Pseudo gleying

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Pseudo-gleying is a process that occurs in soils through the rearrangement of dissolved Fe 2+ and Mn 2+ ions under reducing conditions due to seasonal water saturation caused by stuck or backwater . (Reducing conditions caused by groundwater cause similar processes called gelling ). If the characteristics are sufficiently pronounced, soils affected by backwater are assigned to the soil type pseudogley in the German soil systematics .

Factors

Pseudo-gazing occurs on sites that have a damming layer . There are four possible causes for this:

  • Presence of a soil horizon with a very fine, clay-rich texture , either primarily from the geogenic stratification, or secondarily from the soil genesis as a strong embedding compaction, for example through clay washing
  • Occurrence of a layer change with a lack of pore continuity, such as from gravel to clay or vice versa
  • Wetness due to the extremely large number of central pores that drain very slowly
  • human compression

In addition to one of the above-mentioned dispositions, more rainwater or meltwater must infiltrate into the soil , at least seasonally , than the least permeable layer in the soil can seep through at the same time.

process

The metals iron and - already present in much smaller quantities - manganese (other metals play almost no role) are present in different oxidation states depending on the redox potential of the soil . If there is a lack of oxygen, they are reduced and easily soluble, while in the presence of oxygen they are oxidized and hardly soluble.

The damming layer prevents the precipitation from seeping away completely. This is recognizable z. B. in winter, when puddles remain on remote, elevated fields for a long time. The dammed water is mainly in coarse pores or earthworm tubes, which are saturated with water and no longer contain air. In contrast, air remains in the medium and fine pores around which it flows, as well as in the interior of aggregates .

During the accumulation of water in the soil, the oxidized Fe (III) is reduced to Fe (II) and goes into solution. The oxygen trapped in the soil aggregates oxidizes Fe (II) from the soil solution to orange or rust-colored Fe (III), which precipitates as Fe hydroxide inside the aggregate. The areas close to the pores lose their brown color with the iron and appear gray, while the interior of the aggregate appears orange to dark rust-colored, depending on the extent of the pseudo-gleying, and also black with strong manganese involvement. Typical for pseudo-gleyed floors are gray bands running more or less vertically downwards and numerous rust spots (marbling).

Soil classes

Soils with pseudo-gleying are counted among the terrestrial soils in the German soil systematics and form class S ( backwater soils ) with three soil types. In the international soil classification WRB , soils affected by backwater can be found in the stagnosols and planosols .

Differentiation to gyration

If there is a lack of oxygen due to groundwater, one speaks of gleying . In the German soil systematics, gleye belong to the department of semiterrestrial soils . Very similar processes take place, but they lead to two important differences in appearance:

  • A reduction horizon is established
  • Water saturation occurs from below through capillary ascent in the fine pores and thus in the interior of the unit, so that the iron is transported the other way around than in pseudo-gleying from the interior of the unit to the coarse pores, so that the latter appear orange to rust-colored.

literature

  • F. Scheffer, P. Schachtschnabel: Textbook of soil science. 15th edition. Spectrum, Akad. Verlag, Heidelberg / Berlin 2002, ISBN 3-8274-1324-9 .

Web links

See also: