Difference between revisions of "Possible consequences of eutrophication"

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===Introduction===
 
  
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[[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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==Introduction==
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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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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<ref>Nixon, S.W. and Buckley, B. A. 2002. “A strikingly rich zone” – Nutrient enrichment and secondary production in coastal marine ecosystems. Estuaries 25: 782–796</ref>. However, detrimental ecological impacts can in turn have other negative consequences and impacts which are described below. The entire aquatic [[ecosystem]] may change with eutrophication. The diagram below gives an overview on the eutrophication process and its causes and consequences.
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The ecological impacts of eutrophication are summarized in the figure and discussed in the sections below.
 
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[[Image:Consequences.jpg|500px]]
 
  
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== Ecological impacts <ref>Christopher Mason, ‘Biology of freshwater pollution’, Pearson Education Limited, 2002</ref>==
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[[File:eutrocon.png|705|center]]
  
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'''Increased biomass of phytoplankton resulting in algal blooms'''
 
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[[Image:bluegreenalg.jpg|thumb|right|250px|<small>Algal bloom on the shore of Langstone harbour in Hampshire © Solent News and Photo Agency </small>]]
 
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[[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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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.
 
  
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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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==Ecological impacts==
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===Increased biomass of phytoplankton resulting in [[algal bloom]]s===
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[[File:Plentiful_plankton.jpg|250px|thumb|right|<small>Fig. 1. Envisat satellite image of an algal bloom captured with MERIS (Photo Credit: ESA, 2009)</small>]]
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[[Phytoplankton]] or microalgae are [[photosynthesis|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 blooms (see [[Algal bloom dynamics]]). 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 (Fig. 1) – see the article [[Plankton remote sensing]]. Enclosed and semi-enclosed water bodies (e.g., coastal lagoons) are particularly sensitive to increased nutrient loads (especially nitrogen input from agricultural effluents), potentially leading to ecosystem collapse<ref>Ouaissa, S., Gómez-Jakobsen, F., Yebra, L., Ferrera, I., Moreno-Ostos, E., Dolores Belando, M., Ruiz, J.M. and Mercado, J.M. 2023. Phytoplankton dynamics in the Mar Menor, a Mediterranean coastal lagoon strongly impacted by eutrophication. Marine Pollution Bulletin 192, 115074</ref>.
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===Toxic or inedible phytoplankton species ([[harmful algal blooms]])===
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'''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:
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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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For more details on toxic algal blooms, see the article [[Harmful algal bloom]].
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===Increased blooms of gelatinous zooplankton===
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[[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 can swim. 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. There is some evidence that gelatinous zooplankton organisms increase in relative importance versus crustacean zooplankton in areas where the natural species diversity has been affected by pollution, over-fishing and climate change<ref> Condon, R.H., Duarte, C.M., Pitt, K.A., Robinson, K.L., Lucas, C.H., Sutherland, K.R., Mianzan, H.W., Bogeberg, M., Purcell, J.E., Decker, M.B., Uye, S.-I., Madin, L.P., Brodeur, R.D., Haddock, S.H.D., Malej, A., Parry, G.D., Eriksen, E., Quiñones, J., Acha, M., Harvey, M., Arthur, J.M. and Graham W.M. 2013. Recurrent jellyfish blooms are a consequence of global oscillations. PNAS 110: 1000-1005</ref>.
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===Decreases in water transparency (increased turbidity)===
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The growth of phytoplankton causes 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).
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===Dissolved oxygen depletion or hypoxia===
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[[File:FishKill.jpg|250px|thumb|right|<small>Fig. 2. Fish kill (menhaden) due to severe hypoxia (Photo credit: Chris Deacutis, IAN Image library )</small>]]
