Aquatic ecosystem

An aquatic ecosystem is an ecosystem in a body of water. Communities of organisms that are dependent on each other and on their environment live in aquatic ecosystems. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems.[1]

An estuary mouth and coastal waters, part of an aquatic ecosystem



Marine ecosystems, the largest of all ecosystems,[2] 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.[3] They are distinguished from freshwater ecosystems by the presence of dissolved compounds, especially salts, in the water. Approximately 85% of the dissolved materials in seawater are sodium and chlorine. Seawater has an average salinity of 35 parts per thousand of water. Actual salinity varies among different marine ecosystems.[4]

Oceanic divisions
A classification of marine habitats.

Marine ecosystems can be divided into many zones depending upon water depth and shoreline features. The oceanic zone is the vast open part of the ocean where animals such as whales, sharks, and tuna live. The benthic zone consists of substrates below water where many invertebrates live. The intertidal zone is the area between high and low tides; in this figure it is termed the littoral zone. Other near-shore (neritic) zones can include estuaries, salt marshes, coral reefs, lagoons and mangrove swamps. In the deep water, hydrothermal vents may occur where chemosynthetic sulfur bacteria form the base of the food web.

Classes of organisms found in marine ecosystems include brown algae, dinoflagellates, corals, cephalopods, echinoderms, and sharks. Fishes caught in marine ecosystems are the biggest source of commercial foods obtained from wild populations.[3]

Environmental problems concerning marine ecosystems include unsustainable exploitation of marine resources (for example overfishing of certain species), marine pollution, climate change, and building on coastal areas.[3]


Panorama presa las niñas mogan gran canaria
Freshwater ecosystem.

Freshwater ecosystems cover 0.78% of the Earth's surface and inhabit 0.009% of its total water. They generate nearly 3% of its net primary production.[3] Freshwater ecosystems contain 41% of the world's known fish species.[5]

There are three basic types of freshwater ecosystems:


Primary zones of a lake
The three primary zones of a lake.

Lake ecosystems can be divided into zones. One common system divides lakes into three zones (see figure). The first, the littoral zone, is the shallow zone near the shore. This is where rooted wetland plants occur. The offshore is divided into two further zones, an open water zone and a deep water zone. In the open water zone (or photic zone) sunlight supports photosynthetic algae, and the species that feed upon them. In the deep water zone, sunlight is not available and the food web is based on detritus entering from the littoral and photic zones. Some systems use other names. The off shore areas may be called the pelagic zone, the photic zone may be called the limnetic zone and the aphotic zone may be called the profundal zone. Inland from the littoral zone one can also frequently identify a riparian zone which has plants still affected by the presence of the lake—this can include effects from windfalls, spring flooding, and winter ice damage. The production of the lake as a whole is the result of production from plants growing in the littoral zone, combined with production from plankton growing in the open water.

Wetlands can be part of the lentic system, as they form naturally along most lake shores, the width of the wetland and littoral zone being dependent upon the slope of the shoreline and the amount of natural change in water levels, within and among years. Often dead trees accumulate in this zone, either from windfalls on the shore or logs transported to the site during floods. This woody debris provides important habitat for fish and nesting birds, as well as protecting shorelines from erosion.

Two important subclasses of lakes are ponds, which typically are small lakes that intergrade with wetlands, and water reservoirs. Over long periods of time, lakes, or bays within them, may gradually become enriched by nutrients and slowly fill in with organic sediments, a process called succession. When humans use the watershed, the volumes of sediment entering the lake can accelerate this process. The addition of sediments and nutrients to a lake is known as eutrophication.[3]


Ponds are small bodies of freshwater with shallow and still water, marsh, and aquatic plants.[7] They can be further divided into four zones: vegetation zone, open water, bottom mud and surface film.[8] The size and depth of ponds often varies greatly with the time of year; many ponds are produced by spring flooding from rivers. Food webs are based both on free-floating algae and upon aquatic plants. There is usually a diverse array of aquatic life, with a few examples including algae, snails, fish, beetles, water bugs, frogs, turtles, otters and muskrats. Top predators may include large fish, herons, or alligators. Since fish are a major predator upon amphibian larvae, ponds that dry up each year, thereby killing resident fish, provide important refugia for amphibian breeding.[9] Ponds that dry up completely each year are often known as vernal pools. Some ponds are produced by animal activity, including alligator holes and beaver ponds, and these add important diversity to landscapes.[9]


