Geoscience Reference
In-Depth Information
rise in pH;
oxidation of Fe
2+
to Fe
3+
;
dehydration; this phenomenon is certainly important considering
the strong reduction of water flux with increasing depth, a process
predicted through simulation (Chap. 3, § 3.1.1) and verified by
lysimetric studies
in situ
(Keller 1991);
adsorption on mineral or organic substrates through various
mechanisms: exchange with anions, with H
+
ions, ligand
exchange (non-metallic part of the complex), involvement of van
der Waals forces (Dahlgren and Marrett 1991).
It is useful sometimes to characterize the degree of differentiation of
profiles by the ratios of free iron and free aluminium contents in the A
(or E) and B horizons:
content in B
/
content in A
(extraction with oxalate).
Souchier (1971) proposed refinement of the index by assuming that,
when there is no movement of free iron from the E to the B, its content
will be regularly stepped between the C and E horizons; he introduced a
coefficient K defined graphically and given by
OB
/
OX
(Fig. 11.8, left).
Empirical estimation of redistribution
0
0
Content of free iron
Content of free iron
0
0
E
E
Area 1
Area 3
B
B
O
X
Area 2
C
C
REDIS index =
area 1/ area 2 + area 3
(
)
Souchier's K index =
OB/OX
Fig. 11.8
Characterization of the degree of differentiation of a Podzol.
Actually, when iron oxides are not translocated from E toward the B,
the E horizon will have a higher content of them than mentioned. We
can, therefore, graphically look for the half-line passing through C and
inclined such that area no. 1 is of the same size as area no. 2, that is
to say, the quantity of oxide removed from the top of the profile (area
1) is equal to that accumulated lower down (area 2). The redistribution
can then be expressed by the REDIS index (Legros 1979) given by:
REDIS
, % = 100(
area 1
)/(
area 2
+
area 3
)
