichog The mummichog (''Fundulus heteroclitus'') is a small killifish found along the Atlantic coast of the United States and Canada. Also known as Atlantic killifish, mummies, gudgeons, and mud minnows, these fish inhabit brackish and coastal waters in ...
as a mascot, and has removed thousands of tons of contaminated sediment. In 2006, a 35-acre biological dead zone called Money Point was dredged out, and this let fish return and the wetland recover.


Lake Erie

A seasonal dead zone exists in the central part of
Lake Erie Lake Erie ( "eerie") is the fourth largest lake by surface area of the five Great Lakes in North America and the eleventh-largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also ha ...
from east of
Point Pelee Point Pelee National Park (; french: Parc national de la Pointe-Pelée) is a national park in Essex County in southwestern Ontario, Canada where it extends into Lake Erie. The word is French for 'bald'. Point Pelee consists of a peninsula of la ...
to Long Point and stretches to shores in Canada and the United States. Between the months of July and October the dead zone has the ability to grow to the size of 10,000 square kilometers. Lake Erie has an excess of
phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...
due to agricultural runoff that quickens the growth of algae which then contributes to hypoxic conditions. The superabundance of phosphorus in the lake has been linked to
nonpoint source pollution Nonpoint source (NPS) pollution refers to diffuse contamination (or pollution) of water or air that does not originate from a single discrete source. This type of pollution is often the cumulative effect of small amounts of contaminants gathered ...
such as urban and agricultural runoff as well as
point source pollution A point source of pollution is a single identifiable source of air, water, thermal, noise or light pollution. A point source has negligible extent, distinguishing it from other pollution source geometries (such as nonpoint source or area source) ...
that includes sewage and wastewater treatment plants. The zone was first noticed in the 1960s amid the peak of
eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phyt ...
occurring in the lake. After public concern increased, Canada and the US launched efforts to reduce runoff pollution into the lake in the 1970s as means to reverse the dead zone growth. Scientists in 2018 stated that phosphorus runoff would have to further decrease by 40% to avoid the emergence of the dead zones in the area. The commercial and recreational fishing industry have been significantly impacted by the hypoxic zone. In 2021, the low-oxygenated waters caused a mass-kill event of
freshwater drum The freshwater drum, ''Aplodinotus grunniens'', is a fish endemic to North and Central America. It is the only species in the genus ''Aplodinotus'', and is a member of the family Sciaenidae. It is the only North American member of the group that ...
fish species (also known as ''sheepshead fish''). Water from the lake is also used for human drinking. Water from the lake has been said to acquire a pervasive odor and discoloration when the dead zone is active in the late summer months.


Lower St. Lawrence Estuary

A dead zone exists in the Lower St. Lawrence River area from east the
Saguenay River __NOTOC__ The Saguenay River () is a major river of Quebec, Canada. It drains Lac Saint-Jean in the Laurentian Highlands, leaving at Alma and running east; the city of Saguenay is located on the river. It drains into the Saint Lawrence River. ...
to east of
Baie Comeau Baie-Comeau (; 2021 city population 20,687; CA population 26,643) is a city located approximately north-east of Quebec City in the Côte-Nord region of the province of Quebec, Canada. It is located on the shores of the Saint Lawrence River ne ...
, greatest at depths over and noticed since the 1930s. The main concern for Canadian scientists is the impact on fish found in the area.


Oregon

There is a hypoxic zone covers the coasts of Oregon and Washington that reached peak size in 2006 at an area of over 1,158 square miles. Strong surface winds between April and September cause frequent upwelling that results in an increase of algae blooms, rendering the hypoxia a seasonal occurrence. The upwelling has contributed to lower temperatures within the zone. The dead zone has resulted in sea organisms such as crabs and fish relocating and an interference of
commercial fishing Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must oft ...
. Organisms that cannot relocate have been found to suffocate, leaving them unable to be used by fishermen. In 2009, one scientist described "thousands and thousands" of suffocated, crabs, worms, and sea stars along the seafloor of the hypoxic zone. 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.


Gulf of Mexico 'dead zone'

