Michael Fettweis - Academia.edu (original) (raw)
Papers by Michael Fettweis
Ocean Dynamics
This paper presents the mud dynamics in the harbor basin of Zeebrugge in the Southern North Sea b... more This paper presents the mud dynamics in the harbor basin of Zeebrugge in the Southern North Sea based on an analysis of field data. Mud is typically transported into and within the harbor basin through advection of suspended particulate matter (SPM). Three important timescales have been identified. On the intratidal timescale, sediment import occurs from 2 h before high water to high water. Flood currents in the North Sea (directed northeastward along the Belgian coast) drive the primary gyre in the harbor mouth which is advected into the basin during rising tide. This results in water inflow near the eastern breakwater and outflow near the western breakwater. Because of sediment settling in the harbor, this results in a net import of SPM. During spring tide, the SPM flux into the harbor basin is two to four times higher than during neap tide. However, the volume of sediment removed from the port by maintenance dredging is kept constant over the spring-neap cycle, causing the amount of mud in the harbor basin to grow around spring tide conditions. On the seasonal timescale, mud volume within the harbor basin is larger in winter and reaches a minimum at the beginning of autumn. Moreover, the measured densities within the deposited mud layers are lower in winter than in summer. The most shallow point of the 210-kHz reflector is also more shallow in winter. Finally, the profile of the interface of the mud layer in the sheltered Albert II dock is more horizontal in winter than in summer, suggesting seasonal variations in the strength of the mud layer. The question to what degree the seasonal variation of thickness and density of the fluid mud layer is related to differences in the suspended sediment input, to differences in the settling rates of suspended flocs, or to the mud consolidation rate remains open however. The data do not show a strong influence of meteorological conditions (waves, freshwater inflow) on siltation rates in the harbor basin.
... Activiteitsrapport 3 (1 juli 2009 - 31 december 2009) Michael Fettweis, Dries Van den Eynde, ... more ... Activiteitsrapport 3 (1 juli 2009 - 31 december 2009) Michael Fettweis, Dries Van den Eynde, Frederic Francken, Vera Van Lancker MOMO/4/MF/201003/NL/AR/3 ... De W-SW-wind heeftmarien water aangevoerd met een lage SPM concentratie. ...
![Research paper thumbnail of Volumetric evolution of the Flemish sandbanks: measurements and modelling [PPP]](https://attachments.academia-assets.com/41188368/thumbnails/1.jpg)
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Methods in Oceanography, 2012
Measurements of aggregate size, suspended particulate matter (SPM) concentration and current velo... more Measurements of aggregate size, suspended particulate matter (SPM) concentration and current velocity have been carried out in the Belgian coastal zone (southern North Sea). Two stations were situated in the coastal turbidity maximum zone; another station was located more offshore at the edge of this turbidity maximum. The data have been collected using a LISST 100, OBS sensors, water samples and a bottom mounted ADCP. Turbulence (Kolmogorov microscale) has been modelled for the same period using a 3D numerical model. The results show that the size of the aggregates is significantly smaller in the coastal turbidity maximum area. The processes responsible for the occurrence of smaller aggregate size in the coastal zone compared with the more offshore location are: the higher turbulence; the smaller time available for the aggregates to grow up to an equilibrium size; the higher deposition of mud, resulting in a break-up of the flocs and the lower availability of organic matter, which may limit the size of the flocs.
Proceedings in Marine Science, 2007
Suspended particulate matter, SeaWiFS satellite images, in situ measurements, Belgian coastal wat... more Suspended particulate matter, SeaWiFS satellite images, in situ measurements, Belgian coastal waters Suspended Particulate Matter (SPM) surface concentration maps in the Belgian/Dutch coastal zone are retrieved from Sea WiFS images and are corrected using in situ measurements to obtain depth-averaged SPM concentration maps. A spatial correlation analysis of the derived maps shows that the area could be divided into three subregions where the correlations between the SPM concentrations are higher than 70%. Examination of in situ SPM concentration measurements reveals that during about 1/3 of the tidal cycle the SPM concentration is significantly higher than during the rest of the cycle. Strong vertical gradients are sometimes observed during periods with increased SPM concentration. A satellite image taken during such a period would underestimate the depth-averaged SPM concentration. Images taken during other periods better represents (except for some small corrections) the averaged SPM concentration. The methodology for obtaining the depth-averaged SPM concentration maps from surface SPM distributions derived from SeaWiFS images is positive but can be further improved.
