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(New page: Possible consequences of eutrophication ===Introduction=== Eutrophication is widely seen as a negative trend in lakes and the sea,but on the land it can be even beneficial. Increases...)
 
 
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Possible consequences of eutrophication
 
  
===Introduction===
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==Introduction==
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<P ALIGN="justify">
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Enhanced plant production and improved fish yields are sometimes described as positive impacts of [[Eutrophication|eutrophication]], especially in countries where fish and other aquatic organisms are a significant source of food. However detrimental ecological impacts can in turn have other negative consequences and impacts which are described below. Essentially the entire aquatic [[ecosystem]] changes with eutrophication. The diagram below gives an overview on the eutrophication process and its causes and consequences. </P>
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[[Image:eutrocon.png|705|center]]
  
[[Eutrophication]] is widely seen as a negative trend in lakes and the sea,but on the land it can be even beneficial.
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==Ecological impacts==
Increases in the productivity of plants are more welcomed, particularly where crops and commercially managed forests are concerned. Terrestrial ecosystems are also normally spared from the more harmful side effects of eutrophication.
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==== Increased biomass of phytoplankton resulting in [[algal bloom]]s ====
The ecological impacts of eutrophication are summarized in the figure and discussed in the sections below.
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[[Image:Plentiful_plankton.jpg|175px|thumb|right|<small>Envisat satellite image of an algal bloom captured with MERIS (Photo Credit: ESA, 2009)</small>]]
[[Image:Consequences.jpg|450px]]
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<P ALIGN="justify">[[Phytoplankton]] or microalgae are [[photosynthesizing]] microscopic organisms. They contain chlorophyll and require sunlight in order to live and grow. Most phytoplankton are buoyant and float in the upper part of the ocean where sunlight penetrates the water. In a balanced ecosystem they provide food for a wide range of organisms such as whales, shrimp, snails and jellyfish.
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Among the more important groups are the diatoms, cyanobacteria, dinoflagellates and coccolithophores (see: [[Marine Plankton]]).
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Phytoplankton species require inorganic [[Nutrient|nutrients]] such as nitrates, phosphates, and sulfur which they convert into proteins, fats and carbohydrates. When '''too many''' of these '''nutrients''' (by natural or [[Anthropogenic|anthropogenic]] cause) are available in the water phytoplankton may grow and multiply very fast forming [[Algal_bloom | algal blooms]]. Algal blooms may occur in freshwater as well as marine environments. Only one or a small number of phytoplankton species are involved and some blooms discolor (green, yellow-brown or red) the water due to their high density of pigmented cells. Blooms in the ocean may cover a large area and are easily visible in '''satellite images'''.</P>
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==== Toxic or inedible phytoplankton species (harmful algal blooms)====
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<P ALIGN="justify">'''[[Harmful_algal_bloom | Harmful algal blooms (HAB)]]''' are bloom events involving '''toxic or harmful phytoplankton'''. These cause harm through the production of toxins or by their accumulated biomass, which can effect co-occurring organisms and alter food web dynamics. Impacts include:</P>
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*Human illness,
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*Mortality of fish, birds and mammals following consumption or indirect exposure to HAB toxins,
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*Substantially economic losses to coastal communities and commercial fisheries.
  
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==== Increased blooms of gelatinous zooplankton====
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<P ALIGN="justify">[[Phytoplankton]] are the food source for numerous other organisms, especially the zooplankton. [[Zooplankton]] are heterotrophic plankton. They are primarily transported by ambient water currents but many have locomotion. Through their consumption and processing of phytoplankton and other food sources they play a role in aquatic food webs as a resource for higher trophic levels including fish. Zooplankton can be divided in two important groups: crustacean (copepods and krill) and '''gelatinous zooplankton'''. Gelatinous zooplankton have relatively fragile, plastic gelatinous bodies that contain at least 95% water and which lack rigid skeletal parts. The most well-known are the jellyfish. Eutrophication is believed to cause an '''increase''' in the relative importance of '''gelatinous''' versus crustacean '''zooplankton'''. On many areas of the world where the natural species diversity has been affected by pollution, over-fishing and climate change gelatinous zooplankton organisms may be becoming the dominant species.</P>
  
