Geoscience Reference
In-Depth Information
3.2.3 Translocations
A horizon that loses substances to benefit another is called
eluvial
(E
horizon). The horizon that gains is termed
illuvial
(some B horizons).
The particles of clay are naturally attracted to each other. In kaolinite, it
is mostly hydrogen bonds because the clay mineral is asymmetric and
presents O ions on one face and OH ions on the other. In the case of 2/1
clay minerals, mostly cation bridges and hydrogen bonds determined
by water molecules are involved. Under these conditions, making a
suspension of clay is not easy. This is noticed when we want to conduct
particle-size analysis. All cations must be eliminated. But this is almost
impossible in soils except in some very special cases. The transfer of clay
in suspension is thus limited in the natural environment. We can use, for
this translocation, the term 'clay translocation' or 'argilluviation'. It must
be noted that the term
leaching
corresponds exclusively to translocation
of cations or/and salts in solution (
lixiviation
in French).
Translocation in suspension (clay)
Water-soluble organic acids, especially the fulvic acids, can be associated
with normally insoluble metallic elements (Al
3+
and Fe
3+
). Metal-organic
complexes liable to move are then obtained. The local accumulation
of iron and aluminium in the B horizons of Podzols is traditionally
explained by this mechanism.
Translocation in the complexed state (iron and aluminium)
The compounds brought into solution are mostly evacuated from the
profiles. This is particularly true for the bases (Ca, Mg, K and Na) in
humid climate.
Translocation in solution (bases)
We have already covered the phenomenon in Chapter 2 during our
study of vegetation. We have seen that this recycling is able to restrict
the losses (leaching of bases) but rarely compensates for them fully.
Biological recycling of cations
3.2.4
Concentration and Precipitation
The elements not eliminated from the soil or partly eliminated are
concentrated in place. What is seen in a soil is only what is left! The
Relative concentration