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Experimental Sensitivity Analysis of Oxygen Transfer in the Capillary Fringe

机译：毛细管边缘氧转移的实验灵敏度分析

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摘要

Oxygen transfer in the capillary fringe (CF) is of primary importance for a wide variety of biogeochemical processes occurring in shallow groundwater systems. In case of a fluctuating groundwater table two distinct mechanisms of oxygen transfer within the capillary zone can be identified: vertical predominantly diffusive mass flux of oxygen, and mass transfer between entrapped gas and groundwater. In this study, we perform a systematic experimental sensitivity analysis in order to assess the influence of different parameters on oxygen transfer from entrapped air within the CF to underlying anoxic groundwater. We carry out quasi two-dimensional flow-through experiments focusing on the transient phase following imbibition to investigate the influence of the horizontal flow velocity, the average grain diameter of the porous medium, as well as the magnitude and the speed of the water table rise. We present a numerical flow and transport model that quantitatively represents the main mechanisms governing oxygen transfer. Assuming local equilibrium between the aqueous and the gaseous phase, the partitioning process from entrapped air can be satisfactorily simulated. The different experiments are monitored by measuring vertical oxygen concentration profiles at high spatial resolution with a noninvasive optode technique as well as by determining oxygen fluxes at the outlet of the flow-through chamber. The results show that all parameters investigated have a significant effect and determine different amounts of oxygen transferred to the oxygen-depleted groundwater. Particularly relevant are the magnitude of the water table rise and the grain size of the porous medium.
机译：对于在浅层地下水系统中发生的各种生物地球化学过程，毛细边缘（CF）中的氧气转移至关重要。在地下水位波动的情况下，可以确定毛细区内氧气转移的两种不同机理：垂直的主要是扩散的氧气质量通量，以及夹带的气体和地下水之间的质量转移。在这项研究中，我们进行了系统的实验灵敏度分析，以评估不同参数对CF中截留的空气向底层缺氧地下水中氧气转移的影响。我们针对吸收后的瞬态阶段进行了准二维流过实验，以研究水平流速，多孔介质的平均粒径以及地下水位上升速度和速度的影响。 。我们提出了一个数值流动和运输模型，定量地代表了控制氧气转移的主要机制。假设水相和气相之间存在局部平衡，则可以令人满意地模拟截留空气的分配过程。通过使用非侵入式光电技术在高空间分辨率下测量垂直氧气浓度分布以及通过确定流通室出口处的氧气通量来监控不同的实验。结果表明，所研究的所有参数均具有显着影响，并确定了转移到贫氧地下水中的不同量的氧气。特别重要的是地下水位上升的幅度和多孔介质的粒径。

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  • 来源
    《Ground water》 |2014年第1期|37-49|共13页
  • 作者

    Christina M. Haberer; Olaf A. Cirpka; Massimo Rolle; Peter Grathwohl;

  • 作者单位

    Center for Applied Geoscience, University of Tubingen, HolderlinstraBe 12, D-72O74 Tubingen, Germany;

    University of Tubingen,HolderlinstraBe 12, D-72074 Tubingen, Germany;

    University of Tubingen,HolderlinstraBe 12, D-72074 Tubingen, Germany;

    University of Tubingen,HolderlinstraBe 12, D-72074 Tubingen, Germany;

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