The role of sediment structure in gas bubble storage and release
The role of sediment structure in gas bubble storage and release
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DOI：
10.1002/2016jg003456
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发表时间：
2016-07-01
影响因子：
3.7
通讯作者：
Lorke, A.
中科院分区：
文献类型：
--
作者：
Liu, L.;Wilkinson, J.;Lorke, A.
沸腾是内陆沃茨甲烷排放的重要途径。然而，控制水生沉积物中甲烷气泡形成和释放的机制仍不清楚。通过室内培养实验研究了三种不同类型天然沉积物中甲烷气泡的形成、储存和释放对静水头下降的响应。将均质化的粘土质、粉质和桑迪沉积物（最初在柱的深度上是准均匀的）在室内培养3周。我们观察到三个不同阶段的甲烷气泡的形成和释放：第一阶段微气泡的形成，取代移动的水从沉积物孔隙中可以忽略不计沸腾;第二阶段大气泡的形成，取代周围的沉积物，同时增加沸腾;和第三阶段形成的管道相对稳定的沸腾。最大深度平均体积气体含量在稳定状态下变化从粘土的18.8%到粉砂质的12.0%和桑迪沉积物的13.2%。天然气在沉积柱中的储存表现出强烈的垂直分层性：大部分游离气储存在上层，其厚度随沉积物粒度而变化。个别沸腾发作的幅度与静水头下降呈线性相关，从粘土质到桑迪再到粉砂质沉积物，并且超过了仅从气体膨胀估计的幅度，表明孔隙水甲烷的释放。这些研究结果与能够确定主要沉积物类型和沉积区的流体动力学模型相结合，可以帮助解决内陆沃茨中到大尺度甲烷沸腾的空间不均匀性。
Ebullition is an important pathway for methane emission from inland waters. However, the mechanisms controlling methane bubble formation and release in aquatic sediments remain unclear. A laboratory incubation experiment was conducted to investigate the dynamics of methane bubble formation, storage, and release in response to hydrostatic head drops in three different types of natural sediment. Homogenized clayey, silty, and sandy sediments (initially quasi-uniform through the depth of the columns) were incubated in chambers for 3weeks. We observed three distinct stages of methane bubble formation and release: stage Imicrobubble formation-displacing mobile water from sediment pores with negligible ebullition; stage IIformation of large bubbles, displacing the surrounding sediment with concurrent increase in ebullition; and stage IIIformation of conduits with relatively steady ebullition. The maximum depth-averaged volumetric gas content at steady state varied from 18.8% in clayey to 12.0% in silty and 13.2% in sandy sediment. Gas storage in the sediment columns showed strong vertical stratification: most of the free gas was stored in an upper layer, whose thickness varied with sediment grain size. The magnitude of individual ebullition episodes was linearly correlated to hydrostatic head drop and decreased from clayey to sandy to silty sediment and was in excess of that estimated from gas expansion alone, indicating the release of pore water methane. These findings combined with a hydrodynamic model capable of determining dominant sediment type and depositional zones could help resolve spatial heterogeneities in methane ebullition at medium to larger scales in inland waters.