Analysis of Multi-Temporal Remote Sensing Images - Proceedings of the Second International Workshop, 2004
Suspended particulate matter concentration (SPM) maps at water-surface were retrieved from 172 Se... more Suspended particulate matter concentration (SPM) maps at water-surface were retrieved from 172 SeaWiFS images using the MUMM turbid water extension to the SEADAS4.4 software and a regionally calibrated hydro-optical model. Examination of surface-SPM maps and the depth-averaged SPM derived from a 2D-hydrodynamic and sediment transport model over the BCZ shows interesting similarities. The effect of the neap-spring tide cycle on the satellite-derived SPM distribution is compared to the significant impact of this factor on modeled SPM distributions. Classification of the Belgian waters is carried out using the time-series of SeaWiFS-derived SPM maps and is explained in the light of the SPM transport modelling knowledge. This is preliminary step in this project to provide boundary conditions and initial data of SPM distribution to the coupled model.
Journal of Geophysical Research: Oceans, 2014
ABSTRACT The suspended particulate matter (SPM) concentration in the high turbidity zones of the ... more ABSTRACT The suspended particulate matter (SPM) concentration in the high turbidity zones of the southern North Sea is inversely correlated with chlorophyll (Chl) concentration. During winter SPM concentration is high and Chl concentration low and vice versa during summer. This seasonality has often been associated with the seasonal pattern in wind forcing. However, the decrease in SPM concentration corresponds well with the spring algal bloom. Does the decrease of SPM concentration caused by changing wind conditions cause the start of algae bloom, or does the algae bloom decrease SPM concentrations through enhanced flocculation and deposition? To answer the question, measurements from 2011 of particle size distribution (PSD), SPM and Chl concentrations from the southern North Sea have been analyzed. The results indicate that the frequency of occurrence of macroflocs has a seasonal signal, while seasonality has little impact upon floc size. The data from a highly turbid coastal zone suggest that the maximum size of the macroflocs is controlled by turbulence and the available flocculation time during a tidal cycle, but the strength of the macroflocs is controlled by the availability of sticky organic substances associated with enhanced primary production during spring and summer. The results highlight the shift from mainly microflocs and flocculi in winter towards more muddy marine snow with larger amounts of macroflocs in spring and summer. The macroflocs will reduce the SPM concentrations in the turbidity maximum area as they settle faster. Consequently, the SPM concentration decreases and the light condition increases in the surface layer enhancing algae growth further.
Water Research, 2012
Divalent cations have been reported to develop bridges between anionic polyelectrolytes and negat... more Divalent cations have been reported to develop bridges between anionic polyelectrolytes and negatively-charged colloidal particles, thereby enhancing particle flocculation. However, results from this study of kaolinite suspensions dosed with various anionic polyacrylamides (PAMs) reveal that Ca(2+) and Mg(2+) can lead to colloid stabilization under some conditions. To explain the opposite but coexisting processes of flocculation and stabilization with divalent cations, a conceptual flocculation model with (1) particle-binding divalent cationic bridges between PAM molecules and kaolinite particles and (2) polymer-binding divalent cationic bridges between PAM molecules is proposed. The particle-binding bridges enhanced flocculation and aggregated kaolinite particles in large, easily-settleable flocs whereas the polymer-binding bridges increased steric stabilization by developing polymer layers covering the kaolinite surface. Both the particle-binding and polymer-binding divalent cationic bridges coexist in anionic PAM- and kaolinite-containing suspensions and thus induce the counteracting processes of particle flocculation and stabilization. Therefore, anionic polyelectrolytes in divalent cation-enriched aqueous solutions can sometimes lead to the stabilization of colloidal particles due to the polymer-binding divalent cationic bridges.
