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Journal of Environmental Quality Abstract - Landscape and Watershed Processes

Fire Effects on Stable Isotopes in a Sierran Forested Watershed


This article in JEQ

  1. Vol. 36 No. 1, p. 91-100
    Received: June 16, 2006

    * Corresponding author(s): lsaito@cabnr.unr.edu
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  1. Laurel Saito *a,
  2. Wally W. Millera,
  3. Dale W. Johnsona,
  4. Robert G. Quallsa,
  5. Louis Provencherb,
  6. Erin Carrolla and
  7. Peter Szameitatc
  1. a Dep. of Natural Resources and Environmental Science, Univ. of Nevada Reno, Mail Stop 186, 1000 Valley Road, Reno, NV 89512
    b The Nature Conservancy, One E. First St., Suite 1007, Reno, NV 89501
    c 1475 Folsom Street, #362, Boulder, CO 80302


This study tested the hypothesis that stable C and N isotope values in surface soil and litter would be increased by fire due to volatilization of lighter isotopes. The hypothesis was tested by: (1) performing experimental laboratory burns of organic and mineral soil materials from a watershed at combinations of temperature ranging 100 to 600°C and duration ranging from 1 to 60 min; (2) testing field samples of upland soils before, shortly after, and 1 yr following a wildfire in the same watershed; and (3) testing field soil samples from a down-gradient ash/sediment depositional area in a riparian zone following a runoff event after the wildfire. Muffle furnace results indicated the most effective temperature range for using stable isotopes for tracing fire impacts is 200 to 400°C because lower burn temperatures may not produce strong isotopic shifts, and at temperatures ≥600°C, N and C content of residual material is too low. Analyses of field soil samples were inconclusive: there was a slightly significant effect of the wildfire on δ15N values in upland watershed analyses 1 yr postburn, while riparian zone analyses results indicated that δ13C values significantly decreased ∼0.71‰ over a 9 mo post-fire period (p = 0.015), and ash/sediment layer δ13C values were ∼0.65‰ higher than those in the A horizon. The lack of field confirmation may have been due to overall wildfire burn temperatures being <200°C and/or microbial recovery and vegetative growth in the field. Thus, the muffle furnace experiment supported the hypothesis, but it is as yet unconfirmed by actual wildfire field data.

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