aquatic ecosystem

{{excerpt|Marine ecosystem|paragraphs=1}}

{{excerpt|Marine coastal ecosystem|paragraphs=1|only=paragraph}}

{{excerpt|Ocean surface ecosystem|paragraphs=1|only=paragraph}}

{{excerpt|Freshwater ecosystem|paragraphs=1}}

{{excerpt|Lake ecosystem|paragraphs=1-2|file=no}}

{{excerpt|River ecosystem|paragraphs=1,2}}

{{excerpt|Wetland|paragraphs=1|file=no}}

{{Further|ecosystem}}

Aquatic ecosystems perform many important environmental functions. For example, they recycle nutrients, purify water, attenuate floods, recharge ground water and provide habitats for wildlife.{{cite book

| last = Loeb

| first = Stanford L.

| title = Biological Monitoring of Aquatic Systems

| publisher = CRC Press

| date = 24 January 1994

| isbn = 0-87371-910-7 }} The biota of an aquatic ecosystem contribute to its self-purification, most notably microorganisms, phytoplankton, higher plants, invertebrates, fish, bacteria, protists, aquatic fungi, and more. These organisms are actively involved in multiple self-purification processes, including organic matter destruction and water filtration. It is crucial that aquatic ecosystems are reliably self-maintained, as they also provide habitats for species that reside in them.{{Cite journal |last=Ostroumov |first=S. A. |date=2005 |title=On the Multifunctional Role of the Biota in the Self-Purification of Aquatic Ecosystems |url=https://www.academia.edu/1893226 |journal=Russian Journal of Ecology |volume=36 |issue=6 |pages=414–420 |doi=10.1007/s11184-005-0095-x |bibcode=2005RuJEc..36..414O |s2cid=3172507 |issn=1067-4136}}

In addition to environmental functions, aquatic ecosystems are also used for human recreation, and are very important to the tourism industry, especially in coastal regions.{{cite book|last=Daily|first=Gretchen C.|url=https://archive.org/details/naturesservicess0000unse|title=Nature's Services|date=1 February 1997|publisher=Island Press|isbn=1-55963-476-6|url-access=registration}} They are also used for religious purposes, such as the worshipping of the Jordan River by Christians, and educational purposes, such as the usage of lakes for ecological study.{{Citation |last=Rodrigues |first=João Manuel Garcia |title=Cultural Services in Aquatic Ecosystems |date=2015 |url=https://doi.org/10.1007/978-94-017-9846-4_3 |work=Ecosystem Services and River Basin Ecohydrology |pages=35–56 |editor-last=Chicharo |editor-first=Luis |place=Dordrecht |publisher=Springer Netherlands |language=en |doi=10.1007/978-94-017-9846-4_3 |isbn=978-94-017-9846-4 |access-date=2023-02-18 |editor2-last=Müller |editor2-first=Felix |editor3-last=Fohrer |editor3-first=Nicola|url-access=subscription }}

The biotic characteristics are mainly determined by the organisms that occur. For example, wetland plants may produce dense canopies that cover large areas of sediment or snails or geese may graze the vegetation leaving large mud flats. Aquatic environments have relatively low oxygen levels, forcing adaptation by the organisms found there. For example, many wetland plants must produce aerenchyma to carry oxygen to roots. Other biotic characteristics are more subtle and difficult to measure, such as the relative importance of competition, mutualism or predation.{{cite book|last=Keddy|first=Paul A.|title=Wetland Ecology. Principles and Conservation.|publisher=Cambridge University Press|year=2010|isbn=978-0-521-51940-3|page=497}} There are a growing number of cases where predation by coastal herbivores including snails, geese and mammals appears to be a dominant biotic factor.Silliman, B. R., Grosholz, E. D., and Bertness, M. D. (eds.) (2009). Human Impacts on Salt Marshes: A Global Perspective. Berkeley, CA: University of California Press.