Ocean Dynamics, 2014
ABSTRACT Multimodal particle size distributions (PSDs) of fine-grained cohesive sediments are com... more ABSTRACT Multimodal particle size distributions (PSDs) of fine-grained cohesive sediments are common in marine and coastal environments. The curve-fitting software in this study decomposed such multimodal PSDs into subordinate lognormal PSDs. Four modal peaks, consisting of four-level ordered structures of primary particles, flocculi, microflocs, and macroflocs, were identified and found to alternately rise and sink in a flow-varying tidal cycle due to shear-dependent flocculation. The four modal PSD could be simplified further into two discrete size groups of flocculi and flocs. This allowed the development of a two-class population balance equation (TCPBE) model with flocculi and flocs to simulate flocculation involving multimodal PSDs. The onedimensional vertical (1-DV) TCPBE model further incorporated the Navier-Stokes equation with the k-ε turbulence closure and the sediment mass balance equations. Multimodal flocculation as well as turbulent flow and sediment transport in a flow-varying tidal cycle could be simulated well using the proposed model. The 1-DV TCPBE was concluded to be the simplest model that is capable of simulating multimodal flocculation in the turbulent flow field of marine and coastal zones.
Ocean Dynamics, 2011
Abstract The effect of hydro-meteorological forcings (tidal and wind-induced flows) on the transp... more Abstract The effect of hydro-meteorological forcings (tidal and wind-induced flows) on the transport of suspended particulate matter (SPM), on the formation of high-concentrated mud suspensions and on the occurrence of sandmud suspensions has been studied using ...
Ocean Dynamics, 2011
Large sets of suspended particulate matter (SPM) concentration data from in situ and remote sensi... more Large sets of suspended particulate matter (SPM) concentration data from in situ and remote sensing (moderate resolution imaging spectroradiometer, MODIS) samplings in the Belgian nearshore area (southern North Sea) are combined in order to evaluate their heterogeneity and the sampling techniques. In situ SPM concentration measurements are from a vessel (tidal cycle) and from a tripod. During the tidal cycle measurements, vertical profiles of SPM concentration have been collected; these profiles have been used as a link between satellite surface and near-bed tripod SPM concentrations. In situ time series at fixed locations using a tripod are excellent witnesses of SPM concentrations under all weather conditions and may catch SPM concentration variability with a much finer scale. The heterogeneity has been statistically assessed by comparing the SPM concentration frequency distributions. Tidal cycle, tripod and MODIS datasets have different distributions and represent a different subpopulation of the whole SPM concentrations population. The differences between the datasets are related to meteorological conditions during the measurements; to near-bed SPM concentration dynamics, which are partially uncoupled from processes higher up in the water column; to the sampling methods or schemes and to measurement uncertainties. In order to explain the differences between the datasets, the tripod data have been subsampled using wave height conditions and satellite and tidal cycle sampling schemes.
Marine Pollution Bulletin, 2011
The impact of continuous disposal of fine-grained sediments from maintenance dredging works on th... more The impact of continuous disposal of fine-grained sediments from maintenance dredging works on the suspended particulate matter concentration in a shallow nearshore turbidity maximum was investigated during dredging experiment (port of Zeebrugge, southern North Sea). Before, during and after the experiment monitoring of SPM concentration using OBS and ADV altimetry was carried out at a location 5 km west of the disposal site. A statistical analysis, based on the concept of populations and sub-sampling, was applied to evaluate the effect. The data revealed that the SPM concentration near the bed was on average more than two times higher during the dredging experiment. The disposed material was mainly transported in the benthic layer and resulted in a long-term increase of SPM concentration and formation of fluid mud layers. The study shows that SPM concentration can be used as an indicator of environmental changes if representative time series are available.
