Sediment porewater exchange and solute release during ebullition
Sediment porewater exchange and solute release during ebullition
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沸腾过程中沉积物孔隙水交换和溶质释放
DOI：
10.1016/j.marchem.2005.09.014
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发表时间：
2006
期刊：
影响因子：
3
通讯作者：
S. Klein
中科院分区：
文献类型：
--
作者：
S. Klein
以氟化物为示踪剂，在实验室条件下测定了低渗透甲烷沉积物与上覆水之间的孔隙水沸腾交换。沉积物平衡与氟化物在3.1 mM，然后通过清洗无氟水4.5小时，以减少孔隙水浓度梯度和扩散通量。将平均体积为约0.23 ml的气泡以42 ml/m2/min的恒定速率注入试验室中沉积物-水界面下方4.6 cm处3 h，而对照室中不注入气泡。由于测试室中的沸腾和分子扩散以及仅在控制室中的分子扩散的组合，测试室和控制室的上覆水中的氟化物浓度随时间线性增加。试验箱中的氟通量约50%，大于在控制和差异归因于孔隙水的沸腾交换。试验室中的通量与气泡释放的体积速率密切相关（r2=0.99）。以气泡体积为基础，与释放的氟化物对应的孔隙水体积为0.069±0.006 ml孔隙水/ml气泡。每个气泡释放的体积为0.016±0.003 ml。当沸腾停止时，测试室中的通量降低至略低于对照室中的速率。在考虑到浓度梯度的微小差异后，试验室和对照室中的沸腾后通量几乎相同，表明气泡管和通风孔结构在没有沸腾的情况下不会增强扩散。计算表明，近地表溶质的分子扩散通量大于沸腾通量，但高度产甲烷和沸腾沉积物。
The ebullitive exchange of porewater between low-permeability methanogenic sediment and overlying water was measured in the laboratory using fluoride as a tracer. Sediment was equilibrated with fluoride at 3.1 mM, followed by purging with fluoride-free water for 4.5 h to decrease the porewater concentration gradient and diffusive flux. Bubbles with an average volume of about 0.23 ml were injected 4.6 cm below the sediment–water interface at a constant rate of 42 ml/m2/min for 3 h in the test chambers, while no bubbles were injected in the control chambers. Fluoride concentrations in the overlying water of both test and control chambers increased linearly with time, due to a combination of ebullition and molecular diffusion in the test chambers and molecular diffusion only in the control chambers. The fluoride fluxes in test chambers were about 50% greater than in the controls and the differences are attributed to ebullitive exchange of porewater. The flux in the test chambers correlated strongly (r2=0.99) with the volumetric rate of bubble release. On a bubble volume basis, the volume of porewater corresponding to the fluoride released was 0.069±0.006 ml porewater/ml bubbles. The volume released per bubble was 0.016±0.003 ml. When ebullition was stopped, flux in the test chamber decreased to a rate that was slightly less than in the control chamber. After accounting for slight differences in concentration gradients, the post-ebullition fluxes in the test and control chambers were nearly identical, indicating that the bubble tube and vent structures do not enhance diffusion in the absence of ebullition. Calculations suggest that molecular diffusive fluxes for near surface solutes are greater than ebullitive fluxes in all but highly methanogenic and ebullitive sediments.