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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 respire and so consume oxygen which results in a decrease in dissolved oxygen levels. [[Algal bloom]]s may cause strong fluctuations in dissolved oxygen levels. When the algae population is growing at a fast rate, it may block sunlight from reaching other organisms and cause a decrease of dissolved oxygen levels. When algae die, they are decomposed by bacteria which in this process consume oxygen so that the water can become temporarily hypoxic. Oxygen depletion, or [[Hypoxia|hypoxia]], is a common consequence of eutrophication, both in fresh water and seawater. The '''direct effects''' of hypoxia include '''fish kills''', especially the death of fish that need high levels of dissolved oxygen (Fig. 2).
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There is some evidence that hypoxic conditions promote the growth of cyanobacteria as a consequence of enhanced phosphorus release<ref>Funkey, C.P., Conley, D.J., Reuss, N.S., Humborg, C, Jilbert, T. and Slomp, C.P. 2014. Hypoxia Sustains Cyanobacteria Blooms in the Baltic Sea. Environ. Sci. Technol. 48: 2598−2602</ref>. Many cyanobacteria species produce toxins that are lethal to birds and animals.
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===Eutrophication-driven acidification===
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The respiration of bacteria that decompose dead algae not only causes hypoxia due to oxygen consumption, but also produces CO<sub>2</sub> and thus causes an increase in the carbonic acid content of the water. A sharp increase in acidity (pH even below 7) has been observed in highly eutrophic estuaries and lagoons along the east coast of the US, coinciding with hypoxia<ref>Wallace, R.B., Baumann, H., Grear, J.S., Aller, R.C. and Gobler, C.J. 2014. Coastal ocean acidification: The other eutrophication problem. Estuarine, Coastal and Shelf Science 148: 1-13</ref>. Acidification is an annual feature of these estuaries during summer when algae decay and oxygen depletes. Lowest pH levels (undersaturated with respect to aragonite) occur near the bottom, especially in poorly flushed stratified systems. This poses a serious threat to calcifying benthic organisms, for example scallops and other bivalves that spawn in mid-to-late summer. Eutrophication-driven acidification exacerbates [[ocean acidification]] due to uptake of atmospheric CO<sub>2</sub>.
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===Dead zones===
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Zones with extreme hypoxia are called [https://en.wikipedia.org/wiki/Dead_zone_(ecology) dead zones]. Upwelling of nutrient-rich waters may produce 'natural' dead zones in some ocean regions where water mass circulation is weak. These so-called 'oxygen minimum zones' occur below the photic zone, between about 200 - 1500 m depth, and are related to microbial mineralization of sinking organic material<ref name=BG>Breitburg, D., Gregoire, M. Isensee, K. (eds.) 2018. The ocean is losing its breath: Declining oxygen in the world’s ocean and coastal waters. IOC-UNESCO, IOC Technical Series, No. 137 40pp. (IOC/2018/TS/137)</ref>. However, most severe dead zones occur as a result of anthropogenic eutrophication of stratified water masses. Stratification is mainly caused by temperature-induced density differences between surface waters and deeper waters in the ocean; stratification in estuaries and coastal waters is mainly due to the salinity-induced density difference between seawater and river water. When an algal bloom in the surface layer decays, the deeper water layers become laden with sinking dead algae that are decomposed by oxygen consuming bacteria. Stratification inhibits turbulent mixing of the oxygen-rich surface layer into the underlying water layer that therefore becomes depleted from oxygen.  
  
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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.
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Although many species have adaptations to low oxygen conditions<ref>Altieri, A.H., Johnson, M.D., Swaminathan, S.D., Nelson, H.R. and Gedan, K.B. 2021. Resilience of Tropical Ecosystems to
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Blooms can appear as a green discoloration of the water due to the presence of chlorophyll within their cells.
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Ocean Deoxygenation. Trends in Ecology and Evolution 36: 227-238</ref>, fish and crustaceans suffer significant mortality already at 2 mg/l O<sub>2</sub> <ref>Vaquer-Sunyer, R. and Duarte, C.M. 2008. Thresholds of hypoxia for marine biodiversity. PNAS 105: 15452–15457</ref>. The die-off of [[seagrass meadows]] under low oxygen levels is enhanced by positive feedback from oxygen consuming mineralization, but recolonization by germinating seedlings can be quite rapid <ref>Greve, T.M., Krause-Jensen, D., Rasmussen, M.B. and Christense, P.B. 2005. Means of rapid eelgrass (Zostera marina L.) recolonisation in former dieback areas. Aquatic Botany 82: 143-156</ref>.
  
