The pervasive role of biological cohesion in bedform development

Jonathan Malarkey (), Jaco H. Baas, Julie A. Hope, Rebecca J. Aspden, Daniel R. Parsons, Jeff Peakall, David M. Paterson, Robert J. Schindler, Leiping Ye, Ian D. Lichtman, Sarah J. Bass, Alan G. Davies, Andrew J. Manning and Peter D. Thorne
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Jonathan Malarkey: School of Ocean Sciences, Bangor University
Jaco H. Baas: School of Ocean Sciences, Bangor University
Julie A. Hope: Sediment Ecology Research Group, School of Biology, University of St Andrews
Rebecca J. Aspden: Sediment Ecology Research Group, School of Biology, University of St Andrews
Daniel R. Parsons: Environment and Earth Sciences, University of Hull
Jeff Peakall: School of Earth and Environment, University of Leeds
David M. Paterson: Sediment Ecology Research Group, School of Biology, University of St Andrews
Robert J. Schindler: School of Marine Science and Engineering, Plymouth University
Leiping Ye: Environment and Earth Sciences, University of Hull
Ian D. Lichtman: School of Ocean Sciences, Bangor University
Sarah J. Bass: School of Marine Science and Engineering, Plymouth University
Alan G. Davies: School of Ocean Sciences, Bangor University
Andrew J. Manning: Environment and Earth Sciences, University of Hull
Peter D. Thorne: National Oceanography Centre, Joseph Proudman Building, 6 Brownlow Street

Nature Communications, 2015, vol. 6, issue 1, 1-6

Abstract: Abstract Sediment fluxes in aquatic environments are crucially dependent on bedform dynamics. However, sediment-flux predictions rely almost completely on clean-sand studies, despite most environments being composed of mixtures of non-cohesive sands, physically cohesive muds and biologically cohesive extracellular polymeric substances (EPS) generated by microorganisms. EPS associated with surficial biofilms are known to stabilize sediment and increase erosion thresholds. Here we present experimental data showing that the pervasive distribution of low levels of EPS throughout the sediment, rather than the high surficial levels of EPS in biofilms, is the key control on bedform dynamics. The development time for bedforms increases by up to two orders of magnitude for extremely small quantities of pervasively distributed EPS. This effect is far stronger than for physical cohesion, because EPS inhibit sand grains from moving independently. The results highlight that present bedform predictors are overly simplistic, and the associated sediment transport processes require re-assessment for the influence of EPS.

Date: 2015
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DOI: 10.1038/ncomms7257

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