Editing Fen (section)

==== Carbon ====
Carbon from all types of wetlands, including fens, arrives mostly as [[Organic matter|organic carbon]] from either adjacent upland ecosystems or by photosynthesis in the wetland itself.<ref name=":23" /> Once in the wetland, organic carbon generally has three main fates: oxidation to CO<sub>2</sub> by [[aerobic respiration]], burial as organic matter in peat, or decomposition to [[methane]].<ref name=":23" /> In peatlands, including fens, primary production by plants is greater than decomposition, which results in the accumulation of organic matter as peat. Resident mosses usually carry out decomposition within the fen, and temperate fens are often driven by plant roots' decomposition.<ref>{{Cite journal|last1=Scheffer|first1=Robbert A.|last2=Aerts|first2=Rien|date=December 2000|title=Root decomposition and soil nutrient and carbon cycling in two temperate fen ecosystems|url=http://dx.doi.org/10.1034/j.1600-0706.2000.910316.x|journal=Oikos|volume=91|issue=3|pages=541–549|doi=10.1034/j.1600-0706.2000.910316.x|bibcode=2000Oikos..91..541S |issn=0030-1299}}</ref> These peat stores sequester an enormous amount of carbon.<ref name=":0" /> Nevertheless, it is difficult to determine whether fens net take up or emit [[greenhouse gas]]es.<ref name=":16">{{Cite journal|last1=Loisel|first1=Julie|last2=van Bellen|first2=Simon|last3=Pelletier|first3=Luc|last4=Talbot|first4=Julie|last5=Hugelius|first5=Gustaf|last6=Karran|first6=Daniel|last7=Yu|first7=Zicheng|last8=Nichols|first8=Jonathan|last9=Holmquist|first9=James|date=2017-02-01|title=Insights and issues with estimating northern peatland carbon stocks and fluxes since the Last Glacial Maximum |journal=Earth-Science Reviews|language=en|volume=165|pages=59–80|doi=10.1016/j.earscirev.2016.12.001|bibcode=2017ESRv..165...59L|issn=0012-8252}}</ref> This is because fens emit methane, which is a more potent greenhouse gas than carbon dioxide.<ref name=":0" /> Methanogenic [[archaea]] that reside in the anaerobic layers of peat combine carbon dioxide and [[Hydrogen|hydrogen gas]] to form methane and water.<ref name=":23" /> This methane can then escape into the atmosphere and exert its warming effects.<ref name=":63">{{Cite book|last=Rydin|first=Håkan |title=The biology of peatlands |date=2013 |author2=J. K. Jeglum |isbn=978-0-19-150828-8 |edition=Second |location=Oxford, UK |oclc=861559248}}</ref> Peatlands dominated by brown mosses and sedges such as fens have been found to emit a greater amount of methane than ''[[Sphagnum]]''-dominated peatlands such as bogs.<ref name=":0" /><ref name=":16" />