Freshwater ecosystem.
Freshwater ecosystem.

Freshwater ecosystems are a subset of Earth's aquatic ecosystems. They include lakes, ponds, rivers, streams, springs, bogs, and wetlands.[1] They can be contrasted with marine ecosystems, which have a larger salt content. Freshwater habitats can be classified by different factors, including temperature, light penetration, nutrients, and vegetation. There are three basic types of freshwater ecosystems: Lentic (slow moving water, including pools, ponds, and lakes), lotic (faster moving water, for example streams and rivers) and wetlands (areas where the soil is saturated or inundated for at least part of the time).[2][1] Freshwater ecosystems contain 41% of the world's known fish species.[3]

Freshwater ecosystems have undergone substantial transformations over time, which has impacted various characteristics of the ecosystems.[4] Original attempts to understand and monitor freshwater ecosystems were spurred on by threats to human health (for example cholera outbreaks due to sewage contamination).[5] Early monitoring focused on chemical indicators, then bacteria, and finally algae, fungi and protozoa. A new type of monitoring involves quantifying differing groups of organisms (macroinvertebrates, macrophytes and fish) and measuring the stream conditions associated with them.[6]

Threats to freshwater biodiversity include overexploitation, water pollution, flow modification, destruction or degradation of habitat, and invasion by exotic species.[7] Climate change is putting further pressure on these ecosystems because water temperatures have already increased by about 1°C, and there have been significant declines in ice coverage which have caused subsequent ecosystem stresses.[8]


There are three basic types of freshwater ecosystems: Lentic (slow moving water, including pools, ponds, and lakes), lotic (faster moving water, for example streams and rivers) and wetlands (areas where the soil is saturated or inundated for at least part of the time). Limnology (and its branch freshwater biology) is a study about freshwater ecosystems.[1]

Lentic ecosystems

The three primary zones of a lake
The three primary zones of a lake

A lake ecosystem or lacustrine ecosystem includes biotic (living) plants, animals and micro-organisms, as well as abiotic (non-living) physical and chemical interactions.[9] Lake ecosystems are a prime example of lentic ecosystems (lentic refers to stationary or relatively still freshwater, from the Latin lentus, which means "sluggish"), which include ponds, lakes and wetlands, and much of this article applies to lentic ecosystems in general. Lentic ecosystems can be compared with lotic ecosystems, which involve flowing terrestrial waters such as rivers and streams. Together, these two ecosystems are examples of freshwater ecosystems.

Lentic systems are diverse, ranging from a small, temporary rainwater pool a few inches deep to Lake Baikal, which has a maximum depth of 1642 m.[10] The general distinction between pools/ponds and lakes is vague, but Brown[9] states that ponds and pools have their entire bottom surfaces exposed to light, while lakes do not. In addition, some lakes become seasonally stratified. Ponds and pools have two regions: the pelagic open water zone, and the benthic zone, which comprises the bottom and shore regions. Since lakes have deep bottom regions not exposed to light, these systems have an additional zone, the profundal.[11] These three areas can have very different abiotic conditions and, hence, host species that are specifically adapted to live there.[9]

Lotic ecosystems

This stream operating together with its environment can be thought of as forming a river ecosystem.
This stream operating together with its environment can be thought of as forming a river ecosystem.

River ecosystems are flowing waters that drain the landscape, and include the biotic (living) interactions amongst plants, animals and micro-organisms, as well as abiotic (nonliving) physical and chemical interactions of its many parts.[12][13] River ecosystems are part of larger watershed networks or catchments, where smaller headwater streams drain into mid-size streams, which progressively drain into larger river networks. 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.[14] 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 the loss of deltaic wetlands.[15]

River ecosystems are prime examples of lotic ecosystems. Lotic refers to flowing water, from the Latin lotus, meaning washed. Lotic waters range from springs only a few centimeters wide to major rivers kilometers in width.[16] Much of this article applies to lotic ecosystems in general, including related lotic systems such as streams and springs. Lotic ecosystems can be contrasted with lentic ecosystems, which involve relatively still terrestrial waters such as lakes, ponds, and wetlands. Together, these two ecosystems form the more general study area of freshwater or aquatic ecology.