== Ecological impacts <ref>Christopher Mason, ‘Biology of freshwater pollution’, Pearson Education Limited, 2002</ref>==
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==== Decreases in water transparency (increased turbidity)====
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<P ALIGN="justify">The growth of phytoplankton can cause increased [[Turbidity|turbidity]] or decreased penetration of light into the lower depths of the water column. In lakes and rivers this can inhibit growth of submerged aquatic plants and affect species which are dependent on them (fish, shellfish).</P>
  
=====Increased biomass of phytoplankton resulting in algal blooms=====
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==== Dissolved oxygen depletion or hypoxia resulting in increased incidences of fish kills and / or dead benthic animals====
[[Image:fytock.jpg|right|thumb|<small>Phytoplankton species</small>]]
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[[Image:FishKill.jpg|160px|thumb|right|<small>A menhaden fish kill due severe hypoxia (Photo credit: Chris Deacutis, IAN Image library )</small>]]
[[Phytoplankton]] are free-floating [[photosynthesis|photosynthesizing]] microscopic plants that are mostly unicellular and create organic compounds from carbon dioxide dissolved in the water ([[primary production]]). They obtain energy through the process of photosynthesis and must therefore live in the euphotic zone of an ocean, sea, lake, or other body of water. They are responsible for much of the oxygen present in the Earth's atmosphere.
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<P ALIGN="justify">Oxygen is required for all life forms on the planet. Oxygen is produced by plants during ([[photosynthesis]]). At night animals and plants, as well as aerobic micro-organisms and decomposing dead organisms respire and so consume oxygen which results in a decrease in dissolved oxygen levels. Large fluctuations in dissolved oxygen levels may be the result of an [[algal bloom]]. While the algae population is growing at a fast rate, dissolved oxygen levels decrease. When these algae die, they are decomposed by bacteria which consume oxygen in this process so that the water can become temporarily hypoxic. Oxygen depletion, or [[Hypoxia|hypoxia]], is a common effect of eutrophication in water. The '''direct effects''' of hypoxia include '''fish kills''', especially the death of fish that need high levels of dissolved oxygen. Changes in fish communities may have an impact on the whole aquatic ecosystem and may deplete fish stocks. In extreme cases hypoxic conditions promote the growth of bacteria that produce toxins deadly to birds and animals. Zones where this occurs are called [[Case_studies_eutrophication#Ecological_impacts_of_eutrophication_.28Case_study:_Eutrophication_and_dead_zones.29|dead zones]].</P>
The term phytoplankton encompasses all [[photoautotrophic]] microorganisms in aquatic food webs. Phytoplankton serve as the base of the [[aquatic food webs|aquatic food web]], providing an essential ecological function for all aquatic life.  
 
  
Phytoplankton are classified as microalgae and include species from the following divisions: Cyanobacteria (blue-green algae), Chlorophyta (green algae), Prochlorophyta, Euglenophyta, Pyrrhophyta (dinoflagellates ), Cryptophyta (cryptomonads), Chrysophyta, and Bacillariophyta (includes diatoms).
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==== Species biodiversity decreases and the dominant biota changes====
[[Image:ijslandfoto.jpg|thumb|left|<small>Phytoplankton bloom in Iceland</small>]]
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<P ALIGN="justify">Eutrophication leads to changes in the availability of light and certain nutrients to an ecosystem. This causes shifts in the species composition so that only the more tolerant species survive and new competitive species invade and out-compete original inhabitants. Examples are macroalgae and their massive biomass which inhibits the growth of other aquatic plants and algal blooms that consists of one type of phytoplankton species because other species are expelled.</P>
When conditions are right (i.e.[[nutrients]] or sunlight or temperature or a combination of these), phytoplankton populations can grow explosively, a phenomenon known as an [[algal bloom]]. These conditions can be provided on a local basis by natural run-off from the land or by human inputs (e.g., treated or untreated sewage, farming or urban gardening practices). Blooms in the ocean may cover hundreds of square kilometers and are easily visible in satellite images. A bloom may last several weeks, but the life span of any individual phytoplankton is rarely more than a few days.
 
Blooms can appear as a green discoloration of the water due to the presence of chlorophyll within their cells.
 
