Experimental evidence of how the fractal structure controls the hydrodynamic resistance on granular aggregates moving through water

Maggi, Federico

doi:10.1016/j.jhydrol.2015.07.002

Cited by 21 publications

(8 citation statements)

References 44 publications

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“…Growing attention has been paid to how SPM dynamics changes in the presence of a biological phase in addition to the mineral phase. The consistent finding throughout the recent literature is that although generally larger in size, biomineral aggregates are subject to higher drag and have lower excess density than mineral aggregates because of their lower capacity dimension, and thus, their settling velocity is not substantially different from mineral aggregates (Maggi, 2013(Maggi, , 2015Maggi, Manning, & Winterwerp, 2006;Maggi & Tang, 2015;Shang et al, 2014;Tan et al, 2012;Tang & Maggi, 2016). It is noteworthy that earlier experiments have also shown a high variance in biomineral SPM geometric properties such as size L and capacity dimension d (Tang & Maggi, 2017), thus suggesting that the heterogeneity is particularly high relative to our current NGUYEN ET AL.…”

Section: Introductionsupporting

confidence: 59%

Optical Measurement of Cell Colonization Patterns on Individual Suspended Sediment Aggregates

2017

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Microbial processes can make substantial differences to the way in which particles settle in aquatic environments. A novel method (OMCEC, optical measurement of cell colonization) is introduced to systematically map the biological spatial distribution over individual suspended sediment aggregates settling through a water column. OMCEC was used to investigate (1) whether a carbon source concentration has an impact on cell colonization, (2) how cells colonize minerals, and (3) if a correlation between colonization patterns and aggregate geometry exists. Incubations of Saccharomyces cerevisiae and stained montmorillonite at four sucrose concentrations were tested in a settling column equipped with a full‐color microparticle image velocimetry system. The acquired high‐resolution images were processed to map the cell distribution on aggregates based on emission spectra separation. The likelihood of cells colonizing minerals increased with increasing sucrose concentration. Colonization patterns were classified into (i) scattered, (ii) well touched, and (iii) poorly touched, with the second being predominant. Cell clusters in well‐touched patterns were found to have lower capacity dimension than those in other patterns, while the capacity dimension of the corresponding aggregates was relatively high. A strong correlation of colonization patterns with aggregate biomass fraction and properties suggests dynamic colonization mechanisms from cell attachment to minerals, to joining of isolated cell clusters, and finally cell growth over the entire aggregate. This paper introduces a widely applicable method for analyses of microbial‐affected sediment dynamics and highlights the microbial control on aggregate geometry, which can improve the prediction of large‐scale morphodynamics processes.

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Section: Introductionsupporting

confidence: 59%

Optical Measurement of Cell Colonization Patterns on Individual Suspended Sediment Aggregates

2017

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“…Different drag properties that were not adequately captured by our boundary fractal number analysis could explain this discrepancy. Maggi (2015) showed experimentally that internal and external fractal characteristics of the aggregates can induce nonlinear hydrodynamic effects through their influence on surface roughness and porosity. In particular, feeding activity of the rotifers at the surface of the aggregates could have led to an increase of surface roughness at a scale unexpectedly not resolvable on our images given rotifers' small size (usually a few hundred microns) compared to our millimeter-sized aggregates.…”

Section: Minerals and Zooplankton Roles In Stokes' Law Applicabilitymentioning

confidence: 99%

New guidelines for the application of Stokes' models to the sinking velocity of marine aggregates

Laurenceau-Cornec

Moigne

Gallinari

et al. 2019

Limnology & Oceanography

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Numerical simulations of ocean biogeochemical cycles need to adequately represent particle sinking velocities (SV). For decades, Stokes' Law estimating particle SV from density and size has been widely used. But while Stokes' Law holds for small, smooth, and rigid spheres settling at low Reynolds number, it fails when applied to marine aggregates complex in shape, structure, and composition. Minerals and zooplankton can alter phytoplankton aggregates in ways that change their SV, potentially improving the applicability of Stokes' models. Using rolling cylinders, we experimentally produced diatom aggregates in the presence and absence of minerals and/or microzooplankton. Minerals and to a lesser extent microzooplankton decreased aggregate size and roughness and increased their sphericity and compactness. Stokes' Law parameterized with a fractal porosity modeled adequately size‐SV relationships for mineral‐loaded aggregates. Phytoplankton‐only aggregates and those exposed to microzooplankton followed the general Navier‐Stokes drag equation suggesting an indiscernible effect of microzooplankton and a drag coefficient too complex to be calculated with a Stokes' assumption. We compared our results with a larger data set of ballasted and nonballasted marine aggregates. This confirmed that the size‐SV relationships for ballasted aggregates can be simulated by Stokes' models with an adequate fractal porosity parameterization. Given the importance of mineral ballasting in the ocean, our findings could ease biogeochemical model parameterization for a significant pool of particles in the ocean and especially in the mesopelagic zone where the particulate organic matter : mineral ratio decreases. Our results also reinforce the importance of accounting for porosity as a decisive predictor of marine aggregate SV.

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“…However, how microbial composition changes against a changed environment is a complex problem that has been difficult to explain in its entirety. For instance, microorganisms colonizing and living on SPM (e.g., Grossart et al, ; Kiørboe et al, , ; Kirchman, ) have been found to alter the chemistry, structure, and ambient characteristics of their habitat (e.g., size, surface irregularity, compactness, shear strength, permeability, stability, and sedimentation rate; Jones et al, ; Lubarsky et al, ; Maggi, ; Maggi & Tang, ; Meadows et al, ; Tang & Maggi, ). Offsets in microbial ecological balance stemming from external perturbations such as changes in water temperature, nutrient concentrations, and presence of contaminants may therefore induce modification to the structure, transport, and deposition of SPM.…”

Section: Introductionmentioning

confidence: 99%

Biomodulation of Nitrogen Cycle in Suspended Sediment

Tang

Maggi

2018

JGR Biogeosciences

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Biogeochemical experiments and modeling were coupled to investigate how nutrient leaching to aquatic ecosystems changes the dynamics of microbial community on suspended sediment and how these changes modulate the nitrogen cycle. Mineral suspensions amended with inorganic nitrogen (NH 4+ and NO 3−) and inoculated with native sedimentary microbial strains were tested in a settling column under continuous water quality measurements. Experiments were used to calibrate and validate a kinetic model that explicitly described the chemical adsorption on minerals, aqueous complexation, gas dissolution, microbial metabolism, necromass dynamics, and microbial competition for limiting substrates. Modeling revealed that the interactions between microbial functional groups were highly nonlinear and highly sensitive to changes in nutrient and dissolved oxygen concentrations, showing shifts in regimes where a functional group became prevalent over the others. Our results suggested that necromass dynamics played a major role in sustaining microbial growth in low nutrient conditions and had an important control over the N cycle. The reaction network and model structure presented in this study provide a tool to analyze and predict the long‐term nutrient dynamics of both natural and engineered aquatic ecosystems.

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Experimental evidence of how the fractal structure controls the hydrodynamic resistance on granular aggregates moving through water

Cited by 21 publications

References 44 publications

Optical Measurement of Cell Colonization Patterns on Individual Suspended Sediment Aggregates

Optical Measurement of Cell Colonization Patterns on Individual Suspended Sediment Aggregates

New guidelines for the application of Stokes' models to the sinking velocity of marine aggregates

Biomodulation of Nitrogen Cycle in Suspended Sediment

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