Automatic high-frequency measurements of full soil greenhouse gas fluxes in a tropical forest

Elodie Alice Courtois,Benoit Burban,Laëtitia Bréchet,Clément Stahl,Joke Van Den Berge,Jennifer Larned Soong,Daniel Berveiller,Josep Peñuelas,Ivan August Janssens,Nicola Arriga

doi:10.5194/bg-16-785-2019

Abstract

Abstract. Measuring in situ soil fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) continuously at high frequency requires appropriate technology. We tested the combination of a commercial automated soil CO2 flux chamber system (LI-8100A) with a CH4 and N2O analyzer (Picarro G2308) in a tropical rainforest for 4 months. A chamber closure time of 2 min was sufficient for a reliable estimation of CO2 and CH4 fluxes (100 % and 98.5 % of fluxes were above minimum detectable flux – MDF, respectively). This closure time was generally not suitable for a reliable estimation of the low N2O fluxes in this ecosystem but was sufficient for detecting rare major peak events. A closure time of 25 min was more appropriate for reliable estimation of most N2O fluxes (85.6 % of measured fluxes are above MDF ± 0.002 nmol m−2 s−1). Our study highlights the importance of adjusted closure time for each gas.

Highlights

After water vapor, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are the three main greenhouse gases (GHGs) in terms of radiative forcing
A chamber closure time of 2 min was sufficient for a reliable estimation of CO2 and CH4 fluxes (100 % and 98.5 % of fluxes were above minimum detectable flux – MDF, respectively)
A closure time of 25 min was more appropriate for reliable estimation of most N2O fluxes (85.6 % of measured fluxes are above MDF ± 0.002 nmol m−2 s−1)

Summary

Introduction

Carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are the three main greenhouse gases (GHGs) in terms of radiative forcing. Increases in these GHG concentrations in the atmosphere are driving anthropogenic global warming. Very few reliable long-term datasets on full GHG balances are available from tropical ecosystems, despite their known importance for the global cycles of these three GHGs (Dutaur and Verchot, 2007). This is in part due to the challenges of designing and operating continuous, multi-gas flux analysis systems in tropical forests. Chemical, and biological characteristics are linked to variation in GHG emissions from soils, which in turn can display very high spatial and temporal variability (Arias-Navarro et al, 2017; Silver et al, 1999)

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Conclusion