Erosion of biofilm-bound fluvial sediments

Vignaga, E., Sloan, D.M., Luo, X. , Haynes, H., Phoenix, V.R. and Sloan, W.T. (2013) Erosion of biofilm-bound fluvial sediments. Nature Geoscience, 6(9), pp. 770-774. (doi: 10.1038/ngeo1891)

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The movement of fluvial sediment shapes our rivers. Understanding sediment entrainment has been a goal of hydraulic engineers for almost a century1, 2. Previous sediment entrainment models have been informed by laboratory experiments using grains that were free from biological material3. 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.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Luo, Professor Xiaoyu and Sloan, Professor William and Vignaga, Miss Elisa and Haynes, Dr Heather and Phoenix, Dr Vernon
Authors: Vignaga, E., Sloan, D.M., Luo, X., Haynes, H., Phoenix, V.R., and Sloan, W.T.
College/School:College of Science and Engineering > School of Engineering > Infrastructure and Environment
College of Science and Engineering > School of Geographical and Earth Sciences
College of Science and Engineering > School of Mathematics and Statistics > Mathematics
Journal Name:Nature Geoscience
ISSN (Online):1752-0908

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
456331General and unifying concepts for wastewater treatment plant designWilliam SloanEngineering & Physical Sciences Research Council (EPSRC)EP/F007868/1ENG - ENGINEERING INFRASTRUCTURE & ENVIR
424791Developing theory on the formation, composition and structure of open microbial communities that can be used in engineering designWilliam SloanEngineering & Physical Sciences Research Council (EPSRC)EP/D073693/1ENG - ENGINEERING INFRASTRUCTURE & ENVIR
405371COMIX coupling of biofilm diversity and ecosystem functioning the role of communication and mixing in microbail landscapesWilliam SloanNatural Environment Research Council (NERC)NE/D522211/1ENG - ENGINEERING INFRASTRUCTURE & ENVIR