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'''Toxic or inedible phytoplankton species (harmful algal bloom)'''
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[[File:OceanHypoxia.jpg|thumb|500px|left|<small>Fig. 3. Areas with hypoxia in coastal seas (red) and in the oceans (blue). From IOC-UNESCO 2018<ref name=BG/> Creative Commons Licence.</small>]]
  
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[[Image:redtide.jpg|thumb|right|<small>A red tide: Noctiluca scintillans in New Zealand © M. Godfrey</small>]]
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Fig. 3 shows a map of coastal and ocean regions with frequently occurring hypoxia. The largest and most persistent dead zones are situated in the Baltic Sea, the Black Sea, the Arabian Sea and the Gulf of Mexico. The size of dead zones decreases during severe storms when strong wind-driven turbulent water motion partially neutralizes stratification.
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[[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.
 
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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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'''Increases in blooms of gelatinous zooplankton'''
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Demographic growth and economic development are expected to increase the supply of nutrients<ref>Beusen, A.H.W., Doelman, J.C., Van Beek, L.P.H., Van Puijenbroek, P.J.T.M., M. Mogollon, J., Van Grinsven, H.J.M., Stehfest, E., Van Vuuren, D.P. and Bouwman A.F. 2022. Exploring river nitrogen and phosphorus loading and export to global coastal waters in the Shared Socio-economic pathways. Global Environmental Change 72: 102426</ref>. Oxygen depletion in the ocean and coastal waters and climate change will be further exacerbated through increasing ocean surface temperature and stratification<ref>Baroni, I.R., Palastanga, V. and Slomp, C. P. 2020. Enhanced Organic Carbon Burial in Sediments of Oxygen Minimum Zones Upon Ocean Deoxygenation. Front. Mar. Sci. 6: 839</ref><ref>Li, G., Cheng, L., Zhu, J., Trenberth, K.E., Mann, M.E. and Abraham, J.P. 2020. Increasing ocean stratification over the past half-century. Nature Climate Change https://doi.org/10.1038/s41558-020-00918-2</ref>. In turn, ocean oxygen depletion can generate a positive feedback to climate change through increased production of the greenhouse gas NO<sub>2</sub> by microbial denitrification<ref name=BG/>.
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<br clear=all>
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===Species biodiversity decreases and the dominant biota changes===
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[[File: GreenAlgae_D_Ramirez.jpg|thumb|250px|right|<small>Fig. 4. Macroalgae washed ashore. Photo credit D. Ramirez</small>.]]
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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 outcompeted.
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===Green tides===
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Many observations and experiments provide evidence that the occurrence of so-called 'green tides', consisting of '''marine seaweeds''' or '''macroalgae''', is increased in eutrophicated coastal waters<ref name=SZ>Smetacek, V. and Zingone, A. 2013. Green and golden seaweed tides on the rise. Nature 504, doi:10.1038/nature12860</ref>. These blooms are recognizable by large blades of algae that may wash up onto the shoreline (Fig. 4). Green tides can asphyxiate aquacultures or disrupt traditional artisanal fisheries. Macroalgae can also be valorized as a raw material; harvesting could therefore be an effective solution<ref name=SZ/> (see also [[Seaweed (macro-algae) ecosystem services]]).
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<br clear=all>
  