Wetlands, or simply a wetland, is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils.[17] The primary factor that distinguishes wetlands from terrestrial land forms or water bodies is the characteristic vegetation of aquatic plants, adapted to the unique anoxic hydric soils.[18] Wetlands are considered among the most biologically diverse of all ecosystems, serving as home to a wide range of plant and animal species. Methods for assessing wetland functions, wetland ecological health, and general wetland condition have been developed for many regions of the world. These methods have contributed to wetland conservation partly by raising public awareness of the functions some wetlands provide.[19]

Wetlands occur naturally on every continent.[20] The water in wetlands is either freshwater, brackish or saltwater.[18] The main wetland types are classified based on the dominant plants and/or the source of the water. For example, marshes are wetlands dominated by emergent vegetation such as reeds, cattails and sedges; swamps are ones dominated by woody vegetation such as trees and shrubs (although reed swamps in Europe are dominated by reeds, not trees). Examples of wetlands classified by their sources of water include tidal wetlands (oceanic tides), estuaries (mixed tidal and river waters), floodplains (excess water from overflowed rivers or lakes), springs, seeps and fens (groundwater discharge out onto the surface), and bogs and vernal ponds (rainfall or meltwater).[17][21] Some wetlands have multiple types of plants and are fed by multiple sources of water, making them difficult to classify. The world's largest wetlands include the Amazon River basin, the West Siberian Plain,[22] the Pantanal in South America,[23] and the Sundarbans in the Ganges-Brahmaputra delta.[24]

Wetlands contribute a number of functions that benefit people. These are called ecosystem services and include water purification, groundwater replenishment, stabilization of shorelines and storm protection, water storage and flood control, processing of carbon (carbon fixation, decomposition and sequestration), other nutrients and pollutants, and support of plants and animals.[25] Wetlands are reservoirs of biodiversity and provide wetland products. According to the UN Millennium Ecosystem Assessment, wetlands are more affected by environmental degradation than any other ecosystem on Earth.[26] Wetlands can be important sources and sinks of carbon, depending on the specific wetland, and thus will play an important role in climate change and need to be considered in attempts to mitigate climate change. However, some wetlands are a significant source of methane emissions and some are also emitters of nitrous oxide.[27][28] Constructed wetlands are designed and built to treat municipal and industrial wastewater as well as to divert stormwater runoff. Constructed wetlands may also play a role in water-sensitive urban design.


Further information: Lake ecosystem § Human impacts, River ecosystem § Human impacts, and Ecosystem § Human interactions with ecosystems


Five broad threats to freshwater biodiversity include overexploitation, water pollution, flow modification, destruction or degradation of habitat, and invasion by exotic species.[7] Recent extinction trends can be attributed largely to sedimentation, stream fragmentation, chemical and organic pollutants, dams, and invasive species.[29] Common chemical stresses on freshwater ecosystem health include acidification, eutrophication and copper and pesticide contamination.[30]

Freshwater biodiversity faces many threats.[31] The World Wide Fund for Nature's Living Planet Index noted an 83% decline in the populations of freshwater vertebrates between 1970 and 2014.[32] These declines continue to outpace contemporaneous declines in marine or terrestrial systems. The causes of these declines are related to:[33][31]

  1. A rapidly changing climate
  2. Online wildlife trade and invasive species
  3. Infectious disease
  4. Toxic algae blooms
  5. Hydropower damming and fragmenting of half the world's rivers
  6. Emerging contaminants, such as hormones
  7. Engineered nanomaterials
  8. Microplastic pollution
  9. Light and noise interference
  10. Saltier coastal freshwaters due to sea level rise
  11. Calcium concentrations falling below the needs of some freshwater organisms
  12. The additive—and possibly synergistic—effects of these threats

Extinction of freshwater fauna

Over 123 freshwater fauna species have gone extinct in North America since 1900. Of North American freshwater species, an estimated 48.5% of mussels, 22.8% of gastropods, 32.7% of crayfishes, 25.9% of amphibians, and 21.2% of fish are either endangered or threatened.[29] Extinction rates of many species may increase severely into the next century because of invasive species, loss of keystone species, and species which are already functionally extinct (e.g., species which are not reproducing).[29] Even using conservative estimates, freshwater fish extinction rates in North America are 877 times higher than background extinction rates (1 in 3,000,000 years).[34] Projected extinction rates for freshwater animals are around five times greater than for land animals, and are comparable to the rates for rainforest communities.[29] Given the dire state of freshwater biodiversity, a team of scientists and practitioners from around the globe recently drafted an Emergency Action plan to try and restore freshwater biodiversity.[35]

Current freshwater biomonitoring techniques focus primarily on community structure, but some programs measure functional indicators like biochemical (or biological) oxygen demand, sediment oxygen demand, and dissolved oxygen.[6] Macroinvertebrate community structure is commonly monitored because of the diverse taxonomy, ease of collection, sensitivity to a range of stressors, and overall value to the ecosystem.[36] Additionally, algal community structure (often using diatoms) is measured in biomonitoring programs. Algae are also taxonomically diverse, easily collected, sensitive to a range of stressors, and overall valuable to the ecosystem.[37] Algae grow very quickly and communities may represent fast changes in environmental conditions.[37]

In addition to community structure, responses to freshwater stressors are investigated by experimental studies that measure organism behavioural changes, altered rates of growth, reproduction or mortality.[6] Experimental results on single species under controlled conditions may not always reflect natural conditions and multi-species communities.[6]

The use of reference sites is common when defining the idealized "health" of a freshwater ecosystem. Reference sites can be selected spatially by choosing sites with minimal impacts from human disturbance and influence.[6] However, reference conditions may also be established temporally by using preserved indicators such as diatom valves, macrophyte pollen, insect chitin and fish scales can be used to determine conditions prior to large scale human disturbance.[6] These temporal reference conditions are often easier to reconstruct in standing water than moving water because stable sediments can better preserve biological indicator materials.

Climate change

See also: Effects of climate change on the water cycle § Impacts on freshwater ecosystems

The effects of climate change greatly complicate and frequently exacerbate the impacts of other stressors that threaten many fish,[38] invertebrates,[39] phytoplankton,[40] and other organisms. Climate change is increasing the average temperature of water bodies, and worsening other issues such as changes in substrate composition, oxygen concentration, and other system changes that have ripple effects on the biology of the system.[8] Water temperatures have already increased by around 1°C, and significant declines in ice coverage have caused subsequent ecosystem stresses.[8]

