Assessing the effects of chamber placement, manual sampling and headspace mixing on CH4 fluxes in a laboratory experiment

Abstract

A laboratory experiment was conducted with two types of closed static chambers to estimate the effects of chamber placement, manual headspace sampling and headspace mixing on methane (CH 4 ) fluxes. Chamber fluxes were compared to a known reference flux in a chamber calibration system. The measurements were conducted with three types of soils (coarse dry, fine dry and fine wet quarts sand) at five flux levels ranging from 60 to 2000 μg CH 4 m −2 h −1 . We found that the placement of a non-vented chamber disturbed the initial CH 4 concentration development within the chamber headspace for 10 to 30 s. Excluding this short period from the flux calculation resulted in a lower flux estimate (mean±SE) of 126±26 μg CH 4 m −2 h −1 compared to 134±26 μg CH 4 m −2 h −1 if data from time zero of the enclosure were included. We also found that in non-mixed chambers (no fan mixing) the gas sampling by syringes or gas bottles disturbed the development of CH 4 concentration during the enclosure. Furthermore, flux estimates in non-mixed chambers were significantly underestimated (on average 36%) compared to the measured reference fluxes. However, the use of fans to constantly mix the chamber headspace during enclosure significantly improved the goodnessof-fit of the regression analysis used to calculate the flux and further eliminated the disturbance of the manual sampling on the concentration development. We recommend that chambers should be vented during the placement of the chamber, and that fans are used as an integrated part of static chambers while headspace mixing with syringes should be avoided.

A fertile peatland forest does not constitute a major greenhouse gas sink

“…A lack of fit of the regression model for the increase of gas concentration over time in the measurement chambers is considered to be the largest source of uncertainty, and especially the use of a linear model has been proposed to underestimate fluxes (Levy et al, 2011). Also, the use of a chamber without ventilation seems to underestimate fluxes (Christiansen et al, 2011). In contrast to these findings, a recent publication by Wang et al (2013) demonstrated that CH 4 fluxes as determined by the chamber method (without ventilation) and the eddy covariance agreed very well to each other.…”

“…Marklund et al, 1989;Minkkinen et al, 2001;Jalkanen et al, 2005). The chamber technique has been shown to give different results depending on the equipment and chamber design used (Pumpanen et al, 2004;Christiansen et al, 2011). Despite this, a recent study…”

Nitrous oxide emissions from managed grassland: a comparison of eddy covariance and static chamber measurements

“…As mentioned above, micro-climate and the concentration gradient between the soil and the atmosphere may be altered within a chamber and their small footprint makes them very sensitive to local soil conditions. It has also been demonstrated that chambers present a problem of underestimation of the fluxes if operated without a fan (see Pumpanen et al, 2004;Christiansen et al, 2011). An important additional uncertainty for chamber measurements in grazed and fertilized grassland systems is their effect on grazing behaviour in and around the chamber, and the statistical variability in the fertilizer application across the field.…”

“…Ambus and Christensen, 1994;Davidson et al, 2002). Furthermore, it has been shown that static chambers potentially underestimate fluxes if no fan is used to mix the chamber headspace (Pumpanen et al, 2004;Christiansen et al, 2011). …”

A cost-effective method for reducing soil disturbance-induced errors in static chamber measurement of wetland methane emissions

“…Both WFG and RG chamber caps are equipped with an internal computer fan powered by a 9-volt battery to circulate chamber headspace as recommended by Christiansen et al (2011) and a thermocouple allowing for internal chamber temperature (T) to be recorded during each Fig. 1 Illustrations of the water-filled gutter static chamber design that allows the use of remote rod sampling system (RRSS): Photograph of chamber being deployed using RRSS in the Charles City Wetland in Charles City County, Virginia (a); schematic of chamber disassembled to reveal water-fillable gutter on rim of collar that creates an air tight seal, internal fan to mix headspace air and thermocouple to monitor internal chamber temperature (b); schematic of chamber assembled (c) sample extraction.…”