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 by microorganisms influenced particle deposition to a sediment bed. The particle deposition decreased with increasing EPS, because the EPS filled the pore spaces between individual sediment grains, reducing the porosity of the sediment bed. With decreased porosity, newly deposited particles could not settle in between the grains of the bed, so that particles were more exposed to the flow, making resuspension easier and leading to decreased deposition. For the same level of bio‐cohesion, increasing the near‐bed turbulence diminished deposition. For the vegetated channel, as bio‐cohesion increased, particles were easily resuspended around individual stems due to the enhanced exposure effect, expanding the regions where deposition was excluded and leading to a more heterogeneous spatial distribution of deposition. The effect of EPS was negligible for the smallest velocity magnitude, for which all particles deposited, and for largest velocity magnitude, for which most particles were resuspended.