Aquatic ecosystem
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[[Image:Estuary-mouth.jpg|frame|An estuary mouth and coastal waters, part of an aquatic ecosystem.]]
An '''aquatic ecosystem''' is an [[ecosystem]] located in [[ water bodies]]. [[Biocoenosis|Communities]] of [[biota (ecology)|organisms]] that are dependent on each other and on their environment live in aquatic ecosystems. The two main types of aquatic ecosystems are [[marine ecosystem]]s and [[Freshwater biology|freshwater ecosystem]]s.<ref name=Alexander>{{cite book| last = Alexander| first = David E.| title = Encyclopedia of Environmental Science| publisher = [[Springer]]| date = [[1999-05-01]]| id = ISBN 0-412-74050-8 }}</ref>
==Types of aquatic ecosystems==
Aquatic ecosystems can be divided into two general types: marine ecosystems and freshwater ecosystems.
Neritic (the relatively shallow part of the ocean that lies over the [[continental shelf]]); [[profundal zone|profundal]] (bottom or deep water); [[benthic]] (bottom substrates); [[intertidal zone|intertidal]] (the area between high and low tides); [[estuary|estuaries]].
===Salt Water Ecosystems===
[[Image:Nwhi - French Frigate Shoals reef - many fish.jpg | right | thumb | 300px | A [[coral reef]] near the cool [[Hawaiian Islands]] is an example of a complex marine ecosystem.]]
Marine ecosystems cover approximately 71% of the Earth's surface and contain approximately 97% of the planet's water. They generate 32% of the world's net [[primary production]].<ref name=Alexander/> They are distinguished from freshwater ecosystems by the presence of dissolved [[chemical compound|compounds]], especially [[salt]]s, in the water. Approximately 85% of the dissolved materials in [[seawater]] are [[sodium]] and [[chlorine]]. Seawater has an average salinity of 35 [[concentration|parts per thousand]] (ppt) of water. Actual salinity varies among different marine ecosystems.<ref name=USEPA>{{cite web| last = United States Environmental Protection Agency| authorlink = United States Environmental Protection Agency| title = Marine Ecosystems| date = [[2006-03-02]]| url = http://www.epa.gov/bioiweb1/aquatic/marine.html| accessdate = 2006-08-25 }}</ref>
Marine ecosystems can be divided into the following zones: [[ocean|oceanic]] (the relatively shallow part of the ocean that lies over the [[continental shelf]]); [[profundal zone|profundal]] (bottom or deep water); [[benthic]] (bottom substrates); [[intertidal zone|intertidal]] (the area between high and low tides); [[estuary|estuaries]]; [[salt marsh|salt marshes]]; [[coral reef]]s; and [[hydrothermal vent]]s (where [[Chemosynthesis|chemosynthetic]] [[sulfur]] [[bacteria]] form the food base).<ref name=Alexander/>
[[class (biology)|Classes]] of organisms found in marine ecosystems include [[brown algae]], [[dinoflagellate]]s, [[coral]]s, [[cephalopod]]s, [[echinoderm]]s, and [[shark]]s. Fish caught in marine ecosystems are the biggest source of commercial foods obtained from wild populations.<ref name=Alexander/>
Environmental problems concerning marine ecosystems include unsustainable exploitation of marine resources (for example [[overfishing]] of certain species), [[water pollution]], and building on coastal areas.<ref name=Alexander/>
===Freshwater ecosystems===
Freshwater ecosystems cover 0.8% of the Earth's surface and contain 0.009% of its total water. They generate nearly 3% of its net primary production.<ref name=Alexander/> Freshwater ecosystems contain 41% of the world's known fish species.<ref name=Daily>{{cite book
| last = Daily
| first = Gretchen C.
| title = Nature's Services
| publisher = [[Island Press]]
| date = [[1997-02-01]]
| id = ISBN 1-559-63476-6 }}</ref>
There are three basic types of freshwater ecosystems:
*[[Lentic system ecology|Lentic]]: slow-moving water, including [[pond|pool]]s, [[pond]]s, and [[lake]]s.
*[[Lotic System Ecology|Lotic]]: rapidly-moving water, for example [[stream]]s and [[river]]s.
*[[Wetland]]s: areas where the soil is saturated or inundated for at least part of the time.<ref name=Vaccari>{{cite book
| last = Vaccari
| first = David A.
