Understanding the natural mechanisms that control fire occurrence in terrigenous ecosystems requires long and continuous records of past fires. Proxies, such as sedimentary charcoal and tree-ring fire scars, have temporal or spatial limitations and do not directly detect fire intensity. We show in this study that polycyclic aromatic hydrocarbons (PAHs) produced during wildfires record local fire events and fire intensity. We demonstrate that high performance liquid chromatography with fluorescence detector (HPLC-FLD) is superior to gas chromatography-mass spectrometry (GC-MS) for detecting the low concentrations of sedimentary PAHs derived from natural fires. The HPLC-FLD is at least twice as sensitive as the GC-MS in selective ion monitoring (SIM) mode for parent PAHs and five times as sensitive for retene. The annual samples extracted from varved sediments from Swamp Lake in Yosemite National Park, California are compared with the observational fire history record and show that PAH fluxes record fires within 0.5. km of the lake. The low molecular weight (LMW) PAHs (e.g., fluoranthene, pyrene and benz[. a]anthracene) are the best recorders of fire, whereas the high molecular weight (HMW) PAHs likely record fire intensity. PAHs appear to resolve some of the issues inherent to other fire proxies, such as secondary deposition of charcoal. This study advances our understanding of how PAHs can be used as markers for fire events and poses new questions regarding the distribution of these compounds in the environment.
Bibliographical noteFunding Information:
This work could not have been achieved without the support and help of many individuals. Reviews by A. Vergnoux and an anonymous referee substantially improved this manuscript. We thank Dan Cayan and Jane Teranes for assistance with core collection, Alex Sessions for use of his laboratory for sample preparation, the Limnological Research Center at the University of Minnesota where the cores were processed, Lynn Carlson for GIS assistance, and Jan and Kent van Wagtendonk for directions to National Park Service fire records. This research was supported by NSF062325 and EAR-0902805 to Yongsong Huang, and a grant from the Yosemite Association to R. Scott Anderson. Laboratory of Paleoecology Contribution 137.
Copyright 2012 Elsevier B.V., All rights reserved.
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