See also


  1. ^ a b c G., Wetzel, Robert (2001). Limnology : lake and river ecosystems (3rd ed.). San Diego: Academic Press. ISBN 978-0127447605. OCLC 46393244.
  2. ^ Vaccari, David A. (8 November 2005). Environmental Biology for Engineers and Scientists. Wiley-Interscience. ISBN 0-471-74178-7.
  3. ^ Daily, Gretchen C. (1 February 1997). Nature's Services. Island Press. ISBN 1-55963-476-6.
  4. ^ Carpenter, Stephen R.; Stanley, Emily H.; Vander Zanden, M. Jake (2011). "State of the World's Freshwater Ecosystems: Physical, Chemical, and Biological Changes". Annual Review of Environment and Resources. 36 (1): 75–99. doi:10.1146/annurev-environ-021810-094524. ISSN 1543-5938.
  5. ^ Rudolfs, Willem; Falk, Lloyd L.; Ragotzkie, R. A. (1950). "Literature Review on the Occurrence and Survival of Enteric, Pathogenic, and Relative Organisms in Soil, Water, Sewage, and Sludges, and on Vegetation: I. Bacterial and Virus Diseases". Sewage and Industrial Wastes. 22 (10): 1261–1281. JSTOR 25031419.
  6. ^ a b c d e f Friberg, Nikolai; Bonada, Núria; Bradley, David C.; Dunbar, Michael J.; Edwards, Francois K.; Grey, Jonathan; Hayes, Richard B.; Hildrew, Alan G.; Lamouroux, Nicolas (2011), "Biomonitoring of Human Impacts in Freshwater Ecosystems", Advances in Ecological Research, Elsevier, pp. 1–68, doi:10.1016/b978-0-12-374794-5.00001-8, ISBN 9780123747945
  7. ^ a b Dudgeon, David; Arthington, Angela H.; Gessner, Mark O.; Kawabata, Zen-Ichiro; Knowler, Duncan J.; Lévêque, Christian; Naiman, Robert J.; Prieur-Richard, Anne-Hélène; Soto, Doris (2005-12-12). "Freshwater biodiversity: importance, threats, status and conservation challenges". Biological Reviews. 81 (2): 163–82. CiteSeerX doi:10.1017/s1464793105006950. ISSN 1464-7931. PMID 16336747. S2CID 15921269.
  8. ^ a b c Parmesan, Camille; Morecroft, Mike; Trisurat, Yongyut; et al. "Chapter 2: Terrestrial and Freshwater Ecosystems and their Services" (PDF). Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Intergovernmental Panel on Climate Change.
  9. ^ a b c Brown, A. L. (1987). Freshwater Ecology. Heinimann Educational Books, London. p. 163. ISBN 0435606220.
  10. ^ Brönmark, C.; L. A. Hansson (2005). The Biology of Lakes and Ponds. Oxford University Press, Oxford. p. 285. ISBN 0198516134.
  11. ^ Kalff, J. (2002). Limnology. Prentice Hall, Upper Saddle, NJ. p. 592. ISBN 0130337757.
  12. ^ Angelier, E. 2003. Ecology of Streams and Rivers. Science Publishers, Inc., Enfield. Pp. 215.
  13. ^ ”Biology Concepts & Connections Sixth Edition”, Campbell, Neil A. (2009), page 2, 3 and G-9. Retrieved 2010-06-14.
  14. ^ Alexander, David E. (1 May 1999). Encyclopedia of Environmental Science. Springer. ISBN 0-412-74050-8.
  15. ^ Keddy, Paul A. (2010). Wetland Ecology. Principles and Conservation. Cambridge University Press. p. 497. ISBN 978-0-521-51940-3.
  16. ^ Allan, J.D. 1995. Stream Ecology: structure and function of running waters. Chapman and Hall, London. Pp. 388.
  17. ^ a b Keddy, P.A. (2010). Wetland ecology: principles and conservation (2nd ed.). New York: Cambridge University Press. ISBN 978-0521519403. [1] Archived 2013-04-11 at the Wayback Machine
  18. ^ a b "Official page of the Ramsar Convention". Retrieved 2011-09-25.
  19. ^ Dorney, J.; Savage, R.; Adamus, P.; Tiner, R., eds. (2018). Wetland and Stream Rapid Assessments: Development, Validation, and Application. London; San Diego, CA: Academic Press. ISBN 978-0-12-805091-0. OCLC 1017607532.
  20. ^ Davidson, N.C. (2014). "How much wetland has the world lost? Long-term and recent trends in global wetland area". Marine and Freshwater Research. 65 (10): 934–941. doi:10.1071/MF14173. S2CID 85617334.
  21. ^ "US EPA". 2015-09-18. Retrieved 2011-09-25.
  22. ^ Fraser, L.; Keddy, P.A., eds. (2005). The World's Largest Wetlands: Their Ecology and Conservation. Cambridge, UK: Cambridge University Press. ISBN 978-0521834049.
