P. Bernard

Suspended-matter particle size in some west-European estuaries; part I: Particle-size distribution

Abstract Particle size of suspended matter was measured in five Northwest-European estuaries by Coulter counter and pipette analysis, and in situ with a suspension camera. Particle sizes measured by Coulter counter and pipette analysis became finer at the saltwater contact, but the in situ particle (floc) sizes did not show this. It is concluded that the particle size measured by Coulter counter and pipette analysis indicates the fragility (or firmness) of the flocs. The in situ particle size is variable, and is not related to changes in salinity, the content of organic matter in the flocs or the bulk composition of the organic matter. There is no consistent evidence that salt flocculation is an important factor in river mouths.

Heavy metal contamination in sediments from the Belgian coast and Scheldt estuary

Abstract Sixty-two samples of total sediments and the separated clay/silt size fractions were analysed by energy-dispersive X-ray fluorescence spectrometry to evaluate the pollution level and the trends in samples collected along the Belgian coast over a period of 6 yr and at four stations located in the Scheldt estuary where two of these were sampled periodically for 4 yr. Three correction methods for grain size effects were applied, either to the bulk sediment samples or to the clay/silt size fractions, and the results were compared. Local variations on the concentrations in some of the elements determined were used to establish whether they result from an anthropogenic or natural origin. The level of pollution was assessed as a function of the location, sampling date, and depth.

Suspended-matter particle-size in some West-European estuaries : part II. A review on floc formation and break-up

Abstract The results of particle size measurements in several estuaries with a Coulter counter, by pipette analysis and with a Plankton camera that gives the in situ size are discussed. The in situ size distribution of flocs is probably the result of a complex interaction of processes that induce flocculation. In estuaries, the kinetics of the processes in relation to the tidal cycle are particularly important. There is no evidence for an influence of salinity on in situ floc size distributions. In situ flocs are smaller than the turbulent whirls and probably do not break up after their formation. The floc break-up that occurs during sampling and analysis is an indication of the firmness (strength) of the flocs. The salinity increase at the fresh-saline water contact reduces the floc strength by mobilizing natural polymers (polysaccharides).

Geochemistry of suspended matter from the baltic sea. 1. Results of individual particle characterization by automated electron microprobe

Automated electron probe X-ray microanalysis was used to characterize some 15 000 individual suspension particles from 50 samples of suspended matter collected from different depths at 18 stations throughout the Baltic Sea and the transient area to the North Sea. For each particle, 14 minor and major elements were determined and size information data were obtained. To process this huge amount of results, multivariate analysis techniques were invoked: the particles were classified into specific types and the abundance variations of these groups were studied. It appeared that 80% of all investigated particles contained mostly silicon, and seemed to consist of quartz, and K-rich and Fe-rich aluminosilicates. The abundance of BaSO4 particles averaged 5% throughout the Baltic Sea, but amounted to up to 44% at some stations. The abundance of the Fe-rich particles varied significantly with location and depth, and averaged ∼ 4%. They were often found to be associated with significant amounts of P. Both of these particle types and the Mn-rich particles are thought to be mainly authigenic. Calcium carbonate particles are more abundant towards the North Sea (which seems to act as a source). Principal component analysis of the data revealed that most of the compositional variability can be explained by differences between deep and surface waters and by the influences of inflowing North Sea waters. Additional information about the types and sources of the suspended matter in the Baltic Sea was gained from the comparison and correlation of the single particle results with different fractions of the bulk concentrations of elements such as Al, Ca, Mn, Fe, Zn and Ba.

Elemental concentrations and heavy metal pollution in sediments and suspended matter from the Belgian North Sea and the Scheldt estuary

The elemental composition of sediment and suspended matter samples from the Belgian coastal and offshore regions of the Southern Bight of the North Sea and from the Scheldt estuary has been determined using X-ray fluorescence and atomic absorption spectrometry. Special attention was given to the heavy metals of the black and the grey lists. The bulk sediment and the clay/silt fraction were analyzed. The average heavy metal contents in the fraction <63 μm were comparable to the levels in the suspended matter. Different normalization techniques led to the identification of two different populations of sediments. Most of the sediments were enriched in Cd, Cr, Hg, Pb and Zn but no enrichment was found for Cu and Ni. Comparing these data with older data indicates that little changes in the metal contamination of the sediments in the area investigated has occurred over the last 15 years.

Geochemistry of suspended matter from the Baltic Sea. 2 : Results of bulk trace metal analysis by AAS

Abstract In 1984, on a transect covering the whole Baltic Sea and parts of the adjacent North Sea, 160 water samples were taken and analysed for their concentrations of particulate and dissolved metals. In addition, the suspended materials were investigated for their elemental bulk composition. The particulate fractions represented from about 5% (Cd, Cu and Ni) to 50% (Fe and Pb) of the total (particulate plus dissolved) concentrations. For some elements (Ba, Cd, Cu, Pb and Zn), the particulate matter from the surface microlayer was enriched with respect to those suspended materials taken from 0.2 m depth. This could reflect the atmospheric input of metal-rich aerosols. In anoxic deep waters, maximum contents of Zn (6400 μg g −1 ), Cu (1330 μg g −1 ) and Cd (12 μg g −1 ) were observed in the particulate matter, indicating sulphidic forms. On the other hand, under oxic conditions the distribution coefficients ( K d ) decreased with the water depth (Cd, Fe and Pb). Relative to global background levels, the particulate matter contained metal “excesses” amounting to more than 90% of the total contents (Cd, Mn, Pb and Zn). Automated electron probe X-ray microanalysis (EPXMA) revealed that the elemental composition of sediments is mainly governed by post-depositional processes of early diagenesis and is only weakly related to the composition of suspended matter in the overlying water body. For instance, in relation to surface mud sediments of the central Baltic net-sedimentation basins, Zn, Cd, Cu and Mn had 30–100% higher levels in the suspended materials. The general pattern of metal contents of particulate matter taken from 10 m depth on a transect between the Bothnian Bay and the North Sea were—possibly as a result of anthropogenic inputs—rather similar for Pb, Zn and Cu. For Fe and Mn, the distribution patterns along the transect were probably governed by the natural loading characteristics and by the biogeochemistry of those elements.