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 form the basis for the division of rivers into 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 derive the majority of their food base from algae. Anadromous fish are also an important source of nutrients. Environmental threats to rivers include loss of water, dams, chemical pollution and introduced species.[3] A dam produces negative effects that continue down the watershed. The most important negative effects are the reduction of spring flooding, which damages wetlands, and the retention of sediment, which leads to loss of deltaic wetlands.[9]


Wetlands are dominated by vascular plants that have adapted to saturated soil.[9] There are four main types of wetlands: swamp, marsh, fen and bog (both fens and bogs are types of mire). Wetlands are the most productive natural ecosystems in the world because of the proximity of water and soil. Hence they support large numbers of plant and animal species. Due to their productivity, wetlands are often converted into dry land with dykes and drains and used for agricultural purposes. The construction of dykes, and dams, has negative consequences for individual wetlands and entire watersheds.[9] Their closeness to lakes and rivers means that they are often developed for human settlement.[3] Once settlements are constructed and protected by dykes, the settlements then become vulnerable to land subsidence and ever increasing risk of flooding.[9] The Louisiana coast around New Orleans is a well-known example;[10] the Danube Delta in Europe is another.[11]


Aquatic ecosystems perform many important environmental functions. For example, they recycle nutrients, purify water, attenuate floods, recharge ground water and provide habitats for wildlife.[12] Aquatic ecosystems are also used for human recreation, and are very important to the tourism industry, especially in coastal regions.[5]

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 over-harvesting of commercial species and the introduction of exotic species. Human populations can impose excessive stresses on aquatic ecosystems.[12] There are many examples of excessive stresses with negative consequences. Consider three. 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.[13] The Norfolk Broadlands in England illustrate similar decline with pollution and invasive species.[14] 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.[15]

Abiotic characteristics

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.[9][12] 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.[16] Plants often have to produce aerenchyma, while the shape and size of leaves may also be altered.[17] Conversely, oxygen is fatal to many kinds of anaerobic bacteria.[18]

Nutrient levels are important in controlling the abundance of many species of algae.[19] The relative abundance of nitrogen and phosphorus can in effect determine which species of algae come to dominate.[20] 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.[13] 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.[21]

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.[9]

Freshwater used for irrigation purposes often absorbs levels of salt that are harmful to freshwater organisms.[18]

Biotic characteristics

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.[9] There are a growing number of cases where predation by coastal herbivores including snails, geese and mammals appears to be a dominant biotic factor.[22]

Autotrophic organisms

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.[18] 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.[23]

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.[18] Euryhaline organisms are salt tolerant and can survive in marine ecosystems, while stenohaline or salt intolerant species can only live in freshwater environments.[4]