Marine Geology, 2006
Measurements of aggregate size, suspended particulate matter (SPM) concentration and current velo... more Measurements of aggregate size, suspended particulate matter (SPM) concentration and current velocity have been carried out in the Belgian coastal zone (southern North Sea). Two stations were situated in the coastal turbidity maximum zone; another station was located more offshore at the edge of this turbidity maximum. The data have been collected using a LISST 100, OBS sensors, water samples and a bottom mounted ADCP. Turbulence (Kolmogorov microscale) has been modelled for the same period using a 3D numerical model. The results show that the size of the aggregates is significantly smaller in the coastal turbidity maximum area. The processes responsible for the occurrence of smaller aggregate size in the coastal zone compared with the more offshore location are: the higher turbulence; the smaller time available for the aggregates to grow up to an equilibrium size; the higher deposition of mud, resulting in a break-up of the flocs and the lower availability of organic matter, which may limit the size of the flocs.
Journal of Geophysical Research, 2012
1] Particle size distributions (PSDs) of suspended particulate matters in a coastal zone are logn... more 1] Particle size distributions (PSDs) of suspended particulate matters in a coastal zone are lognormal and multimodal in general. The multimodal PSD, which is caused by the mixing of multiple particle and aggregate size groups under flocculation and erosion/resuspension, is a record of the particle and aggregate dynamics in a coastal zone. Curve-fitting software was used to decompose the multimodal PSD into subordinate lognormal PSDs of primary particles, flocculi, microflocs, and macroflocs. The curve-fitting analysis for a time series of multimodal PSDs in the Belgian coastal zone showed the dependency of the multimodality on (1) shear-dependent flocculation in a flood and ebb tide, (2) breakage-resistant flocculation in the spring season, and (3) silt-sized particle erosion and advection in a storm surge. Also, for modeling and simulation purposes, the curve-fitting analysis and the settling flux estimation for the multimodal PSDs showed the possibility of using discrete groups of primary particles, flocculi, microflocs, and macroflocs as an approximation of a continuous multimodal PSD.
Ocean Dynamics
This paper presents the mud dynamics in the harbor basin of Zeebrugge in the Southern North Sea b... more This paper presents the mud dynamics in the harbor basin of Zeebrugge in the Southern North Sea based on an analysis of field data. Mud is typically transported into and within the harbor basin through advection of suspended particulate matter (SPM). Three important timescales have been identified. On the intratidal timescale, sediment import occurs from 2 h before high water to high water. Flood currents in the North Sea (directed northeastward along the Belgian coast) drive the primary gyre in the harbor mouth which is advected into the basin during rising tide. This results in water inflow near the eastern breakwater and outflow near the western breakwater. Because of sediment settling in the harbor, this results in a net import of SPM. During spring tide, the SPM flux into the harbor basin is two to four times higher than during neap tide. However, the volume of sediment removed from the port by maintenance dredging is kept constant over the spring-neap cycle, causing the amount of mud in the harbor basin to grow around spring tide conditions. On the seasonal timescale, mud volume within the harbor basin is larger in winter and reaches a minimum at the beginning of autumn. Moreover, the measured densities within the deposited mud layers are lower in winter than in summer. The most shallow point of the 210-kHz reflector is also more shallow in winter. Finally, the profile of the interface of the mud layer in the sheltered Albert II dock is more horizontal in winter than in summer, suggesting seasonal variations in the strength of the mud layer. The question to what degree the seasonal variation of thickness and density of the fluid mud layer is related to differences in the suspended sediment input, to differences in the settling rates of suspended flocs, or to the mud consolidation rate remains open however. The data do not show a strong influence of meteorological conditions (waves, freshwater inflow) on siltation rates in the harbor basin.
