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Modelling particle size distribution dynamics in marine waters
Li, X.; Zang, J.-J.; Lee, J.H.W. (2004). Modelling particle size distribution dynamics in marine waters. Wat. Res. 38(5): 1305-1317
In: Water Research. Elsevier: Oxford; New York. ISSN 0043-1354, more
Peer reviewed article  

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  • Li, X.
  • Zang, J.-J.
  • Lee, J.H.W.

    Numerical simulations were carried out to determine the particle size distribution (PSD) in marine waters byaccounting for particle influx, coagulation, sedimentation and breakage. Instead of the conventional rectilinear modeland Euclidean geometry, a curvilinear collision model and fractal scaling mathematics were used in the models. Asteady-state PSD can be achieved after a period of simulation regardless of the initial conditions. The cumulative PSDin the steadystate follows a power-law function, which has three linear regions after log-log transformation, withdifferent slopes corresponding to the three collision mechanisms, Brownian motion, fluid shear and differentialsedimentation. The PSD slope varies from -3.5 to -1.2 as a function of the size range and the fractal dimension of theparticles concerned. The environmental conditions do not significantlyalter the PSD slope, although they maychangethe position of the PSD and related particle concentrations. The simulation demonstrates a generalityin the shape ofthe steady-state PSD in the ocean, which is in agreement with many field observations. Breakage does not affect the sizedistribution of small particles, while a strong shear maycause a notable change in the PSD for larger and fractalparticles only. The simplified approach of previous works using dimensional analysis still offers valuableapproximations for the PSD slopes, although the previous solutions do not always agree with the simulation results.The variation in the PSD slope observed in field investigations can be reproduced numerically. It is argued that nonsteady-state conditions in natural waters could be the main reason for the deviation of PSD slopes. A change in thenature of the particles, such as stickiness, and environmental variables, such as particle input and shear intensity, couldforce the PSD to shift from one steadystate to another. During such a transition, the PSD slope mayvaryto someextent with the particle population dynamics.

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