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[[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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==Human health impacts==
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[[Image:jellyck.jpg|thumb|right|<small>Gelatinous zooplankton (Athorybia) © L. Madin, NOAA, Census of Marine Life, 2006</small>]]
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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<ref>Eutrophication and health. European Commission 2002. Office for Official Publications of the European Communities: Luxembourg. ISBN 92-894-4413-4.28 pp.</ref>. The table gives an overview of some species that are regularly observed and represent a risk for seafood consumers<ref name=B16>Berdalet, E., Fleming, L.E., Gowen, R., Davidson, K., Hess, P., Backer, L.C., Moore, S.K., Hoagland, P. and Enevoldsen, H. 2016. Marine harmful algal blooms, human health and wellbeing: challenges and opportunities in the 21st century. J. Mar. Biol. Assoc. U.K. 96: 61–91</ref>.
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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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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.  
 
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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).  
 
  
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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.
 
  
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'''Increased biomass of benthic and epiphytic algae'''
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{|border="1" align=center cellspacing="0" cellpadding = "8" width="825px"
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!style="background-color:#398C9D" |'''Disease'''
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'''Decreases in water transparency (increased turbidity)'''
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!style="background-color:#398C9D" |'''Symptoms'''
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!style="background-color:#398C9D" |'''Species'''
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'''Dissolved oxygen depletion (hypoxia)'''
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!style="background-color:#398C9D" |'''Carriers'''
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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.
 
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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.
 
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Hypoxia develops when a series of conditions occur together.
 
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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.
 
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'''Increased incidences of fish kills and dead benthic animals'''
 
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'''Species biodiversity decreases and the dominant biota changes'''
 
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== Human health impacts ==
 
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[[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.
 
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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.
 
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The various effects are summarizes in the table.
 
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{|  border="1" cellpadding="5"
 
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|- style="background: #DDFFDD;"
 
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! Disease
 
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! Symptoms
 
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! Species
 
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! Carriers
 
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! Cases
 
 
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| Amnesic shellfish poisoning (ASP)
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| '''A'''mnesic '''s'''hellfish '''p'''oisoning (ASP)
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| Mental confusion and loss of memory, disorientation and sometimes coma
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| Mental confusion and memory loss, disorientation and sometimes coma
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| 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)
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| Canada (1987): 153 cases, 3 deaths
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|-  
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|-
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| '''N'''eurotoxic '''s'''hellfish '''p'''oisoning (NSP)
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| Neurotoxic shellfish poisoning (PSP)
 
 
| Muscular paralysis, state of shock and sometimes death
 
| Muscular paralysis, state of shock and sometimes death
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| 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
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| Florida (1977?)
 
 
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|-
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| Venerupin shellfish poisoning (VSP)
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| '''V'''enerupin '''s'''hellfish '''p'''oisoning (VSP)
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| 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
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| 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
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| Japan (1889): 81 cases, 51 deaths, Japan (1941): 6 cases, 5 deaths, Norway (1979): 70 cases
 
 
|-
 
|-
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| Diarrhoeic shellfish poisoning (DSP)
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| '''D'''iarrhoeic '''s'''hellfish '''p'''oisoning (DSP)
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| Gastrointestinal (diarrhoea, vomiting and abdominal pain)
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| Gastrointestinal symptoms (diarrhoea, vomiting and abdominal pain)
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| 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'']
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| Filtering shellfish (oysters, mussels, cockles and clams)
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| Filtering shellfish (oysters, mussels and clams)
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| Japan (1976-1982): 1300 cases, France (1984-1986): 4000 cases, Scandinavia (1984): 300-400 cases
 