See also


  1. ^ Alexander, David E. (1 May 1999). Encyclopedia of Environmental Science. Springer. ISBN 0-412-74050-8.
  2. ^ "University of California Museum of Paleontology: The Marine Biome". Retrieved 27 September 2018.
  3. ^ a b c d e f g Alexander, David E. (1 May 1999). Encyclopedia of Environmental Science. Springer. ISBN 0-412-74050-8.
  4. ^ a b United States Environmental Protection Agency (2 March 2006). "Marine Ecosystems". Retrieved 25 August 2006.
  5. ^ a b Daily, Gretchen C. (1 February 1997). Nature's Services. Island Press. ISBN 1-55963-476-6.
  6. ^ Vaccari, David A. (8 November 2005). Environmental Biology for Engineers and Scientists. Wiley-Interscience. ISBN 0-471-74178-7.
  7. ^ Clegg, J. (1986). Observer's Book of Pond Life. Frederick Warne, London. 460 p.
  8. ^ Clegg, J. (1986). Observer's Book of Pond Life. Frederick Warne, London. 460 p. p.160-163.
  9. ^ a b c d e f g h i Keddy, Paul A. (2010). Wetland Ecology. Principles and Conservation. Cambridge University Press. p. 497. ISBN 978-0-521-51940-3.
  10. ^ Keddy, P.A., D. Campbell, T. McFalls, G. Shaffer, R. Moreau, C. Dranguet, and R. Heleniak. 2007. The wetlands of lakes Pontchartrain and Maurepas: past, present and future. Environmental Reviews 15: 1- 35.
  11. ^ Gastescu, P. (1993). The Danube Delta: geographical characteristics and ecological recovery. Earth and Environmental Science, 29, 57–67.
  12. ^ a b c Loeb, Stanford L. (24 January 1994). Biological Monitoring of Aquatic Systems. CRC Press. ISBN 0-87371-910-7.
  13. ^ a b 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.
  14. ^ Moss, B. (1983). The Norfolk Broadland: experiments in the restoration of a complex wetland. Biological Reviews of the Cambridge Philosophical Society, 58, 521–561.
  15. ^ 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.
  16. ^ Graham, J. B. (1997). Air Breathing Fishes. San Diego, CA: Academic Press.
  17. ^ Sculthorpe, C. D. (1967). The Biology of Aquatic Vascular Plants. Reprinted 1985 Edward Arnold, by London.
  18. ^ a b c d Manahan, Stanley E. (1 January 2005). Environmental Chemistry. CRC Press. ISBN 1-56670-633-5.
  19. ^ 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.
  20. ^ Smith, V. H. (1983). Low nitrogen to phosphorus ratios favor dominance by bluegreen algae in lake phytoplankton. Science, 221, 669–71.
  21. ^ 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.
  22. ^ 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.
  23. ^ Chapman, J.L.; Reiss, M.J. (10 December 1998). Ecology. Cambridge University Press. ISBN 0-521-58802-2.


External links

Amy Rosemond

Amy D. Rosemond is an American aquatic ecosystem ecologist, biogeochemist, and professor in the Odum School of Ecology at the University of Georgia. Rosemond studies how global change affects freshwater ecosystems, including effects of watershed urbanization, nutrient pollution, and changes in biodiversity on ecosystem function. She was elected an Ecological Society of America fellow in 2018, and has been elected to serve as the Society for Freshwater Science president from 2019-2020.


Aquatic(s) means relating to water; living in or near water or taking place in water; does not include groundwater, as "aquatic" implies an environment where plants and animals live.

Aquatic(s) may also refer to:

Aquatic animal, either vertebrate or invertebrate, which lives in water for most or all of its life

Aquatic ecosystem, environmental system located in a body of water

Aquatic plants, also called hydrophytic plants or hydrophytes, are plants that have adapted to living in or on aquatic environments

Aquatic (album), 1994 album by the Australian experimental jazz trio, The Necks

Aquatics, another name for water sports


Creosote is a category of carbonaceous chemicals formed by the distillation of various tars and pyrolysis of plant-derived material, such as wood or fossil fuel. They are typically used as preservatives or antiseptics.Some creosote types were used historically as a treatment for components of seagoing and outdoor wood structures to prevent rot (e.g., bridgework and railroad ties, see image). Samples may be commonly found inside chimney flues, where the coal or wood burns under variable conditions, producing soot and tarry smoke. Creosotes are the principal chemicals responsible for the stability, scent, and flavor characteristic of smoked meat; the name is derived from Greek, Modern κρέας (kreas), meaning 'meat', and σωτήρ (sōtēr), meaning 'preserver'.The two main kinds recognized in industry are coal-tar creosote and wood-tar creosote. The coal-tar variety, having stronger and more toxic properties, has chiefly been used as a preservative for wood; coal-tar creosote was also formerly used as an escharotic, to burn malignant skin tissue, and in dentistry, to prevent necrosis, before its carcinogenic properties became known. The wood-tar variety has been used for meat preservation, ship treatment, and such medical purposes as an anaesthetic, antiseptic, astringent, expectorant, and laxative, though these have mostly been replaced by modern formulations.Varieties of creosote have also been made from both oil shale and petroleum, and are known as oil-tar creosote when derived from oil tar, and as water-gas-tar creosote when derived from the tar of water gas. Creosote also has been made from pre-coal formations such as lignite, yielding lignite-tar creosote, and peat, yielding peat-tar creosote.

