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Seasonal and spatial dynamics of the microphytobenthic biomass on a subtropical intertidal sand flat (25°32'S; 48°24'W) was investigated monthly from September 1995 to July 1996. Chlorophyll-a and Phaeophytin-a contents, temperature, salinity, inorganic nitrogen and phosphate pore water concentrations and sediment characteristics were assessed in the upper (HW), middle (MW) and lower (LW) sections of the flat. Microphytobenthic biomass content showed a conspicuous seasonal and spatial gradient. Higher chlorophyll-a contents were registered in the HW section of the tidal flat (from 11.78 µg.gsed-1 to 38.18 µg.gsed-1) decreasing towards the LW section (from 6.23 µg.gsed-1 to 18.23 µg.gsed-1). Microphytobenthic seasonality was determined mainly by turbulence of the water column, which was influenced by atmospheric events. The sediment properties and nutrient concentrations had a significant effect on the spatial and seasonal distribution of pigments on the intertidal flat. A dinâmica sazonal e espacial da biomassa microfitobêntica em uma planície arenosa intermareal (25º32'S; 48º24'W) foi investigada mensalmente de setembro de 1995 a julho de 1996. A concentração de clorofila-a e feofitina-a, a temperatura, salinidade, concentração de nitrogênio inorgânico e fosfato na água intersticial, além das características do sedimento, foram inferidas na região superior (HW), mediana (MW) e inferior (LW) da planície. A biomassa microfitobêntica apresentou gradientes sazonal e espacial bem definidos. Maiores concentrações de clorofila-a foram registradas na região superior da planície entre marés (HW, de 11.78 µg.gsed-1 até 38.18 µg.gsed-1), decrescendo em direção a região inferior da planície (LW, de 6.23 µg.gsed-1 a 18.23 µg.gsed-1). A sazonalidade microfitobêntica foi determinada principalmente pela turbulência da coluna de água, influenciada pelos eventos atmosféricos. As propriedades do sedimento e as concentrações de nutrientes foram significantes para a distribuição espacial e sazonal dos pigmentos na planície entre marés.

This paper describes apparatus, techniques and methods used by participants in MAST G6M project 4 (Cohesive Sediments) for determining cohesive sediment properties. This comparison of methods aims to stimulate a more general discussion on standardisation of techniques which will lead to characterisation of muds in terms of physical parameters. Such characterisation would allow inter-comparison of muds from different sources. Methods are given for sediment properties of grain size distribution, settling velocity and rheological parameters and for water-bed exchange properties of permeability, effective stress and critical shear stress for erosion and deposition. Accuracy and repeatability are discussed. A typical range of values is indicated for each of these parameters.

