Editing Fen (section)

=== Bog–rich-fen gradient ===
Bogs and fens can be thought of as two ecosystems on a gradient from poor to rich, with bogs at the poor end, extremely rich fens at the rich end, and poor fens in between.<ref>{{Cite journal|last1=Szumigalski|first1=Anthony R.|last2=Bayley|first2=Suzanne E.|date=December 1996 |title=Net above-ground primary production along a bog-rich fen gradient in Central Alberta, Canada |journal=Wetlands|volume=16|issue=4|pages=467–476|doi=10.1007/bf03161336|bibcode=1996Wetl...16..467S |s2cid=24686070|issn=0277-5212}}</ref> In this context, "rich" and "poor" refer to the species richness, or how [[Biodiversity|biodiverse]] a fen or bog is.<ref name=":6" /> The richness of these species is strongly influenced by pH and concentrations of calcium and bicarbonate. These factors assist in identifying where along the gradient a particular fen falls.<ref>{{Cite journal|last=Bourbonniere|first=Richard A.|date=January 2009 |title=Review of Water Chemistry Research in Natural and Disturbed Peatlands |journal=Canadian Water Resources Journal|language=en|volume=34|issue=4|pages=393–414|doi=10.4296/cwrj3404393|bibcode=2009CaWRJ..34..393B |s2cid=98764979|issn=0701-1784}}</ref> In general, rich fens are [[minerotrophic]], or dependent on mineral-rich groundwater, while bogs are [[ombrotrophic]], or dependent on precipitation for water and nutrients.<ref name=":6" /> Poor fens fall between these two.

==== Rich fens ====
[[File:Extreme Rich Fen.jpg|thumb|upright=1.3|Small extreme rich fen in southwestern Minnesota. The white flowers, ''[[Parnassia glauca]]'', are a fen indicator species in Minnesota.]]
Rich fens are strongly minerotrophic; that is, a large proportion of their water comes from mineral-rich ground or surface water. Fens that are more distant from surface waters such as rivers and lakes, however, are more rich than fens that are connected.<ref name=":3" /> This water is dominated by calcium and bicarbonate, resulting in a slightly acidic to slightly basic pH characteristic of rich fens.<ref name=":6" /><ref name=":14">{{cite book |last1=Zoltai |first1=S. C. |last2=Vitt |first2=D. H. |chapter=Canadian wetlands: Environmental gradients and classification |date=1995 |doi=10.1007/978-94-011-0427-2_11 |editor=C. Max Finlayson |editor2=A. G. van der Valk |title=Classification and Inventory of the World's Wetlands |pages=131–137 |location=Dordrecht |publisher=Springer Netherlands |isbn=978-94-010-4190-4}}</ref> These conditions promote high biodiversity. Within rich fens, there is a large amount of variability. The richest fens are the extreme rich (marl) fens, where marl deposits are often build up.<ref name=":10" /> These are often pH 7 or greater.<ref name=":6" /> Rich and intermediate rich fens are generally neutral to slightly acidic, with a pH of approximately 7 to 5. Rich fens are not always very productive; at high calcium concentrations, calcium ions bind to phosphate anions, reducing the availability of phosphorus and decreasing primary production.<ref name=":23"/><ref name=":6" /> Rich bogs with limited primary production can stabilize with the accumulation of mosses and [[mycorrhiza]], which promote phosphorus cycling and can support the growth of new vegetation and bacteria.<ref name=":5" /> Brown mosses (family ''[[Amblystegiaceae]]'') and sedges (genus ''[[Carex]]'') are the dominant vegetation.<ref name=":14" /> However, an accumulation of mosses such as ''[[Sphagnum]]'' can lead to the acidification of the rich fen, potentially converting it into a poor fen.<ref>{{Cite web|title=Poor Fen - Michigan Natural Features Inventory|url=https://mnfi.anr.msu.edu/communities/description/10662/Poor-Fen|access-date=2021-05-08|website=mnfi.anr.msu.edu|archive-date=2021-05-08|archive-url=https://web.archive.org/web/20210508211654/https://mnfi.anr.msu.edu/communities/description/10662/Poor-Fen|url-status=live}}</ref> Compared to poor fens, rich fens have higher concentrations of bicarbonate, base cations (Na<sup>+</sup>, Ca<sup>2+</sup>, K<sup>+</sup>, Mg<sup>2+</sup>), and [[sulfate]].<ref name=":11" />

==== Poor fens ====
Poor fens are, in many ways, an intermediate between rich fens and bogs. Hydrologically, they are more similar to rich fens than to bogs, but regarding vegetation composition and chemistry, they are more similar to bogs than rich fens.<ref name=":14" /> They are much more acidic than their rich counterparts, with a pH of approximately 5.5 to 4.<ref name=":6" /> Peat in poor fens tends to be thicker than that of rich fens, which cuts off vegetation access to the mineral-rich soil underneath.<ref name=":23"/> In addition, the thicker peat reduces the influence of mineral-rich groundwater that buffers the pH.<ref name=":23"/> This makes the fen more ombrotrophic, or dependent on nutrient-poor precipitation for its water and nutrients.<ref name=":23"/> Poor fens may also form in areas where the groundwater supplying the fen flows through sediments that don't dissolve well or have low buffering capacity when dissolved.<ref name=":10" /> Species richness tends to be lower than that of rich fens but higher than that of bogs.<ref name=":6" /> Poor fens, like bogs, are dominated by ''Sphagnum'' mosses, which acidify the fen and decrease nutrient availability.<ref name=":14" />