Geoscience Reference
In-Depth Information
the metal ion or whether the metal is reduced
in situ
with consequent
destabilization of the clay mineral (Dong
et al.
2003). This microbial
dissolution could be an alternative to ferrolysis to explain the diminution
of clay reserves in the upper part of soils affected by excess water.
12.4.3 Classification and Typology
Gleysols thus correspond to the old concept of 'gley', a term proposed
in 1905 by the Russian scientist Vysotsky to designate a more or less
compact, grey material with greenish tinge, seen under the effect of
excess water (it is the Russian equivalent of the American 'muck').
Stagnosols correspond to soils with a temporary perched water table.
They are thus the 'stagnogleys' of Francophones, although the designers
of the WRB link them with the French 'pseudogleys'. These are soils
in which iron-reduction phenomena are important. But, in contrast to
'Albeluvisols', they do not have degradation tongues.
When signs of excess water are only incidental, the soil is classified
under other groups. It is enough if a
Gleyic colour pattern
or a
Stagnic
colour pattern
is observed for a soil to be described as 'Gleyic' or 'Stagnic',
for example, Stagnic Podzol. Of course a Gleysol cannot be 'Gleyic' or a
Stagnosol 'Stagnic' (such usage would be a pleonasm).
Soils with excess water being most variable, the 'qualifiers' used
for characterizing Gleysols and Stagnosols are numerous and it is not
necessary to reproduce them here.
In the American classification, the soils that we are here concerned
with are not grouped together. They are found in various Orders, in
Suborders corresponding to 'aquic conditions'. The prefix 'Aqu' then
indicates their almost permanent saturation with water: Aqu-ents,
Aqu-epts, Aqu-olls and so on.
Classification
In this topic, given the black and white reproduction, it is not easy to
present photographs of soils with mottles. Actually, reddish-brown and
light blue colours are often rendered by the same shade of grey! Figure
12.10 shows soils in which the colours are contrasted.
Example of Stagnosol
12.5
MARSHES AND PEATLANDS
In soils permanently saturated with water, we can distinguish marshes
or swamps (organic soils with a large mineral fraction, often neutral
