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

机译：在实验室实验中评估腔室放置，手动采样和顶空混合对CH4通量的影响

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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 (CH4) 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 mu g CH4 m(-2) h(-1). We found that the placement of a non-vented chamber disturbed the initial CH4 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 mu g CH4 m(-2) h(-1) compared to 134 +/- 26 mu g CH4 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 CH4 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 goodness-of-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.
机译：对两种类型的封闭式静态腔室进行了实验室实验，以评估腔室放置，手动顶空进样和顶空混合对甲烷（CH4）通量的影响。将腔室通量与腔室校准系统中的已知参考通量进行比较。使用三种类型的土壤（粗干，细干和细湿夸脱的沙子）进行了测量，五个通量范围为60至2000μgCH4 m（-2）h（-1）。我们发现，放置一个非通风的腔室会干扰腔室顶部空间中最初的CH4浓度发展10到30 s。从通量计算中排除此短暂时间后，与134 +/- 26μgCH4相比，通量估计值较低（平均值+/- SE）为126 +/- 26μgCH4 m（-2）h（-1）如果包括来自机柜时间零的数据，则为m（-2）h（-1）。我们还发现，在非混合室（无风扇混合）中，通过注射器或气瓶进行的气体采样会干扰封闭过程中CH4浓度的升高。此外，与测得的参考通量相比，非混合室中的通量估计值被大大低估了（平均36％）。但是，使用风扇在封闭期间不断混合腔室顶部空间，显着提高了用于计算通量的回归分析的拟合优度，并进一步消除了手动采样对浓度发展的干扰。我们建议在放置腔室时对腔室进行排气，并且将风扇用作静态腔室的组成部分，同时应避免与注射器的顶空混合。

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