... Activiteitsrapport 3 (1 juli 2009 - 31 december 2009) Michael Fettweis, Dries Van den Eynde, ... more ... Activiteitsrapport 3 (1 juli 2009 - 31 december 2009) Michael Fettweis, Dries Van den Eynde, Frederic Francken, Vera Van Lancker MOMO/4/MF/201003/NL/AR/3 ... De W-SW-wind heeftmarien water aangevoerd met een lage SPM concentratie. ...
Methods in Oceanography, 2012
Measurements of aggregate size, suspended particulate matter (SPM) concentration and current velo... more Measurements of aggregate size, suspended particulate matter (SPM) concentration and current velocity have been carried out in the Belgian coastal zone (southern North Sea). Two stations were situated in the coastal turbidity maximum zone; another station was located more offshore at the edge of this turbidity maximum. The data have been collected using a LISST 100, OBS sensors, water samples and a bottom mounted ADCP. Turbulence (Kolmogorov microscale) has been modelled for the same period using a 3D numerical model. The results show that the size of the aggregates is significantly smaller in the coastal turbidity maximum area. The processes responsible for the occurrence of smaller aggregate size in the coastal zone compared with the more offshore location are: the higher turbulence; the smaller time available for the aggregates to grow up to an equilibrium size; the higher deposition of mud, resulting in a break-up of the flocs and the lower availability of organic matter, which may limit the size of the flocs.
Proceedings in Marine Science, 2007
Suspended particulate matter, SeaWiFS satellite images, in situ measurements, Belgian coastal wat... more Suspended particulate matter, SeaWiFS satellite images, in situ measurements, Belgian coastal waters Suspended Particulate Matter (SPM) surface concentration maps in the Belgian/Dutch coastal zone are retrieved from Sea WiFS images and are corrected using in situ measurements to obtain depth-averaged SPM concentration maps. A spatial correlation analysis of the derived maps shows that the area could be divided into three subregions where the correlations between the SPM concentrations are higher than 70%. Examination of in situ SPM concentration measurements reveals that during about 1/3 of the tidal cycle the SPM concentration is significantly higher than during the rest of the cycle. Strong vertical gradients are sometimes observed during periods with increased SPM concentration. A satellite image taken during such a period would underestimate the depth-averaged SPM concentration. Images taken during other periods better represents (except for some small corrections) the averaged SPM concentration. The methodology for obtaining the depth-averaged SPM concentration maps from surface SPM distributions derived from SeaWiFS images is positive but can be further improved.
Analysis of Multi-Temporal Remote Sensing Images - Proceedings of the Second International Workshop, 2004
Suspended particulate matter concentration (SPM) maps at water-surface were retrieved from 172 Se... more Suspended particulate matter concentration (SPM) maps at water-surface were retrieved from 172 SeaWiFS images using the MUMM turbid water extension to the SEADAS4.4 software and a regionally calibrated hydro-optical model. Examination of surface-SPM maps and the depth-averaged SPM derived from a 2D-hydrodynamic and sediment transport model over the BCZ shows interesting similarities. The effect of the neap-spring tide cycle on the satellite-derived SPM distribution is compared to the significant impact of this factor on modeled SPM distributions. Classification of the Belgian waters is carried out using the time-series of SeaWiFS-derived SPM maps and is explained in the light of the SPM transport modelling knowledge. This is preliminary step in this project to provide boundary conditions and initial data of SPM distribution to the coupled model.
