Automation of soil flux chamber measurements: potentials and pitfalls

Abstract

Abstract. Recent technological advances have enabled the wider application of automated chambers for soil greenhouse gas (GHG) flux measurements, several of them commercially available. However, only few studies addressed the difficulties and challenges associated with operating these systems. In this contribution we compared two commercial soil GHG chamber systems–the LI-8100A Automated Soil CO2 Flux System and the Greenhouse Gas Monitoring System AGPS. From April 2014 until August 2014, the two systems monitored in parallel soil respiration (SR) fluxes at a recently harvested poplar plantation, which provided a bare field situation directly after the harvest as well as a closed canopy later on. For the bare field situation (15 April–30 June 2014), the cumulated average SR obtained from the unfiltered datasets of the LI-8100A and the AGPS were 520 and 433 g CO2 m−2, respectively. For the closed canopy phase (01 July–31 August 2014), which was characterized by a higher soil moisture content, the cumulated average SR estimates were not significantly different with 507 and 501 g CO2 m−2 for the AGPS and the LI-8100A, respectively. Flux quality control and filtering did not significantly alter the results obtained by the LI-8100A, whereas the AGPS SR estimates were reduced by at least 20 %. The main reasons for the observed differences in the performance of the two systems were (i) a lower data coverage provided by the AGPS due to technical problems; (ii) incomplete headspace mixing in the AGPS chambers; (iii) lateral soil CO2 diffusion below the collars during AGPS chamber measurements; (iv) increased root growth within the LI-8100A collars; and (v) a possible overestimation of nighttime SR fluxes by the LI-8100A. In contrast to the LI-8100A, the AGPS had the gas sample inlets installed inside the collars and not the chambers. This unique design feature enabled for the first time the detection of disturbed chamber measurements during nights with a stratified atmosphere, resulting in unbiased nighttime SR estimates. Thus besides providing high temporal frequency flux data, automated chamber systems offer another possibility to greatly improve our understanding of SR fluxes.

Contribution of advection to nighttime ecosystem respiration at a mountain grassland in complex terrain

“…We are aware that also the chamber method are prone to some errors (e.g. Riederer et al 2014), but little and contrasting information exist on its potentials and pitfalls (Görres et al 2015;Koskinen et al 2014). Indeed, only few studies used automated chambers, especially on the whole ecosystem scale, and a standardised procedure for checking the quality of data as for EC still does not exist (Vargas et al, 2011).…”

“…In order to obtain independent measures of ecosystem respiration, four automated opaque CO 2 flux chambers (model 8100-104, LI-COR, Inc.) were installed near the advection transects during the advection campaign and near EC-1 in all the other years. Being applied in a low-canopy site, this enclosure system allows estimating ecosystem respiration directly without the need for upscaling component CO 2 flux measurements (Görres et al, 2015). CO 2 flux from the automated chambers was derived as the rate of change of CO 2 mixing ratio in the measurement chamber according to the manufacturer software, and data were considered as outliers and removed when the coefficient of determination of the gradient fit was lower than 0.99.…”

“…Automated chambers are easier to use in low canopies, where the main sources of uncertainty could be represented by the system design and the small-scale spatial variability in the sources/sinks of CO 2 (Baldocchi 2014;Görres et al 2015).…”

Soil ploughing for forest regeneration leads to changes in carbon decomposition – a case study with stable isotopes

“…Dynamic closed chambers have been widely used to assess gas exchange between the atmosphere and the analyzed surface (Chojnicki et al, 2008;Görres et al, 2016). This technique is mainly used in measuring fluxes of CH 4 , CO 2 and N 2 O when high spatial variability prevents the use of the Eddy Covariance method .…”

Theoretical model for diffusive greenhouse gas fluxes estimation across water-air interfaces measured with the static floating chamber method

“…Based on the same theory, Venterea (2010) developed a more easily adaptable method, which requires knowing soil properties (texture, bulk density, water content, temperature, pH and so on), to determine the magnitude of theoretical flux bias. Now, more commercially available automated chamber systems are deployed for soil-air flux measuring, which can provide high temporal frequency soil gas fluxes (Görres et al, 2015). Sahoo and Mayya (2010) developed a two dimensional theory by considering both lateral and vertical diffusion in soil, which could provide a more reasonable explanation for the gas concentration in the deployed chambers over time.…”