『Abstract
The relationship and mechanisms among weathering processes, cation
fluxes, clay mineralogy, organic matter composition and stability
were studied in soils developing on basaltic material in southern
Italy (Sicily). The soils were transitions between Phaeozems and
Vertisols. Intense losses of the elements Na, Ca and Mg were measured
indicating that weathering has occurred over a long period of
time. The main weathering processes followed the sequence: amphibole,
mica, volcanic glass or if ash was the primary source→smectite→interstratified
smectite-kaolinite→kaolinite. Kaolinite formation was strongly
related to high Al, Mg and Na losses. The good correlation between
oxyhydroxides and kaolinite in the soils suggests that (macro)
aggregates have formed due to physical or electrostatic interactions
between the 1:1 clay minerals and oxides. The stability of organic
matter was investigated with a H2O2-treatment
that assumes that chemical oxidation mimics the natural oxidative
processes. The ratio of C after the H2O2 treatment to the total organic C ranged from
1-28%. No correlation between clay content and organic matter
(labile or stable fraction) was found. The refractory organic
fraction was enriched in aliphatic compounds and did not greatly
interact with the kaolinite, smectite or poorly crystalline Fe
or Al phases. A part of this fraction (most probably proteins)
was bound to crystalline Fe-oxides. In contrast, the oxidisable
fraction showed a strong relationship with poorly crystalline
oxyhydroxides and kaolinite. Surprisingly, smectite did not contribute
to the stabilisation of any of the organic C fractions. The stabilisation
of organic matter in the soils has, therefore, two main mechanisms:
1) the protection of labile (oxidisable with H2O2) organic matter, including also aromatic-rich
compounds such as charcoal, by the formation of aggregates with
oxyhydroxides and kaolinite and 2) the formation of a refractory
fraction enriched in aliphatic compounds.
Keywords: Weathering; Mass balance; Clay mineralogy; Organic matter
stability; Mediterranean soils; FT-IR spectroscopy』
1. Introduction
2. Investigation area and sites
3. Materials and methods
3.1. Soil sampling
3.2. Soil mineralogy and grain sizes
3.3. Soil chemistry
3.4. SOM fractions
3.5. Calculation of weathering rates
4. Results
4.1. Soil physical and chemical aspects
4.2. soil and clay mineralogy
4.3. Mass balance calculations
4.4. Soil organic matter
5. Discussion
5.1. Mineralogy
5.2. Mass balances, weathering
5.3. Soil organic matter
6. Conclusions
Acknowledgements
References