Vertical distribution of suspended particulate matter in the Zaire river,estuary and plume

Light transmission and hydrographic data were measured in situ simultaneously in the Zaire river estuary and on the shelf off the river extending to the Angola Basin. Profiles of light transmission indicate that the majority of the particles derived from the river are transported offshore into the Angola Basin through deep waters under the surface plume. The Zaire river is associated with a submarine canyon which extends well into the Zaire estuary and cuts across the shelf. Bottom nepheloid layers were well developed along the canyon axis. The sediments along the canyon axis were mostly sands, and thus the submarine canyon appears to provide an efficient transport route of fine-grained material to the Angola Basin across the shelf.The surface plume is so highly stratified that vertical mixing appears very limited across the plume boundary, and downward transport of suspended particles must be accomplished by particle settling. Profiles containing small-scale layers of turbid water under the surface plume are considered indications of settling particles from the surface river plume.     

In situ distribution of suspended matter during the tidal cycle in the elbe estuary

In situ size of suspended particles was measured with an underwater photographic system in the Elbe estuary. The data from the measurements at a stationary position indicate that the formation of large flocs took place at low current velocities and that the size distributions varied with the tidal cycle as a consequence of flocculation, deposition and resuspension processes.Flocculation of suspended particles in the estuary is interpreted as a dynamic process: the size of flocs changes with time and their distribution depends on the rates of aggregation and disaggregation of the particles. This is related to physical factors of which turbulence and differential particle settling play key roles in producing large flocs. Fluid shear is responsible for disaggregation of large flocs. Salinity and the organic content of particles may affect flocculation processes with respect to the particle cohesive interaction, but they have no critical effect on the variation of floc size during the tidal cycle in the estuary.     

Desorption of metals from suspended material in the rhine estuary

Aliquots of suspended matter collected from Rhine river water were resuspended in distilled water, in diluted artificial sea water (1 : 1), in artificial sea water, and in ‘nitrate sea water’, respectively at pH's 7.5 and 8.0. The desorption of heavy metals into these solutions was calculated in relation to the concentrations as determined by extraction in 4 M hydrochloric acid. The heavy metal concentrations after resuspension and the relative desorption percentages were compared with calculated inorganic metal ion speciation. These comparisons, though quantitatively not quite satisfactory, demonstrated that complex formation is important in desorption processes during estuarine mixing. The order of decreasing desorption of metals into 1 : 1 diluted sea water and sea water in the experiments is : Cd > Zn > Mn > Ni > Co > Cu > Cr; fo for Fe and Pb no desorption was found.Analyses of samples collected at a tidal station at Hoek van Holland show that both suspended matter and filtered water are depleted in most heavy metals. Certainly, in this tidal area suspended matter and adsorbed and dissolved heavy metals do not show a conservative mixing behaviour. In order to correlate experimental results and field obsevartions, large scale flocculation and sedimentation of suspended matter must be accepted at an early stage of estuarine mixing. It is not certain whether this can be proved; future research should include more chemical indicators for testing these estuarine processes.     

Flocculation and de-flocculation of suspended matter in estuaries

Flocculation and de-flocculation have been observed in estuaries and the processes involved are discussed. Salt flocculation plays a minor role, if any. Flocs are mainly formed by a combination of two groups of processes: those bringing particles together, and those keeping them together. The first group is related to the flow conditions in the water and to organisms that clog particles into faeces or pseudofaeces or attach them to mucus. The second is related to the formation of sticky organic matter by a variety of organisms. Two main types of flocs have been observed: microflocs with a diameter up to 125 μm, and macroflocs with a maximum size of 3–4 mm. Microflocs consist of mineral particles and organic matter. Their formation is strongly related to the origin of the organic matter, to the organisms producing it, and to conditions of (temporary) deposition and resuspension. Mucopolysaccharides, produced by bacteria, algae and higher plants and mobilized from the suspended matter at low salinity, are important in glueing particles together. The microflocs, together with single mineral particles, are the basic building units of macroflocs. Macroflocs are fragile and formed in the water under conditions of viscous flow. Their maximum size is determined by turbulent shear, the size of the smallest turbulent whirls on the Kolmogorov scale being of the same order as the maximum floc size. They are easily destroyed during sampling. In estuaries the microflocs of fluvial origin are broken up by organisms consuming the organic matter in the microflocs, and reflocculated into new microflocs with newly formed organic matter of estuarine origin. The size of the microflocs, as seen under a microscope or determined by size analysis, is likely to be determined mainly by the binding strength of the organic matter in relation to the total mass of the floc and the physical disturbance produced during sampling and size analysis.     

