resuspension

Resuspension is the process by which settled particles are entrained again into a surrounding medium, returning to suspension or becoming part of a moving slurry or cloud. In aquatic systems, resuspension refers to sediment lifted from the bed or banks into the water column by flowing water, waves, or currents. In the atmosphere, it describes the re-entrainment of dust, pollen, and other particulates into the air after deposition.

Initiation of resuspension typically requires a shear stress or aerodynamic lift that exceeds a critical value. This critical threshold depends on particle size and density, surface roughness, moisture, cohesion between particles, and any biofilms or vegetation on the surface. Once particles are in motion, they are transported by advection and turbulent diffusion and may settle again if flow conditions subside. Different particle types show different behaviors: non-cohesive sands and silts respond to stronger forcing, while cohesive clays may resist movement due to interparticle bonds. In air, wind speed governs the onset of soil resuspension, which can be reduced by surface moisture, crust formation, and vegetation.

Implications of resuspension are widespread. In water, it increases turbidity, redistributes nutrients and sediments, and can remobilize attached pollutants. In air, it raises concentrations of particulate matter, with potential health and climate effects. Human activities such as dredging, mining, construction, and farming can markedly enhance resuspension through disturbance or exposure of surface material. Measurement and modeling often focus on resuspension fluxes or rates, utilizing threshold-based concepts and transport equations, along with observational tools like sediment traps, turbidity meters, or air-quality monitors. Mitigation strategies include moisture management, vegetation or ground cover, windbreaks, and controlling flow or disturbance to limit particle entrainment.