A quantidade e a distribuição de tamanho dos sedimentos transportados pela enxurrada são influenciadas pelo manejo, cobertura e cultivo do solo e pela chuva, entre outros fatores, constituindo-se em aspecto importante no planejamento conservacionista do solo. O objetivo deste trabalho foi quantificar os sedimentos transportados pela enxurrada e relacioná-los com a velocidade de enxurrada, durante o cultivo da soja, em um experimento de chuva simulada sobre um Nitossolo Háplico alumínico típico, nos sistemas de manejo do solo conduzido desde 1998: semeadura direta em solo nunca preparado e com resíduos queimados (SQ); e uma aração e duas gradagens (AG). Nesses tratamentos, cultivaram-se aveia, soja, ervilhaca, milho, aveia, feijão, nabo forrageiro, soja, ervilhaca, milho e soja, nesta sequência, durante cinco anos e meio. Estudou-se um tratamento adicional, em que o solo foi mantido sem cultivo, porém preparado com uma aração e duas gradagens na mesma época de semeadura das culturas nos demais tratamentos (SC). No último cultivo da soja, cinco testes de chuva simulada foram aplicados sobre os tratamentos, com intensidade variando de 63 a 67 mm h-1 e duração de uma hora, 24 h após ter sido aplicada uma chuva (molhamento) com intensidade de 65 mm h-1 e duração suficiente para iniciar a enxurrada. Os sedimentos foram quantificados em amostras de enxurrada coletadas 10 min antes do término de cada chuva simulada. O tamanho de sedimentos foi influenciado pelo sistema de manejo do solo e pela quantidade de chuva: na condição sem cultivo do solo, houve maior quantidade de sedimentos de maior diâmetro do que na condição em que o solo foi cultivado; na condição de solo cultivado, a quantidade de sedimentos de menor diâmetro foi maior do que no solo sem cultivo; e houve tendência de aumentar a quantidade de sedimentos na enxurrada com o aumento do número de chuva simulada, nas diversas condições de manejo do solo e de tamanhos de sedimento. O modelo exponencial ajustou-se aos dados de quantidade e tamanho dos sedimentos e aos de velocidade da enxurrada e cobertura do solo; a quantidade de sedimentos diminuiu com a redução de tamanho destes, e a velocidade da enxurrada diminuiu com o aumento da cobertura do solo. O modelo potencial ajustou-se aos dados de D50 e velocidade da enxurrada, tendo o D50 aumentado com o aumento da velocidade. Quantity and size distribution of sediments transported by runoff are influenced by soil management, cover and crop systems, and by rainfall, among other factors, representing an important aspect in soil conservation planning. The objective of this study was to quantify runoff sediments and relate them with runoff velocity, during soybean growth, in a simulated rainfall experiment initiated in 1998 on a typical Hapludox, under the following soil management systems: conventional tillage with one plowing plus two diskings (CT) and notillage on a never tilled soil with burned residues (NT). In these treatments, the rotation crop systems consisted of oat, soybean, vetch, corn, oats, bean, fodder radish, soybean, vetch, corn, and soybean. An additional treatment with bare soil with one plowing plus two diskings (BS) was also studied. Five simulated rainfall tests were applied to the treatments in the last soybean crop cycle, with an intensity of 63–67 mm h-1 for one hour, 24 h after a pre-wetting rainfall, with an intensity of 65 mm h-1 and long enough to initiate runoff. The sediments were quantified in runoff samples collected 10 minutes before the end of each simulated rainfall test, and were related with the runoff velocity. The sediment size in the runoff was influenced by soil management systems and the rainfall quantity. In the treatment without soil cover (BS), the quantity of coarse sediments was higher than in the treatments with cultivated soil, whereas in CT and NT treatments the quantity of fine-sized sediments was higher than in the BS treatment. More sediments tended to be transported in the runoff with the application of more rainfall events. The sediment quantity transported by runoff was related with the sediment size, fitting to a positive exponential model, while runoff velocity decreased exponentially with increased soil cover. The D50 index was related with other variables, fitting to the potential model and increasing with runoff velocity.

Worldwide about 80% of the warm-water coral reefs have been harmed, and about 25% irreversibly damaged from direct human pressures. The effects of sedimentation on reef-building corals are well documented, as previous studies focused mostly on the coral response. The processes of how sediment actually damages corals, and the role of contrasting sediment properties have remained poorly understood. In this study we therefore focused on the sediments and investigated the harming processes. Our central hypothesis was that bacteria play a crucial role in the damage that sediment causes to corals. This thesis presents the advancement of two existing methods, data from mesocosm experiments, as well as field data, obtained with the new submersible microsensor system DOMS. This work revealed that harmful effects of sediment exposure on reef-building warm-water corals are tightly linked to sediment properties, primarily the percentage of silt grains, the organic matter content and the microbial activity, demonstrating that the exposure to organic-rich fine sediment is particularly dangerous for coral reefs, and that the demise of sediment-covered corals is mediated by microbial activity.

The frequency and distribution of benthos species in the north coast of Gorgan Bay (proposed site for cage and pen culture) were studied. Sampling was carried out in three water depths 1, 2 and 3 meters and 10 stations in each depth using Van Veen sampler with 3 replications. Totally, 12 families were identified: Nereidae, Ampharitidae, Spionidae Amphipodae, Osteracodae, Mytilidae, Dreissenidae, Cardidae, Neritidae, Pyrgulidae, .Lithoglyphidae and Planorbidae of which Osteracodae and Ampharitidae with 26% and 1% had maximum and minimum abundance, respectively in all depths. The maximum and minimum abundance of benthos was 6025 per square meter in waters 3 meters deep and 52 per square meter in waters 1 meter deep. In addition, sediment texture and total organic matter (TOM) were analyzed which showed that 2 and 3 meter deep waters had the maximum percent of T.O.M (7.8%) in spring and autumn while the minimum T.O.M (2.5%) in 1 meter deep waters was observed in winter.

