Field-based cavity ring-down spectrometry of δ13C in soil-respired CO2

Munksgaard, Niels C., Davies, Kalu, Wurster, Chris M., Bass, Adrian M., and Bird, Michael I. (2013) Field-based cavity ring-down spectrometry of δ13C in soil-respired CO2. Isotopes in Environmental and Health Studies, 49 (2). pp. 232-242.

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Measurement of soil-respired CO2 at high temporal resolution and sample density is necessary to accurately identify sources and quantify effluxes of soil-respired CO2. A portable sampling device for the analysis of δ13C values in the field is described herein.

CO2 accumulated in a soil chamber was batch sampled sequentially in four gas bags and analysed by Wavelength-Scanned Cavity Ring-down Spectrometry (WS-CRDS). A Keeling plot (1/[CO2] versus δ13C) was used to derive δ13C values of soil-respired CO2. Calibration to the δ13C Vienna Peedee Belemnite scale was by analysis of cylinder CO2 and CO2 derived from dissolved carbonate standards. The performance of gas-bag analysis was compared to continuous analysis where the WS-CRDS analyser was connected directly to the soil chamber.

Although there are inherent difficulties in obtaining absolute accuracy data for δ13C values in soil-respired CO2, the similarity of δ13C values obtained for the same test soil with different analytical configurations indicated that an acceptable accuracy of the δ13C data were obtained by the WS-CRDS techniques presented here. Field testing of a variety of tropical soil/vegetation types, using the batch sampling technique yielded δ13C values for soil-respired CO2 related to the dominance of either C3 (tree, δ13C=−27.8 to−31.9 ‰) or C4 (tropical grass, δ13C=−9.8 to−13.6 ‰) photosynthetic pathways in vegetation at the sampling sites. Standard errors of the Keeling plot intercept δ13C values of soil-respired CO2 were typically<0.4 ‰ for analysis of soils with high CO2 efflux (>7–9 μmol m−2 s−1).

Item ID: 28737
Item Type: Article (Research - C1)
ISSN: 1477-2639
Keywords: carbon-13, field measurement, isotope ecology, isotope measurements, methods and equipment, laser spectroscopy, soil-respired CO2
Funders: Australian Research Council (ARC)
Projects and Grants: ARC Linkage, Infrastucture and Facilities (LIEF) grant LE110100144, ARC Federation Fellowship FF0883221
Date Deposited: 07 Aug 2013 05:39
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0503 Soil Sciences > 050304 Soil Chemistry (excl Carbon Sequestration Science) @ 100%
SEO Codes: 96 ENVIRONMENT > 9603 Climate and Climate Change > 960303 Climate Change Models @ 100%
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