Enallagma cyathigerum

Enallagma cyathigerum (common blue damselfly, common bluet, or northern bluet) is a species found mainly between latitudes 40°N and 72°N. The species can reach a length of 32 to 35 mm (1.3 to 1.4 in). It is common in many different countries including Russia, Canada, United States, Europe and South Korea. Damselflies are an important link between the health of the aquatic ecosystem and its response to climate change.

Exploitation of natural resources

The exploitation of natural resources is the use of natural resources for economic growth, sometimes with a negative connotation of accompanying environmental degradation. It started to emerge on an industrial scale in the 19th century as the extraction and processing of raw materials (such as in mining, steam power, and machinery) developed much further than it had in preindustrial areas. During the 20th century, energy consumption rapidly increased. Today, about 80% of the world’s energy consumption is sustained by the extraction of fossil fuels, which consists of oil, coal and gas. Another non-renewable resource that is exploited by humans is subsoil minerals such as precious metals that are mainly used in the production of industrial commodities. Intensive agriculture is an example of a mode of production that hinders many aspects of the natural environment, for example the degradation of forests in a terrestrial ecosystem and water pollution in an aquatic ecosystem. As the world population rises and economic growth occurs, the depletion of natural resources influenced by the unsustainable extraction of raw materials becomes an increasing concern.


Ichthyoplankton (from Greek: ἰχθύς, ikhthus, "fish"; and πλαγκτός, planktos, "drifter") are the eggs and larvae of fish. They are mostly found in the sunlit zone of the water column, less than 200 metres deep, which is sometimes called the epipelagic or photic zone. Ichthyoplankton are planktonic, meaning they cannot swim effectively under their own power, but must drift with the ocean currents. Fish eggs cannot swim at all, and are unambiguously planktonic. Early stage larvae swim poorly, but later stage larvae swim better and cease to be planktonic as they grow into juveniles. Fish larvae are part of the zooplankton that eat smaller plankton, while fish eggs carry their own food supply. Both eggs and larvae are themselves eaten by larger animals.Fish can produce high numbers of eggs which are often released into the open water column. Fish eggs typically have a diameter of about 1 millimetre (0.039 in). The newly hatched young of oviparous fish are called larvae. They are usually poorly formed, carry a large yolk sac (for nourishment) and are very different in appearance from juvenile and adult specimens. The larval period in oviparous fish is relatively short (usually only several weeks), and larvae rapidly grow and change appearance and structure (a process termed metamorphosis) to become juveniles. During this transition larvae must switch from their yolk sac to feeding on zooplankton prey, a process which depends on typically inadequate zooplankton density, starving many larvae.

Ichthyoplankton can be a useful indicator of the state and health of an aquatic ecosystem. For instance, most late stage larvae in ichthyoplankton have usually been preyed on, so ichthyoplankton tends to be dominated by eggs and early stage larvae. This means that when fish, such as anchovies and sardines, are spawning, ichthyoplankton samples can reflect their spawning output and provide an

index of relative population size for the fish. Increases or decreases in the number of adult fish stocks can be detected more rapidly and sensitively by monitoring the ichthyoplankton associated with them, compared to monitoring the adults themselves. It is also usually easier and more cost effective to sample trends in egg and larva populations than to sample trends in adult fish populations.

Intermittent river

Intermittent (or temporary) rivers cease to flow every year or at least twice every five years. Such rivers drain large arid and semi-arid areas, covering approximately a third of the earth’s surface. The extent of temporary rivers is increasing, as many formerly perennial rivers are becoming temporary because of increasing water demand, particularly for irrigation. The combination of dry crusted soils and the highly erosive energy of the rain cause sediment resuspension and transport to the coastal areas. They are among the aquatic habitats most altered by human activities. During the summer even under no flow conditions the point sources are still active such as the wastewater effluents, resulting in nutrients and organic pollutants accumulating in the sediment. Sediment operates as a pollution inventory and pollutants are moved to the next basin with the first flush. Their vulnerability is intensified by the conflict between water use demand and aquatic ecosystem conservation. Advanced modelling tools have been developed to better describe intermittent flow dynamic changes such as the tempQsim model.