Journal of Geophysical Research: Oceans, 2014
ABSTRACT The suspended particulate matter (SPM) concentration in the high turbidity zones of the ... more ABSTRACT The suspended particulate matter (SPM) concentration in the high turbidity zones of the southern North Sea is inversely correlated with chlorophyll (Chl) concentration. During winter SPM concentration is high and Chl concentration low and vice versa during summer. This seasonality has often been associated with the seasonal pattern in wind forcing. However, the decrease in SPM concentration corresponds well with the spring algal bloom. Does the decrease of SPM concentration caused by changing wind conditions cause the start of algae bloom, or does the algae bloom decrease SPM concentrations through enhanced flocculation and deposition? To answer the question, measurements from 2011 of particle size distribution (PSD), SPM and Chl concentrations from the southern North Sea have been analyzed. The results indicate that the frequency of occurrence of macroflocs has a seasonal signal, while seasonality has little impact upon floc size. The data from a highly turbid coastal zone suggest that the maximum size of the macroflocs is controlled by turbulence and the available flocculation time during a tidal cycle, but the strength of the macroflocs is controlled by the availability of sticky organic substances associated with enhanced primary production during spring and summer. The results highlight the shift from mainly microflocs and flocculi in winter towards more muddy marine snow with larger amounts of macroflocs in spring and summer. The macroflocs will reduce the SPM concentrations in the turbidity maximum area as they settle faster. Consequently, the SPM concentration decreases and the light condition increases in the surface layer enhancing algae growth further.
Water Research, 2012
Divalent cations have been reported to develop bridges between anionic polyelectrolytes and negat... more Divalent cations have been reported to develop bridges between anionic polyelectrolytes and negatively-charged colloidal particles, thereby enhancing particle flocculation. However, results from this study of kaolinite suspensions dosed with various anionic polyacrylamides (PAMs) reveal that Ca(2+) and Mg(2+) can lead to colloid stabilization under some conditions. To explain the opposite but coexisting processes of flocculation and stabilization with divalent cations, a conceptual flocculation model with (1) particle-binding divalent cationic bridges between PAM molecules and kaolinite particles and (2) polymer-binding divalent cationic bridges between PAM molecules is proposed. The particle-binding bridges enhanced flocculation and aggregated kaolinite particles in large, easily-settleable flocs whereas the polymer-binding bridges increased steric stabilization by developing polymer layers covering the kaolinite surface. Both the particle-binding and polymer-binding divalent cationic bridges coexist in anionic PAM- and kaolinite-containing suspensions and thus induce the counteracting processes of particle flocculation and stabilization. Therefore, anionic polyelectrolytes in divalent cation-enriched aqueous solutions can sometimes lead to the stabilization of colloidal particles due to the polymer-binding divalent cationic bridges.
Ocean Dynamics, 2014
ABSTRACT Multimodal particle size distributions (PSDs) of fine-grained cohesive sediments are com... more ABSTRACT Multimodal particle size distributions (PSDs) of fine-grained cohesive sediments are common in marine and coastal environments. The curve-fitting software in this study decomposed such multimodal PSDs into subordinate lognormal PSDs. Four modal peaks, consisting of four-level ordered structures of primary particles, flocculi, microflocs, and macroflocs, were identified and found to alternately rise and sink in a flow-varying tidal cycle due to shear-dependent flocculation. The four modal PSD could be simplified further into two discrete size groups of flocculi and flocs. This allowed the development of a two-class population balance equation (TCPBE) model with flocculi and flocs to simulate flocculation involving multimodal PSDs. The onedimensional vertical (1-DV) TCPBE model further incorporated the Navier-Stokes equation with the k-ε turbulence closure and the sediment mass balance equations. Multimodal flocculation as well as turbulent flow and sediment transport in a flow-varying tidal cycle could be simulated well using the proposed model. The 1-DV TCPBE was concluded to be the simplest model that is capable of simulating multimodal flocculation in the turbulent flow field of marine and coastal zones.
Ocean Dynamics, 2011
Abstract The effect of hydro-meteorological forcings (tidal and wind-induced flows) on the transp... more Abstract The effect of hydro-meteorological forcings (tidal and wind-induced flows) on the transport of suspended particulate matter (SPM), on the formation of high-concentrated mud suspensions and on the occurrence of sandmud suspensions has been studied using ...
