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Several structural changes were recognized by CPMAS 13C-NMR and resolution-enhanced IR spectroscopy after humic acids (HA) and fulvic acids (FA) were subjected to labratory heating at 350ºC. The NMR results suggested that the HA underwent decarboxylation, selective transformation of aliphatic material, and increase in the number of aromatic carbons when subjected to heating for 120 s, whereas after subsequent heating no predominant aromatic neoformations were observed, and the elimination of alkyl structures occured preferentially at this stage. The infrared spectroscopy revealed a well-defined lignin pattern in the original HA, that tended to disappear with heating. The results obtained in the laboratory experiments agreed with several of the differences found between the NMR patterns of the humic substances from the unburnt soil area and from that affected by forest fire. It suggested that the changes observed play important roles in the colloidal properties and the water-repellency observed in the heated humic substances and in the post-fire soil area.
Cataloging Information
- carbon
- chemistry
- fulvic acids
- heat
- heat effects
- heating effects
- humic acids
- humus
- laboratory fires
- lignin
- Mediterranean habitats
- Nmr
- organic soils
- pH
- Quercus rotundifolia
- sampling
- soils
- statistical analysis
- water repellent soils
- wildfires
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