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Título: | Chemical composition of burnt organic matter and its relation with temperature and time of heating |
Autor: | Granged, Arturo; Jiménez Morillo, N. T. CSIC ORCID; Rosa Arranz, José M. de la; Jordán, A.; Zavala, Lorena M.; González-Vila, Francisco Javier CSIC ORCID ; González-Pérez, José Antonio CSIC ORCID | Fecha de publicación: | 23-nov-2016 | Editor: | Universidade de Aveiro | Citación: | Conferencia Internacional FUEGORED2016 23 a 26 noviembre de 2016 Universidad de Aveiro (Portugal) | Resumen: | Fire is considered one of the main disturbing factors of ecosystems at global scale. Among other impacts, fire causes include physical and chemical changes on soil organic matter (SOM) (González-Pérez et al., 2004). One of the main consequences of burning is the formation of highly refractory material with a high degree of aromatization, black carbon (BC) (Hedges et al., 2000). The chemical composition of BC and the intensity of fire impacts on SOM depend strongly on fire conditions (De la Rosa et al., 2008). Therefore, the knowledge of the intensity and duration of temperature peaks is key to understand these processes (Davis, 1959). Nevertheless, in situ-determination is difficult. Burning experiments under laboratory conditions and traditional analytical techniques have provided hardly interpretable and contradictory results on temperature and time of heating. The main objective of this research is to study the relations between temperature and fire resilience with the chemical composition of fire-affected organic matter, through the combination of two new analytical techniques: [i] solid-state 13C-NMR spectroscopy and [ii] carbon isotope ratio mass spectrometry. To achieve this, litter samples were collected below the canopy of oaks (Quercus suber) in the Doñana National Park (SW Spain). Litter was air dried and heated at 250, 300 and 350 oC in a muffle furnace during different periods of time (5 and 15 minutes). Unburned air-dried litter samples were used as control. After heating, litter samples were analyzed using 13C-NMR spectroscopy and ¿13C ratio mass spectrometry. 13C-NMR analyses showed that increasing temperature and time of heating contributed to a decreased content of both O-Alkyl C compounds (60-110 ppm, carbohydrates) and lignin-derived compounds (45-60 ppm) and increased content of aromatic compounds (110-160 ppm). Litter samples heated at 350 oC during 15 minutes showed the highest aromaticity (65%). The progressive increase of aromaticity may be related to the degradation of thermolabile compounds, like polysaccharides, becoming highly aromatic compounds (Almendros et al., 2003; Baldock & Smernik, 2002). On the other hand, lignin defunctionalization may also be occurring, which also contributes to the formation of aromatic compounds (Knicker, 2007). ¿13C values showed no significant differences among treatments below 300 oC and 15 minutes of heating compared to the control. Above these thresholds, the carbon isotope composition showed a progressive depletion, reaching a value of -31.8 ¿ at 300 oC and 15 minutes of heating (5.4 ¿ lower than control). The temperature-induced 13C-depletion may be explained by a removal of compounds rich in heavy isotopes, such as those derived from carbohydrates, by condensation in compounds with a high degree of aromatization (Bird & Ascough, 2012) or both processes. After 13C-NMR and ¿13C experiments, the highest aromatization was observed in samples heated at 300 oC during 15 minutes. Both techniques showed that ¿13C composition changes only when the proportion of aromatic compounds exceeds the proportion of O-Alkyl C. These results suggest that, in the case of fires with medium-high temperatures and duration, the combined utilization of these techniques may be a powerful tool to approach temperature peaks and time of heating. | URI: | http://hdl.handle.net/10261/158846 |
Aparece en las colecciones: | (IRNAS) Comunicaciones congresos |
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