Autotrophic organisms are producers that generate organic compounds from inorganic material. Algae use solar energy to generate biomass from carbon dioxide and are possibly the most important autotrophic organisms in aquatic environments.{{cite book|last=Manahan|first=Stanley E.|title=Environmental Chemistry|date=1 January 2005|publisher=CRC Press|isbn=1-56670-633-5}} The more shallow the water, the greater the biomass contribution from rooted and floating vascular plants. These two sources combine to produce the extraordinary production of estuaries and wetlands, as this autotrophic biomass is converted into fish, birds, amphibians and other aquatic species.

Chemosynthetic bacteria are found in benthic marine ecosystems. These organisms are able to feed on hydrogen sulfide in water that comes from volcanic vents. Great concentrations of animals that feed on these bacteria are found around volcanic vents. For example, there are giant tube worms (Riftia pachyptila) 1.5 m in length and clams (Calyptogena magnifica) 30 cm long.{{cite book| last = Chapman| first = J.L.|author2=Reiss, M.J.| title = Ecology| publisher = Cambridge University Press| date = 10 December 1998| isbn = 0-521-58802-2 }}

Heterotrophic organisms consume autotrophic organisms and use the organic compounds in their bodies as energy sources and as raw materials to create their own biomass.

Euryhaline organisms are salt tolerant and can survive in marine ecosystems, while stenohaline or salt intolerant species can only live in freshwater environments.{{cite web|last=United States Environmental Protection Agency|author-link=United States Environmental Protection Agency|date=2 March 2006|title=Marine Ecosystems|url=http://www.epa.gov/bioiweb1/aquatic/marine.html|access-date=2006-08-25}}

An ecosystem is composed of biotic communities that are structured by biological interactions and abiotic environmental factors. Some of the important abiotic environmental factors of aquatic ecosystems include substrate type, water depth, nutrient levels, temperature, salinity, and flow. It is often difficult to determine the relative importance of these factors without rather large experiments. There may be complicated feedback loops. For example, sediment may determine the presence of aquatic plants, but aquatic plants may also trap sediment, and add to the sediment through peat.

The amount of dissolved oxygen in a water body is frequently the key substance in determining the extent and kinds of organic life in the water body. Fish need dissolved oxygen to survive, although their tolerance to low oxygen varies among species; in extreme cases of low oxygen, some fish even resort to air gulping.Graham, J. B. (1997). Air Breathing Fishes. San Diego, CA: Academic Press. Plants often have to produce aerenchyma, while the shape and size of leaves may also be altered.Sculthorpe, C. D. (1967). The Biology of Aquatic Vascular Plants. Reprinted 1985 Edward Arnold, by London. Conversely, oxygen is fatal to many kinds of anaerobic bacteria.

Nutrient levels are important in controlling the abundance of many species of algae.Smith, V. H. (1982). The nitrogen and phosphorus dependence of algal biomass in lakes: an empirical and theoretical analysis. Limnology and Oceanography, 27, 1101–12. The relative abundance of nitrogen and phosphorus can in effect determine which species of algae come to dominate.Smith, V. H. (1983). Low nitrogen to phosphorus ratios favor dominance by bluegreen algae in lake phytoplankton. Science, 221, 669–71. Algae are a very important source of food for aquatic life, but at the same time, if they become over-abundant, they can cause declines in fish when they decay.Vallentyne, J. R. (1974). The Algal Bowl: Lakes and Man, Miscellaneous Special Publication No. 22. Ottawa, ON: Department of the Environment, Fisheries and Marine Service. Similar over-abundance of algae in coastal environments such as the Gulf of Mexico produces, upon decay, a hypoxic region of water known as a dead zone.Turner, R. E. and Rabelais, N. N. (2003). Linking landscape and water quality in the Mississippi River Basin for 200 years. BioScience, 53, 563–72.

The salinity of the water body is also a determining factor in the kinds of species found in the water body. Organisms in marine ecosystems tolerate salinity, while many freshwater organisms are intolerant of salt. The degree of salinity in an estuary or delta is an important control upon the type of wetland (fresh, intermediate, or brackish), and the associated animal species. Dams built upstream may reduce spring flooding, and reduce sediment accretion, and may therefore lead to saltwater intrusion in coastal wetlands.

