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GLOBAL BIOGEOCHEMICAL CYCLES, VOL. 18, GB3014, doi:10.1029/2003GB002194, 2004

Chemistry of burning the forest floor during the FROSTFIRE experimental burn, interior Alaska, 1999

J. W. Harden

U.S. Geological Survey, Menlo Park, California, USA


J. C. Neff

U.S. Geological Survey, Denver Federal Center, Denver, Colorado, USA


D. V. Sandberg

Pacific Northwest Research Station, USDA Forest Service, Corvallis, Oregon, USA


M. R. Turetsky

U.S. Geological Survey, Menlo Park, California, USA


R. Ottmar

Seattle Forestry Science Laboratory, Seattle, Washington, USA


G. Gleixner

Max Planck Institute for Biogeochemistry, Jena, Germany


T. L. Fries

U.S. Geological Survey, Menlo Park, California, USA


K. L. Manies

U.S. Geological Survey, Menlo Park, California, USA


Abstract

Wildfires represent one of the most common disturbances in boreal regions, and have the potential to reduce C, N, and Hg stocks in soils while contributing to atmospheric emissions. Organic soil layers of the forest floor were sampled before and after the FROSTFIRE experimental burn in interior Alaska, and were analyzed for bulk density, major and trace elements, and organic compounds. Concentrations of carbon, nutrients, and several major and trace elements were significantly altered by the burn. Emissions of C, N, and Hg, estimated from chemical mass balance equations using Fe, Al, and Si as stable constituents, indicated that 500 to 900 g C and up to 0 to 4 × 10−4 g Hg/m2 were lost from the site. Calculations of nitrogen loss range from −4 to +6 g/m2 but were highly variable (standard deviation 19), with some samples showing increased N concentrations post-burn potentially from canopy ash. Noncombustible major nutrients such as Ca and K also were inherited from canopy ash. Thermogravimetry indicates a loss of thermally labile C and increase of lignin-like C in char and ash relative to unburned counterparts. Overall, atmospheric impacts of boreal fires include large emissions of C, N and Hg that vary greatly as a function of severe fire weather and its access to deep organic layers rich in C, N, and Hg. In terrestrial systems, burning rearranges the vertical distribution of nutrients in fuels and soils, the proximity of nutrients and permafrost to surface biota, and the chemical composition of soil including its nutrient and organic constituents, all of which impact C cycling.

Received 24 November 2003; accepted 24 June 2004; published 28 August 2004.

Keywords: combustion; experimental burn; boreal forest; black spruce; feathermoss; Hg.

Index Terms: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 0330 Atmospheric Composition and Structure: Geochemical cycles; 1615 Global Change: Biogeochemical processes (4805); 1030 Geochemistry: Geochemical cycles (0330).

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Citation: Harden, J. W., J. C. Neff, D. V. Sandberg, M. R. Turetsky, R. Ottmar, G. Gleixner, T. L. Fries, and K. L. Manies (2004), Chemistry of burning the forest floor during the FROSTFIRE experimental burn, interior Alaska, 1999, Global Biogeochem. Cycles, 18, GB3014, doi:10.1029/2003GB002194.