  
=====Toxic or inedible phytoplankton species (harmful algal bloom)=====
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==== Increased biomass of macroalgae====
[[Image:redtide.jpg|thumb|right|<small>A red tide</small>]]
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<P ALIGN="justify">Algal blooms may also consist of '''marine seaweeds''' or '''macroalgae'''. These blooms are recognizable by large blades of algae that may wash up into the shoreline. The seaweed is harmless when it is alive, but when decomposed by anaerobic bacteria toxic gases (such as the colorless hydrogen sulfide (H<sub>2</sub>S)) can be released.</P>
[[Harmful algal blooms]] (HAB) are algal bloom events involving toxic or otherwise harmful phytoplankton such as dinoflagellates of the genus Alexandrium or diatoms of the genus Pseudo-nitzschia. To the human eye,algal blooms can appear greenish, brown, and even reddish- orange (red tides) depending upon the algal species, the aquatic ecosystem, and the concentration of the organisms.
 
Harmful algal blooms may cause harm through the production of toxins or by their accumulated biomass, which can affect co-occurring organisms and alter food-web dynamics. Impacts include human illness (see human health impacts) and mortality following consumption of or indirect exposure to HAB toxins, substantial economic losses to coastal communities and commercial fisheries, and HAB-associated fish, bird and mammal mortalities.
 
  
 
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==Human health impacts==
 
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<P ALIGN="justify">Harmful algal bloom species have the capacity to produce '''toxins''' dangerous to humans. Algal [[Toxic|toxins]] are observed in marine ecosystems where they can accumulate in shellfish and more generally in seafood reaching dangerous levels for human as well as animal health. Examples include paralytic, neurotoxic and diarrhoeic shellfish poisoning. Several algal species able of producing toxins harmful to human or marine life have been identified in European coastal waters. The table gives an overview of some species that are regularly observed and represent a risk for seafood consumers.</P>
=====Increases in blooms of gelatinous zooplankton=====
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{|border="1" align=center cellspacing="0" cellpadding = "8" width="825px"
 
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!style="background-color:#398C9D" |'''Disease'''
[[Zooplankton]] are [[heterotrophic]] plankton. They are primarily transported by ambient water currents,but many have locomotion and are primarily found in surface waters where food resources (phytoplankton or other zooplankton) are abundant.
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!style="background-color:#398C9D" |'''Symptoms'''
[[Image:jellyck.jpg|thumb|right|<small>Gelatinous zooplankton</small>]]
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!style="background-color:#398C9D" |'''Species'''
Through their consumption and processing of phytoplankton and other food sources, zooplankton play a role in [[aquatic food webs]], as a resource for consumers on higher trophic levels (including fish).They represent a range of organism sizes including small protozoans and large metazoans.
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!style="background-color:#398C9D" |'''Carriers'''
Zooplankton can be divided in two important groups: crustacean and gelatinous zooplankton. Crustacean zooplankton (copepods and krill) are arthropods with a chitinous exoskeleton. These are the most abundant zooplankton.
 
Gelatinous zooplankton have relatively fragile,plastic gelatinous bodies that are at least 95% water and which lack rigid skeletal parts. The most well-known are the "jellyfish" (hydromedusae and scyphomedusae).
 
 
 
Eutrophication is believed to cause an increase in the relative importance of gelatinous zooplankton vs. crustacean zooplankton.In many areas of the world where the natural species diversity has been affected by pollution, over-fishing and, now, climate change, gelatinous plankton organisms may be becoming the dominant predator species.
 
 
 
=====Increased biomass of benthic and epiphytic algae=====
 
=====Decreases in water transparency (increased turbidity)=====
 
=====Dissolved oxygen depletion (hypoxia)=====
 
 
 
Oxygen is required for all life forms on this planet (with the exception of some bacteria). Oxygen depletion, or hypoxia, is a common effect of eutrophication in bottom waters. This effect may be episodic, occurring annually (most common in summer/autumn), persistent, or periodic in the coastal zone.
 
The direct effects of hypoxia include fish kills, which not only deplete valuable fish stocks and damage the ecosystem, but are unpleasant for local residents and can harm local tourism. Oxygenated water is necessary for aquatic animals to breathe. Mobile animals, such as adult fish, can often survive hypoxia by moving into oxygenated waters. When they cannot, such as when young fish need to spend time in the habitat that has become hypoxic area, the result is a fish kill. Non-mobile animals, such as clams, cannot move into healthier waters and are often killed by hypoxic episodes. This causes a severe reduction of the amount, or in extreme cases the complete loss, of animal life in hypoxic zones.
 
