Biological Cohesion of Sediment Bed Diminishes Net Deposition of Fine Non‐Cohesive Particles Over Bare Bed and Within Model Emergent Canopies

Abstract

This study investigated how Extracelluar Polymetric Substances (EPS) produced bymicroorganisms influenced particle deposition to a sediment bed. The particle deposition decreased withincreasing EPS, because the EPS filled the pore spaces between individual sediment grains, reducing theporosity of the sediment bed. With decreased porosity, newly deposited particles could not settle in between thegrains of the bed, so that particles were more exposed to the flow, making resuspension easier and leading todecreased deposition. For the same level of bio‐cohesion, increasing the near‐bed turbulence diminisheddeposition. For the vegetated channel, as bio‐cohesion increased, particles were easily resuspended aroundindividual stems due to the enhanced exposure effect, expanding the regions where deposition was excluded andleading to a more heterogeneous spatial distribution of deposition. The effect of EPS was negligible for thesmallest velocity magnitude, for which all particles deposited, and for largest velocity magnitude, for whichmost particles were resuspended.