A recent companion paper reported an experimental protocol used to analyze sediment properties. This protocol identified for both freshwater and marine sediments a surface layer with specific dynamic properties (critical erosion shear stresses in the range 0.025-0.05Nm-2) and a second layer with critical erosion shear stresses about ten times larger. The present study compares these former results with recent work which extended the applicability domain of the Shields diagram to very fine particles. The surface layer is shown to consist in fine and unconsolidated sediments that behave like noncohesive material whereas the second layer is characterized as being cohesive. The surface layer is mainly representative of recent deposits of suspended particles. This points out the existence of a fluffy layer of fine sized particles resting near the bed, with specific erosion characteristics, which has to be considered separately when studying sediment properties. © 2007 ASCE.

Signals received by low-frequency multibeam echosounders are strongly affected by sound penetration inside the upper sediment layers and by backscattering from buried layers down to depths of a few meters; this may lead to serious ambiguities and misinterpretations of experimental data. These phenomena are modeled here using a concept of equivalent input backscattering strength (EIBS), based on a combination of classical models of local backscattering strength and propagation inside fluid layered media. The local backscattering strength at a buried interface is expressed first to account for the impedance adaptation due to the overlying layers, for the angular refraction effects due to the velocity profile, and for the layered structure of the underlying medium. It is then transferred to the upper water-sediment interface, accounting fur propagation inside the layered stack; the transfer coefficient is obtained from the classical theory of plane wave propagation in layered media. The volume backscattering effects are processed in the same way and account for the finite thickness of the layers. The various contributions are finally summed to give the backscattering strength, at the upper interface, that features the various effects of propagation and attenuation inside the layered structure.

The Belgian Continental Shelf (BCS) is characterized by a set of isolated subtidal sandbank systems, which greatly increase the habitat heterogeneity of the area. The meiobenthos of these sandbanks was investigated during 1997 and 1998. In total, 10 sandbanks have been sampled, belonging to three different geographically isolated systems: the Flemish Banks, the Hinder Banks and the Zeeland Banks. No obvious differences in sedimentological characteristics between the sandbanks were found, but biologically some differences could be detected. The more offshore Hinder Banks had the most diverse meiobenthos, while the Flemish Banks harboured the lowest number of meiobenthic taxa. Seasonal and regional differences in terms of densities are a result of a coupling with the primary production in the water column, with October showing highest densities and the offshore Hinder Banks harbouring lowest densities. The meiobenthos on the sandbanks was less dense (450-500 ind. 10 cm-2) than that in the deeper channels between the sandbanks (1250-1600 ind. 10 cm-2). These differences were attributed to high hydrodynamic stress around the sandbanks, preventing phytoplankton from reaching the sandbanks. Moreover, higher current speed above the sediment increases the risk for the meiobenthos of being eroded or suspended during storms. Four different communities could be identified. These did not reflect the geographical position on the BCS but seem to be influenced by local differences in sedimentological characteristics within sandbanks and sandbank systems. These sedimentological differences influenced the taxon diversity as well. Sediment preferences for less abundant taxa were investigated in several ways, and results indicated that sediments with a median grain-size were poor in terms of densities and number of taxa, while coarser sediments were richer in taxon diversity. Sediments with a median grain-size between 300-450 µm were rich both in terms of diversity and density, while sediments with a median grain-size of >450 µm still showed high diversity, but lower densities.

The Arap and Melez Rivers discharge to Izmir Bay bringing wastewater together with rainwater coming from their catchment areas. There is an artificial harbor built at the discharge point of the Melez River acting as a sedimentation area for the suspended matter carried by these rivers. This area has a storage capacity of 3 to 4 years. After this period, the sediments are dredged and disposed from the region. In this study, various studies were carried out in order to determine the geotechnical properties and pollution parameters of the sediments; the results of many previous studies are also given. In the analyses done on dredging samples, it was observed that sulfur, oil and grease, phosphorus, nitrogen and heavy metal concentrations were very high. The reason for these high concentrations is the direct discharge of untreated wastewater formed in the industries located along the Arap and Melez Rivers. The pollutants carried to Izmir Bay by these rivers then settle down inside the artificial harbor and reach high concentrations in bottom sediments. As a result of this study, some possible environmental effects of land disposal of this material are discussed and suggestions are given for final disposal alternatives. © 1995, International Association on Water Quality. All rights reserved.

