Preferential flow in the vadose zone and interface dynamics: Impact of microbial exudates
Preferential flow in the vadose zone and interface dynamics: Impact of microbial exudates
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DOI：
10.1016/j.jhydrol.2017.12.065
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发表时间：
2018-03-01
影响因子：
6.4
通讯作者：
Darnault, Christophe J. G.
中科院分区：
文献类型：
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作者：
Li, Biting;Pales, Ashley R.;Darnault, Christophe J. G.
在水文循环中，入渗过程是水进入土壤和地下水系统的一个关键组成部分。土壤入渗过程的非线性动力学产生了优先流，影响了土壤中的水分分布。优先流受水、土壤、植物和微生物之间相互作用的影响。虽然植物根系及其根沉积物与土壤水分运移之间的关系已被广泛研究，但微生物渗出物的影响仅在少数情况下进行了研究。在这里，作者研究了两种人工微生物渗出物儿茶酚和核黄素对渗透过程的影响，特别是不稳定的指状流，一种优先流动形式。流动实验研究了微生物渗出物的类型和浓度对不稳定指状流动的影响，在一个充满ASTM C778级配硅砂的二维槽中进行。利用光透射法（LTM）将通过砂水系统传输的光强捕获并转化为含水饱和度，对多孔介质中水的流动进行可视化和表征，并对多孔介质中水的时空分布进行成像和测量。利用光透射法测定了手指的流动模式、水饱和度的垂直和水平剖面，以及手指的尺寸（宽度）、数量和速度。通过测量（固）气-微生物渗出液体系的接触角和界面张力，研究了微生物渗出液对水润湿性的影响。所有入渗试验均观察到不稳定湿润锋产生指状流。实验结果表明，微生物渗出液的加入对渗透过程有影响，其饱和度剖面和手指宽度的测量结果与对照NaCl溶液不同。这些差异可能是由于微生物渗出物存在时持水能力的提高。最低儿茶酚溶液浓度（10 μ M）在所有儿茶酚溶液浓度和包括对照溶液在内的所有其他溶液（7.24 cm）中产生最大的指宽（9.69 cm）。此外，介质对儿茶酚溶液的润湿性随浓度的增加而增加。最高核黄素溶液浓度（1000 μ M）产生的指宽最高（7.75 cm）。然而，核黄素溶液的润湿性随浓度的增加而降低。我们的研究表明，微生物渗出物是微生物在环境中产生和释放的生化化合物，能够影响土壤入渗过程。本研究结果还表明，当Miller and Miller（1956）的标度理论应用于多孔介质的水动力标度时，应将（cos θ）（1/2）表示的接触角的影响纳入手指尺寸即手指宽度的标度中。(C) 2018 Elsevier B.V.版权所有
In the hydrological cycle, the infiltration process is a critical component in the distribution of water into the soil and in the groundwater system. The nonlinear dynamics of the soil infiltration process yield preferential flow which affects the water distribution in soil. Preferential flow is influenced by the interactions between water, soil, plants, and microorganisms. Although the relationship among the plant roots, their rhizodeposits and water transport in soil has been the subject of extensive study, the effect of microbial exudates has been studied in only a few cases. Here the authors investigated the influence of two artificial microbial exudates-catechol and riboflavin-on the infiltration process, particularly unstable fingered flow, one form of preferential flow. Flow experiments investigating the effects of types and concentrations of microbial exudates on unstable fingered flow were conducted in a two-dimensional tank that was filled with ASTM C778 graded silica sand. The light transmission method (LTM) which is based on capturing the light intensity transmitted through a sand-water system and then converting it into degree of water saturation was used to visualize and characterize the flow of water in porous media as well as to image and measure the spatial and temporal distribution of water in porous media. Flow patterns, vertical and horizontal profiles of the degree of water saturation of the fingers, as well as measurements of the fingers dimension (width), number, and velocity were determined using the light transmission method. Interfacial experiments exploring the influence of microbial exudates on the wettability behavior of water were performed by measuring the contact angle and the interfacial tension of the (solid)-gas-microbial exudate solution systems. Unstable wetting front generating fingered flow was observed in all infiltration experiments. The experimental results showed that the microbial exudate addition affected the infiltration process, as the measurements of the degree of saturation profiles and widths of the fingers differed from those of the control NaCl solution. These differences may be due to an improved water holding capacity in the presence of the microbial exudates. The lowest catechol solution concentration (10 mu M) produced the largest finger width (9.69 cm) among the tested catechol solution concentrations and all the other solutions including the control solution (7.24 cm). Moreover, the wettability of the medium for the catechol solution increased with an increase in concentration. The highest riboflavin solution concentration (1000 mu M) generated the highest finger width (7.75 cm) among the tested riboflavin solution concentrations. However, the wettability of the medium for the riboflavin solution decreased with an increase in concentration. Our study demonstrated that the microbial exudates which are biochemical compounds produced and released by microbes in the environment are capable of influencing the soil infiltration process. The results of this study also demonstrated that the influence of the contact angle expressed as (cos theta)(1/2) should be integrated in the scaling of the finger dimension, i.e., finger width, when the Miller and Miller (1956) scaling theory is applied for the hydrodynamic scaling in porous media. (C) 2018 Elsevier B.V. All rights reserved.