Geoscience Reference
In-Depth Information
9. Sometimes there are pockets of E in the Bs and pockets of Bs in
the E. But, in all cases, the Bh forms the transition, appearing as
a kind of edging at the boundary between the other two (Lucas
et
al
. 1986;
Horbe
et al
.
2004) as shown in Fig. 11.9. This undoubtedly
reminds us of Fig. 1.3 (Chap. 1) and the arguments developed
regarding invasion of one horizon by another.
10. Let us assume that the E and B horizons are of equal thickness
and that all the iron and all the aluminum from the E migrate to
the B. In the end, the contents of Fe and Al in the B would have
doubled while the contents in the E would become zero. In other
words, according to these hypotheses, one-half of the Fe and
one-half of the Al found in the B are necessarily autochthonous.
But our hypotheses are erroneous: the B horizons are often
thicker than the E at least in Podzols of the temperate regions;
depletion of the surface layer is rarely complete; lastly, we are
mistaken in thinking that transport from the E to the B is done
perfectly without drainage to streams. Thus, in the general sense,
much more than half of the iron and the aluminium found in the
B was necessarily there
ab initio
. This is what the REDIS index
said! The role of migrations, therefore, has been exaggerated. As
regards carbon, it is the same. Old literature has often insisted
that the humic acid moved vertically in soils. But methods of
examination and measurement having made progress, it has
been shown that a major part of the carbon of the B horizons
in Podzols corresponds to debris of roots, fungi and bacteria
(Souchier 1984; Schwartz
et al
. 1986; Sanborn and Lavkulich
1989; Phillips and Fitzpatrick 1999; Nierop and Buurman 1999;
Rumpel 2006, etc.).
11. Hydrological monitoring
in situ
has shown that the amounts of Fe
and Al passing through the E horizons are very small (Souchier
1971; Dambrine 1985, 1986). Should it be deduced then, as some
authors have stated, that Podzols, although poorly developed
vertically and apparently young, are actually old, stabilized and
no more active? Then how do we get thicker Podzols?
In other words, the 'vertical migration' model does not explain all
the observed facts!
11.3.3 Models of Farmer and of Ugolini and Dahlgren
The Farmer models (1979 and 1984)
Scientists have observed the presence of aluminosilicic gels in the B
horizons of Podzols. The Si/Al ratio of these products was more or less