The distribution of suspended matter in the Dutch coastal zone

Results are presented of suspended matter observations taken at bi-weekly intervals during the period 1975–1983, in a strip 70 km wide along the Dutch coast. The average distribution showed a (weak) minimum zone located north of Noordwijk at a distance of about 30 km from and parallel to the Dutch coast, between the salinity maximum and the coast. Variability was large between different years, seasons and individual cruises. A clear seasonal cycle emerged from the observed suspended-matter patterns: in winter a pronounced minimum existed, while in summer generally a monotonically decreasing concentration was measured, to open-sea values much lower than in winter. This seasonal cycle may be explained by a combination of variation in wind, river discharge and the activity of suspended-matter sources. The Flemish Banks and Channel waters are the main sources supplying suspended matter to the Dutch coastal area. Especially the varying transport through the Strait of Dover, large in winter, small in summer, determines the seasonal variation in the total amount of suspended matter. The existence of a localized turbidity minimum is tied to relatively large discharges from the Rhine and associated steep salinity gradients, also occurring mainly in winter and early spring. A simple model of cross-shore density-driven circulation shows the possible influence of the strong salinity gradients on the sedimentation of suspended matter. Particles with a settling rate comparable to the vertical velocity component of the circulation are forced to move offshore until they reach an area they sink out of the surface layer. The strength of this circulation is determined by the cross-shore density gradient due to the inflow of fresh water from the Rhine-Meuse estuary.     

Elementary composition of suspended particulate matter in the North Sea

The concentrations of the elements Al, Si, Ti, Fe, Mn, Ca, Mg, K, Cu, Zn, Cr, Pb, Ni, Cd, V and of particulate organic carbon (POC) were determined in 210 samples of suspended matter collected at 119 stations in the North Sea in January-February 1980. The distribution of these 15 elements and POC in the suspended matter in the North Sea was studied, as well as their relation with total suspended matter concentrations and salinity. The interrelationships between these elements were found to differ in different regions of the North Sea, which is related to the origin of the suspended material and the degree of mixing. A cluster analysis including all determined elements at all stations showed that the suspended matter in the North Sea consists of three clearly separated, specific types. One type was found in the northern part of the North Sea, the second in the southern part of the North Sea, while the third type was mainly observed in the Norwegian Channel, Skagerrak and eastern English Channel.The observed distributions are in agreement with what is known on the dispersal and deposition of suspended matter in the North Sea. Material from the southern North Sea hardly reaches the central and northern North Sea and the northern parts of the Norwegian Channel. The distribution of Mn is very strongly related to the accumulation of Mn in the top layers of finegrained bottom sediments and to the resuspension of Mn-enriched particles.     

流沙湾悬浮物数量动态变化规律的初步研究

在流沙湾设置9个观测站,对透明度和悬浮物数量动态变化规律进行了研究,结果表明：海湾水温周年平均值为26.4 ℃,变化范围为19.0～31.9 ℃;水域透明度年平均值为133.3 cm,变化范围为50～240 cm;悬浮物含量变化在9.12～29.90 mg/L之间,平均为18.70 mg/L。水域悬浮物含量有较明显的月变化规律（P＜0.05）,总的变化趋势是年水体悬浮物浓度呈先升高后降低的折线起伏变化分布。悬浮物含量多数观测站最高值出现在5月份,其平均值为26.81 mg/L。水体悬浮物数量的水平分布表现为5号站、6号站和9号站含量较高,1号站、3号站和8号站含量较低,即沿岸观测站高于航道与湾口。     

Distribution,organic content and particle size of suspended matter in the north sea

