Sedimentation rates measurements

Figure 3. Rates of sulfate reduction (all measured with 35S) reported in the literature (references in Table I) show no obvious relationship to either sediment carbon content or carbon sedimentation rates (measured with sediment traps). The lowest reported rate of sulfate reduction occurs in the lake with the lowest carbon sedimentation rate, but there is no evidence of carbon limitation among the other lakes. Error bars indicate the range of reported sulfate reduction rates.

To overcome the bias resulting from uneven dispersal of tracer or inhibitor, sediment rate measurements are often made in slurries, which destroy the gradient structure of sediments, which is essential to the in situ fluxes. Slurries may provide useful information on potential rates, but not in situ rates. Potential nitrification rates and rates measured in intact cores were not correlated in estuarine sediments (Caffrey et ah, 2003). The lack of correlation was explained by the inclusion of variable amounts of anoxic sediments in the slurries from which the potential rates were derived. 

The approach is most useful in water samples because complete mixing of the tracer is possible. In sediments, rate measurements are constrained by the inhomogeneous nature of the sample and the dependence of rates on the structure of the environment. In this situation, fluxes between overlying water and sediment cores can be analyzed to obtain areal rates. In conjunction with tracer addition, estimates of nitrification rates can be obtained from the dilution ofN02 or N03 in the overlying water due to its production in the sediments (Capone et ai, 1992). The isotope pairing method for measurement of denitrification (Nielsen, 1992 Rysgaard et ai, 1993) is essentially an isotope dilution approach from which both nitrification and denitrification rates can be calculated. 

Sedimentation Rate. Sedimentation rate measurements have also been em-ployed, even in concentrated solutions, but are perhaps more suited to transport phenomena and conformational studies (Chapter 9), although useful thermodynamic data are obtained indirectly. 

Thickener-Basin Depth The pulp depth required in the thickener will be greatly affected by the role that compression plays in determining the rate of sedimentation. If the zone-settling conditions define the area needed, then depth of pulp will be unimportant and can be largely ignored, as the normal depth found in the thickener will be sufficient. On the other hand, with the compression zone controlling, depth of pulp will be significant, and it is essential to measure the sedimentation rate under these conditions. 

Finally, it should be emphasized that in all these studies more than one particle characteristic should be determined and this will usually entail more than one method of measurement. These can include various sizing techniques and the value of microscopy should not be ignored. Often, however, end-use tests provide the most meaningful data e.g. sedimentation rates or filtrability. 

Chapters 11 and 12 focus on the oceans. The first of these describes the use of U-series nuclides in the modern ocean, where they have been particularly useful during the last decade to study the downward flux of carbon. The second ocean chapter looks at the paleoceanographic uses of U-series nuclides, which include assessment of sedimentation rates, ocean circulation rates, and paleoproductivity. Both of these ocean chapters demonstrate that knowledge of the behavior of the U-series is now sufficiently well developed that their measurement provides useful quantitative information about much more than just the geochemistry of these elements. 

Erythrocyte sedimentation rate (ESR) A nonspecific inflammatory marker that may be elevated in some infections and inflammatory diseases specifically, the ESR is obtained from a blood sample by measuring the distance that red blood cells precipitate after 1 hour. 

Hewitt and Harrison61 incubated inorganic210 Pb(NC>3)2 with sediments and measured 210Pb alkyllead after a 14-day period. The conversion rate was very low, viz the ratio of 210Pb alkyllead to 210Pb added to sediment after 14 days was between 0.9 and 2.6 x 10 7. 

Table 1. Sedimentation Rates and Curve Fitting of 210Pb Measurements in Cores Collected at the U. S. Radioactive Waste Disposal Sites Near the Farallon Islands 60 km off San Francisco and at the Hudson Canyon, 350 km off New York City.

The sedimentation history of the upper Hudson Canyon has been measured at the 430 m depth level by Drake et al., [10]. The average sedimentation rate over the past 6,300 years, as determined by 14C dating of a piston core, has been an average of 70-80 cm/103 yrs the past 2,000 years appear to have a sedimentation rate of about 150 cm/103 years, Drake et al., [10]. 

Aggett, J. and L.S. Roberts. 1986. Insight into the mechanism of accumulation of arsenate and phosphate in hydro lake sediments by measuring the rate of dissolution with ethylenediaminetetracetic acid. Environ. Sci. Technol. 20 183-186. 

Sedimentation classifiers, 76 619-620 in depth filtration theory, 11 339 in particle size measurement, 78 142-144 in solid-liquid separation, 76 656-657 Sedimentation rate... 

This model requires an excess of sulfate over reducible carbon. Concentrations may be measured in solutions squeezed from sediment cores, diffusion coefficients are known from standard chemical data tables and sedimentation rates determined from 14C, 210Pb, or 230Th dating. Therefore, this model finds its best use in the recovery of the kinetics of organic matter decay. A discussion of this and similar equations and numerical applications may be found in Berner (1980). 

Measurements of radionuclides and metals in marine sediments and particulate matter are conducted for a variety of purposes, including the determination of sedimentation rates, trace metal and radionuclide fluxes through the water column, enrichment of metals in specific phases of the sediments, and examination of new sedimentary phases produced after sediment deposition. Such studies address fundamental questions concerning the chronology of deep-sea and near-shore sedimentary deposits, removal mechanisms and cycling of metals in the ocean, and diagenesis within deep-sea sediments. 

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