Landscape limnology

Landscape limnology is the spatially explicit study of lakes, streams, and wetlands as they interact with freshwater, terrestrial, and human landscapes to determine the effects of pattern on ecosystem processes across temporal and spatial scales. Limnology is the study of inland water bodies inclusive of rivers, lakes, and wetlands; landscape limnology seeks to integrate all of these ecosystem types.

The terrestrial component represents spatial hierarchies of landscape features that influence which materials, whether solutes or organisms, are transported to aquatic systems; aquatic connections represent how these materials are transported; and human activities reflect features that influence how these materials are transported as well as their quantity and temporal dynamics.

Limnetic zone

The limnetic zone is the open and well-lit area of a freestanding body of fresh water, such as a lake or pond. Not included in this area is the littoral zone, which is the shallow, near-shore area of the water body. Together, these two zones comprise the photic zone.

There are two main sources of oxygen to the photic zone: atmospheric mixing and photosynthesis. Unlike the profundal zone, the limnetic zone is the layer that receives sufficient sunlight, allowing for photosynthesis. For this reason, it is often simply referred to as the photic zone. The limnetic zone is the most photosynthetically-active zone of a lake since it is the primary habitat for planktonic species. Because phytoplankton populations are densest here, it is the zone most heavily responsible for oxygen production within the aquatic ecosystem.Limnetic communities are quite complex. Zooplankton populations often consist of copepods, cladocerans, and rotifers occurring in the open water of lakes. Most limnetic communities will consist of one dominant species of copepod, one dominant cladoceran, and one dominant rotifer. Zooplankters are able to move more freely through the limnetic zone than in the littoral zone, both vertically and horizontally. This is because the bottom of a lake is richer in debris and substrates that provide habitat niches. A limnetic zooplankton population will usually consist of two to four species, each in a different genus.In addition to zooplankton, organisms in the limnetic zone include insects and fish. Many species of freshwater fish live in the limnetic zone because of the abundance of food, though these species often transition to the littoral zone as well.


Limnology ( lim-NOL-ə-jee; from Greek λίμνη, limne, "lake" and λόγος, logos, "knowledge"), is the study of inland aquatic ecosystems.

The study of limnology includes aspects of the biological, chemical, physical, and geological characteristics and functions of inland waters (running and standing waters, fresh and saline, natural or man-made). This includes the study of lakes, reservoirs, ponds, rivers, springs, streams, wetlands, and groundwater. A more recent sub-discipline of limnology, termed landscape limnology, studies, manages, and seeks to conserve these ecosystems using a landscape perspective, by explicitly examining connections between an aquatic ecosystem and its watershed. Recently, the need to understand global inland waters as part of the Earth System created a sub-discipline called global limnology. This approach considers processes in inland waters on a global scale, like the role of inland aquatic ecosystems in global biogeochemical cycles.Limnology is closely related to aquatic ecology and hydrobiology, which study aquatic organisms and their interactions with the abiotic (non-living) environment. While limnology has substantial overlap with freshwater-focused disciplines (e.g., freshwater biology), it also includes the study of inland salt lakes.

Loagan Bunut National Park

The Loagan Bunut National Park (Malay: Taman Negara Loagan Bunut) is a national park located in Miri Division, Sarawak, Malaysia, on the Borneo island. The park was named after the Loagan Bunut lake nearby, which is connected to Sungai Bunut (sungai is Malay for river), Sungai Baram and Sungai Tinjar. This park occupies a space of 100 km2 (39 sq mi) and is well known for its rich biodiversity and unique aquatic ecosystem.The national park was gazetted on January 1, 1990 and it was opened to public on August 29, 1991.


Macrobenthos consists of the organisms that live at the bottom of a water column and are visible to the naked eye. In some classification schemes, these organisms are larger than 1 mm; in another, the smallest dimension must be at least 0.5 mm. They include polychaete worms, pelecypods, anthozoans, echinoderms, sponges, ascidians, crustaceans.

A visual examination of macroorganisms at the bottom of an aquatic ecosystem can be a good indicator of water quality.