Hypoxia develops when a series of conditions occur together.
 
One of the most important conditions is that there must be a large amount of algae. These algae have to sink or otherwise end up on the bottom. This happens when the algae die without being eaten, or when they are eaten by small animals (zooplankton) whose fecal pellets sink to the bottom. On the bottom, the algae or fecal pellets decompose. This process of decomposition consumes oxygen. If the water is not well-mixed, there is no way to replace the oxygen consumed by decomposition, and hypoxia is likely to occur.
 
 
 
=====Increased incidences of fish kills and dead benthic animals=====
 
=====Species biodiversity decreases and the dominant biota changes=====
 
 
 
== Human health impacts ==
 
 
 
[[Harmful algal blooms]] have the capacity to produce toxins dangerous to humans. Algal toxins are observed in marine ecosystems where they can accumulate in shellfish and more generally in seafood, reaching dangerous levels for human and animal health. Examples include paralytic, neurotoxic, and diarrhoetic shellfish poisioning.
 
Around 40 algal species able of producing toxins harmful to human or marine life have been identifie in european coastal waters. Among these Dinophysis, Gymnodium, Pseudo-nitzschia are frequently observed and represent a risk for seafood consumers.
 
The various effects are summarizes in the table.
 
 
 
{| border="1" cellpadding="5"  
 
|- style="background: #DDFFDD;"
 
! Disease
 
! Symptoms
 
! Species
 
! Carriers
 
! Cases
 
 
|-
 
|-
| Amnesic shellfish poisoning (ASP)
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| '''A'''mnesic '''s'''hellfish '''p'''oisoning (ASP)
| Mental confusion and loss of memory, disorientation and sometimes coma
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| Mental confusion and memory loss, disorientation and sometimes coma
| Diatoms from the genus Nitzschia<ref> Guiry, M.D. (2012). Nitzschia. In: Guiry, M.D. & Guiry, G.M. (2012). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=149045</ref>
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| Diatoms of the genus [http://www.marinespecies.org/aphia.php?p=taxdetails&id=149045 ''Nitzschia'']
 
| Shellfish (mussels)
 
| Shellfish (mussels)
| Canada (1987): 153 cases, 3 deaths
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|-  
|-
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| '''N'''eurotoxic '''s'''hellfish '''p'''oisoning (NSP)
| Neurotoxic shellfish poisoning (PSP)
 
 
| Muscular paralysis, state of shock and sometimes death
 
| Muscular paralysis, state of shock and sometimes death
| Genus Gymnodinium<ref> Guiry, M.D. (2012). Gymnodinium. In: Guiry, M.D. & Guiry, G.M. (2012). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=109475</ref>
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| Genus [http://www.marinespecies.org/aphia.php?p=taxdetails&id=109475 ''Gymnodinium'']
 
| Oysters, clams and crustaceans
 
| Oysters, clams and crustaceans
| Florida (1977?)
 
 
|-
 
|-
| Venerupin shellfish poisoning (VSP)
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| '''V'''enerupin '''s'''hellfish '''p'''oisoning (VSP)
| Gastrointestinal, nervous, haemorrhagic, hepatic and in extreme cases delirium and hepatic coma
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| Gastrointestinal, nervous and hemorrhagic, hepatic symptoms and in extreme causes delirium and hepatic coma
| Genus Prorocentrum<ref>Guiry, M.D. (2012). Prorocentrum. In: Guiry, M.D. & Guiry, G.M. (2012). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=109566</ref>
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| Genus [http://www.marinespecies.org/aphia.php?p=taxdetails&id=109566 ''Prorocentrum'']
 
| Oysters and clams
 
| Oysters and clams
| Japan (1889): 81 cases, 51 deaths, Japan (1941): 6 cases, 5 deaths, Norway (1979): 70 cases
 