Data on suspended matter concentrations and the organic content of the suspended matter for January 1980 showed a division in the North Sea between the southern North Sea (high suspended matter concentrations, but relatively low organic content) and the central and northern North Sea (low suspended matter concentrations, but relatively high organic content). The Skagerrak, which receives suspended matter from the southern as well as from the central and northern North Sea, took up an intermediate position.In summer suspended matter concentrations were lower than in winter but more variable, in concentration as well as in organic content, because of admixtures of particulate matter from primary production. On deposition of the suspended matter, a considerable part of the organic matter was apparently lost (in the order of 75% or more), resulting in low organic-matter concentrations of fine-grained bottom deposits.Particle-size distributions followed two main types: one (A) with a sharp peak at 30 to 100 μm, and one (B) bell-shaped with a peak at 5 to 15 μm. Type A occurred in deeper water and consisted of particles with a high organic-matter content, type B occurred in shallow areas and consisted of particles with a low organic-matter content. The suspended particles were mainly microflocs of mineral particles and organic matter. The mineral particles of both types were predominantly of 2 to 5 μm size, which was determined after oxidation of the organic matter. It is concluded that particles of type-B distributions are regularly exchanged with the bottom through deposition and resuspension, which results in low organic-matter contents and prevents the microflocs reaching large sizes. Paricles of type-A distributions, on the contrary, can reach much larger sizes, because mostly they remain in suspension and do not lose organic matter, so that they do not easily fall apart.     

Distribution and particle size of suspended matter in the Southern Bight of the North sea and the Eastern channel

The distribution of suspended matter content in the Southern Bight is related to the resultant current pattern. Suspended matter is concentrated in the coastal waters and high concentrations occur where resultant currents of different directions meet near to the large gyres off the Belgian-Dutch coast and off East Anglia. Suspended matter is chiefly supplied to the Southern Bight from the Channel through Strait Dover-Calais (at least 8 to 11.5 × 10⁶, probably 11.5 to 15 × 10⁶tons·a⁻¹. Other sources are the rivers that enter the Southern Bight (ca 2 × 10⁶ tons·a⁻¹), coastal erosion (ca 0.3 × 10⁶ tons·a⁻¹), erosion of the sea floor (in the order of several million tons·a⁻¹) and the atmosphere (ca 0.5 × 10⁶ tons·a⁻¹). Supply from primary production is small (less than 1 × 10⁶ tons·a⁻¹). Total supply of suspended matter to the Southern Bight is 17.5 to 21.5 × 10⁶ tons·a⁻¹. The concentration of suspended matter in the coastal waters is probably related to a shoreward displacement of bottom water.Particle size determinations were made (with a Coulter Counter) during the winter in the absence of living plankton. Measurements were made directly after sampling or within several hours. In the Belgian-Dutch Coastal Water particle size is somewhat finer than in Strait Dover-Calais and in the central part of the Southern Bight (the “Channel Water”). In the English Coastal Water particle size is more variable. The bulk of the suspended particles has a diameter of 5 to 20 μm but there is a variable admixture of particles of 1 to 3 μm. Most size distributions are a mixture of two log-normal distributions. In the Belgian-Dutch coastal water, in the eastern Channel and in Strait Dover-Calais regularly approximately log-normal distributions are present. The size distributions reflect the multiple origin of the suspended material and the variable conditions of deposition, resuspension and aggregation.     

The control of trace metal concentrations in coastal seawater through partition onto suspended particulate matter

The distribution of total metal concentration between dissolved and particulate phases in coastal seawater has been examined as a function of suspended particulate matter (SPM) loading. Partition between dissolved and particulate phases, as defined by a distribution coefficient, is demonstrated to be an important control on the concentration in each phase. The possible impact of anthropogenic inputs on trends in coastal water concentrations are contrasted for waters with a high (Netherlands), and a low (U.K.), SPM loading. For a given increase in input trends will be more readily detected in areas with a slow SPM loading. It is concluded that trends in coastal seawater concentrations will only become apparent after river inputs have dramatically increased. Monitoring coastal water concentrations of dissolved and particulate phase trace metals is not therefore likely to be a sufficiently sensitive technique to detect trends.     