Macroinvertebrate Community Index

Macroinvertebrate Community Index (MCI) is an index used in New Zealand to measure the water quality of fresh water streams. The presence or lack of macroinvertebrates such as insects, worms and snails in a river or stream can give a biological indicator on the health of that waterway. The MCI assigns a number to each species of macroinvertebrate based on the sensitivity of that species to pollution. The index then calculates an average score. A higher score on the MCI generally indicates a more healthy stream.The MCI (Macroinvertebrate Community Index) relies on an allocation of scores to freshwater macroinvertebrates based on their pollution tolerances. Freshwater macroinvertebrates found in pristine conditions would score higher than those found in polluted areas. MCI values can be calculated using macroinvertebrate presence-absence data using this equation:MCI = [(site score)/(# of scoring taxa)]*20

Previous water quality assessments have relied on both chemical and habitat analysis, however, these methods have been proven to be insufficient due to pollution from nonpoint sources. Species living in an aquatic environment may be the best natural indicator of environmental quality and reveal the effects of any habitat alteration or pollution, and have proved to respond to a wide range of stressors such as sedimentation, urbanization, agricultural practices and forest harvesting effects. Any changes that may occur in macroinvertebrate communities that lead to a reduction in diversity increase the dominance of pollution-tolerant invertebrates, such as oligochaetes and chironomids. Thus, a lack of species diversity and low biotic index scores of inhabitant macroinvertebrates may be an indicator of poor water quality. The risk of water quality degradation is the greatest in low-elevation areas, where high intensity agriculture and urban development are the dominant land uses.Macroinvertebrate communities are the preferred indicators of aquatic ecosystem health because they are very easy to both collect and identify, and have short life spans, thus responding very quickly to changes in their environment. The MCI methods of utilizing macroinvertebrate communities to assess the overall health of an aquatic environment continues to be the most reliable, applicable, and widely acclaimed method around the world.Variations on the MCI

In addition to the MCI indexed defined above, there are also two other variations of the MCI. The QMCI (Quantitative Macroinvertebrate Community Index) and the SQMCI (Semi-Quantitative Macroinvertebrate Community Index). Both MCI and QMCI are widely used in countries like New Zealand. The combination of widespread use and good performance of the MCI and the QMCI in detecting water quality in aquatic ecosystems has sparked interest in further refinement of the methods in New Zealand. The QMCI, just like the MCI, was initially designed to evaluate the organic enrichment in aquatic ecosystems. The third index, the SQMCI, was created to reduce sampling and processing efforts required for the QMCI. The SQMCI will respond in a similar matter to the QMCI in community dominance, however, will require fewer samples to achieve the same precision. The SQMCI gives a comparative appraisal to the QMCI with under 40% of the exertion, in circumstances that macroinvertebrate densities are not required. This diminishes expenses and also enhances the logical solidness of biomonitoring projects. Both the QMCI and SQMCI are similar to the MCI in the way that they are graded on a 1 (extremely tolerant) to 10 (highly intolerant) scale. However, they differ in the way that MCI is calculated using presence-absence data whereas QMCI uses quantitative or percentage data. Having a qualitative, quantitative, and semi-quantitative version of the same index has raised some questions as to if this is a good thing or not. All three indexes have the same purpose, which is to measure the quality of an aquatic ecosystem, however, there are no clear recommendations about when each one is most appropriate to be used. In a study conducted on 88 rivers, Searsbrook et al. (2000) concluded MCI is more useful than the QMCI for recognizing changes in stream water quality over time. Having three forms of a similar index may prompt to various conclusions and also opens the route for specific utilization of either file to give bias to a specific position or position taken by a specialist. Consistency on the different versions of MCI have not yet been formally measured despite the communication that has been made to the public, managers and politicians.QMCI values can be calculated using:

QMCI = ∑_(i=1)^(i=s)▒(n_i*a_i)/N

SQMCI values can be calculated similar to QMCI except that coded abundances are substituted for actual counts. Example:

SQMCI = ∑_(i=1)^(i=s)▒(n_i*a_i)/N

Factors Influencing MCI

There are several factors which can affect the data acquisition of MCI when assessing the water quality of an aquatic ecosystem. Hard-bottom and Soft-bottom channels can often yield different results and many researchers will use two different versions of the MCI. For example, in a study by Stark & Mallard (2007) they discuss that hard and soft bottom channels have separate versions of the MCI and the two versions can not be combined into one data set because of the differences in taxa and tolerance values.Spatial variability is also of interest in terms of affecting the data acquired through MCI. Sites which are progressively down stream often tend to yield a lower MCI value. There may also be confounding influences between riffles, runs, or pools with a single stream reach.