 
|-
 
|-
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| Paralytic shellfish poisoning (PSP)
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| '''P'''aralytic '''s'''hellfish '''p'''oisoning (PSP)
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| 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
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| 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
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| 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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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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Finfish can also be a vector 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<ref name=B16/>. People are poisoned when consuming contaminated fish. Symptoms include gastrointestinal and neurological effects.
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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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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. The seaweed is harmless to humans but decreases the fitness for use of the water for water sports (swimming, boating and fishing).
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===Aesthetic impacts===
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[[Image:Beach_closed.jpg|200px|thumb|right|<small>Fig. 5. Beaches can be closed as a result of toxic algal blooms (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 (H<sub>2</sub>S) is released. This gas is characterized by a very unpleasant characteristic foul odor of rotten eggs.
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===Economic impacts===
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Due to the toxins produced by harmful algal blooms commercial fish and shellfish may become '''unsuitable for consumption''' resulting in potential economic and financial problems for the fishing industries. In extreme cases beaches are closed due to the presence of toxic algal blooms (Fig. 5). The annual economic costs related to illness and death caused by consumption of poisoned fish products is estimated at around 30 million US$ worldwide<ref>Kouakou, C.R.C. and Poder, T.G. 2019. Economic impact of harmful algal blooms on human health: a systematic review. Journal of Water and Health  17.4: 499-516</ref>. The fishing industry is suffering economic losses because consumers refrain from consuming fish and shellfish products due to the perceived danger of poisoning. For the USA, the loss related to this avoidance behavior is estimated at around 1 billion US$ per year<ref>Parsons, G.R., Morgan, A.O., Whitehead, J.C. and Haab, T.C. 2006. The Welfare Effects of Pfiesteria-Related Fish Kills: A Contingent Behavior Analysis of Seafood Consumers. Agricultural and Resource Economics Review 35(1)</ref>.
 +
 
 +
The Baltic Sea harbours one of the the largest dead zones in the world. Lost revenues from ecosystem services (fishing, recreation, but also non-use values) as a result of eutrophication amount to 3-4 billion euros, according to an estimate by HELCOM<ref>Hyytiainen, K., Hasler, B., Ericsdotter, S., Nekoro, M., Blyh, K., Artell, J., Ahlvik, L. and Ahtiainen, J. 2013. Worth it: Benefits outweigh costs in reducing eutrophication in the Baltic. BalticSTERN Summary Report for HELCOM 2013 Ministerial Meeting</ref>.
 +
 
  
  
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== Recreational and aesthetic impacts ==
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==Related articles==
 +
:[[Harmful algal bloom]]
 +
:[[Nutrient conversion in the marine environment]]
 +
:[[Algal bloom dynamics]]
 +
:[[ What causes eutrophication?]]
 +
:[[Threats to the coastal zone]]
 +
:[[Estuarine turbidity maximum]]
 +
:[[Case studies eutrophication]]
 +
:[[Coupled hydrodynamic - water quality - ecological modelling]]
  
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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.
+
See also other articles in the [[:Category:Eutrophication]]  
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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.
 
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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).
 
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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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==References==
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<references/>
  
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== Economic impacts ==
 
  
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Nearly all of the above mentioned impacts have direct or indirect economic impacts.
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{{author
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In some specific cases, local authorities must rely on [[eutrophic]] waters for producing drinking water.
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|AuthorID=26102
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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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|AuthorFullName= Knockaert, Carolien
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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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|AuthorName=Carolienk}}
  
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==Links==
 
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European Commission, Eutrophication and health (2002)(PDF)[http://ec.europa.eu/environment/water/water-nitrates/pdf/eutrophication.pdf]
 
  
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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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{{Review
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== References ==
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|name=Job Dronkers|AuthorID=120|
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}}
  
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<references/>
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[[Category:Eutrophication]]

Latest revision as of 11:05, 20 February 2024

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[1]. However, detrimental ecological impacts can in turn have other negative consequences and impacts which are described below. The entire aquatic ecosystem may change 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

Fig. 1. 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 (see Algal bloom dynamics). 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 (Fig. 1) – see the article Plankton remote sensing. Enclosed and semi-enclosed water bodies (e.g., coastal lagoons) are particularly sensitive to increased nutrient loads (especially nitrogen input from agricultural effluents), potentially leading to ecosystem collapse[2].

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.

