Geoscience Reference
In-Depth Information
Drains forced into the soil
Vegetative
cover
A
B
Soil
in situ
C
Shored up cutting
Apparatus for collecting waters
Fig. 1.8
Installation
in situ
of lysimeters in a pit with cast walls, covered to protect against
frost and to prevent deliberate or inadvertent damage (Dambrine 1985; Keller 1991).
This approach has been very useful in the context of study of podzolic
soils (Dambrine 1985; Keller and Vedy 1991).
1.2.7 Experimental Approach
Pédro (1964), in his thesis, used a Soxhlet apparatus to reproduce in
the laboratory certain kinds of weathering (Fig. 1.9). The rock sample
E to be weathered is placed as shown in the diagram. A flask, initially
containing distilled water, is taken to boiling. The steam passes through
the tube R and is condensed in a cooling apparatus so that the water
collected falls on the sample E. When the water soaking E reaches the
level of the siphon S, it starts flowing out and falls in the flask, along
with the products that weathering has dissolved. Then the process starts
again with pure (because distilled) water. The apparatus approximates
the cycle of water (evaporation, condensation, infiltration, transport).
At the end of several weeks or months of the experiment, the
author recovered the various fractions obtained:
resistate
(unweathered
fraction),
eluviate
(decomposition and neoformation in place),
leachate
(solubilized and exported fraction). This apparatus allows adjustment
of various settings: (i) number of cycles and, thus, the volume of water
that has passed through the sample; (ii) oxygenation, because the treated
sample can be totally immersed or go above the siphon; (iii) reaction
temperature; (iv) pH, which is controlled by introduction of carbon
dioxide or various acids through the top opening of the apparatus.
These experiments, superbly conceived and interpreted, clarified the
mechanisms of weathering of rocks on the surface of the Earth.