Depth and velocity have also been raised as a concern with regards to effecting results, however Stark (1993) investigated the influences of the sampling method, water depth, current velocity and substratum on the results and found that both MCI and QMCI are independent of depth, velocity, and substratum from macroinvertebrate samples collected from stony riffles. This finding is an advantage for the assessment of water pollution.

There have been several studies conducted on seasonal variability, which has been considered the main influential factor on the assessment of water quality. It has been concluded that all models should test data that has been collected in the season as the reference data, which is being used.

There have been several other factors such as water temperature, invertebrate life histories and dissolved oxygen levels that have all been explained as causes of seasonal variability. Warmer seasons have biotic indices that are indicative of poorer stream health. Warmer seasons such as summer, would have increased temperatures therefore increasing water temperature and decreasing the amount of dissolved oxygen in the water making the environment less ideal to aquatic macroinvertebrates. In return, this effects the density of macroinvertebrate population and changes the results of the indices.


PCDitch is a dynamic aquatic ecosystem model used to study eutrophication effects in ditches. PCDitch models the nutrient fluxes in the water, the sediment and the vegetation, as well as the competition between different groups of vegetation. PCDitch is used both by scientists and water quality managers.

Pepsi Fruit Juice Flood

The Pepsi Fruit Juice Flood, also known as Pepsi's Fruit Juice Release, was a flood of 176,000 barrels (28 million litres; 7.4 million US gallons) of fruit and vegetable juices into the streets of Lebedyan, Russia and the Don River, caused by the collapse of a PepsiCo warehouse.On April 25, 2017, a PepsiCo warehouse's roof collapsed unexpectedly. The warehouse was located in Lebedyan, the center of Pepsi's operations in Russia, and operated by Lebedyansky. The warehouse contained storage containers housing a variety of fruit and vegetable juices. The collapse of the roof caused two injuries and sent 28 million litres (7.4 million US gallons) of juices into the streets of Lebedyan and the Don River. However, no deaths resulted from the spill.Pineapple, apricot, tangerine, grape, mango, pomegranate, apple, cherry, orange, grapefruit and tomato juices were all part of the spill. There was some concern that the juices might have damaged the aquatic ecosystem of the Don River, but water samples showed that there was no evidence of environmental damage caused by the spill.Pepsi officials apologized for the incident, offered to pay for all damages caused, and stated that they were working with local officials to determine the cause of the warehouse collapse.

Stream metabolism

Stream metabolism, also known as aquatic ecosystem metabolism in lakes, can be expressed as net ecosystem productivity (NEP), the difference between gross primary productivity (GPP) and ecosystem respiration (ER). Analogous to metabolism within an individual organism, stream metabolism represents how energy is created (primary production) and used (respiration) within an aquatic ecosystem. In net heterotrophic ecosystems, GPP:ER is <1 (ecosystem using more energy than it is creating); in net autotrophic ecosystems it is >1 (ecosystem creating more energy than it is using) (Odum 1956). A net heterotrophic ecosystem often means that allochthonous (coming from outside the ecosystem) inputs of organic matter, such as leaves or debris are needed to fuel ecosystem respiration rates, because respiration is greater than production within the ecosystem. However, it is important to note that autochthonous (coming from within the ecosystem) pathways may also remain important in heterotrophic ecosystems. A net autotrophic ecosystem, conversely, has available primary productivity (from algae, the main primary producer in aquatic ecosystems) to fuel upper trophic levels such as insects or fishes (but again, allochthonous pathways may still be important to these systems).

Stream metabolism can be influenced by a variety of factors, including physical characteristics of the stream (slope, width, depth, and speed/volume of flow), biotic characteristics of the stream (abundance and diversity of organisms ranging from bacteria to fish), light and nutrient availability to fuel primary production, water chemistry and temperature, and natural or human-caused disturbance, such as dams, removal of riparian vegetation, nutrient pollution, wildfire or flooding.

