Editing Fen (section)

== Definition ==
Rigidly defining types of wetlands, including fens, is difficult for a number of reasons. First, wetlands are diverse and varied [[ecosystem]]s that are not easily categorized according to inflexible definitions. They are often described as a transition between [[Terrestrial ecosystem|terrestrial]] and [[Aquatic ecosystem|aquatic]] ecosystems with characteristics of both.<ref name=":02"/> This makes it difficult to delineate the exact extent of a wetland. Second, terms used to describe wetland types vary greatly by region.<ref name=":22"/> The term ''[[bayou]],'' for example, describes a type of wetland, but its use is generally limited to the southern United States.<ref>{{Cite web|title=bayou|url=https://dictionary.cambridge.org/us/dictionary/english/bayou|access-date=2021-02-23|website=dictionary.cambridge.org|language=en-US|archive-date=2019-03-29|archive-url=https://web.archive.org/web/20190329085644/https://dictionary.cambridge.org/us/dictionary/english/bayou|url-status=live}}</ref> Third, different languages use different terms to describe types of wetlands. For instance, in Russian, there is no equivalent word for the term ''[[swamp]]'' as it is typically used in North America.<ref name=":02"/> The result is a large number of [[wetland classification]] systems that each define wetlands and wetland types in their own way.<ref name=":22"/> However, many classification systems include four broad categories that most wetlands fall into: [[marsh]], swamp, [[bog]], and fen.<ref name=":22"/> While classification systems differ on the exact criteria that define a fen, there are common characteristics that describe fens generally and imprecisely. A general definition provided by the textbook ''Wetlands'' describes a fen as "a peat-accumulating wetland that receives some drainage from surrounding mineral soil and usually supports marsh like vegetation."<ref name=":02"/>

Three examples are presented below to illustrate more specific definitions for the term ''fen''.

=== Canadian Wetland Classification System definition ===
In the Canadian Wetland Classification System, fens are defined by six characteristics:<ref name=":1">{{Cite book|last=Canada Committee on Ecological Land Classification. National Wetlands Working Group|url=https://www.worldcat.org/oclc/43464321|title=The Canadian wetland classification system|date=1997|publisher=Wetlands Research Branch, University of Waterloo|others=Barry G. Warner, C. D. A. Rubec|isbn=0-662-25857-6|edition=2nd|location=Waterloo, Ont.|oclc=43464321|access-date=2021-03-20|archive-date=2022-01-12|archive-url=https://web.archive.org/web/20220112234321/https://www.worldcat.org/title/canadian-wetland-classification-system/oclc/43464321|url-status=live}}</ref>

# Peat is present.
# The surface of the wetland is level with the [[water table]]. Water flows on the surface and through the subsurface of the wetland.
# The water table fluctuates. It may be at the surface of the wetland or a few centimeters above or below it.
# The wetland receives a significant amount of its water from mineral-rich groundwater or surface water.<ref name=":1"/>
# Decomposed [[Cyperaceae|sedges]] or brown moss peat are present.
# The vegetation is predominantly [[graminoid]]s and shrubs.

=== ''Wetland Ecology: Principles and Conservation'' (Keddy) definition ===
In the textbook ''Wetland Ecology: Principles and Conservation'', Paul A. Keddy offers a somewhat simpler definition of a fen as "a wetland that is usually dominated by sedges and grasses rooted in shallow peat, often with considerable groundwater movement, and with pH greater than 6."<ref name=":22"/> This definition differentiates fens from swamps and marshes by the presence of peat.

=== ''The Biology of Peatlands'' (Rydin) definition ===
In ''The Biology of Peatlands'' fens are defined by the following criteria:<ref name=":62"/>

# The wetland is not flooded by lake or stream water.
# Woody vegetation 2 meters or taller is absent or canopy cover is less than 25%.
# The wetland is [[minerotrophic]] (it receives its nutrients from mineral-rich groundwater).

A further distinction is made between open and wooded fens, where open fens have canopy cover less than 10% and wooded fens have 10–25% canopy cover. If tall shrubs or trees dominate, the wetland is instead classified as a wooded bog or [[Freshwater swamp forest|swamp forest]], depending on other criteria.