Carbon kinetic isotope effect accompanying microbial oxidation of methane in boreal forest soils

Journal Article · Sat Nov 01 04:00:00 EST 1997 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/S0016-7037(97)00277-9· OSTI ID:585487

Reeburgh, W S; Hirsch, A I ^[1]; Sansone, F J; Popp, B N ^[2]

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1. Univ. of California, Irvine, CA (United States)
2. Univ. of Hawaii, Honolulu, HI (United States); and others

Atmospheric methane (CH{sub 4}) oxidation occurs in soils at sites in the Bonanza Creek L.T.E.R. near Fairbanks, Alaska, USA, at rates {le}2 mg CH{sub 4} m{sup -2} d{sup -1}; the maximum CH{sub 4} oxidizing activity is located in loess at a depth of {approximately}15 cm. Methane, carbon dioxide, and stable isotope ({delta}{sup 13}C-CH{sub 4}, {delta}{sup 13}C-CO{sub 2}) depth distributions were measured at two sites: South facing Aspen (AS2) and North facing Black Spruce (BS2). The combined effects of diffusion and oxidation are similar at both sites and result in a CH{sub 4} concentration decrease (1.8-0.1 ppm) and a {delta}{sup 13}C-CH{sub 4} increase (-48{per_thousand} to -43{per_thousand}) from the soil surface to 60-80 cm depth. Isotope flux ratio and diffusion-consumption models were used to estimate the kinetic isotope effect (KIE); these results agree with the observed top-to-bottom difference in {delta}{sup 13}C-CH{sub 4}, which is the integrated result of isotope fractionation due to diffusion and oxidation. The KIE for CH{sub 4} oxidation determined from these measurements is 1.022-1.025, which agrees with previous KIE determinations based on changes in headspace CH{sub 4} concentration and {delta}{sup 13}C-CH{sub 4} over time. A much lower soil respiration rate in the North facing Black Spruce soils is indicated by fivefold lower soil CO{sub 2} concentrations. The similarity in CH{sub 4} oxidation at the two sites and the differences in inferred soil respiration at the two sites suggest that soil CH{sub 4} oxidation and soil respiration are independent processes. The soil organic matter responsible for the CO{sub 2} flux has a {delta}{sup 13}C estimated to be -27 to -28 {per_thousand}. 23 refs., 4 figs., 2 tabs.

• OSTI ID: 585487
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 22 Vol. 61; ISSN 0016-7037; ISSN GCACAK
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
55 BIOLOGY AND MEDICINE
BASIC STUDIES
58 GEOSCIENCES
ALASKA
BOREAL REGIONS
CARBON SINKS
ECOLOGICAL CONCENTRATION
FORESTS
GREENHOUSE GASES
METHANE
MICROORGANISMS
OXIDATION
SOILS