A laboratory study of the hydraulic conductivity (HC) of a marine clay with monovalent, divalent and trivalent cations revealed large differences in HC. The exchangeable cations employed in this study are Na, K, NH4, Mg, Ca and Al in order of increasing valency. An interpretation of the results derived from consolidation tests suggests that HC is significantly affected by the valency and size of the adsorbed cations. An increase in the valency of the adsorbed cations leads to quicker rates of consolidation and higher HC, while, for a constant valency an increase in the hydrated radius of the adsorbed cations results in a lower rate of consolidation and HC. The reduction in HC was related to the dispersion and deflocculation of clay. Lower valency and higher hydrated radii of the exchangeable cations enable the double layer repulsive forces to predominate, thereby increase dispersion and defloccalation. ? 1995, The Clay Minerals Society.

The authors review the sedimentological characteristics of superficial beach sands using samples taken every 15 m along two transversal beach profiles separated by a distance of 1 km along the Belgian coast near Klemskerke. The westernmost spot (KP37) has been sampled four months after a beach nourishment with sands supplied from the Ravelingen bank situated at a few kilometers off Ostend. At the sampling time (31-1-'79) strong beach erosion attacked the youngest dunes near by the eastern station (KP 38). Granulometric characteristics and heavy-mineral characteristics (weight of heavy minerals in the sand fraction 63-2000µm, weight of heavy minerals in the different grades, heavy-mineral composition of the over-all sand fraction, length of the most occurring heavy minerals) of the beach sands as well as of the nourishment sands and of the youngest dune sands have been analysed. The results have been used to study the sedimentological variations in relation to the micromorphological position on the beach, the differences between both stations and the intluence of reworked Ravelingen sands and youngest dune sands upon the beach material. The three main sediment groups belong to different heavy-mineral associations. The youngest dune sands are similar to the H-group (BAAK), the nourishment sands of the Ravelingen to the beach sands south of Bergen (Holland coast) (EDELMAN-EISMA). The beach sands themselves show similarity to the Rhine-AS-Kreftenheye association (ZONNEVELD). This study of mineralogical and granulometrical characteristics offers interesting prospects of the identification of dune and beach sediments, of present day eolian sands and of some off-shore bank sands along the Belgian coast. It shows as well that these mineralogically different sediments may be used,if reworked, as natural tracers for the analyses of beach dynamics and sediment movements. The beach micromorphology commands greatly the sedimentological differences of the superficial beach sands. Especially the length of the heavy minerals proved to be an interesting argument. The heavy-mineral content varies greatly with the granulometric grade.

The composition of the Quaternary surface sediments in the Coastal Area is known in detail since the making of the geological map and especially since the systematic soil survey. The knowledge of the deeper Quaternary sediments however remains still fragmentary .Field work by the Center for Hydrogeological Research at the State University of Ghent has provided new data about the relief of the Tertiary substratum and the lithostratigraphy of the Pleistocene and Holocene sediments of the eastern part of the Coastal Area. A south-north section indicates the existence, in the burried surface of the Tertiary substratum, of two degradation levels (between -17 and -22 and between -8 and -6). Several lithostratigraphic units have been distinguished. The deepest deposit is the gravel-sand Ostend formation of Eemian age. This deposit is covered by the sandy Uitkerke formation of Weichselian age. The Wenduine formation on top of this sand is very heterogeneous; it has been formed during the transition between Pleistocene and Holocene. Along the edge of Inner Flanders the -8 level is overlain by the clayey Meetkerke formation with Hydrobia. In seaward direction this formation becomes sandy when passing laterally into the Houtave formation. The chronostratigraphic relationship between the two formations is not clear although the latter was probably deposited during the Atlantic. They are covered by the sands of the Zuienkerke formation, of which the northern part is also of Atlantic age. During this period and the Subboreal the Nieuwmunster peat was formed. This peat has been covered by the Dunkirk formation, except in the "Moere" of Meetkerke.