Gas bubble transport and emissions for shallow peat from a northern peatland: The role of pressure changes and peat structure
Gas bubble transport and emissions for shallow peat from a northern peatland: The role of pressure changes and peat structure
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北部泥炭地浅层泥炭的气泡传输和排放：压力变化和泥炭结构的作用
DOI：
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
L. Slater
中科院分区：
文献类型：
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作者：
Xi Chen;L. Slater
气泡是泥炭地释放甲烷的重要途径。泥炭中控制气泡传输和排放的机制仍不确定。因此，在实验室实验中测试了静水压力和泥炭结构对浅层泥炭中气泡动力学的影响。从凸起的沼泽中取出泥炭整料并保持在饱和状态。通过土壤物理特性（孔隙率、体积密度）支持的非侵入性介电常数测量确定了三个不同的层。实验的第一阶段涉及监测稳定压力和温度条件下气泡的积累。数据显示，有证据表明气泡受到 10 至 15 厘米深度的浅半限制层的阻碍。随着时间的推移，记录在样品盒侧面观察到的可见气泡，以估计体积气体含量垂直分布的变化。使用复折射率模型 (CRIM) 得出的孔隙率估计表明，当施加的压力足够高时，气泡会扩大孔隙空间。第二阶段涉及通过在过饱和条件下反复增加和减少静水压力来触发捕获的气泡的释放。顶部空间压头和甲烷密度变化的比较证实，压力下降期间增加的浮力对于触发沸腾比压力增加期间增加流动性更重要。我们的研究结果证明了静水压力的变化对气泡尺寸的影响以及泥炭织物阻力的变化在调节泥炭地甲烷释放方面的重要性。
Gas bubbles are an important pathway for methane release from peatlands. The mechanisms controlling gas bubble transport and emissions in peat remain uncertain. The effects of hydrostatic pressure and peat structure on the dynamics of gas bubbles in shallow peat were therefore tested in laboratory experiments. A peat monolith was retrieved from a raised bog and maintained in a saturated state. Three distinct layers were identified from noninvasive permittivity measurements supported by soil physical properties (porosity, bulk density). Phase I of the experiment involved monitoring for the accumulation of gas bubbles under steady pressure and temperature conditions. The data showed evidence for gas bubbles being impeded by a shallow semiconfining layer at depths between 10 and 15 cm. Visible gas bubbles observed on the side of the sample box were recorded over time to estimate changes in the vertical distribution of volumetric gas content. Porosity estimates derived using the Complex Refraction Index Model (CRIM) suggest that gas bubbles enlarge the pore space when the exerted pressure is high enough. Phase II involved triggering release of trapped bubbles by repeatedly increasing and decreasing hydrostatic pressure in an oversaturated condition. Comparison of changes in pressure head and methane density in the head space confirmed that the increasing buoyancy force during drops in pressure is more important for triggering ebullition than increasing mobility during increases in pressure. Our findings demonstrate the importance of changes in hydrostatic pressure on bubble size and variations in resistance of the peat fabric in regulating methane releases from peatlands.