 
|-
 
|-
| Diarrhoeic shellfish poisoning (DSP)
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| '''D'''iarrhoeic '''s'''hellfish '''p'''oisoning (DSP)
| Gastrointestinal (diarrhoea, vomiting and abdominal pain)
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| Gastrointestinal symptoms (diarrhoea, vomiting and abdominal pain)
| Genus Dinophysis<ref>WoRMS (2012). Dinophysis. In: Guiry, M.D. & Guiry, G.M. (2012). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=109462</ref> and Prorocentrum
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| Genus [http://www.marinespecies.org/aphia.php?p=taxdetails&id=109462 ''Dinophysis''] and [http://www.marinespecies.org/aphia.php?p=taxdetails&id=109566 ''Prorocentrum'']
| Filtering shellfish (oysters, mussels, cockles and clams)
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| Filtering shellfish (oysters, mussels and clams)
| Japan (1976-1982): 1300 cases, France (1984-1986): 4000 cases, Scandinavia (1984): 300-400 cases
 
 
|-
 
|-
| Paralytic shellfish poisoning (PSP)
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| '''P'''aralytic '''s'''hellfish '''p'''oisoning (PSP)
| Muscular paralysis, difficulty in breathing, shock and in extreme cases death by respiratory arrest
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| Muscular paralysis, difficulty in breathing, shock and in extreme causes death by respiratory arrest
| Genus Alexandrium<ref>WoRMS (2012). Alexandrium Halim, 1960 emend. Balech, 1989. In: Guiry, M.D. & Guiry, G.M. (2012). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=109470</ref>
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| Genus [http://www.marinespecies.org/aphia.php?p=taxdetails&id=109470 ''Alexandrium''] and [http://www.marinespecies.org/aphia.php?p=taxdetails&id=109475 ''Gymnodinium'']
 
| Oysters, mussels, crustacean and fish
 
| Oysters, mussels, crustacean and fish
| Philippine (1983): 300 cases, 21 deaths, United Kingdom (1968): 78 cases, Spain (1976): 63 cases, France (1976): 33 cases, Italy (1976): 38 cases, Swiss (1976): 23 cases, Germany (1976): 19 cases
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|-
 
|}
 
|}
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<P ALIGN="justify">Other marine mammals can be vectors for toxins, as in the case of ciguatera, where it is typically predator fish whose flesh is contaminated with the toxins originally produced by dinoflagellates and then poison humans. Symptoms include gastrointestinal and neurological effects.</P>
  
Other marine animals can be vectors for toxins, as in the case of ciguetera, where it is typically a predator fish that accumulates the toxin and then poisons humans.
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==Socio-economic impacts==
 
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Nearly all of the above described impacts have a direct or indirect socio-economic impact.
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==== Impact on recreation and tourism ====
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<P ALIGN="justify">The enrichment of nutrients to an ecosystem can result in a massive growth of macroalgae. The existence of such dense algal growth areas can inhibit or prevent access to waterways. This decreases the fitness for '''use of the water for water sports''' (swimming, boating and fishing).</P>
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==== Aesthetic impacts====
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[[Image:Beach_closed.jpg|200px|thumb|right|<small>As a result of toxic algal blooms beaches can be closed (Photo credit: Elizabeth Halliday, Woods Hole Oceanographic Institution)</small>]]
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Algal blooms are unsightly and can have unpleasant smells for example:
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* The appearance of a '''white yellowish foam''' on the beach in spring, for example on the shores along the North Sea. The foam is formed by the wind that sweeps up the decaying remains of ''Phaeocystis'' algal colonies. An extreme case is shown in [[Foam beach, Sydney]].
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* When macroalgae or seaweed are decomposed by anaerobic bacteria hydrogen sulfide is (H<sub>2</sub>S) released. This gas is characterized by a very unpleasant characteristic foul odor of rotten eggs.
  
== Recreational and aesthetic impacts ==
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==== Economical impacts====
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<P ALIGN="justify">In some specific cases local authorities must rely on eutrophic waters for production of drinking water. Infected waters increases the '''costs of water treatment''' in order to avoid taste, odor and toxin problems in the water. Due to the toxins produced by harmful algal blooms commercial fish and shellfish may become '''unsuitable for consumption''' resulting in potential economical and financial problems for the fishing industries. In extreme cases beaches are closed due to the presence of toxic algal blooms.</P>
  
The enrichment of [[nutrients]] can result in a massive growth of green algae. The existence of large areas (mats) can inhibit or prevent access to waterways. This decreases the fitness for use of the water for water sports such as skiing, yachting and fishing. The presence of unsightly and smelling scums also makes any recreational use of the water body unpleasant.
 