  23. ^ "WWF Pantanal Programme". Retrieved 2011-09-25.
  24. ^ Giri, C.; Pengra, B.; Zhu, Z.; Singh, A.; Tieszen, L.L. (2007). "Monitoring mangrove forest dynamics of the Sundarbans in Bangladesh and India using multi-temporal satellite data from 1973 to 2000". Estuarine, Coastal and Shelf Science. 73 (1–2): 91–100. Bibcode:2007ECSS...73...91G. doi:10.1016/j.ecss.2006.12.019.
  25. ^ "Wetlands". USDA- Natural Resource Conservation Center.
  26. ^ Davidson, N.C.; D'Cruz, R. & Finlayson, C.M. (2005). Ecosystems and Human Well-being: Wetlands and Water Synthesis: a report of the Millennium Ecosystem Assessment (PDF). Washington, DC: World Resources Institute. ISBN 978-1-56973-597-8.
  27. ^ Bange, Hermann W. (2006). "Nitrous oxide and methane in European coastal waters". Estuarine, Coastal and Shelf Science. 70 (3): 361–374. Bibcode:2006ECSS...70..361B. doi:10.1016/j.ecss.2006.05.042.
  28. ^ Thompson, A. J.; Giannopoulos, G.; Pretty, J.; Baggs, E. M.; Richardson, D. J. (2012). "Biological sources and sinks of nitrous oxide and strategies to mitigate emissions". Philosophical Transactions of the Royal Society B. 367 (1593): 1157–1168. doi:10.1098/rstb.2011.0415. PMC 3306631. PMID 22451101.
  29. ^ a b c d Ricciardi, Anthony; Rasmussen, Joseph B. (1999-10-23). "Extinction Rates of North American Freshwater Fauna". Conservation Biology. 13 (5): 1220–1222. doi:10.1046/j.1523-1739.1999.98380.x. ISSN 0888-8892. S2CID 85338348.
  30. ^ Xu, F (September 2001). "Lake Ecosystem Health Assessment: Indicators and Methods". Water Research. 35 (13): 3157–3167. doi:10.1016/s0043-1354(01)00040-9. ISSN 0043-1354. PMID 11487113.
  31. ^ a b Reid, AJ; et al. (2019). "Emerging threats and persistent conservation challenges for freshwater biodiversity". Biological Reviews. 94 (3): 849–873. doi:10.1111/brv.12480. PMID 30467930.
  32. ^ "Living Planet Report 2018 | WWF". Retrieved 2019-04-09.
  33. ^ Reid, Andrea Jane; Cooke, Steven J. "Freshwater wildlife face an uncertain future". The Conversation. Retrieved 2019-04-09.
  34. ^ Burkhead, Noel M. (September 2012). "Extinction Rates in North American Freshwater Fishes, 1900–2010". BioScience. 62 (9): 798–808. doi:10.1525/bio.2012.62.9.5. ISSN 1525-3244.
  35. ^ Tickner, David; Opperman, Jeffrey J; Abell, Robin; Acreman, Mike; Arthington, Angela H; Bunn, Stuart E; Cooke, Steven J; Dalton, James; Darwall, Will; Edwards, Gavin; Harrison, Ian (2020-04-01). "Bending the Curve of Global Freshwater Biodiversity Loss: An Emergency Recovery Plan". BioScience. 70 (4): 330–342. doi:10.1093/biosci/biaa002. ISSN 0006-3568. PMC 7138689. PMID 32284631.
  36. ^ Johnson, R. K.; Wiederholm, T.; Rosenberg, D. M. (1993). Freshwater biomonitoring and benthic macroinvertebrates, 40-158. pp. 40–158.
  37. ^ a b Stevenson, R. Jan; Smol, John P. (2003), "Use of Algae in Environmental Assessments", Freshwater Algae of North America, Elsevier, pp. 775–804, doi:10.1016/b978-012741550-5/50024-6, ISBN 9780127415505
  38. ^ Arthington, Angela H.; Dulvy, Nicholas K.; Gladstone, William; Winfield, Ian J. (2016). "Fish conservation in freshwater and marine realms: status, threats and management". Aquatic Conservation: Marine and Freshwater Ecosystems. 26 (5): 838–857. doi:10.1002/aqc.2712. ISSN 1099-0755.
  39. ^ Prather, Chelse M.; Pelini, Shannon L.; Laws, Angela; Rivest, Emily; Woltz, Megan; Bloch, Christopher P.; Del Toro, Israel; Ho, Chuan-Kai; Kominoski, John; Newbold, T. A. Scott; Parsons, Sheena; Joern, A. (2012). "Invertebrates, ecosystem services and climate change: Invertebrates, ecosystems and climate change". Biological Reviews. 88 (2): 327–348. doi:10.1111/brv.12002. PMID 23217156. S2CID 23578609.
  40. ^ Winder, Monika; Sommer, Ulrich (2012). "Phytoplankton response to a changing climate". Hydrobiologia. 698 (1): 5–16. doi:10.1007/s10750-012-1149-2. ISSN 0018-8158. S2CID 16907349.