Biases in methane chamber measurements in peatlands

Abstract

A b s t r a c t. The paper presents results of CH 4 emission measurements at peatland with the application of the dynamic chamber technique. The measurements were conducted in two types of chambers differing in shape, height, volume and technology used to assure their tightness. The study tested how the following factors: 1) forced chamber headspace mixing or its absence, 2) mistakes of the person conducting measurements, 3) improper application of linear technique for calculating CH 4 fluxes, and 4) simulated air sampling typical for static chambers, influence the significance of errors and the underestimation rate of CH 4 fluxes measured in situ. It was indicated that chamber headspace mixing allows estimating methane fluxes with a smaller error than in the case of measurements conducted without mixing, and CH 4 fluxes in such conditions can be 47 to 58% higher (depending on the chamber type) than in a chamber without fans. Using dynamic chambers and a fast analyzer to measure methane fluxes allows shortening the methane measurement process to a few minutes. On the other hand, using static chambers for methane flux measurements may lead to 70% underestimation of the calculated flux.K e y w o r d s: chamber measurements, methane, flux calculation method, biases in chamber measurements

Technical Note: Semi-rigid chambers for methane gas flux measurements on tree stems

“…These techniques were originally designed to measure CH 4 and carbon dioxide (CO 2 ) from samples manually taken with syringes and analysed by gas chromatography. The ratio between the gas exchange surface and the chamber volume (S c / V tot ) was transposed from soil chambers and was not necessarily adapted to the lower fluxes found in tree stems, and are therefore often too high (Hutchinson and Livingston, 2001). In other words, if the chambers are too large for a given exchange surface, mixing problems may occur, making it important to circulate the air in their headspace (Hutchinson and Livingston, 1993;Rusch and Rennenberg, 1998).…”

Dependence of spectral characteristics on parameters describing CO2 exchange between crop species and the atmosphere

“…Air circulated between the chamber and the analyser within a closed loop. The measurement system comprised a CR1000 data logger (Campbell Scientific, USA) recording data on CO 2 concentration every 5 s (Chojnicki et al, 2010;Juszczak, 2013;Juszczak et al, 2012Juszczak et al, , 2013. Additionally, a SKP215 sensor (Skye Instruments Ltd. UK) installed in the chamber was also used to measure the intensity of incoming photosynthetically active radiation (PARi) during the NEP measurements, while a set of T-107 thermistors (Campbell Scientific, Utah, USA) was used to measure soil temperature at 2 and 5 cm depths.…”

“…Apart from the EC technique, gas fluxes exchanged between the ecosystem and the atmosphere are also measured using e.g. the chamber technique, applied in this paper (Juszczak, 2013;Urbaniak et al, 2016). It is a method based on point measurements and, therefore, is very well adapted to heterogeneous surfaces, in which EC systems may not be applied.…”

Exchange of the Greenhouse Gases Methane and Nitrous Oxide Between the Atmosphere and a Temperate Peatland in Central Europe

“…One of the disadvantages of chamber measurements is that they are commonly done manually, thus a frequency of the measurements is rather small and often not sufficient to capture a number of transient fluxes that occur within hours and are related to ebullition (Lai 2009). What is more, manual chamber measurements introduce many artifacts that may influence measured fluxes significantly (Davidson et al 2002;Christiansen et al 2011;Juszczak 2013). Considering the above, the automated chambers are usually deployed in order to do analyses several times per day.…”