Spatial and Seasonal Variation of Biomineral Suspended Particulate Matter Properties in High-Turbid Nearshore and Low-Turbid Offshore Zones

Fettweis, M.; Lee, Byung Joon

doi:10.3390/w9090694

Cited by 39 publications

(32 citation statements)

References 53 publications

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“…The effect of suspended sediment on the transmission losses can be expected to cause little uncertainties in the sandy and gravelly areas outside the turbidity maximum zone in Belgian waters; it could, however, become moderate to prohibitive in deeper areas or in case of dense plumes of sediments in the water column related to human activities (dredging, trawling). In general, considering jointly the seasonal and spatial variations of SPMc in the BPNS [70], a maximal water depth of~50 m over the region, and the preliminary observations from this investigation, it may be surmised that for the gravelly and sandy clear-water areas (offshore and in the SW nearshore areas), the effect of suspended sediment will always be small, since the highest volume concentrations are to be expected in the lowest layer of the water column, thus involving too short a sound travel path to significantly affect the echo level. Previous investigations on the effect of near-bed SPM on BS for the first study area can be found in [33,54] and actually reported negligible effects.…”

Section: Short-term Backscatter Tidal Dependencementioning

confidence: 99%

“…Direction and consistency of the trend, regardless of the noise envelope, can be a valuable proxy of change and bypass conflicting results from surveys acquired at different tidal and/or seasonal moments. Interpretation of serial backscatter surveys in such environments should largely benefit both from time series of driving variables (collected via the deployment of benthic landers as in [49,70]) and from regional predictive oceanographic models providing local conditions usable for designing monitoring surveys accordingly.…”

Section: Implications For Repeated Backscatter Mapping Using Mbesmentioning

confidence: 99%

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Insights into the Short-Term Tidal Variability of Multibeam Backscatter from Field Experiments on Different Seafloor Types

Montereale-Gavazzi

Roche²,

Degrendele³

et al. 2019

Geosciences

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Three experiments were conducted in the Belgian part of the North Sea to investigate short-term variation in seafloor backscatter strength (BS) obtained with multibeam echosounders (MBES). Measurements were acquired on predominantly gravelly (offshore) and sandy and muddy (nearshore) areas. Kongsberg EM3002 and EM2040 dual MBES were used to carry out repeated 300-kHz backscatter measurements over tidal cycles (~13 h). Measurements were analysed in complement to an array of ground-truth variables on sediment and current nature and dynamics. Seafloor and water-column sampling was used, as well as benthic landers equipped with different oceanographic sensors. Both angular response (AR) and mosaicked BS were derived. Results point at the high stability of the seafloor BS in the gravelly area (<0.5 dB variability at 45° incidence) and significant variability in the sandy and muddy areas with envelopes of variability >2 dB and 4 dB at 45° respectively. The high-frequency backscatter sensitivity and short-term variability are interpreted and discussed in the light of the available ground-truth data for the three experiments. The envelopes of variability differed considerably between areas and were driven either by external sources (not related to the seafloor sediment), or by intrinsic seafloor properties (typically for dynamic nearshore areas) or by a combination of both. More specifically, within the gravelly areas with a clear water mass, seafloor BS measurements where unambiguous and related directly to the water-sediment interface. Within the sandy nearshore area, the BS was shown to be strongly affected by roughness polarization processes, particularly due to along- and cross-shore current dynamics, which were responsible for the geometric reorganization of the morpho-sedimentary features. In the muddy nearshore area, the BS fluctuation was jointly driven by high-concentrated mud suspension dynamics, together with surficial substrate changes, as well as by water turbidity, increasing the transmission losses. Altogether, this shows that end-users and surveyors need to consider the complexity of the environment since its dynamics may have severe repercussions on the interpretation of BS maps and change-detection applications. Furthermore, the experimental observations revealed the sensitivity of high-frequency BS values to an array of specific configurations of the natural water-sediment interface which are of interest for monitoring applications elsewhere. This encourages the routine acquisition of different and concurrent environmental data together with MBES survey data. In view of promising advances in MBES absolute calibration allowing more straightforward data comparison, further investigations of the drivers of BS variability and sensitivity are required.

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Section: Short-term Backscatter Tidal Dependencementioning

confidence: 99%

Section: Implications For Repeated Backscatter Mapping Using Mbesmentioning

confidence: 99%

Insights into the Short-Term Tidal Variability of Multibeam Backscatter from Field Experiments on Different Seafloor Types

Montereale-Gavazzi

Roche²,

Degrendele³

et al. 2019

Geosciences

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“…Due to the rapid settling of sediment inside the harbor, strong gradients are expected in the size and composition of the remaining SPM. The SPM inside the harbor has larger floc sizes and lower densities with higher organic content, while outside the harbor, the SPM occurs as bio-mineral aggregates as described by Fettweis and Lee (2017). The echo intensity of the backscattered acoustic signal should therefore only be seen as an estimate of the SPM concentration.…”

Section: Spm Concentration Measurements From Adcp Transects Inside Anmentioning

confidence: 99%

Mud dynamics in the Port of Zeebrugge

et al. 2019

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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.

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“…Their concerns already integrate the natural complexity since Mengual et al [348] relate to erosion of sand-mud mixtures, and Fettweis and Lee [349] to the biological influence on aggregation in coastal waters.…”

Section: Highlights Of Research Papersmentioning

confidence: 99%

“…Fettweis and Lee [349] analyse the variability of aggregates measured in the Belgian coastal waters from 2004 to 2011. Here "aggregate" is preferred to "floc", following the recommendation of Milliman [350] who writes that "flocculation" suggests an electrochemical process and denies biological influences.…”

Section: Highlights Of Research Papersmentioning

confidence: 99%

Why and How Do We Study Sediment Transport? Focus on Coastal Zones and Ongoing Methods

Ouillon

2018

Water

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Scientific research on sediment dynamics in the coastal zone and along the littoral zone has evolved considerably over the last four decades. It benefits from a technological revolution that provides the community with cheaper or free tools for in situ study (e.g., sensors, gliders), remote sensing (satellite data, video cameras, drones) or modelling (open source models). These changes favour the transfer of developed methods to monitoring and management services. On the other hand, scientific research is increasingly targeted by public authorities towards finalized studies in relation to societal issues. Shoreline vulnerability is an object of concern that grows after each marine submersion or intense erosion event. Thus, during the last four decades, the production of knowledge on coastal sediment dynamics has evolved considerably, and is in tune with the needs of society. This editorial aims at synthesizing the current revolution in the scientific research related to coastal and littoral hydrosedimentary dynamics, putting into perspective connections between coasts and other geomorphological entities concerned by sediment transport, showing the links between many fragmented approaches of the topic, and introducing the papers published in the special issue of Water on "Sediment transport in coastal waters".

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Spatial and Seasonal Variation of Biomineral Suspended Particulate Matter Properties in High-Turbid Nearshore and Low-Turbid Offshore Zones

Cited by 39 publications

References 53 publications

Insights into the Short-Term Tidal Variability of Multibeam Backscatter from Field Experiments on Different Seafloor Types

Insights into the Short-Term Tidal Variability of Multibeam Backscatter from Field Experiments on Different Seafloor Types

Mud dynamics in the Port of Zeebrugge

Why and How Do We Study Sediment Transport? Focus on Coastal Zones and Ongoing Methods

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