Unveiling the temperature and fire intensity of wildfire through nuclear magnetic resonance and stable isotope analysis

Fire is considered one of the main disturbing factors of ecosystems at global scale. Causing 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 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, fire intensity and duration may help to understand these processes. Nonetheless, in situ-determination is difficult. Burning experiments under laboratory conditions and traditional analytical techniques have provided contradictory results with respect to the impact of temperature and time of heating. Therefore the present research studies the relations between temperature and fire duration (are you sure that this is the right word?) with the composition of the resulting fire-affected organic matter. To achieve this, litter samples were collected below well-developed oak-canopy (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 two different time periods (5 and 15 minutes). Unburnt air-dried litter samples were used as control. After heating, litter samples were analysed using solid-state CPMAS 13C-NMR spectroscopy and carbon isotope ratio mass spectrometry (C-IRMS).