Freshwater used for irrigation purposes often absorbs levels of salt that are harmful to freshwater organisms.

{{Further|Ecosystem#Human interactions with ecosystems|Freshwater ecosystem#Threats|Marine ecosystem#Threats|Human impact on marine life}}

The health of an aquatic ecosystem is degraded when the ecosystem's ability to absorb a stress has been exceeded. A stress on an aquatic ecosystem can be a result of physical, chemical or biological alterations to the environment. Physical alterations include changes in water temperature, water flow and light availability. Chemical alterations include changes in the loading rates of biostimulatory nutrients, oxygen-consuming materials, and toxins. Biological alterations include over-harvesting of commercial species and the introduction of exotic species. Human populations can impose excessive stresses on aquatic ecosystems. Climate change driven by anthropogenic activities can harm aquatic ecosystems by disrupting current distribution patterns of plants and animals. It has negatively impacted deep sea biodiversity, coastal fish diversity, crustaceans, coral reefs, and other biotic components of these ecosystems.{{Cite journal |last=Prakash |first=Sadguru |title=Impact of Climate Change on Aquatic Ecosystem and ITS Biodiversity: An Overview |date=2021 |url=http://ijbi.org.in/papers/10.%20IJBI%20Dec%202021%20Dr%20Sadguru.pdf |journal=International Journal of Biological Innovations |volume=03 |issue=2 |doi=10.46505/IJBI.2021.3210|s2cid=237639194 }} Human-made aquatic ecosystems, such as ditches, aquaculture ponds, and irrigation channels, may also cause harm to naturally occurring ecosystems by trading off biodiversity with their intended purposes. For instance, ditches are primarily used for drainage, but their presence also negatively affects biodiversity.{{Cite journal |last1=Koschorreck |first1=Matthias |last2=Downing |first2=Andrea S. |last3=Hejzlar |first3=Josef |last4=Marcé |first4=Rafael |last5=Laas |first5=Alo |last6=Arndt |first6=Witold G. |last7=Keller |first7=Philipp S. |last8=Smolders |first8=Alfons J. P. |last9=van Dijk |first9=Gijs |last10=Kosten |first10=Sarian |date=2020-02-01 |title=Hidden treasures: Human-made aquatic ecosystems harbour unexplored opportunities |url=https://doi.org/10.1007/s13280-019-01199-6 |journal=Ambio |language=en |volume=49 |issue=2 |pages=531–540 |doi=10.1007/s13280-019-01199-6 |issn=1654-7209 |pmc=6965596 |pmid=31140158|bibcode=2020Ambio..49..531K }}

There are many examples of excessive stresses with negative consequences. The environmental history of the Great Lakes of North America illustrates this problem, particularly how multiple stresses, such as water pollution, over-harvesting and invasive species can combine. The Norfolk Broadlands in England illustrate similar decline with pollution and invasive species.Moss, B. (1983). The Norfolk Broadland: experiments in the restoration of a complex wetland. Biological Reviews of the Cambridge Philosophical Society, 58, 521–561. Lake Pontchartrain along the Gulf of Mexico illustrates the negative effects of different stresses including levee construction, logging of swamps, invasive species and salt water intrusion.Keddy, P. A., Campbell, D., McFalls T., Shaffer, G., Moreau, R., Dranguet, C., and Heleniak, R. (2007). The wetlands of lakes Pontchartrain and Maurepas: past, present and future. Environmental Reviews, 15, 1–35.

• {{annotated link|Aquatic plant}}
• {{annotated link|Hydrobiology}}
• {{annotated link|Hydrosphere}}
• {{annotated link|Limnology}}
• Ocean
• {{annotated link|Stephen Alfred Forbes}} - one of the founders of aquatic ecosystem science
• {{annotated link|Stream metabolism}}

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{{commons category multi|Freshwater ecosystems}}

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{{Wetlands}}

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Category:Aquatic ecology

Category:Ecosystems

Category:Aquatic plants

Category:Fisheries science

Category:Systems ecology

Category:Water