Many beaches on the North Sea coast are ruined by Phaecystis blooms. When these so-called foam algae die, large flakes of yellowish foam arise at the beach.
 
In extreme cases beaches can be closed by the presence of toxic algal blooms (HAB). Those may be a health hazard to both human and animals (see higher).
 
If the water is used for water treatment purposes, various taste and odeur problems can occur. These lower the perceived quality of the treated water, although do not cause human health problems.
 
  
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==Related articles==
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* [[Algal bloom dynamics]]
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* [[Threats to the coastal zone]]
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* [[Estuarine turbidity maximum]]
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* [[Coupled hydrodynamic - water quality - ecological modelling]]
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* Articles in the [[:Category:Eutrophication]]
  
  
== Economic impacts ==
 
  
Nearly all of the above mentioned impacts have direct or indirect economic impacts.
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==Literature sources==
In some specific cases, local authorities must rely on [[eutrophic]] waters for producing drinking water.
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#Eutrophication and health. European Commission (2002). Office for Official Publications of the European Communities: Luxembourg. ISBN 92-894-4413-4.28 pp.
Infected water increases the costs of water treatment in order to avoid taste, odeur and toxineproblems in the treated water. Due to the toxins produced by[[ harmful algal blooms]] commercial fish and shellfish may come unsuitable for consumption. Other fish may die due to oxygen limitation.
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#The National Eutrophication monitoring Programme Implementation Manual (Murray et al., 2002).
An example of the scale of the potential economic impact arising from the occurrence of harmful algal blooms in estuaries, is the estimated cost to the US economy of US$100 million per year. This estimated cost includes lost fishery production and the related costs of human illness, stock losses, lost tourism and recreational value.
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#Guiry, Michael D. (2013). Nitzschia Hassall, 1845. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=149045 on 2013-04-22.
 +
#Guiry, Michael D. (2013). Gymnodinium Stein, 1878. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=109475 on 2013-04-22.
 +
#Guiry, Michael D. (2013). Prorocentrum Ehrenberg, 1834. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=109566 on 2013-04-22.
 +
#WoRMS (2013). Dinophysis Ehrenberg, 1839. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=109462 on 2013-04-22.
 +
#Guiry, Michael D.; Moestrup, Ø. (2013). Alexandrium Halim, 1960. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=109470 on 2013-04-22.
  
==Links==
 
European Commission, Eutrophication and health (2002)(PDF)[http://ec.europa.eu/environment/water/water-nitrates/pdf/eutrophication.pdf]
 
  
Republic of South-Africa, Department Water Affairs,South African National Water Quality Monitoring Programmes Series, National Eutrophication Monitoring Programme - Implementation Manual-Final Draft,2.Eutrophication (PDF) [http://www.dwaf.gov.za/iwqs/eutrophication/NEMP/EutrophicationMonitoringProgramme.pdf]
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{{author
== References ==
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|AuthorID=26102
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|AuthorFullName= Knockaert, Carolien
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|AuthorName=Carolienk}}
  
<references/>
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[[Category:Eutrophication]]

Latest revision as of 10:56, 30 July 2020

Introduction

Enhanced plant production and improved fish yields are sometimes described as positive impacts of eutrophication, especially in countries where fish and other aquatic organisms are a significant source of food. However detrimental ecological impacts can in turn have other negative consequences and impacts which are described below. Essentially the entire aquatic ecosystem changes with eutrophication. The diagram below gives an overview on the eutrophication process and its causes and consequences.

