Isotope (14C and 13C) analysis of deep peat CO2 using a passive sampling technique

Garnett, M.H. and Hardie, S.M.L. (2009) Isotope (14C and 13C) analysis of deep peat CO2 using a passive sampling technique. Soil Biology and Biochemistry, 41(12), pp. 2477-2483. (doi: 10.1016/j.soilbio.2009.09.004)

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We developed and tested a new method to collect CO<sub>2</sub> from the surface to deep layers of a peatland for radiocarbon analysis. The method comprises two components: i) a probe equipped with a hydrophobic filter that allows entry of peat gases by diffusion, whilst simultaneously excluding water, and, ii) a cartridge containing zeolite molecular sieve that traps CO<sub>2</sub> passively. We field tested the method by sampling at depths of between 0.25 and 4 m at duplicate sites within a temperate raised peat bog. CO<sub>2</sub> was trapped at a depth-dependent rate of between ∼0.2 and 0.8 ml d<sup>−1</sup>, enabling sufficient CO<sub>2</sub> for routine <sup>14</sup>C analysis to be collected when left in place for several weeks. The age of peatland CO<sub>2</sub> increased with depth from modern to not, vert, similar170 BP for samples collected from 0.25 m, to ∼4000 BP at 4 m. The CO<sub>2</sub> was younger, but followed a similar trend to the age profile of bulk peat previously reported for the site (Langdon and Barber, 2005). δ<sup>13</sup>C values of recovered CO<sub>2</sub> increased with depth. CO<sub>2</sub> collected from the deepest sampling probes was considerably <sup>13</sup>C-enriched (up to not, vert, similar+9‰) and agreed well with results reported for other peatlands where this phenomenon has been attributed to fermentation processes. CO<sub>2</sub> collected from plant-free static chambers at the surface of the mire was slightly <sup>14</sup>C-enriched compared to the contemporary atmosphere, suggesting that surface CO<sub>2</sub> emissions were predominantly derived from carbon fixed during the post-bomb era. However, consistent trends of enriched 13C and depleted <sup>14</sup>C in chamber CO<sub>2</sub> between autumn and winter samples were most likely explained by an increased contribution of deep peat CO<sub>2</sub> to the surface efflux in winter. The passive sampling technique is readily portable, easy to install and operate, causes minimal site disturbance, and can be reliably used to collect peatland CO<sub>2</sub> from a wide range of depths.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Garnett, Dr Mark
Authors: Garnett, M.H., and Hardie, S.M.L.
Subjects:G Geography. Anthropology. Recreation > GE Environmental Sciences
Q Science > QH Natural history > QH345 Biochemistry
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Soil Biology and Biochemistry
Journal Abbr.:Soil biol. biochem.
ISSN (Online):1879-3428
Published Online:18 September 2009
Copyright Holders:Copyright © 2009 Elsevier
First Published:First published in Soil Biology and Biochemistry 41(12):2477-2483
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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