View source for Gleysol

{{Short description|Saturated soil type}}
[[Image:Gleysol.gif|thumb|300px|right|Distribution of Gleysols]]
A '''gleysol''' or '''gley soil''' is a [[hydric soil]] that unless drained is saturated with [[groundwater]] for long enough to develop a characteristic {{linktext|gleyic}} colour pattern. The pattern is essentially made up of reddish, brownish, or yellowish colours at surfaces of [[ped|soil particles]] and/or in the upper [[soil horizon]]s mixed with greyish/blueish colours inside the peds and/or deeper in the soil. Gleysols are also known as ''Gleyzems'', ''meadow soils'', ''Aqu''-suborders of [[Entisols]], [[Inceptisols]] and [[Mollisols]] ([[USDA soil taxonomy]]), or as ''groundwater soils'' and ''hydro-morphic soils''.

The term '''gley''', or '''glei''', is derived from {{Langx|uk|глей|translit=hlei}}, and was introduced into scientific terminology in 1905 by the [[Ukraine|Ukrainian]] scientist [[Georgy Vysotsky]].<ref>{{Cite OED|term=gley|access-date=2022-12-27}}</ref>
[[File:GleyClay.jpg|thumb|The clay on the right is exposed to air and is oxidized a reddish hue. The clay on the left is identical, but sealed in a glass jar for two weeks in an anaerobic setting, causing redox and color change to gley.]]
Gleysols occur within a wide range of [[compaction (geology)|unconsolidated materials]], mainly [[fluvial]], [[marine (ocean)|marine]] and [[lake|lacustrine]] [[sediment]]s of [[Pleistocene]] or [[Holocene]] age, having [[base (chemistry)|basic]] to [[acid]]ic [[mineralogy]]. They are found in [[depression (geology)|depression]] areas and low [[landscape]] positions with shallow groundwater.

Wetness is the main limitation on agriculture of virgin gleysols;{{Fact|date=January 2025}} these are covered with natural [[swamp]] [[vegetation]] and lie idle or are used for extensive [[grazing]]. Farmers use artificially-drained gleysols for [[agriculture|arable cropping]], [[dairy farming]] and [[horticulture]]. Gleysols in the [[tropics]] and [[subtropics]] are widely planted with [[rice]].

Gleysols occupy an estimated 720 million hectares worldwide. They are [[1938 USDA soil taxonomy|azonal soils]] and occur in nearly all [[climate]]s. The largest extent of Gleysols is in northern [[Russia]], [[Siberia]], [[Canada]], [[Alaska]], [[China]] and [[Bangladesh]]. An estimated 200 million hectares of gleysols are found in the tropics, mainly in the [[Amazon Basin|Amazon]] region, equatorial [[Africa]], and the coastal swamps of [[Southeast Asia]].

[[Image:gleysoil.JPG|thumb|A [[stagnohumic gleysoil]] in a [[forest plantation]] in [[Mid-Wales]], [[United Kingdom]]. The organic-rich [[topsoil]] is over a grey and orange mottled [[subsoil]] developed in glacial [[till]] ("boulder clay").]]

They exhibit a greenish-blue-grey [[soil color]] because of [[anoxic waters|anoxic]] [[wetland]] conditions. On exposure, as the iron in the soil [[Oxidation#Oxidizers|oxidizes]] colors are transformed to a mottled pattern of reddish, yellow or orange patches.  During [[soil formation]] (''gleying''), the oxygen supply in the soil profile is restricted due to soil moisture at saturation. Anaerobic micro-organisms support cellular respiration by using alternatives to free oxygen as [[electron acceptors]] to support [[cellular respiration]]. Where [[anaerobic organisms]]  [[redox|reduce]] [[ferric oxide]] to [[ferrous oxide]], the reduced mineral compounds produce the typical gleysoil color. [[Green rust]], a [[layered double hydroxide]] (LDH) of Fe(II) and Fe(III) can be found as the mineral [[fougerite]] in gleysoils.<ref name="Trolard2007">{{cite journal |last1=Trolard |first1=Fabienne |last2=Bourrié |first2=Guilhem |last3=Abdelmoula |first3=Mustapha |last4=Refait |first4=Philippe |last5=Feder |first5=Frédéric |title=Fougerite, a new mineral of the pyroaurite-iowaite group: Description and crystal structure |journal=Clays and Clay Minerals |date=June 2007 |volume=55 |issue=3 |pages=323–334 |doi=10.1346/CCMN.2007.0550308 |bibcode=2007CCM....55..323T }}</ref><ref name="Génin2005">{{cite journal |last1=Génin |first1=Jean-Marie R. |last2=Aïssa |first2=Rabha |last3=Géhin |first3=Antoine |last4=Abdelmoula |first4=Mustapha |last5=Benali |first5=Omar |last6=Ernstsen |first6=Vibeke |last7=Ona-Nguema |first7=Georges |last8=Upadhyay |first8=Chandan |last9=Ruby |first9=Christian |title=Fougerite and FeII–III hydroxycarbonate green rust; ordering, deprotonation and/or cation substitution; structure of hydrotalcite-like compounds and mythic ferrosic hydroxide |journal=Solid State Sciences |date=May 2005 |volume=7 |issue=5 |pages=545–572 |doi=10.1016/j.solidstatesciences.2005.02.001 }}</ref>

