Geoscience Reference
In-Depth Information
In the forested part of the toposequence, from the bottom to the
top, the soils are increasingly acid and differentiated. Podzols occur
in the 1700-2200 m section (larch, then larch + rhododendrons). In the
mountain pastures, however, the profiles are less differentiated and
richer in organic matter. The same sequence is found in the entire Alps:
on the Aiguilles Rouges massif (Dambrine 1986), above the Arc 2000
ski station (Mourier 2003), in Switzerland on the northeastern flank of
Mont Blanc (Keller 1991), etc. It is characteristic of high mountains on
acid igneous rocks, the Himalayas in particular. But in Asia, the latitude
is lower, which results in general warming of the climate at the same
altitude. The soil sequence is therefore displaced in altitude. Podzols are
then located between 2900 and 4000 m (Bottner 1984; Lorphelin 1985;
Legros 1992).
11.4.2 Groundwater Podzols
In Canada (Pagé and de Kimpe 1987), Ferruginous Podzols have their
B horizons above the zone of fluctuation of the groundwater. They
mostly contain non-complexed iron and complexed as well as non-
complexed aluminium. The E horizons are found only in well-drained
environments. On the contrary, Humic Podzols are found in humid
soil climates. Their Bh horizons are situated in the zone of fluctuation
of the groundwater. They contain little iron and aluminium because
those elements have been evacuated. What is left behind is in complexed
form.
Approximately the same type of distribution is found in France in
the Landes. There, Groundwater Podzols cover nearly one million ha
(Righi and Wilbert 1984).
In tropical environments, Podzols with hydromorphic features are
quite abundant. They are primary Podzols, that is, directly differentiated
in the parent materials, mostly alluvia. The Bs horizon is more or less
absent. The Bh, often hardened to an ironstone, is also in the zone of
fluctuation of the groundwater (Dubroeucq and Volkoff 1988; Schwartz
1988b). It is about 2-3 metres thick. When the groundwater nears the
surface and does not fluctuate, these Podzols are replaced by Histosols
(peats).
11.4.3 Secondary tropical Podzols
Generalities
The secondary Podzols of the tropics are, undoubtedly, less abundant
than the primary Podzols mentioned above, but they are of particular
interest because of their genesis: they are differentiated at the expense
