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

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.

Disentangling Drought and Nutrient Effects on Soil Carbon Dioxide and Methane Fluxes in a Tropical Forest

“…Above or below this optimum, soil CO 2 efflux decreased by a maximum factor of 1.4. This finding is in agreement with previous studies performed in the same site (Rowland et al, 2014;Courtois et al, 2019). On the one hand, excess SWC can create a physical barrier for gas diffusion between the soil and the atmosphere, and a biological inhibitor for root and microbial activities because of the decrease, or even absence, of O 2 (Wood et al, 2013).…”

“…Furthermore, soil water saturation can create a physical barrier for gas diffusion, and potentially stop the root and microbial activities because of a lack of available O 2 . Studies on drought effects on soil CH 4 flux however remain sparse, although all showed an increase in CH 4 consumption (Davidson et al, 2004(Davidson et al, , 2008 with extremely high spatial heterogeneity (Wood and Silver, 2012;Courtois et al, 2019). In our study however, soils are mainly a source under drought treatment, with highest CH 4 emissions when SWC was about 20% in the dry plots.…”

“…The volumes of each collar were summed, corresponding to a total volume of 3.882 ± 0.193 L for the UGGA/chamber system. The fluxes were measured during 5 min measurement periods (CO 2 and CH 4 concentration logged every 20 s), this period was sufficient to detect fluxes of each gas (Courtois et al, 2019). Two consecutive days (hereafter referred to as a sampling campaign) were necessary to measure the soil gas fluxes, because of the restricted time period of measurement.…”

Reply to RC3

“…Data used in this study can be freely accessed through the Zenodo repository: https://doi.org/10.5281/zenodo. 2555299 (Courtois and Stahl, 2019).…”

A Method for Estimating Annual Cumulative Soil/Ecosystem Respiration and CH4 Flux from Sporadic Data Collected Using the Chamber Method

“…In recent years, this limitation has been largely overcome by the introduction of computer-controlled automatic sampling systems [11,12]. However, the automatic equipment is usually expensive to install, although increasingly more studies have started to use this new efficient system [13][14][15][16][17]. Thus, for the archived data now available, the observation frequency is often less than once a month, determined according to the practicability of accessing the site, and usually in the daytime.…”