The area of temporary hypoxic bottom water that occurs most summers off the coast of
Louisiana Louisiana , group=pronunciation (French: ''La Louisiane'') is a state in the Deep South and South Central regions of the United States. It is the 20th-smallest by area and the 25th most populous of the 50 U.S. states. Louisiana is bord ...
in the Gulf of Mexico is the largest recurring hypoxic zone in the United States. It occurs only during the summer months of the year due to summer warming, regional circulation, wind mixing and high freshwater discharge. The
Mississippi River The Mississippi River is the List of longest rivers of the United States (by main stem), second-longest river and chief river of the second-largest Drainage system (geomorphology), drainage system in North America, second only to the Hudson B ...
, which is the drainage area for 41% of the continental United States, dumps high-nutrient runoff such as
nitrates Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insolu ...
and
phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...
into the Gulf of Mexico. According to a 2009 fact sheet created by
NOAA The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditio ...
, "seventy percent of nutrient loads that cause hypoxia are a result of this vast drainage basin". which includes the heart of U.S.
agribusiness Agribusiness is the industry, enterprises, and the field of study of value chains in agriculture and in the bio-economy, in which case it is also called bio-business or bio-enterprise. The primary goal of agribusiness is to maximize profit w ...
, the
Midwest The Midwestern United States, also referred to as the Midwest or the American Midwest, is one of four Census Bureau Region, census regions of the United States Census Bureau (also known as "Region 2"). It occupies the northern central part of ...
. The condition is brief and seasonal, but is depicted on maps as persistent for maximum policy impact. 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. Nitrogen is indeed needed to increase crop yields, but plants are inefficient at taking it up, and often more fertilizers are used than plants actually need. Therefore, only a percentage of applied nitrogen ends up in the crops; and in some areas that number is less than 20%. Even though
Iowa Iowa () is a U.S. state, state in the Midwestern United States, Midwestern region of the United States, bordered by the Mississippi River to the east and the Missouri River and Big Sioux River to the west. It is bordered by six states: Wiscon ...
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. 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. In 2012, Iowa introduced the Iowa Nutrient Reduction Strategy, which "is a science and technology-based framework to assess and reduce nutrients to Iowa waters and the Gulf of Mexico. It is designed to direct efforts to reduce nutrients in surface water from both point and nonpoint sources in a scientific, reasonable and cost effective manner." The strategy continues to evolve, using voluntary methods to reduce Iowa's negative contributions through outreach, research, and implementation of nutrient holding practices. In order to help reduce agricultural runoff into the Mississippi Basin, Minnesota passe
''MN'' Statute 103F.48
in 2015, also known as the "Buffer Law", which was designed to implement mandatory
riparian buffer A riparian buffer or stream buffer is a vegetated area (a " buffer strip") near a stream, usually forested, which helps shade and partially protect the stream from the impact of adjacent land uses. It plays a key role in increasing water quality i ...
s between farmland and public waterways across the State of Minnesota. Th
Minnesota Board of Water and Soil Resources
(BWSR) issued a January 2019 report stating that compliance with the 'Buffer Law' has reached 99%.


Size

The area of hypoxic bottom water that occurs for several weeks each summer in the Gulf of Mexico has been mapped most years from 1985 through 2017. The size varies annually from a record high in 2017 when it encompassed more than 22,730 square kilometers (8,776 square miles) to a record low in 1988 of 39 square kilometers (15 square miles). The 2015 dead zone measured 16,760 square kilometers (6,474 square miles). Nancy Rabalais of the Louisiana Universities Marine Consortium in Cocodrie, Louisiana predicted the dead zone or hypoxic zone in 2012 will cover an area of 17,353 square 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 square 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. 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 larger than the previous year".


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." 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. Courtney et al. hypothesize, that nutrient loading may have contributed to the increases in red snapper in the northern and western Gulf of Mexico. In 2017, Tulane University offered a $1 million challenge grant for growing crops with less fertilizer.


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. 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." In July 2007, a dead zone was discovered off the coast of
Texas Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...
where the
Brazos River The Brazos River ( , ), called the ''Río de los Brazos de Dios'' (translated as "The River of the Arms of God") by early Spanish explorers, is the 11th-longest river in the United States at from its headwater source at the head of Blackwater ...
empties into the Gulf.


Energy Independence and Security Act of 2007

The
Energy Independence and Security Act of 2007 The Energy Independence and Security Act of 2007Pub.L. 110-140, originally named the Clean Energy Act of 2007, is an Act of Congress concerning the energy policy of the United States. As part of the Democratic Party's 100-Hour Plan during th ...
calls for the production of of renewable fuels by 2022, including of corn-based ethanol, a tripling of current production that would require a similar increase in corn production. 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. According to , a professor of crop physiology at the
University of Illinois at Urbana-Champaign The University of Illinois Urbana-Champaign (U of I, Illinois, University of Illinois, or UIUC) is a public land-grant research university in Illinois in the twin cities of Champaign and Urbana. It is the flagship institution of the Un ...
, 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 ''Proceedings of the National Academy of Sciences of the United States of America'' (often abbreviated ''PNAS'' or ''PNAS USA'') is a peer-reviewed multidisciplinary scientific journal. It is the official journal of the National Academy of S ...
, showed that scaling up corn production to meet the goal would increase nitrogen loading in the Dead Zone by 10–18%. This would boost nitrogen levels to twice the level recommended by the Mississippi Basin/Gulf of Mexico Water Nutrient Task Force ( Mississippi River Watershed Conservation Programs), a coalition of federal, state, and tribal agencies that have monitored the dead zone since 1997. The task force says a 30% reduction of nitrogen runoff is needed if the dead zone is to shrink.


