Modeling flocculation processes : intercomparison of a size class-based model and a distribution-based model

Type Article
Date 2011-07
Language English
Author(s) Maerz Joeran1, Verney RomaricORCID2, Wirtz Kai3, Feudel Ulrike1
Affiliation(s) 1 : Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg,POB 2503, 26111 Oldenburg, Germany
2 : IFREMER, Hydrodynam & Sediment Dynam Lab DYNECO PHYSED, F-29280 Plouzane, France
3 : GKSS Research Center, Institute for Coastal Research, Geesthacht, Germany
Source Continental Shelf Research (0278-4343) (Pergamon-elsevier Science Ltd), 2011-07 , Vol. 31 , N. 10 , P. S84-S93
DOI 10.1016/j.csr.2010.05.011
WOS© Times Cited 29
Keyword(s) Suspended particulate matter (SPM), Flocculation/aggregation, Size class-based model, Distribution-based model, Tidal dynamics, Model comparison
Abstract Modeling suspended particulate matter (SPM) dynamics is essential to calculate sediment transport budgets and to provide relevant knowledge for the understanding of biogeochemical cycles in coastal waters. Natural flocs are characterized by their size, shape, structure and density that determine their settling velocity and therefore their vertical as well as horizontal transport. During transport, several processes, in particular aggregation and fragmentation, alter these particle properties. In the present study, we compare two different 0D modeling approaches for flocculation processes, a size class-based (SCB) model and a distribution-based (DB) model that follows the first moment of the particle distribution function. The study leads to an improved understanding of both models, which aim to better resolve SPM dynamics in spatial and ecosystem models in the near future. Both models are validated using data from laboratory experiments. The time evolution of the particle dynamics subjected to tidal forcing is represented equally well by both models, in particular in terms of (i) the mean diameter, (ii) the computed mean settling velocity and (iii) the particle size distribution. A sensitivity study revealed low sensitivity to changes in the collision efficiency and initial conditions, but a high sensitivity with respect to the particles’ fractal dimension. The latter is an incitation to enhance the knowledge on processes related to changes of fractal dimension in order to further improve SPM transport models. The limitations of both models are discussed. The model intercomparison revealed that the SCB model is useful for studies focussing on the time evolution of floc distributions, especially under highly variable conditions. By contrast, the DB model is more suitable for studies dealing with larger spatial scales and, moreover, with coupled marine physical–biogeochemical systems, as it is computationally very effective.
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