Search publications of the members of the Royal Belgian institute of natural Sciences
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Multimodality of a particle size distribution of cohesive suspended 2 particulate matters in a coastal zone
- 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.
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Historical (1900) seafloor composition in the Belgian-Dutch part of the North Sea: A reconstruction based on calibrated visual sediment descriptions
- Concerns about human-induced degradation of marine ecosystems are presently being translated into European Directives aimed at a restoration of healthier seas. However, anthropogenic alterations are ancient and data on the pristine ecosystem are lacking, making the evaluation of their cumulative effects in the long run challenging. In the Belgian and Dutch parts of the North Sea, a historic data-set (the Gilson’s archive) exists to describe various compartments of the marine ecosystem in the first decade of the 20th century (1899–1914). The bulk of samples were acquired in the nearshore (up to 10 nautical miles off the coast) and further offshore in the Hinder banks area. In this contribution, we focus on the sediment information, which consists of 2200 visual descriptions of geo-referenced seafloor samples and 690 archived sub-samples, to reconstruct the seafloor composition 100 years ago. Estimates of mud levels, sand grain size, shell debris levels as well as occurrence of gravel, pebbles and cobbles were derived from the descriptions and standardized. Mud levels and sand grain-size categories were calibrated by means of grain-size analysis of archived samples (n 1⁄4 383 analyses). Large patches of very high mud levels (50–100%) used to occur close to the shore, along the central and eastern coast. The visual sand grain-size categories display a significant trend in their median grain-size, enabling us to identify distinct patches of fine (o 250 m m) and medium (250 o Xo 500 m m) sands. High levels of shell debris were found in the offshore; in coastal waters, they fringed the high turbidity zone typical of this area. Gravel grounds were identified in gullies bordering offshore sand banks and were colonized with an abundant bushy epifauna. Long-term changes were briefly considered. The nearshore mud levels are reduced in the present-day due to specific human impacts. Thick layers of poorly consolidated mud now occur mostly in the artificially dug navigation channels, at disposal sites and around port areas. Offshore, richly colonized biogenic reefs of native flat oyster (Ostrea edulis) were destroyed by targeted oyster fishery as early as in the 1860s. Since the 1920s, seabed disturbance caused by trawling activities steadily increased. We thereby demonstrate a degradation path from richly colonized biogenic reefs toward continuously disturbed sandy gravel grounds in the present day. Our conclusion is likely valid for many such grounds in the English Channel and southern North Sea. Major long-term changes observed thus far are clearly related to specific human activities. This reconstruction work will enable to better define the amplitude of human-induced changes in this portion of the North Sea, a necessary pre-requisite to the definition of meaningful environmental health targets.
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Sediment mobility in response to tidal and wind-driven flows along the Belgian inner shelf, southern North Sea
- 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 sand–mud suspensions has been studied using long-term multi-parametric observations. Data have been collected in a coastal turbidity maximum area (southern North Sea) where a mixture of sandy and muddy sediments prevails. Data have been classified according to variations in subtidal alongshore currents, with the direction of subtidal flow depending on wind direction. This influences the position of the turbidity maximum; as such also the origin of SPM. Winds blowing from the NE will increase SPM concentration, whilst SW winds will induce a decrease. The latter is related to advection of less turbid English Channel water, inducing a shift of the turbidity maximum towards the NE and the Westerschelde estuary. Under these conditions, marine mud will be imported and buffered in the estuary. Under persistent NE winds, high-concentrated mud suspensions are formed and remain present during several tidal cycles. Data show that SPM consists of a mixture of flocs and locally eroded sand grains during high currents. This has implications towards used instrumentation: SPM concentration estimates from optical backscatter sensors will only be reliable when SPM consists of cohesive sediments only; with mixtures of cohesive and non-cohesive sediments, a combination of both optical and acoustic sensors are needed to get an accurate estimate of the total SPM concentration.
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Evaluation of in situ and remote sensing sampling methods for SPM concentrations on the Belgian continental shelf (southern North Sea)
- 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.
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Competition between kaolinite flocculation and stabilization in divalent cation solutions dosed with anionic polyacrylamides
- 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 Ca2+ and Mg2+ 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.
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Potyphyllum, a new phillipsastreid genus of rugose corals in the Upper Frasnian of Belgium with precisions about the age of the Petit-Mont Member.
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Liste des espèces d'araignées capturées dans une aulnaie tourbeuse située ) Moha (Wanze, Liège)
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Comaroma simoni Bertkau, araignée nouvelle pour la faune belge.
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Dicymbium brevisetosum Locket (Araneae, Linyphiidae), nieuw voor de Belgische fauna
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Contribution à la connaissance de la faune aranéologique et enomologique de la région de Buzenol (Province du Luxembourg)
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Araignées des Hautres Fagnes. II. Ecologie
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Early life stages of flatfish: otolith microstructure reveals patterns of dispersal and juvenile dynamics
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Models as Support to Eutrophication Management in the North Atlantic Ocean (EMoSEM)
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Impact of climate change on sole larval recruitment in the North Sea and match-mismatch between larvae and phytoplankton
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Tracing back nutrients from Southern North Sea eutrophicated areas up to the watersheds
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Impact of climate change on larval recruitment and connectivity of sole in the North Sea
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Integrating field data to parametrize a larval transport model of sole and improve knowledge on recruitment and connectivity
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Ecosystem Models as Support to Eutrophication Management in the North Atlantic Ocean (EMoSEM)
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How much of the sole early life stage mortality variabiltiy is explained by egg and larval dispersal and by mismatch with algal bloom in the North Sea?
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Calibration of a sole larval transport model using ICES survey assessments
