Sediment cores methods

The method above, however, is not suitable when one needs a precise study of the vertical distribution of pesticides. Generally, the concentration of pesticides in paddy sediment is highest at the surface. Special care is required to avoid contamination with surface soil when the sediment is collected. The sediment core should be collected in two stages. First, a pipe with a diameter greater than that of the core sampler is inserted in the sediment and then water inside the pipe is removed gently with a syringe, pipet, etc. Next, a layer of surface soil (1-3 cm) is taken with a spatula or a trowel and then subsurface soil is collected with a core sampler to the desired depth see also Figure 4. 

This study demonstrates the use of multiple-core methods to obtain whole-basin sediment fluxes from a suite of lakes and the application of these data to questions of atmospheric metal deposition. Multiple-core data can be economically produced by integrating longer core sections and reducing the number stratigraphic units for analysis. As few as three 210Pb analyses per core can yield a modern accumulation rate additional samples provide more historical detail. 

Methods for dating sediment cores using 210Pb and 137Cs were similar to those described by Robbins and Edgington (34). 137Cs content was de-... 

There has been one significant study of PBBs in sediment from the Great Lakes. Zhu and Hites [22] measured BB-153 in one sediment core from northern Lake Michigan and in one core from eastern Lake Erie. In both cases, the cores were dated (that is, core depths were correlated with particular years) and focusing factors were determined using the well-known lead-210 method. The concentrations (ng/g) of BB-153 are shown in Fig. 4 as a function of year of deposition for Lake Erie. At this location, BB-153 was found in the deepest layer, representing 1972 the concentrations reached a max-... 

We will present the basic requirements for preparing a bimane derivatized sample for HPLC analysis ana the preparation or appropriate blanks. We will then discuss the specific methods used for the three studies presented in the results section i) phytoplankton studies ii) sediment core studies iii) sulfide metabolism studies in invertebrate-bacteria symbiosis. 

The rate constants calculated by EF profiles (Equation (4.6)) are necessarily crude as several assumptions must hold the initial enantiomer composition is known, only a single stereoselective reaction is active, and the amount of time over which transformation takes place is known. These assumptions may not necessarily hold. For example, for reductive dechlorination of PCBs in sediments, it is possible for degradation to take place upstream followed by resuspension and redeposition elsewhere [156, 194]. The calculated k is an aggregate of all reactions, enantioselective or otherwise, involving the chemical in question. This includes degradation and formation reactions, so more than one reaction will confound results. Biotransformation may not follow first-order kinetics (e.g. no lag phase is modeled). The time period may be difficult to estimate for example, in the Lake Superior chiral PCB study, the organism s lifespan was used [198]. Likewise, in the Lake Hartwell sediment core PCB dechlorination study, it is likely that microbial activity stopped before the time periods selected [156]. However, it should be noted that currently all methods to estimate biotransformation rate constants in field studies are equally crude [156]. 

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. 

Up to about 1960, freshwater pH readings were taken only infrequently, and the colorimetric methods of pH measurements used were commonly inaccurate (Haines et al., 1983), particularly in waters with low ionic strength. Thus, reconstruction of the pH of lakes and streams from the literature, even for the mid-1950s, is problematic. However, dated lake sediment cores have now been analyzed for fossil diatom and chrysophyte assemblages. Statistical interpretation... 

Layers from sediment cores of up to 2 m length were obtained from selected sampling locations in the urban area of Berlin and in Brandenburg at Lake Quenz (S12, H5, H7, H8, T2, T3) using a deep-freezing method (Schwarzbauer et al., 2001). The sample from station H8 represents a sediment layer of 1984/85 and the sediment sample from station T2b is dated back to 1979/80, as determined by gamma spectrometric measurements of Pb-210 and Cs-137 of sediment core slices. 

In order to understand the full extent of the mercury problem in these times, one has only to consider the enormous loss rates. From the total of 2865 tons of mercury purchased in the U.S. in 1968, 76% or 2160 tons were lost to the environment. According to calculations of Kemp et al. (1974), the Lake Ontario reservoir contained a mass of 500 to 600 metric tons of "excess" mercury, i.e. discharged from anthropogenic sources. With the improvements in the methods of chlor-alkali electrolysis and by subsequent purification of waste streams the mercury loss has been reduced from 100 g per metric ton of manufactured chlorine to approx. 2 g per ton or less (Anon., 1973). The effect of these measures can be seen from concentration profiles of mercury in sediment cores taken off the mouth of Niagara River by Mudroch (1983), where a very distinct decrease from formerly approx. 4-7 ug Hg/g to less than lug Hg/g in recent years has occurred (Figure 2-6). 

While studies on sediment cores only provide iirformation on the local core position, lateral variations in physical properties can be imaged by remote sensing methods like high-resolution seismic or sediment echosounder profiling. They facilitate core-to-core correlations over large distances and allow to evaluate physical property logs within the local sedimentation environment. 

In what follows the theoretical background of the most common physical properties and their measuring tools are described. Examples for the wet bulk density and porosity can be found in Section 2.2. For the acoustic and elastic parameters first the main aspects of Biot-Stoll s viscoelastic model which computes P- and S-wave velocities and attenuations for given sediment parameters (Biot 1956a, b, Stoll 1974, 1977, 1989) are summarized. Subsequently, analysis methods are described to derive these parameters from transmission seismograms recorded on sediment cores, to compute additional properties like elastic moduli and to derive the permeability as a related parameter by an inversion scheme (Sect. 2.4). 

Breitzke M., Grobe H., Kuhn G, Muller R, 1996. Full waveform ultrasonic transmission seismograms - a fast new method for the determination of physical and sedimentological parameters in marine sediment cores. Journal of Geophysical Research 101 22123-22141... 

Weaver, P.P.E., Schultheiss P.J., 1990. Current methods for obtaining, logging and splitting marine sediment cores. Marine Geophysical Researches 12 85-100... 

A simple method of pore water preparation from a sediment core that is still kept in a plastic liner has been described by Jahnke (1988). In this method, which is also suitable for employing on anoxic... 

Fig. 3.30 Corelation of various sediment cores from the Cape Basin by means of sedimentary iron content profiles. This method permitted a safe projection of an age model available for one core to several other cores. (Wien et al. 2005a).

Sulfate reduction rates in marine shelf sediments commonly lie in the range of 1-100 nmol cm May (Jorgensen 1982). Since the sulfate concentration in the pore water is around 28 mM or 20 pmol cm the turn-over time of the sulfate pool is in the order of 1-50 years. A purely chemical experiment would thus require a month to several years of incubation. This clearly illustrates why a radiotracer technique is required to measure the rate within several hours. In sediment cores from the open eastern equatorial Pacific obtained by the Ocean Drilling Program it has been possible to push the detectability of this radiotracer method to its physical limit by measuring sulfate reduction rates of <0.001 nmol cm d in 9 million year old sediments at 300 m below the seafloor (Parkes et al. 2005). 

Ferdelman, T.G., 1980. The distribution of sulfur, iron, manganese, copper, and uranium in a salt marsh sediment core as determined by a sequential extraction method. Masters thesis. University Delaware. 

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