512
Climatic Geomorphology
450
400
SUPERSATURATED
350
300
._1
250
E
v
o'3
O
0 200
0
150
100
50
I
I
I
s'o
UNDERSATURATED
(Aggressive)
0
2'5
7~5
1()0
1~'5
1,50
1-75
Equilibrium CO 2 (mg/L)
200
Figure 20.8. Saturation equilibrium curves for solution of calcium carbonate at different temperatures as
a function of equilibrium carbon dioxide in solution (after Trombe (1952)).
The effect of temperature on carbon dioxide dissolution is very small, because at about
30~ it dissolves three times less than at 0~ Air in the soil, however, can reach CO2
values of up to 30 to 60 times the content of a normal atmosphere (0.03% in volume).
In only weakly aerated tropical soils values of 20 to 25% CO2 can be obtained. This seems
to be due to the decomposition of organic matter and to root respiration. Therefore, the
biogenic carbon dioxide is the primary factor in the dissolution of carbonates and its
content is a function of temperature and precipitation, factors that activate the vegetation
development. As a consequence, in humid tropical zones chemical corrosion of limestones
reaches very high values.
3.3. Weathering degrees and products
Weathering degrees of the alteration products are variable and several indexes are used
to differentiate them (Taylor and Eggleton, 2001). These are based on qualitative scales
of friability (Ollier, 1965, 1984), on the mechanical properties of the regolith (Lumb, 1962,
Climatic Geomorphology
450
400
SUPERSATURATED
350
300
._1
250
E
v
o'3
O
0 200
0
150
100
50
I
I
I
s'o
UNDERSATURATED
(Aggressive)
0
2'5
7~5
1()0
1~'5
1,50
1-75
Equilibrium CO 2 (mg/L)
200
Figure 20.8. Saturation equilibrium curves for solution of calcium carbonate at different temperatures as
a function of equilibrium carbon dioxide in solution (after Trombe (1952)).
The effect of temperature on carbon dioxide dissolution is very small, because at about
30~ it dissolves three times less than at 0~ Air in the soil, however, can reach CO2
values of up to 30 to 60 times the content of a normal atmosphere (0.03% in volume).
In only weakly aerated tropical soils values of 20 to 25% CO2 can be obtained. This seems
to be due to the decomposition of organic matter and to root respiration. Therefore, the
biogenic carbon dioxide is the primary factor in the dissolution of carbonates and its
content is a function of temperature and precipitation, factors that activate the vegetation
development. As a consequence, in humid tropical zones chemical corrosion of limestones
reaches very high values.
3.3. Weathering degrees and products
Weathering degrees of the alteration products are variable and several indexes are used
to differentiate them (Taylor and Eggleton, 2001). These are based on qualitative scales
of friability (Ollier, 1965, 1984), on the mechanical properties of the regolith (Lumb, 1962,