| title = Environmental Biology for Engineers and Scientists
| publisher = [[Wiley-Interscience]]
| date = [[2005-11-08]]
| id = ISBN 0-471-74178-7 }}</ref>
Lake ecosystems can be divided into zones: [[pelagic zone|pelagic]] (open offshore waters); profundal; littoral (nearshore shallow waters); and [[riparian zone|riparian]] (the area of land bordering a body of water). Two important subclasses of lakes are ponds, which typically are small lakes that intergrade with wetlands, and water [[reservoir|reservoirs]]. Many lakes, or bays within them, gradually become enriched by nutrients and fill in with organic sediments, a process called [[eutrophication]]. Eutrophication is accelerated by human activity within the water [[catchment area|catchment area]] of the lake.<ref name=Alexander/>
The major zones in river ecosystems are determined by the river bed's gradient or by the velocity of the current. Faster moving turbulent water typically contains greater concentrations of dissolved oxygen, which supports greater biodiversity than the slow moving water of pools. These distinctions forms the basis for the division of rivers into [[upland and lowland (freshwater ecology)|upland and lowland]] rivers. The food base of streams within riparian forests is mostly derived from the trees, but wider streams and those that lack a [[canopy (forest)|canopy]] derive the majority of their food base from algae. [[Fish migration|Anadromous fish]] are also an important source of nutrients. Environmental threats to rivers include loss of water, dams, chemical pollution and introduced species.<ref name=Alexander/>
Wetlands are dominated by [[vascular plant]]s that have adapted to saturated soil. Wetlands are the most productive natural ecosystems because of the proximity of water and soil. Due to their productivity, wetlands are often converted into dry land with [[ditch|dykes]] and [[drainage|drains]] and used for agricultural purposes. Their closeness to lakes and rivers means that they are often developed for human settlement.<ref name=Alexander/>
====Pond ecosystems====
This is a specific type of freshwater ecosystem that is largely based on the [[autotroph]] [[algae]] which provide the base trophic level for all life in the area. The largest predator in a pond ecosystem will normally be a fish and in-between range smaller insects and microorganisms. It may have a scale of organisms from small bacteria to big creatures like water snakes, beetles, water bugs, and turtles.
==Functions of aquatic ecosystems==
Aquatic ecosystems perform many important environmental functions. For example, they [[biogeochemical cycle|recycle nutrients]], purify water, attenuate floods, recharge ground water and provide habitats for wildlife.<ref name=Loeb>{{cite book
| last = Loeb
| first = Stanford L.
| title = Biological Monitoring of Aquatic Systems
| publisher = [[CRC Press]]
| date = [[1994-01-24]]
| id = ISBN 0-873-71910-7 }}</ref> Aquatic ecosystems are also used for human recreation, and are very important to the [[tourism]] industry, especially in coastal regions.<ref name=Daily/>
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 of 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 the introduction of exotic species. Human populations can impose excessive stresses on aquatic ecosystems.<ref name=Loeb/>
==Abiotic characteristics of aquatic ecosystems==
An ecosystem is composed of biotic communities and abiotic environmental factors, which form a self-regulating and self-sustaining unit. Abiotic environmental factors of aquatic ecosystems include temperature, salinity, and flow.<ref name=Loeb/>
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. Conversely, oxygen is fatal to many kinds of [[Anaerobic respiration|anaerobic]] bacteria.<ref name=Manahan>{{cite book| last = Manahan| first = Stanley E.| title = Environmental Chemistry| publisher = [[CRC Press]]| date = [[2005-01-01]]| id = ISBN 1-56670-633-5 }}</ref>
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. Freshwater used for [[irrigation]] purposes often absorb levels of salt that are harmful to freshwater organisms.<ref name=Manahan/> Though some salt can be good for organisms.
==Biotic characteristics of aquatic ecosystems==
The organisms (also called biota) found in aquatic ecosystems are either autotrophic or heterotrophic.<ref name=Manahan/>
===Autotrophic organisms===
[[Autotroph]]ic organisms are producers that generate organic compounds from inorganic material. Algae use solar energy to generate biomass from carbon dioxide and are the most important autotrophic organisms in aquatic environments.<ref name=Manahan/> Chemosynthetic bacteria are found in benthic marine ecosystems. These organisms are able to feed on [[hydrogen sulfide]] in water that comes from [[volcanic vent]]s. Great concentrations of animals that feed on this bacteria are found around volcanic vents. For example, there are [[giant tube worm]]s (''Riftia pachyptila'') 1.5m in length and clams (''[[Calyptogena magnifica]]'') 30cm long.<ref name=Chapman>{{cite book| last = Chapman| first = J.L.| coauthors = Reiss, M.J.| title = Ecology| publisher = [[Cambridge University Press]]| date = [[1998-12-10]]| id = ISBN 0-521-58802-2 }}</ref>
===Heterotrophic organisms===
[[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]].<ref name=Manahan/> [[Euryhaline]] organisms are salt tolerant and can survive in marine ecosystems, while [[stenohaline]] or salt intolerant species can only live in freshwater environments.<ref name=USEPA/>
==See also==
* [[Ecoregion]]
* [[Marine debris]]
==References==
<references/>
==External links==
{{commons|Category:Freshwater ecosystems}}
*[http://www.ec.gc.ca/water/en/nature/aqua/e_aqua.htm Aquatic Ecosystems at Environment Canada]
*[http://www.ucmp.berkeley.edu/glossary/gloss5/biome/aquatic.html The Aquatic Biome]
*[http://video.google.ca/videoplay?docid=1653451790600950363 Pond Life - Video]
*[http://www.canal.ird.fr/programmes/recherches/fadio/fadio1_us/index.htm Fish Aggregating Devices as Instrumented Observatories of pelagic ecosystems (FADIO) - Video Canal IRD]
{{fisheries and fishing}}
[[Category:Aquatic ecology|*]]
[[Category:Ecosystems]]
[[Category:Fisheries science]]
[[Category:Sustainability]]
[[Category:Systems ecology]]
[[Category:Water]]
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[[es:Ecosistema acuático]]
[[ro:Ecosistem acvatic]]
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