For more details on toxic algal blooms, see the article Harmful algal bloom.

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 can swim. 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. There is some evidence that gelatinous zooplankton organisms increase in relative importance versus crustacean zooplankton in areas where the natural species diversity has been affected by pollution, over-fishing and climate change[3].

Decreases in water transparency (increased turbidity)

The growth of phytoplankton causes 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

Fig. 2. Fish kill (menhaden) due to 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 respire and so consume oxygen which results in a decrease in dissolved oxygen levels. Algal blooms may cause strong fluctuations in dissolved oxygen levels. When the algae population is growing at a fast rate, it may block sunlight from reaching other organisms and cause a decrease of dissolved oxygen levels. When algae die, they are decomposed by bacteria which in this process consume oxygen so that the water can become temporarily hypoxic. Oxygen depletion, or hypoxia, is a common consequence of eutrophication, both in fresh water and seawater. The direct effects of hypoxia include fish kills, especially the death of fish that need high levels of dissolved oxygen (Fig. 2). There is some evidence that hypoxic conditions promote the growth of cyanobacteria as a consequence of enhanced phosphorus release[4]. Many cyanobacteria species produce toxins that are lethal to birds and animals.

Eutrophication-driven acidification

The respiration of bacteria that decompose dead algae not only causes hypoxia due to oxygen consumption, but also produces CO2 and thus causes an increase in the carbonic acid content of the water. A sharp increase in acidity (pH even below 7) has been observed in highly eutrophic estuaries and lagoons along the east coast of the US, coinciding with hypoxia[5]. Acidification is an annual feature of these estuaries during summer when algae decay and oxygen depletes. Lowest pH levels (undersaturated with respect to aragonite) occur near the bottom, especially in poorly flushed stratified systems. This poses a serious threat to calcifying benthic organisms, for example scallops and other bivalves that spawn in mid-to-late summer. Eutrophication-driven acidification exacerbates ocean acidification due to uptake of atmospheric CO2.

Dead zones

Zones with extreme hypoxia are called dead zones. Upwelling of nutrient-rich waters may produce 'natural' dead zones in some ocean regions where water mass circulation is weak. These so-called 'oxygen minimum zones' occur below the photic zone, between about 200 - 1500 m depth, and are related to microbial mineralization of sinking organic material[6]. However, most severe dead zones occur as a result of anthropogenic eutrophication of stratified water masses. Stratification is mainly caused by temperature-induced density differences between surface waters and deeper waters in the ocean; stratification in estuaries and coastal waters is mainly due to the salinity-induced density difference between seawater and river water. When an algal bloom in the surface layer decays, the deeper water layers become laden with sinking dead algae that are decomposed by oxygen consuming bacteria. Stratification inhibits turbulent mixing of the oxygen-rich surface layer into the underlying water layer that therefore becomes depleted from oxygen.

Although many species have adaptations to low oxygen conditions[7], fish and crustaceans suffer significant mortality already at 2 mg/l O2 [8]. The die-off of seagrass meadows under low oxygen levels is enhanced by positive feedback from oxygen consuming mineralization, but recolonization by germinating seedlings can be quite rapid [9].

Fig. 3. Areas with hypoxia in coastal seas (red) and in the oceans (blue). From IOC-UNESCO 2018[6] Creative Commons Licence.

Fig. 3 shows a map of coastal and ocean regions with frequently occurring hypoxia. The largest and most persistent dead zones are situated in the Baltic Sea, the Black Sea, the Arabian Sea and the Gulf of Mexico. The size of dead zones decreases during severe storms when strong wind-driven turbulent water motion partially neutralizes stratification.

Demographic growth and economic development are expected to increase the supply of nutrients[10]. Oxygen depletion in the ocean and coastal waters and climate change will be further exacerbated through increasing ocean surface temperature and stratification[11][12]. In turn, ocean oxygen depletion can generate a positive feedback to climate change through increased production of the greenhouse gas NO2 by microbial denitrification[6].

