Erosion of biofilm-bound fluvial sediments
Erosion of biofilm-bound fluvial sediments
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DOI：
10.1038/ngeo1891
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发表时间：
2013-09
影响因子：
18.3
通讯作者：
E. Vignaga;D. Sloan;Xiaoyu Luo;H. Haynes;V. Phoenix;W. Sloan
中科院分区：
文献类型：
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作者：
E. Vignaga;D. Sloan;Xiaoyu Luo;H. Haynes;V. Phoenix;W. Sloan
河流沉积物的运动塑造了我们的河流。近世纪来，认识泥沙运动一直是水利工程工作者的目标。以前的泥沙夹带模型是通过使用不含生物物质的颗粒的实验室实验得出的。然而，在自然河流环境中，沉积物总是被细菌覆盖，通常形成可见的生物膜，其中包括不同的物种聚集在粘性胞外多糖中。在这里，我们报告的实验室水槽与蓝藻生长在沉积物。我们表明，流行的模型，其中颗粒滚动在剪切速度的一些临界阈值，不适用于生物膜结合的沉积物。相反，生物稳定沉积物的行为更像一个弹性膜。流体流动在膜中产生振荡，这可能变得不稳定。超过一个特定的速度阈值，膜破裂和生物膜结合的沉积物块成为夹带灾难性的失败。我们使用一个数学模型的振荡膜在不可压缩流显示，不稳定的振荡将发生在广泛的弹性材料的属性在现实的河流流速。我们发现，在振荡发生的水平长度尺度是一个控制因素的生物稳定的沉积物初期泥沙夹带。
The movement of fluvial sediment shapes our rivers. Understanding sediment entrainment has been a goal of hydraulic engineers for almost a century,. Previous sediment entrainment models have been informed by laboratory experiments using grains that were free from biological material. In natural river settings, however, sediments are invariably covered by bacteria, often forming visible biofilms, which comprise diverse consortia of species housed in sticky extracellular polysaccharides. Here we report experiments in a laboratory flume with cyanobacteria grown over sediment. We show that the prevailing model, where grains roll over one another at some critical threshold in shear velocity, does not hold for biofilm-bound sediments. Instead, biostabilized sediment behaves more like an elastic membrane. Fluid flow produces oscillations in the membrane, which can become unstable. Beyond a particular threshold in velocity, the membrane fails catastrophically by ripping and clumps of biofilm-bound sediment become entrained. We use a mathematical model of an oscillating membrane in incompressible flow to show that unstable oscillations will occur over a wide range of elastic material properties at realistic river flow velocities. We find that the horizontal length scale over which oscillations occur is a controlling factor for incipient sediment entrainment of biostabilized sediments.