Sedimentation causes

Only a few studies have been directly concerned with chemical and biological processes in sewer sediments. However, relatively high anaerobic activity in terms of H2S formation of sediment deposits compared with what is generally observed in sewer biofilms is observed (Section 6.2.5). This activity may indicate H2S formation in the deep parts of the sediment caused by the production... 

A special device was used to collect artificially resuspended sediment. In this device, the sediment was placed in a tube with overlying water. An oscillating grid placed in the water above the sediment caused a steady state resuspension equilibrium, under the same conditions as typically generated by winds and currents in the lagoon. This overlying water was then filtered, and the resuspended material analysed. 

Jet u 200 M drilling fluids required smearing of borehole walls in fine-grained soils and sediments causing sealing Diameter limitations fluid level (water and NAPL) difficult sampling accuracy limited produced fluids... 

Bioirrigation The movement of water through marine sediments caused by benthic animals. 

Bioturbation The physical mixing of sediments caused by the burrowing and feeding activities of benthic organisms. 

Compaction Compression in marine sediments caused by over pressure. Leads to a reduction in sediment porosity. 

Pressure solution The dissolution of deeply buried solids in marine sediments caused by the increase of mineral solubfiity as a result of increasing pressure. 

Prograde metamorphism of sediments causes the liberation of volatiles, which can be described by two end-member processes (Valley 1986) ... 

The concentration dependence of sedimentation causes an additional reshaping of the boundary, called boundary sharpening. The faster moving material is at a higher concentration than the slower material, with the result that the boundary is progressively sharpened as the concentration increases that is, it shifts to the left. The dependence of sedimentation constant on concentration and on the concentration of other molecules around the sedimenting molecule, which causes the above effects, are too difficult to measure. In some systems with spherical macromolecules, approximate corrections have been made (5). The extrapolation of s to zero polymer concentration should eliminate the major part of these effects. 

This is suitable for the formulations in which the percentage of solid ingredients, suspended in liquid is to be increased. The advantage of density difference between the molten medium and suspended particles is used in this process. The concentration of heavier particles is increased in the lower part of the casing either by natural sedimentation or by forced sedimentation caused by vibrating the whole casting assembly. The sedimentation process is controlled by a number of parameters such as particle size of solid suspension, temperature of melt, period of sedimentation, viscosity of melt, concentration of solid ingredients and column of melt etc. 

Gravitational sedimentation causes a change in the particle size distribution anywhere in and below the cloud compared with the size distribution at stabilization time. Thus, to reconstruct the size distribution at stabilization time, corrections must be applied to the size distributions measured in the samples. These corrections were calculated by assuming Stokesian settling modified by a drag slip correction. It was assumed further that at stabilization time the cloud was axially symmetric and consisted of spherical particles. Wind and diffusion effects were neglected. 

Existing data lend mixed support to the hypothesis that sulfate reduction is limited by availability of electron donors. Laboratory studies have shown that sulfate reduction in sediments can be stimulated by addition of carbon substrates or hydrogen (e.g., 85, 86). Increases in storage of reduced sulfur in sediments caused by or associated with addition of organic matter (108, 109) also have been interpreted as an indication that sulfate reduction is carbon-limited. Addition of nutrients to Lake 227 in the Experimental Lakes Area resulted in increased primary production and increased storage of sulfur in sediments (110, 111). Natural eutrophication has been observed to cause the same effect (23, 24, 112). Small or negligible decreases in sulfate concentrations in pore waters of ultra-oligotrophic lakes have been interpreted... 

Total S content cannot indicate whether increased carbon inputs to sediments cause increased diffusion of sulfate into sediments or restrict reoxidation and release of S from sediments, because the net effect is the same. In a survey of 14 lakes, Rudd et al. (80) did not observe a strong correlation between organic matter content per volume and net diffusive flux of sulfate. However, in English lakes the lowest C S ratios occur in the most productive lakes (24) whether this represents enhanced influx or retarded release is not clear. Among 11 Swiss lakes, ratios of C to S sedimentation rates are relatively constant and substantially below C S ratios in seston net S fluxes... 

Erickson, M.L. and Barnes, R.J. (2005) Glacial sediment causing regional-scale elevated arsenic in drinking water. Ground Water, 43(6), 796-805. 

Sedimentation potential— (also called electrophoretic or Dorn potential) Potential difference established during sedimentation (caused, e.g., by gravitation or centrifugation) of small charged particles (suspended in solution dispersion of solid particles or emulsion of immiscible liquid droplets). 