Ocean Dynamics, 2011
Large sets of suspended particulate matter (SPM) concentration data from in situ and remote sensi... more Large sets of suspended particulate matter (SPM) concentration data from in situ and remote sensing (moderate resolution imaging spectroradiometer, MODIS) samplings in the Belgian nearshore area (southern North Sea) are combined in order to evaluate their heterogeneity and the sampling techniques. In situ SPM concentration measurements are from a vessel (tidal cycle) and from a tripod. During the tidal cycle measurements, vertical profiles of SPM concentration have been collected; these profiles have been used as a link between satellite surface and near-bed tripod SPM concentrations. In situ time series at fixed locations using a tripod are excellent witnesses of SPM concentrations under all weather conditions and may catch SPM concentration variability with a much finer scale. The heterogeneity has been statistically assessed by comparing the SPM concentration frequency distributions. Tidal cycle, tripod and MODIS datasets have different distributions and represent a different subpopulation of the whole SPM concentrations population. The differences between the datasets are related to meteorological conditions during the measurements; to near-bed SPM concentration dynamics, which are partially uncoupled from processes higher up in the water column; to the sampling methods or schemes and to measurement uncertainties. In order to explain the differences between the datasets, the tripod data have been subsampled using wave height conditions and satellite and tidal cycle sampling schemes.
Marine Pollution Bulletin, 2011
The impact of continuous disposal of fine-grained sediments from maintenance dredging works on th... more The impact of continuous disposal of fine-grained sediments from maintenance dredging works on the suspended particulate matter concentration in a shallow nearshore turbidity maximum was investigated during dredging experiment (port of Zeebrugge, southern North Sea). Before, during and after the experiment monitoring of SPM concentration using OBS and ADV altimetry was carried out at a location 5 km west of the disposal site. A statistical analysis, based on the concept of populations and sub-sampling, was applied to evaluate the effect. The data revealed that the SPM concentration near the bed was on average more than two times higher during the dredging experiment. The disposed material was mainly transported in the benthic layer and resulted in a long-term increase of SPM concentration and formation of fluid mud layers. The study shows that SPM concentration can be used as an indicator of environmental changes if representative time series are available.
Marine Geology, 2006
Measurements of aggregate size, suspended particulate matter (SPM) concentration and current velo... more Measurements of aggregate size, suspended particulate matter (SPM) concentration and current velocity have been carried out in the Belgian coastal zone (southern North Sea). Two stations were situated in the coastal turbidity maximum zone; another station was located more offshore at the edge of this turbidity maximum. The data have been collected using a LISST 100, OBS sensors, water samples and a bottom mounted ADCP. Turbulence (Kolmogorov microscale) has been modelled for the same period using a 3D numerical model. The results show that the size of the aggregates is significantly smaller in the coastal turbidity maximum area. The processes responsible for the occurrence of smaller aggregate size in the coastal zone compared with the more offshore location are: the higher turbulence; the smaller time available for the aggregates to grow up to an equilibrium size; the higher deposition of mud, resulting in a break-up of the flocs and the lower availability of organic matter, which may limit the size of the flocs.
Journal of Geophysical Research, 2012
1] Particle size distributions (PSDs) of suspended particulate matters in a coastal zone are logn... more 1] Particle size distributions (PSDs) of suspended particulate matters in a coastal zone are lognormal and multimodal in general. The multimodal PSD, which is caused by the mixing of multiple particle and aggregate size groups under flocculation and erosion/resuspension, is a record of the particle and aggregate dynamics in a coastal zone. Curve-fitting software was used to decompose the multimodal PSD into subordinate lognormal PSDs of primary particles, flocculi, microflocs, and macroflocs. The curve-fitting analysis for a time series of multimodal PSDs in the Belgian coastal zone showed the dependency of the multimodality on (1) shear-dependent flocculation in a flood and ebb tide, (2) breakage-resistant flocculation in the spring season, and (3) silt-sized particle erosion and advection in a storm surge. Also, for modeling and simulation purposes, the curve-fitting analysis and the settling flux estimation for the multimodal PSDs showed the possibility of using discrete groups of primary particles, flocculi, microflocs, and macroflocs as an approximation of a continuous multimodal PSD.