Nitrite and ammonia in the Tamar estuary

Seasonal variations in the axial distributions of nitrite and ammonia in the Tamar estuary, southwest England, have been recorded by continuous autoanalytical profiling at approximately monthly intervals together with measurements of salinity, turbidity and dissolved oxygen. In contrast to the persistent apparent conservativeness of nitrate in this estuary, these reduced species of nitrogen have shown marked non-conservative behaviour.Ammonia distributions generally showed a maximum in the middle to upper estuary which was variably located relative to salinity and had a magnitude which tended to vary with the spring-neap tidal condition. These maxima are attributed to releases from the sediment which are facilitated by tidal sediment disturbance.During the winter months, nitrite distributions reflected conservative mixing of riverine nitrite but internal inputs within the low salinity, turbidity maximum zone became increasingly significant from spring to late summer in phase with an increasing degree of local oxygen depletion. It appears that nitrite is generated within the water column by bacterially mediated oxidation of ammonia.Anthropogenic inputs significantly augment both constituents in the outer estuary.     

Suspended-sediment transport in the Dollard estuary

For an analysis of suspended-sediment transport in the Dollard estuary, water samples were taken and current velocities and directions measured on the tidal flats and in the channels. Measurements carried out during fair-weather conditions in summer were compared with measurements carried out during a heavy gale in winter. During the onset of the flood, high suspended-sediment concentrations occurred as a result of resuspension of the top layer of the bottom sediment. Measurements carried out in the channels pointed to sediment transport from the estuary seaward, but inward transport over the flats during fair weather apparently compensates for the outflow during ebb and storms: the result is a net deposition in the order of 1 to 2 mm (up to 8 mm) per year, as previously observed in this area.     

Distribution of dissolved and particulate minor and major elements in the river and coastal environment of East Java during the Snellius-II expedition

The concentration and distribution of dissolved Cu, Zn, Cd, Ni, Pb and Fe, and Cu, Zn, Cd, Ni, Pb, Cr, Fe, Si, Ca, Mg, Mn and K in suspended matter have been determined in the rivers Porong and Solo and in Strait Madura (East Java), during the dry- and wet-monsoon periods. Based on element/Al ratios, the suspended matter supplied by each of the two rivers can be traced offshore. The main source of material supplied to the coastal area is the Solo river. The distribution of the trace-metal content in suspended matter collected in the rivers can be described as a mixture of metal-rich, organic-rich particles and a metal-poor, detrital fraction. Due to the presence of mud barriers at the river mouths, particles with high trace-element contents are trapped in the estuaries. Compared to European rivers the dissolved trace-metal concentrations in these rivers are relatively low. The dissolved concentrations of the different trace elements in Strait Madura show no uniform distribution pattern during the two sampling periods.     

On arsenic speciation in the Tagus estuary

New evidence is presented pointing to the presence in estuarine waters both of trimethylarsenic forms (TMA) and of an organoarsenical component refractory to the hydride method.Although not previously detected in estuarine and coastal studies, TMA concentrations were measured in the Tagus estuary in August 1984. The results are presented together with total inorganic, monomethyl (MMA) and dimethyl arsenic (DMA) species quantified in the same occasion. Further digestion of a separate water sample gave positive increments for the methylarsenicals (MMA+DMA+TMA), with special relevance for DMA, suggesting the presence of a heavier organo-arsenical, undetectable in undigested samples with our current analytical capabilities. This component seems to be present in concentrations greater than MMA and TMA. That same sample was passed through a molecular fractionation scheme to get indications of the molecular weight of that unknown component. The results suggest a molecular weight of less than 210 although the limitations of the method do not allow a definitive conclusion.     

The role of small,low density particles on the partition of selected PCB congeners between water and suspended matter (North Sea area)

The dissolved and particulate suspended concentrations of five PCB congeners (with 3–7 chlorine atoms) in the Southern Bight (North Sea) are interpreted in terms of an equilibrium partitioning model. K_d values for riverine/coastal samples generally increase with chlorine number of the congeners (K_d = 10⁴–10⁶). Values are more than an order of magnitude larger at the low suspended matter concentrations offshore (< 1 mg·dm⁻³). This is interpreted in terms of the presence of different SPM fractions with different contents of PCB: a fraction consisting of low size/density particles carrying high contents of PCBs, dominates at low SPM concentrations. The contribution of particulate forms to the total PCB concentration per unit volume may, therefore, be significant even at low SPM concentrations.