Methane emissions from sheep pasture, measured with an open-path eddy covariance system
Methane emissions from sheep pasture, measured with an open-path eddy covariance system
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DOI：
10.1111/j.1365-2486.2011.02466.x
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发表时间：
2011-12-01
影响因子：
11.6
通讯作者：
Skiba, Ute M.
中科院分区：
文献类型：
--
作者：
Dengel, Sigrid;Levy, Peter E.;Skiba, Ute M.
甲烷（CH4）是一种重要的温室气体，对全球变暖的贡献为0.4-0.5 wm（-2）。甲烷的排放有几个来源，包括湿地、稻田、白蚁和反刍动物。以前对农场动物甲烷通量的测量都是在非自然条件下、在实验室室内或戴着笨重的口罩的动物身上进行的。本研究利用新开发的LI-COR LI-7700开路甲烷分析仪，引入了CH4的涡动相关测量，以测量羊在牧场自由放牧时的场尺度通量。在夏季条件下，上午的甲烷通量平均为30 nmol m(2) s(1)，而下午的甲烷通量则在100 nmol m(-2) s（-1）以上，大约比土壤的少量甲烷排放大两个数量级。甲烷排放与气温或光合有效辐射没有明确的关系，但一些昼夜模式很明显，可能与羊的放牧行为和新陈代谢有关。在测量期间（2010年60-277天），累积甲烷通量为0.34 mol CH4 m(-2)，相当于134.3 g CO2当量m（-2）。相比之下，在同一时期测量到的二氧化碳（CO2）汇为819 g CO2当量m(-2)，但很可能其中大部分将在冬季释放回大气或作为场外损失（通过微生物和动物呼吸）。通过将甲烷通量除以每天田间羊的数量，我们计算出每头牲畜的CH4排放量为7.4 kg CH4羊（-1）年（-1），接近IPCC公布的8 kg CH4羊（-1）年（-1）的排放系数。
Methane (CH4) is an important greenhouse gas, contributing 0.4-0.5 W m(-2) to global warming. Methane emissions originate from several sources, including wetlands, rice paddies, termites and ruminating animals. Previous measurements of methane flux from farm animals have been carried out on animals in unnatural conditions, in laboratory chambers or fitted with cumbersome masks. This study introduces eddy covariance measurements of CH4, using the newly developed LI-COR LI-7700 open-path methane analyser, to measure field-scale fluxes from sheep grazing freely on pasture. Under summer conditions, fluxes of methane in the morning averaged 30 nmol m (2) s (1), whereas those in the afternoon were above 100 nmol m(-2) s(-1), and were roughly two orders of magnitude larger than the small methane emissions from the soil. Methane emissions showed no clear relationship with air temperature or photo-synthetically active radiation, but some diurnal pattern was apparent, probably linked to sheep grazing behaviour and metabolism. Over the measurement period (days 60-277, year 2010), cumulative methane fluxes were 0.34 mol CH4 m(-2), equating to 134.3 g CO2 equivalents m(-2). By comparison, a carbon dioxide (CO2) sink of 819 g CO2 equivalents m(-2) was measured over the same period, but it is likely that much of this would be released back to the atmosphere during the winter or as off-site losses (through microbial and animal respiration). By dividing methane fluxes by the number of sheep in the field each day, we calculated CH4 emissions per head of livestock as 7.4 kg CH4 sheep(-1) yr(-1), close to the published IPCC emission factor of 8 kg CH4 sheep(-1) yr(-1).