705

Ecological impacts

Increased biomass of phytoplankton resulting in algal blooms

Envisat satellite image of an algal bloom captured with MERIS (Photo Credit: ESA, 2009)

Phytoplankton or microalgae are photosynthesizing microscopic organisms. They contain chlorophyll and require sunlight in order to live and grow. Most phytoplankton are buoyant and float in the upper part of the ocean where sunlight penetrates the water. In a balanced ecosystem they provide food for a wide range of organisms such as whales, shrimp, snails and jellyfish. Among the more important groups are the diatoms, cyanobacteria, dinoflagellates and coccolithophores (see: Marine Plankton). Phytoplankton species require inorganic nutrients such as nitrates, phosphates, and sulfur which they convert into proteins, fats and carbohydrates. When too many of these nutrients (by natural or anthropogenic cause) are available in the water phytoplankton may grow and multiply very fast forming algal blooms. Algal blooms may occur in freshwater as well as marine environments. Only one or a small number of phytoplankton species are involved and some blooms discolor (green, yellow-brown or red) the water due to their high density of pigmented cells. Blooms in the ocean may cover a large area and are easily visible in satellite images.

Toxic or inedible phytoplankton species (harmful algal blooms)

Harmful algal blooms (HAB) are bloom events involving toxic or harmful phytoplankton. These cause harm through the production of toxins or by their accumulated biomass, which can effect co-occurring organisms and alter food web dynamics. Impacts include:

  • Human illness,
  • Mortality of fish, birds and mammals following consumption or indirect exposure to HAB toxins,
  • Substantially economic losses to coastal communities and commercial fisheries.

Increased blooms of gelatinous zooplankton

Phytoplankton are the food source for numerous other organisms, especially the zooplankton. Zooplankton are heterotrophic plankton. They are primarily transported by ambient water currents but many have locomotion. Through their consumption and processing of phytoplankton and other food sources they play a role in aquatic food webs as a resource for higher trophic levels including fish. Zooplankton can be divided in two important groups: crustacean (copepods and krill) and gelatinous zooplankton. Gelatinous zooplankton have relatively fragile, plastic gelatinous bodies that contain at least 95% water and which lack rigid skeletal parts. The most well-known are the jellyfish. Eutrophication is believed to cause an increase in the relative importance of gelatinous versus crustacean zooplankton. On many areas of the world where the natural species diversity has been affected by pollution, over-fishing and climate change gelatinous zooplankton organisms may be becoming the dominant species.

Decreases in water transparency (increased turbidity)

The growth of phytoplankton can cause increased turbidity or decreased penetration of light into the lower depths of the water column. In lakes and rivers this can inhibit growth of submerged aquatic plants and affect species which are dependent on them (fish, shellfish).

Dissolved oxygen depletion or hypoxia resulting in increased incidences of fish kills and / or dead benthic animals

A menhaden fish kill due severe hypoxia (Photo credit: Chris Deacutis, IAN Image library )

Oxygen is required for all life forms on the planet. Oxygen is produced by plants during (photosynthesis). At night animals and plants, as well as aerobic micro-organisms and decomposing dead organisms respire and so consume oxygen which results in a decrease in dissolved oxygen levels. Large fluctuations in dissolved oxygen levels may be the result of an algal bloom. While the algae population is growing at a fast rate, dissolved oxygen levels decrease. When these algae die, they are decomposed by bacteria which consume oxygen in this process so that the water can become temporarily hypoxic. Oxygen depletion, or hypoxia, is a common effect of eutrophication in water. The direct effects of hypoxia include fish kills, especially the death of fish that need high levels of dissolved oxygen. Changes in fish communities may have an impact on the whole aquatic ecosystem and may deplete fish stocks. In extreme cases hypoxic conditions promote the growth of bacteria that produce toxins deadly to birds and animals. Zones where this occurs are called dead zones.

Species biodiversity decreases and the dominant biota changes

Eutrophication leads to changes in the availability of light and certain nutrients to an ecosystem. This causes shifts in the species composition so that only the more tolerant species survive and new competitive species invade and out-compete original inhabitants. Examples are macroalgae and their massive biomass which inhibits the growth of other aquatic plants and algal blooms that consists of one type of phytoplankton species because other species are expelled.

Increased biomass of macroalgae

Algal blooms may also consist of marine seaweeds or macroalgae. These blooms are recognizable by large blades of algae that may wash up into the shoreline. The seaweed is harmless when it is alive, but when decomposed by anaerobic bacteria toxic gases (such as the colorless hydrogen sulfide (H2S)) can be released.