Gleysoils may be sticky and hard to work, especially where the gleying is caused by surface water held up on a slowly permeable layer.  However, some [[ground-water gley]] soils have [[Permeability (fluid)|permeable]] lower [[soil horizons|horizons]], including, for example, some sands in hollows within sand dune systems (known as slacks), and in some [[alluvial]] situations.

Groundwater gleysoils develop where [[drainage]] is poor because the [[water table]] ([[phreatic]] surface) is high, whilst surface-water gleying occurs when [[Precipitation (meteorology)|precipitation]] input at the surface does not drain freely through the ground. A reducing environment exists in the saturated layers, which become mottled greyish-blue or greyish-brown due to its [[ferrous iron]] and organic matter content.  The presence of reddish or orange mottles indicates localised re-oxidation of ferrous salts in the soil matrix, and is often associated with root channels, animal burrows, or cracking of the soil material during dry spells.

In the [[World Reference Base for Soil Resources]] (WRB),<ref>{{Cite web|url = https://wrb.isric.org/files/WRB_fourth_edition_2022-12-18.pdf|title = World Reference Base for Soil Resources, fourth edition|author = IUSS Working Group WRB|year = 2022|publisher = International Union of Soil Sciences, Vienna|access-date = 2023-08-16|archive-date = 2023-08-11|archive-url = https://web.archive.org/web/20230811210038/https://wrb.isric.org/files/WRB_fourth_edition_2022-12-18.pdf|url-status = live}}</ref> soils with [[redox]] processes due to ascending [[groundwater]] belong to the Reference Soil Group '''Gleysols'''. Soils with redox processes due to [[water stagnation|stagnant water]] are '''[[Stagnosol]]s''' and '''[[Planosol]]s'''.

== See also ==
* [[Pedogenesis]]
* [[Pedology (soil study)]]
* [[Soil classification]]
* [[Anaerobic respiration]]
* [[Fougerite]], the natural form of [[green rust]]
* [[Blue goo]]
* [[Redox]]
* [[Redox gradient]]

== External links ==
{{Wiktionary|gley}}
* [https://wrb.isric.org/picture-gallery/ Profile photos (with classification)] {{Webarchive|url=https://web.archive.org/web/20231203094523/https://wrb.isric.org/picture-gallery/ |date=2023-12-03 }} WRB homepage
* [https://www.iuss.org/index.php?article_id=73|title=IUSS Profile photos (with classification)] {{Webarchive|url=https://web.archive.org/web/20180930231253/https://www.iuss.org/index.php?article_id=73%7Ctitle=IUSS |date=2018-09-30 }} IUSS World of Soils

== References ==
{{Reflist}}

== Further reading ==
* {{cite book |doi=10.1007/978-3-540-30461-6 |title=Soils of the World |date=2022 |last1=Zech |first1=Wolfgang |last2=Schad |first2=Peter |last3=Hintermaier-Erhard |first3=Gerd |isbn=978-3-540-30460-9 }}

{{Soil type}}

{{DEFAULTSORT:Gley Soil}}
[[Category:Pedology]]
[[Category:Types of soil]]