Comparison and evaluation of hierarchical cluster techniques applied to automated electron probe x-ray microanalysis data

Abstract For the processing of the large amount of data generated by automated electron probe x-ray microanalysis (EPXMA) of particulate samples, hierarchical cluster analysis are invoked. To evaluate the performance of seven hierarchical cluster techniques, cluster analyses were performed on a number of known mineral mixtures and the degree of correct classification was measured quantitatively by kappa statistics. In addition to the evaluation of the different cluster techniques, the influence on the cluster result of a number of experimental parameters was determined. In practice, ten mineral combinations were studied as a function of the mineral mixture ratio, using both normalized and unnormalized variables. For this purpose a total of 7000 cluster and kappa analyses were performed. In general, it seemed that Wards method was most successful in finding the correct classification. For one mineral mixture, 2100 results were studied to elucidate the effect of the mixture size, of working with correlated/uncorrelated variables (principal component space) and of the quantification of the EPXMA data (different deconvolution techniques applied to quantitative data obtained by the Armstrong-Buseck ZAF corrections).

Dispersal of suspended matter in Makasar Strait and the Flores Basin

Abstract In November 1984 in Makasar and the Flores Basin water samples were collected (T, S, dissolved O 2 , total CO 2 ), bottom samples (sediment composition) and suspended matter (particle composition, particle size). A sediment trap was moored in the Flores Basin at 4600 m depth for nearly four months, covering the dry season. In the Flores Basin there are indications for bottom flow resuspending bottom material or preventing suspended material from settling; in Makasar Strait there is probably inflow of deep water both from the south and from the north, resulting in a very slow bottom water flor. Bottom deposits in Makasar Strait and the Flores Basin are predominantly terrigenous, with an admixture of organic carbonate and silica (mostly coccoliths). Volcanic material is primarily present near to the volcanoes in the south and reaches the deeper basins by slumping. In the suspended matter no volcanic particles and little planktonic material were found, although the latter form 10 to 15% of the top sediment and of the material deposited in the sediment trap. In suspension particles with a large concentration of tin (Sn) were found associated mainly with iron. They probably come from northern Kalimantan or northern Sulawesi. Suspended matter concentrations were mainly less than 0.5 mg·dm −3 , only off the Mahakam river mouth were concentrations higher than 1 mg·dm −3 . Particle size was erratic because of the variable composition of the coarser particles in suspension. Organic matter concentrations in suspension (in mg·dm −3 ) roughly follow the distribution of total suspended matter but organic content (in %) of the suspended matter does not show any trends. All organic matter in suspension is of marine origin except in the Mahakam river and estuary. Deposition rates, as estimated from the sediment trap results, are 150 mg·cm −2 ·a −1 for the total sediment, 26 mg·cm −2 ·a −1 for carbonate and 13 mg·cm −2 ·a −1 for organic matter. Flocs and fibres in suspension were only found in and below the Mahakam river plume that reaches ca 400 km from the river mouth to the southeast, and in surface waters associated with plankton (diatoms). The formation of these flocs (broken-up macroflocs or marine snow) is primarily related to particle concentration, turbulence, and the presence of organisms that produce sticky material or glue particles together.

Characterization of Individual Estuarine and Marine Particles by LAMMA and EPXMA

Abstract Laser microprobe mass analysis (LAMMA) was applied to particulate matter from the Atlantic Ocean. Inferring information about the surface layer by LAMMA was not probe X-ray microanalysis (EPXMA). Geochemically relevant groups of particles had been identified by EPXMA and cluster analysis. For both locations, the most abundant ones appeared to be those rich in silicon and the alumino-silicates. Afterwards LAMMA was applied to obtain more information about the trace element composition and surface characteristics. The iron-rich phase appeared to contain significant amounts of heavy metals and of phosphate. Lead appeared to be associated in detectable amounts with alumino-silicates in the Scheldt but not with those in the Atlantic Ocean. Inferring information about the surface layer by LAMMA was not always unambiguous.

Electron microprobe analysis of suspended matter in the Angola Basin

Abstract Electron microprobe analysis of suspended-matter samples collected at different water depths at ten stations in the Angola Basin indicated that at each station, from top to bottom, the elementary composition of the suspended matter was very similar and differed from the composition of the suspended matter at the adjacent stations. This indicates that the downward settling of the suspended matter is much faster than the horizontal transport and mixing by the currents. Assuming that the suspended matter settles in the form of flocs, or is scavenged by settling flocs, the suspended matter can indeed reach the bottom in a shorter period than needed for the currents to cover the distance between adjacent stations. Comparison with sediment trap data from the literature shows that also lateral transports and/or deep water gyres have to be invoked to further increase residence times of suspended matter in the water column.