Human health impacts

Harmful algal bloom species have the capacity to produce toxins dangerous to humans. Algal toxins are observed in marine ecosystems where they can accumulate in shellfish and more generally in seafood reaching dangerous levels for human as well as animal health. Examples include paralytic, neurotoxic and diarrhoeic shellfish poisoning. Several algal species able of producing toxins harmful to human or marine life have been identified in European coastal waters. The table gives an overview of some species that are regularly observed and represent a risk for seafood consumers.

Disease Symptoms Species Carriers
Amnesic shellfish poisoning (ASP) Mental confusion and memory loss, disorientation and sometimes coma Diatoms of the genus Nitzschia Shellfish (mussels)
Neurotoxic shellfish poisoning (NSP) Muscular paralysis, state of shock and sometimes death Genus Gymnodinium Oysters, clams and crustaceans
Venerupin shellfish poisoning (VSP) Gastrointestinal, nervous and hemorrhagic, hepatic symptoms and in extreme causes delirium and hepatic coma Genus Prorocentrum Oysters and clams
Diarrhoeic shellfish poisoning (DSP) Gastrointestinal symptoms (diarrhoea, vomiting and abdominal pain) Genus Dinophysis and Prorocentrum Filtering shellfish (oysters, mussels and clams)
Paralytic shellfish poisoning (PSP) Muscular paralysis, difficulty in breathing, shock and in extreme causes death by respiratory arrest Genus Alexandrium and Gymnodinium Oysters, mussels, crustacean and fish

Other marine mammals can be vectors for toxins, as in the case of ciguatera, where it is typically predator fish whose flesh is contaminated with the toxins originally produced by dinoflagellates and then poison humans. Symptoms include gastrointestinal and neurological effects.

Socio-economic impacts

Nearly all of the above described impacts have a direct or indirect socio-economic impact.

Impact on recreation and tourism

The enrichment of nutrients to an ecosystem can result in a massive growth of macroalgae. The existence of such dense algal growth areas can inhibit or prevent access to waterways. This decreases the fitness for use of the water for water sports (swimming, boating and fishing).

Aesthetic impacts

As a result of toxic algal blooms beaches can be closed (Photo credit: Elizabeth Halliday, Woods Hole Oceanographic Institution)

Algal blooms are unsightly and can have unpleasant smells for example:

  • The appearance of a white yellowish foam on the beach in spring, for example on the shores along the North Sea. The foam is formed by the wind that sweeps up the decaying remains of Phaeocystis algal colonies. An extreme case is shown in Foam beach, Sydney.
  • When macroalgae or seaweed are decomposed by anaerobic bacteria hydrogen sulfide is (H2S) released. This gas is characterized by a very unpleasant characteristic foul odor of rotten eggs.

Economical impacts

In some specific cases local authorities must rely on eutrophic waters for production of drinking water. Infected waters increases the costs of water treatment in order to avoid taste, odor and toxin problems in the water. Due to the toxins produced by harmful algal blooms commercial fish and shellfish may become unsuitable for consumption resulting in potential economical and financial problems for the fishing industries. In extreme cases beaches are closed due to the presence of toxic algal blooms.


Related articles


Literature sources

  1. Eutrophication and health. European Commission (2002). Office for Official Publications of the European Communities: Luxembourg. ISBN 92-894-4413-4.28 pp.
  2. The National Eutrophication monitoring Programme Implementation Manual (Murray et al., 2002).
  3. Guiry, Michael D. (2013). Nitzschia Hassall, 1845. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=149045 on 2013-04-22.
  4. Guiry, Michael D. (2013). Gymnodinium Stein, 1878. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=109475 on 2013-04-22.
  5. Guiry, Michael D. (2013). Prorocentrum Ehrenberg, 1834. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=109566 on 2013-04-22.
  6. WoRMS (2013). Dinophysis Ehrenberg, 1839. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=109462 on 2013-04-22.
  7. Guiry, Michael D.; Moestrup, Ø. (2013). Alexandrium Halim, 1960. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=109470 on 2013-04-22.


The main author of this article is Knockaert, Carolien
Please note that others may also have edited the contents of this article.

Citation: Knockaert, Carolien (2020): Possible consequences of eutrophication. Available from http://www.coastalwiki.org/wiki/Possible_consequences_of_eutrophication [accessed on 1-10-2020]