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What is Fen?

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Fen is one of the wetlands types and wetlands are considered as one of the most important and diverse ecosystems. They serve an important role in feeding and nesting sites for various species and also one-third of the rare and endangered species of the Earth depends upon the wetlands directly or indirectly which makes them more important. In this article, we will learn about one of the wetland types i.e. Fens, which are biological hotspots where peat formation, as well as water presence throughout the year, can be seen. This topic plays an important role in Geology and Environmental Studies.

The Ramsar Convention of 1971 in Iran is related to wetlands and under the text of the Convention (Article 1.1), wetlands are defined as: “areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres”. According to the estimates of UNEP-World Conservation Monitoring Centre, roughly 6% of the Earth’s land surface are wetlands of which 2% are lakes, 30% bogs, 26% fens, 20% swamps, and 15% floodplains. 

Fen Meaning

It is derived from the term "Fenn" which was an old English word which supposed to have a proto-German origin. It is one of the types of wetlands and wetlands work as transitional zones between the terrestrial and aquatic ecosystems. It is a type of wetland where peat formation can be seen and which is fed by both grounds as well surface waters which are rich in minerals. Besides fens, bogs are also called peat formulating wetlands and both these are also known as mires. Water chemistry of fens is considered to be its unique feature which leads to having more minerals as well as more pH level as compared to bogs. It also consists of grasses, wildflowers, sedges, etc. The term "carr" is also associated with fens wetlands and is a type of fen where this wetland supports trees.


Some of the standard definitions are mentioned below.

  • The Environmental Protection Agency defines fens as "peat-forming wetlands that receive nutrients from sources other than precipitation" (EPA 2008) and as "freshwater peat-forming wetlands covered mostly by grasses, sedges, reeds, and wildflowers" (EPA 2004).

  • The National Wetlands Research Center of the U.S. Geological Survey defines fen as "waterlogged, spongy ground containing alkaline decaying vegetation characterized by reeds, that develops into peat" (NWRC 2007).

  • According to 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."


The various features of fens are mentioned below.

  • The water level in fens wetlands is present throughout the year. It fluctuates very little because the water table here is high. The stability of water in this type of wetland is stable.

  • The water should not be drained along with the land close to it in order to prevent the area from drying and prevention of over weeds.

  • A low level of oxygen leads to the decaying of the dead plants slowly which leads to peat formation in the fen.

  • Due to the accumulation of peat in fens, the input of groundwater can be reduced or cut off which leads to making fens ombrotrophic. Fens can become more acidic in this way and can transit to big wetlands as well.

  • Though they can be found all over the world most of the fens wetlands are found in the Northern Hemisphere especially in between mid to high latitudes.

  • The composition of species can differ due to change in the chemistry of water but mostly they are dominated by sedges & mosses.

Types of Fens

These can be of the following types:

  • One of the most common types of fens is sloping fens which are formed at the base of the mountains or hills. Because of the slope water discharges here from the landscape lying above. In the below diagram, the green area denotes the area of fen. 

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  • Another type of fens is basin fens which are used to originate as lakes or ponds as these are consist of partially decomposed plants. Generally, these are flat and occur at the margin of open water. As we can see in the diagram, water is being received from both the sources say ground and surface and when it is stable, floating peat mats can be seen.

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  • Another type is spring fens which are local points of groundwater discharge and these points support small fens which are generally and mostly tens of metres in terms of diameter. It is considered a topographic feature of fen meadow.

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  • Lava discontinuity is one of another type that is generally found where lava beds are lying on each other. These types of fens are found on very steep slopes and also have peat and some sort of vegetation. 

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We have learned about fen meaning and its features. The importance of fens are mentioned below:

  • Fens are one of the most important types of wetlands.

  • It contains a variety of flora and fauna. 

  • It supports that vegetation that flourishes in fertile swamps as well as in bogs along with various animal species as well.

  • It helps in the prevention of overflowing of the rivers by preventing sediments to flow into the rivers. 

  • They work as groundwater discharge sites.

  • They work as important shallow aquifers indicators.

  • These wetlands serve as a home to black mad fish which is considered a rare species.

  • They are an important biodiverse ecosystem that serves as a habitat for endangered as well as rare species.

Flora & Fauna

Due to the high level of mineral content and high pH level, it supports more diversity than bogs as it receives more water from the ground and surface. 

  • According to the EPA, Whereas bogs are dominated by mosses, fens often are covered by rushes, sedges, grasses, and wildflowers. Some fens have parallel ridges of vegetation that form perpendicular to the downslope flow of the water, with less productive hollows separating these ridges (EPA 2008). 

  • The examples of flora species found in pools are Beaked sedge, Whorl grass, Needle spike-rush, Sweet grasses, Common reed, Swamp meadow grass, and in typical fens are Flat sedge, Blysmus compressus, Great fen sedge, Lesser tufted sedge, Lesser pond sedge, Davall's sedge, Dioecious sedge, Brown sedge, Tufted sedge, Slender sedge, Flea sedge, Greater pond sedge, Common spike-rush, etc whereas in fen carr are Narrow small-reed; Calamagrostis stricta Purple small-reed, Tussock sedge, Cyperus sedge, Wood club rush, etc.

  • If we talk about fauna, then insects and insects eating species are common here like mosquitoes and horseflies, etc. along with insect-eating birds, as well as insect-eating mammals like shrews, voles, and muskrats, etc.


Thus, to sum in the end we can say that fens are one of the important types of wetlands that serve as transitional zones and 26% of the total wetlands are fens. Here, peat formation can be seen and consists of water content from both the ground as well as a surface which leads to having high mineral content and high pH level. This type of wetlands is also similar to bogs but there are many diverse wetlands as compared to bogs and if the pH level of these wetlands gets lowers it can be transitioned into bogs as well. It supports various kinds of flora and fauna as well. In this article, we have covered what fen, fen meaning, features, importance, and other related aspects which will help to understand one of the types of wetlands.

FAQ (Frequently Asked Questions)

Question1. What do You Mean by Fens Wetlands?

Answer. Fens are a kind of wetlands that contain peat formation and contains sufficient water with low pH value that is received from the groundwater as well as surface water which are mineral-rich in nature. It is less acidic due to it consists of more nutrients than bogs. These types of wetlands are an important ecosystem that supports various flora and fauna and provides a home to a number of endangered as well as rare species.

Question2. What is the difference between Fens and Bogs?

Answer. Fens and bogs are important types of wetlands. Most of the water in fens came from ground and surfaces whereas in bogs water came from rain and snow. This factor leads to create a difference in the pH level of these two wetlands. The fens have a high pH value whereas bogs have a low. The former is considered less acidic than the latter and thus contains more nutrients as well. The fens have more flora and fauna diversity than bogs. They both are called mires and peat formation can be seen in both the wetlands.

Question3. Why are Fens Important?

Answer. Fens are one of the important types of wetlands that contain a variety of flora and fauna. It supports that vegetation that flourishes in fertile swamps as well as in bogs along with various fauna species. It helps in the prevention of rivers overflowing by preventing sediments to flow into them. They work as groundwater discharge sites and as important shallow aquifers indicators. This ecosystem serves as a home to black mad fish which is considered a rare species. Not only this, these are a biodiverse ecosystem that serves as an important habitat of endangered as well as rare species.