The decreasing redox potential favors the reduction of iron-3-phosphate to iron-2-phosphate, which is dissolved from the sediments causing a strong increase of phosphate in the anoxic deepwater. Nitrate and nitrite are unstable under these conditions. Ammonium resulting from the microbial decomposition of organic compounds is the only stable nitrogen compound in the presence of hydrogen sulfide. Microbial processes also seem to be responsible for the accumulation of silicate in anoxic deep waters. 

Core 316920 from the Landsort Deep is one example of disturbed sedimentation and thus unfavorable for comparison to the data of the other areas. At the depth 5-15 cm an abnormal decrease of the curves down to namral backgrounds is visible, indicating sedimentation of older sediments caused by sliding and/or resuspension at the slope of the basin. Anyway, the data are presented here because disturbed sedimentation is quite a normal process in many areas. A selection of cores from different sites of each of the basins (as we have done in the Eastern Gotland Basin) would have been better, but it is sometimes impossible. 

Sedimentation. Caused by deposits of particulate matter such as clay, sand, or rust. 

As mentioned in the beginning of this section bioturbation and advection by sedimentation cause particle transport in the sediment. In Fig. 7.20 three scenarios are schematically shown representing constant molecular diffusive and... 

The x-ray observations by Ihn et al. showed that the o-axis is oriented normal to the surface of the mats, implying that mats are formed by whiskers laying flat down on top of each other. But the preferred orientation is of the same kind as the anisotropy already described above for regular solution-grown films. Not surprisingly, the same type of anisotropy was found for PQT from cyclohexanone [110] and n-dodecane [93]. Importantly it was found that the orientation effect is not related whatsoever to the sedimentation (caused by gravitation) of whiskers into mats, because the anisotropy was found to exist also in mats taken from the vertical walls of the vessel after evaporation of the solvent. The question about the acmal mechanism for the preferred orientation therefore remains unanswered. Concerning the thickness of the whiskers MSrdalen et... 

Compaction of deep sediments (except Holocene sediments) includes both tectonic downwarping of basement sediments and compaction of Tertiary, Pleistocene, and older sediments. Tectonic downwarping is probably the only factor in major depositional areas such as large deltas, where the loads from massive amounts of sediments cause the bottom of the sedimentary basin to warp. In most studies of modern sediments, very little is known about this factor, so it is often treated as an unknown or something outside of the system. 

Remobilization of reduced Fe and Mn within the sediment causes changes in the Fe Mn ratios. This means that small scale changes in the ratio need have nothing to do with either supply or capture (e.g., Bryant et al., 1997). 

The methane content of the porewater profiles shows increasing concentration from the surface to 20-30 cm depth and then remains nearly constant. For a surface water temperature and sediment water temperature of 30°C the saturation of methane occurs at approximately 1 mM, which is exceeded by many of the porewaters at depths below 25 cm. Presumably this supersaturation is required for ebullition to be significant. The decrease in methane toward shallower water is probably due to consumption in the oxygenated zone and escape by diffusion and ebullition from the porewater to the atmosphere. It is interesting to note that at site JC-3 (July 91), the sediment below 25 cm has more than twice as much methane as does the sediment below a 5. patens mat (Fig. 5a). Because the mat is not completely floating all the time, we suggest that when the mat is close to or contacts the sediment it disturbs the sediment sufficiently to cause methane release. Another possibility is that the plant stem and/or roots connection of the mat to the sediment causes disturbance and release of the trapped methane. 

Sedimentation causes a flow Js in the direction of the centrifugal field. The flow Jd due to diffusion attempts to maintain concentrational homogeneity, and works against Js. For the resulting flow, we have... 

Cyclones designed for use with liquids are referred to as hydrocyclones, hydraulic cyclones or hydroclones. The basic principle employed to effect either concentration or classification of the solids is centrifugal sedimentation, caused by introducing the feed suspension tangentially into the unit they are particularly attractive for many applications because they have no moving parts. Specific aspects of design are provided by Svarovsky (1984). 

Measured activity levels in environmental samples are the result of the complex interactions of these factors which cannot be clearly foreseen. The variability in samples of soils, plants, animals and sediments causes uncertainties in the determination of activity levels in environmental samples. 

Diffusion of dissolved species in interstitial water in sediments cause mass transport between seawater and interstitial water (Berner 1971, 1980 Lasaga and Holland 1976). 

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