Measuring stream metabolic state is important to understand how disturbance may change the available primary productivity, and whether and how that increase or decrease in NEP influences foodweb dynamics, allochthonous/autochthonous pathways, and trophic interactions. Metabolism (encompassing both ER and GPP) must be measured rather than primary productivity alone, because simply measuring primary productivity does not indicate excess production available for higher trophic levels. One commonly used method for determining metabolic state in an aquatic system is daily changes in oxygen concentration, from which GPP, ER, and net daily metabolism can be estimated.

Disturbances can affect trophic relationships in a variety of ways, such as simplifying foodwebs, causing trophic cascades, and shifting carbon sources and major pathways of energy flow (Power et al. 1985, Power et al. 2008). Part of understanding how disturbance will impact trophic dynamics lies in understanding disturbance impacts to stream metabolism (Holtgrieve et al. 2010). For example, in Alaska streams, disturbance of the benthos by spawning salmon caused distinct changes in stream metabolism; autotrophic streams became net heterotrophic during the spawning run, then reverted to autotrophy after the spawning season (Holtgrieve and Schindler 2011). There is evidence that this seasonal disturbance impacts trophic dynamics of benthic invertebrates and in turn their vertebrate predators (Holtgrieve and Schindler 2011, Moore and Schindler 2008). Wildfire disturbance may have similar metabolic and trophic impacts in streams.

Stream pool

A stream pool, in hydrology, is a stretch of a river or stream in which the water depth is above average and the water velocity is below average.

Wildlife of Djibouti

The Wildlife of Djibouti, consisting of flora and fauna, is in a harsh landscape with forest accounting for less than one percent of the total area of the country. The flora and fauna species are most found in the northern part of the country in the ecosystem of the Day Forest National Park at an average altitude 1,500 metres (4,900 ft), including the massif Goda, with a peak of 1,783 metres (5,850 ft). It covers an area of 3.5 square kilometres (1.4 sq mi) of Juniperus procera forest, with many of the trees rising to 20 metres (66 ft) height. This forest area is the main habitat of critically endangered and endemic Djibouti francolin, and another recently noted vertebrate, Platyceps afarensis. The area also contains many species of woody and herbaceous plants, including boxwood and olive trees, which account for sixty percent of the total identified species in the country.Wildlife flora and fauna are also found in the country's wetland ecosystem which includes two large lakes, Lake Assal and Lake Abbe (only a small part of the flats of this lake are in Djibouti), and many salt pans which are flooded occasionally from the wadis and the coastal tidal wetlands. The coastal belt of Djibouti also has a diversity of marine life or aquatic ecosystem, including coral reefs.According to the country profile related to biodiversity of wildlife in Djibouti, the country contains some 820 species of plants, 493 species of invertebrates, 455 species of fish, 40 species of reptiles, 3 species of amphibians, 360 species of birds and 66 species of mammals. Wildlife of Djibouti is also listed as part of Horn of Africa biodiversity hotspot and the Red Sea and Gulf of Aden coral reef hotspot.


Xenophagy (Greek "strange" + "eating") and allotrophy (Greek "other" + "nutrient") are changes in established patterns of biological consumption, by individuals or groups.

• In entomology, xenophagy is a categorical change in diet, such as an herbivore becoming carnivorous, a predator becoming necrophagous, a coprophage becoming necrophagous or carnivorous, or a reversal of such changes. Allotrophy is a less extreme change in diet, such as in the case of the seven-spot ladybird, which can diversify a diet of aphids to sometimes include pollen. There are several apparent cases of allotrophy in Israeli Longitarsus beetles.• In microbiology, xenophagy is the process by which a cell directs autophagy against pathogens, as reflected in the study of antiviral defenses. Cellular xenophagy is an innate component of immune responses, though the general importance of xenophagy is not yet certain.• In ecology, allotrophy is also reflected in eutrophication, being a change in nutrient source such as an aquatic ecosystem that starts receiving new nutrients from drainage of the surrounding land.

Aquatic ecosystems
Food webs
Example webs
Ecology: Modelling ecosystems: Other components
Groups of organisms in aquatic ecosystems
Classification systems
Ponds, Pools, and Puddles

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