Species biodiversity decreases and the dominant biota changes

Fig. 4. Macroalgae washed ashore. Photo credit D. Ramirez.

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 outcompeted.

Green tides

Many observations and experiments provide evidence that the occurrence of so-called 'green tides', consisting of marine seaweeds or macroalgae, is increased in eutrophicated coastal waters[13]. These blooms are recognizable by large blades of algae that may wash up onto the shoreline (Fig. 4). Green tides can asphyxiate aquacultures or disrupt traditional artisanal fisheries. Macroalgae can also be valorized as a raw material; harvesting could therefore be an effective solution[13] (see also Seaweed (macro-algae) ecosystem services).

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[14]. The table gives an overview of some species that are regularly observed and represent a risk for seafood consumers[15].


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


Finfish can also be a vector 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[15]. People are poisoned when consuming contaminated fish. 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. The seaweed is harmless to humans but decreases the fitness for use of the water for water sports (swimming, boating and fishing).

Aesthetic impacts

Fig. 5. Beaches can be closed as a result of toxic algal blooms (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 (H2S) is released. This gas is characterized by a very unpleasant characteristic foul odor of rotten eggs.

Economic impacts

Due to the toxins produced by harmful algal blooms commercial fish and shellfish may become unsuitable for consumption resulting in potential economic and financial problems for the fishing industries. In extreme cases beaches are closed due to the presence of toxic algal blooms (Fig. 5). The annual economic costs related to illness and death caused by consumption of poisoned fish products is estimated at around 30 million US$ worldwide[16]. The fishing industry is suffering economic losses because consumers refrain from consuming fish and shellfish products due to the perceived danger of poisoning. For the USA, the loss related to this avoidance behavior is estimated at around 1 billion US$ per year[17].

The Baltic Sea harbours one of the the largest dead zones in the world. Lost revenues from ecosystem services (fishing, recreation, but also non-use values) as a result of eutrophication amount to 3-4 billion euros, according to an estimate by HELCOM[18].


Related articles

Harmful algal bloom
Nutrient conversion in the marine environment
Algal bloom dynamics
What causes eutrophication?
Threats to the coastal zone
Estuarine turbidity maximum
Case studies eutrophication
Coupled hydrodynamic - water quality - ecological modelling

