title: Fire effects on stable isotopes in a Sierran forested watershed.
abstract: 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 degrees 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 degrees C because lower burn temperatures may not produce strong isotopic shifts, and at temperatures>or=600 degrees 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 delta15N values in upland watershed analyses 1 yr postburn, while riparian zone analyses results indicated that delta13C values significantly decreased approximately 0.71 per thousand over a 9 mo post-fire period (p=0.015), and ash/sediment layer delta13C values were approximately 0.65 per thousand higher than those in the A horizon. The lack of field confirmation may have been due to overall wildfire burn temperatures being <200 degrees 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.
authors.affiliation: Dep. of Natural Resources and Environmental Science, Univ. of Nevada Reno, Mail Stop 186, 1000 Valley Road, Reno, NV 89512, USA. lsaito@cabnr.unr.edu
authors.forename: Laurel
authors.initials: L
authors.lastname: Saito
authors.forename: Wally W
authors.initials: WW
authors.lastname: Miller
authors.forename: Dale W
authors.initials: DW
authors.lastname: Johnson
authors.forename: Robert G
authors.initials: RG
authors.lastname: Qualls
authors.forename: Louis
authors.initials: L
authors.lastname: Provencher
authors.forename: Erin
authors.initials: E
authors.lastname: Carroll
authors.forename: Peter
authors.initials: P
authors.lastname: Szameitat
mesh_terms: D005390:Fires; D007554:Isotopes; D014197:Trees
chemical_list: D007554:Isotopes