Effects of microbial activity on incipient motion and erosion of sediment

Sediment erosion can be significantly affected by microbial activity. In this study, samples of sediments (inorganic sands) with different particle sizes were inoculated with microorganisms and incubated for different time periods to examine sediment erosion and incipient motion of the sediment. Microbial activity created biofilm which adhered to particles on the upper layer and in the interstices of the sediment, so increasing the viscosity of the sediment and smoothing the sediment–water interface. The critical shear stress consistently showed the same changes for all samples at different incubation periods: it increased rapidly in the early stage, reached a maximum in the middle stage, and decreased slightly in the late stage. This behavior was similar to the growth pattern of the biofilm. As the median diameter of sediment particles increased, the effect of microbial activity on sediment characteristics lessened. The effect of the biofilm was analyzed, and we modified the Shields number to evaluate the resistance to erosion and incipient motion conditions for the sediment after microbial activity. Analysis of the Shields curve for the biofilm-bound sediments showed that microbial activity significantly influences the resistance to erosion of the sediment when the Reynolds number (Re*) ranged from 0.2 to 50, but the influence is relatively small outside that range.