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. Recovery also depends upon stratification levels within the area, so heavily stratified areas in warmer waters are less likely to recover from anoxic or hypoxic conditions in addition to being more susceptible to eutrophication driven hypoxia. The difference in recovery ability and susceptibility to hypoxia in stratified marine environments is expected to complicate recovery efforts of dead zones in the future as
ocean warming In oceanography and climatology, ocean heat content (OHC) is a term for the energy absorbed by the ocean, where it is stored for indefinite time periods as internal energy or enthalpy. The rise in OHC accounts for over 90% of Earth’s excess the ...
continues. 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 The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Rom ...
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 The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nationa ...
and the demise of centrally planned economies in Eastern and
Central Europe Central Europe is an area of Europe between Western Europe and Eastern Europe, based on a common historical, social and cultural identity. The Thirty Years' War (1618–1648) between Catholicism and Protestantism significantly shaped the a ...
. Fishing has again become a major economic activity in the region. 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. From 1985 to 2000, the
North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian ...
dead zone had nitrogen reduced by 37% when policy efforts by countries on the
Rhine River ), Surselva, Graubünden, Switzerland , source1_coordinates= , source1_elevation = , source2 = Rein Posteriur/Hinterrhein , source2_location = Paradies Glacier, Graubünden, Switzerland , source2_coordinates= , source ...
reduced sewage and industrial emissions of nitrogen into the water. Other cleanups have taken place along the
Hudson River The Hudson River is a river that flows from north to south primarily through eastern New York. It originates in the Adirondack Mountains of Upstate New York and flows southward through the Hudson Valley to the New York Harbor between Ne ...
'Dead Zones' Multiplying In World's Oceans
by John Nielsen. 15 Aug 2008, Morning Edition, NPR.
and
San Francisco Bay San Francisco Bay is a large tidal estuary in the U.S. state of California, and gives its name to the San Francisco Bay Area. It is dominated by the big cities of San Francisco, San Jose, and Oakland. San Francisco Bay drains water f ...
. Other methods of reversal can be found
here Here is an adverb that means "in, on, or at this place". It may also refer to: Software * Here Technologies, a mapping company * Here WeGo (formerly Here Maps), a mobile app and map website by Here Television * Here TV (formerly "here!"), a ...
.


See also

*
Algal bloom An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term ''algae'' encompass ...
*
Anoxic event Oceanic anoxic events or anoxic events ( anoxia conditions) describe periods wherein large expanses of Earth's oceans were depleted of dissolved oxygen (O2), creating toxic, euxinic (anoxic and sulfidic) waters. Although anoxic events have not ...
*
Anoxic waters Anoxic waters are areas of sea water, fresh water, or groundwater that are depleted of dissolved oxygen. The US Geological Survey defines anoxic groundwater as those with dissolved oxygen concentration of less than 0.5 milligrams per litre. Anoxic ...
* Cultural eutrophication *
Desert A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About on ...
*
Eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phyt ...
*
Fish kill The term fish kill, known also as fish die-off, refers to a localized die-off of fish populations which may also be associated with more generalized mortality of aquatic life.University of Florida. Gainesville, FL (2005) ''Plant Management in Fl ...
* Hypoxia *
Marine pollution Marine pollution occurs when substances used or spread by humans, such as industrial, agricultural and residential waste, particles, noise, excess carbon dioxide or invasive organisms enter the ocean and cause harmful effects there. The major ...
*
Ocean deoxygenation Ocean deoxygenation is the reduction of the oxygen content of the global oceans and coastal zones due to human activities as a consequence of anthropogenic emissions of carbon dioxide and eutrophication-driven excess production. It is manifest ...
* Oxygen minimum zone *
Shutdown of thermohaline circulation The Atlantic meridional overturning circulation (AMOC) is part of a global thermohaline circulation in the oceans and is the zonally integrated component of surface and deep currents in the Atlantic Ocean. It is characterized by a northward fl ...


Notes


References

* * * * * *Minnesota Board of Water and Soil Resources (BWSR, 2018), http://bwsr.state.mn.us/buffers/ *Minnesota 'Buffer Law' statute
''MN'' Statute 103F.48
*BWSR Update, January 2019: http://bwsr.state.mn.us/buffers/Buffers_Public_Waters_Progress_Map.pdf *Ronnberg, C., & Bonsdorff, E. (2004, Feb). Baltic Sea eutrophication: area-specific ecological consequences rticle; 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

* * * *
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:
MSNBC report on dead zones
March 29, 2004 *Joel Achenbach

''
The Washington Post ''The Washington Post'' (also known as the ''Post'' and, informally, ''WaPo'') is an American daily newspaper published in Washington, D.C. It is the most widely circulated newspaper within the Washington metropolitan area and has a large n ...
'', July 31, 2008 *Joel Achenbach, ttps://www.washingtonpost.com/wp-dyn/content/article/2008/08/14/AR2008081401910.html?hpid=topnews "'Dead Zones' Appear In Waters Worldwide: New Study Estimates More Than 400" ''The Washington Post'', August 15, 2008


External links


Louisiana Universities Marine Consortium
*

* *, an online nutrient trading tool developed by th
World Resources Institute
designed to address issues of eutrophication. See also th
PA NutrientNet
website designed for Pennsylvania's nutrient trading program. {{Authority control Aquatic ecology Chemical oceanography Ecotoxicology Environmental issues with water Fishing industry Ocean pollution Oceanographical terminology Water pollution Algal blooms