See also other articles in the Category:Eutrophication


References

  1. ↑ Nixon, S.W. and Buckley, B. A. 2002. “A strikingly rich zone” – Nutrient enrichment and secondary production in coastal marine ecosystems. Estuaries 25: 782–796
  2. ↑ Ouaissa, S., Gómez-Jakobsen, F., Yebra, L., Ferrera, I., Moreno-Ostos, E., Dolores Belando, M., Ruiz, J.M. and Mercado, J.M. 2023. Phytoplankton dynamics in the Mar Menor, a Mediterranean coastal lagoon strongly impacted by eutrophication. Marine Pollution Bulletin 192, 115074
  3. ↑ Condon, R.H., Duarte, C.M., Pitt, K.A., Robinson, K.L., Lucas, C.H., Sutherland, K.R., Mianzan, H.W., Bogeberg, M., Purcell, J.E., Decker, M.B., Uye, S.-I., Madin, L.P., Brodeur, R.D., Haddock, S.H.D., Malej, A., Parry, G.D., Eriksen, E., Quiñones, J., Acha, M., Harvey, M., Arthur, J.M. and Graham W.M. 2013. Recurrent jellyfish blooms are a consequence of global oscillations. PNAS 110: 1000-1005
  4. ↑ Funkey, C.P., Conley, D.J., Reuss, N.S., Humborg, C, Jilbert, T. and Slomp, C.P. 2014. Hypoxia Sustains Cyanobacteria Blooms in the Baltic Sea. Environ. Sci. Technol. 48: 2598−2602
  5. ↑ Wallace, R.B., Baumann, H., Grear, J.S., Aller, R.C. and Gobler, C.J. 2014. Coastal ocean acidification: The other eutrophication problem. Estuarine, Coastal and Shelf Science 148: 1-13
  6. ↑ 6.0 6.1 6.2 Breitburg, D., Gregoire, M. Isensee, K. (eds.) 2018. The ocean is losing its breath: Declining oxygen in the world’s ocean and coastal waters. IOC-UNESCO, IOC Technical Series, No. 137 40pp. (IOC/2018/TS/137)
  7. ↑ Altieri, A.H., Johnson, M.D., Swaminathan, S.D., Nelson, H.R. and Gedan, K.B. 2021. Resilience of Tropical Ecosystems to Ocean Deoxygenation. Trends in Ecology and Evolution 36: 227-238
  8. ↑ Vaquer-Sunyer, R. and Duarte, C.M. 2008. Thresholds of hypoxia for marine biodiversity. PNAS 105: 15452–15457
  9. ↑ Greve, T.M., Krause-Jensen, D., Rasmussen, M.B. and Christense, P.B. 2005. Means of rapid eelgrass (Zostera marina L.) recolonisation in former dieback areas. Aquatic Botany 82: 143-156
  10. ↑ Beusen, A.H.W., Doelman, J.C., Van Beek, L.P.H., Van Puijenbroek, P.J.T.M., M. Mogollon, J., Van Grinsven, H.J.M., Stehfest, E., Van Vuuren, D.P. and Bouwman A.F. 2022. Exploring river nitrogen and phosphorus loading and export to global coastal waters in the Shared Socio-economic pathways. Global Environmental Change 72: 102426
  11. ↑ Baroni, I.R., Palastanga, V. and Slomp, C. P. 2020. Enhanced Organic Carbon Burial in Sediments of Oxygen Minimum Zones Upon Ocean Deoxygenation. Front. Mar. Sci. 6: 839
  12. ↑ Li, G., Cheng, L., Zhu, J., Trenberth, K.E., Mann, M.E. and Abraham, J.P. 2020. Increasing ocean stratification over the past half-century. Nature Climate Change https://doi.org/10.1038/s41558-020-00918-2
  13. ↑ 13.0 13.1 Smetacek, V. and Zingone, A. 2013. Green and golden seaweed tides on the rise. Nature 504, doi:10.1038/nature12860
  14. ↑ Eutrophication and health. European Commission 2002. Office for Official Publications of the European Communities: Luxembourg. ISBN 92-894-4413-4.28 pp.
  15. ↑ 15.0 15.1 Berdalet, E., Fleming, L.E., Gowen, R., Davidson, K., Hess, P., Backer, L.C., Moore, S.K., Hoagland, P. and Enevoldsen, H. 2016. Marine harmful algal blooms, human health and wellbeing: challenges and opportunities in the 21st century. J. Mar. Biol. Assoc. U.K. 96: 61–91
  16. ↑ Kouakou, C.R.C. and Poder, T.G. 2019. Economic impact of harmful algal blooms on human health: a systematic review. Journal of Water and Health 17.4: 499-516
  17. ↑ Parsons, G.R., Morgan, A.O., Whitehead, J.C. and Haab, T.C. 2006. The Welfare Effects of Pfiesteria-Related Fish Kills: A Contingent Behavior Analysis of Seafood Consumers. Agricultural and Resource Economics Review 35(1)
  18. ↑ Hyytiainen, K., Hasler, B., Ericsdotter, S., Nekoro, M., Blyh, K., Artell, J., Ahlvik, L. and Ahtiainen, J. 2013. Worth it: Benefits outweigh costs in reducing eutrophication in the Baltic. BalticSTERN Summary Report for HELCOM 2013 Ministerial Meeting


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 (2024): Possible consequences of eutrophication. Available from http://www.coastalwiki.org/wiki/Possible_consequences_of_eutrophication [accessed on 27-04-2024]



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