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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-213
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-213
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 17 Jun 2019

Submitted as: research article | 17 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Abiotic CO2 sources confound interpretation of temperature responses of in situ respiration in geothermally warmed forest soils of Iceland

Marja Maljanen1, Heli Yli-Moijala1, Bjarni Didrik Sigurdsson2, and Christina Biasi1 Marja Maljanen et al.
  • 1University of Eastern Finland, Department of Environmental and Biological Sciences, P.O. Box 1627, Finland
  • 2Agricultural University of Iceland, Keldnaholt, 112 Reykjavik, Iceland

Abstract. Carbon dioxide (CO2) efflux and δ13C in CO2 were measured along a natural geothermal soil temperature (Ts) gradient in upland Sitka spruce forest soil in a volcanic area in Iceland in July 2014 and 2016. The gradient that reaches from ambient soil temperature up to 40 °C warming at 10 cm depth was originally formed in May 2008, following a major earthquake. The CO2 efflux from the forest floor was measured using the static chamber method. In addition, subsurface soil CO2 concentrations and δ13C values of CO2 were studied. In summer 2014, soil surface CO2 efflux increased steadily with increasing soil temperature across a temperature gradient of 40 °C (from 260 to 3900 mg m−2 h−1). In 2016 the trend had changed; the maximum CO2 efflux (2100 mg m−2 h−1) was measured at 20 °C Ts warming and a similar nonlinear trend was observed in soil CO2 concentrations in 2016. The 13C isotope analysis of CO2 suggested that a proportion of the CO2 emitted from the warmer plots was geothermally derived. The plot with the highest geothermal source was different in 2014 and 2016, which explained the shift in the temperature dependence of the total CO2 efflux. Our study showed that a significant amount of CO2 emitted from the higher warming levels of geothermal temperature gradients can have non-biotic origin and this has to be taken into account when measuring respiration fluxes on such volcanic sites.

Marja Maljanen et al.
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Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Marja Maljanen et al.
Marja Maljanen et al.
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We studied the proportion of biotic and abiotic CO2 fluxes from soil using static chamber method and stable isotope approach from a geothermally warmed area in southern Iceland. These sites can be used cost efficiently to study the effects of soil warming on the ecosystem. However, our study showed that a significant amount of CO2 emitted from the higher warming levels can have non-biotic origin and this has to be taken into account when measuring respiration fluxes on such volcanic sites.
We studied the proportion of biotic and abiotic CO2 fluxes from soil using static chamber method...
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