Characterization of sediments exports by overland flow using alaytical pyrolysis in a burnt forest area in North-Central Portugal

Wildfire may cause significant changes to soil organic carbon (SOM) on the forest floor and in the topsoil. This may have important implications for the export of particulate organic carbon from recently burnt forest areas. especially considering the often-observed increases in runoff and erosion following fire and leaching from the ash/soil. Carbon losses by post-fire runoff. however. have been poorly studied in Mediterranean regions. This research gap is being addressed by the FIRECNUTS project (PTDC/AGR-CFL/ 104559/2008). The study area is located in north-central Portugal. It was burnt by a wildfire in the summer of 2010. affecting some 250 ha of forest plantations of Maritime Pine (Pinus pinaster) and especially eucalypt (Eucalyptus globulus). This work focuses on characterization of sediments exports by overland flow of eucalypt plantations -one of the prevailing ando at the same time. most fire-prone forest types in north-central Portugal -that were collected at 4 occasions with roughly 6-monthly intervals, starting immediately after a wildfire in August 2010. The sediments were analyzed by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) in order to discern the molecular composition of the OM of sediment exports caused by post-fire runoff. Py-GC/ MS chromatogram showed in all the sediments. the presence of aromatic compounds mainly composed by benzenes and naphthalenes. typically found in burnt OM. In addition. methoxyphenols. derived from lignin and n-alkanes/ enes pairs were identified. Preliminary results suggest that wildfire caused j) the degradation and transport of the most labile structures and ii) formation of newly thermally-altered OM.