Intact cores

FIGURE 14.13 (a) Schematic showing intact soil core incubations used to determine the solute exchange 

The temperature of the water bath is controlled as needed, but under most conditions in situ water column temperatures are maintained. Prior to starting the core flux measurements, the overlying water is removed from each core, filtered through a 0.45 pm pore size polyethersulfone filter and gently replaced into the respective cores to a final water column depth of approximately 15 cm. The water column is slowly bubbled with ambient air throughout the incubation period, both to ensure an aerobic water column and to completely mix the water column. Small aliquots ( 20 mL) of water samples are collected and prepared for analysis of desired solutes. 

Solute fluxes are calculated from the change in concentration with time by using the following equation  

FIGURE 14.14 Flux of dissolved oxygen from the water column to the sediment, measured using the intact sediment cores and laboratory incubations. (Reddy, K. R., Unpublished Results, University of Florida.) 

Much of the coastal sedimentation accretion work has been conducted in the Mississippi River deltaic plain, where vertical accretion rates are large, and where there are also very high rates of subsidence and coastal land loss. In other coastal areas of the United States and Europe, a wide range of results have been found, with sedimentation rates varying from 0 to 1.5 cm year . Many coastal marshes are not accreting at a rate sufficient to compensate for the present rates of sea level rise. Many factors affect accretion rates in wetlands. These include plant community, density of vegetation, tidal elevation, sediment input from riverine, estuarine and marine sources, proximity to sediment sources, total organic matter input from primary productivity of wetland, and relative sea level rise. 

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When films of poly(Dat-Tyr-Hex carbonate) were exposed to strongly alkaline conditions (1 M NaOH at 37 C), a rapid decrease in the weight of the devices was seen. The thickness of the films decreased steadily, while the molecular weight of the intact core of the polymer matrix remained virtually unchanged. These... 

For the determination of the phosphate group a new procedure was established (64a) using a two-step deacylation of the rough form LPS (E. coli F515 and S. minnesota R595) and h.p.l.c. purification of the intact core-backbone oligosaccharide. Data obtained by H-, 13C-, and 31P-n.m.r. spectroscopy as well as f.a.b.-m.s. analysis unequivocally showed the presence of 4 -phos-phate at GlcN (II). A similar procedure was also applied to E. coli J5 LPS (66a). 

Figure 2. Rates of sulfate reduction in lake sediments reported in the literature range over 3 orders of magnitude and are not correlated with lake sulfate concentrations. All measurements were made with l5S in intact cores or core sections. References are given in Table I.

Figure 4. A, Pore-water profiles (October 15, 1990) in Lake Sempach typically indicate that sulfate is consumed within the upper 3 cm. B, Diffusion rates for sulfate calculated from the profile in panel A (T = 5°C) indicate that the rate is maximal just below the interface, but all rates are less than 2 nmol/cm2 per hour. C, Sulfate reduction rates measured with 15S in intact cores on the same date are 2 orders of magnitude greater and do not exhibit the same depth profile as diffusion rates. Error bars indicate the standard deviation among 10-15 replicates. The sulfate profile in panel A was measured by centrifuging pore water from cores identical to those in which sulfate reduction was measured. D, The 35S measurements indicate that 50% of the areal sulfate reduction occurs below 2-cm depth and 25% occurs below 5-cm depth. The pore-water profile indicates that negligible...

Measured rates of sulfate reduction can be sustained only if rapid reoxidation of reduced S to sulfate occurs. A variety of mechanisms for oxidation of reduced S under aerobic and anaerobic conditions are known. Existing measurements of sulfide oxidation under aerobic conditions suggest that each known pathway is rapid enough to resupply the sulfate required for sulfate reduction if sulfate is the major end product of the oxidation (Table IV). Clearly, different pathways will be important in different lakes, depending on the depth of the anoxic zone and the availability of light. All measurements of sulfate reduction in intact cores point to the importance of anaerobic reoxidation of sulfide. Little is known about anaerobic oxidation of sulfide in fresh waters. There are no measurements of rates of different pathways, and it is not yet clear whether iron or manganese oxides are the primary electron acceptors. 

The objective of this study was to demonstrate the physical transport of TCE by EO through cores of undisturbed soil. While research approaches have been performed on packed columns of pure clay (e.g. kaolinite), few have used native soils, and only in the form of slurries. At this time, no information is available for transport of TCE by EO through intact cores of natural soil. Therefore, the results of EO experiments using undisturbed soil are more applicable to actual site conditions than using single mineral soil. Parameters governing TCE transport in the soil are used in a one dimension advective model to describe TCE transport during the experiment. 

Millard, C., Meier, H., Broomfield, C. (1994). Exposure of human lymphocytes to bis-(2-chloroethyl)sulfide solubilizes truncated and intact core histones. Biochim. Biophys. Acta 1224 389-94. 

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. 

Christensen D. (1984) Determination of substrates oxidized by sulfate reduction in intact cores of marine sediments. Limnol. Oceanogr. 29, 189-192. 

Figure 2. Effect of effective stress on porosity (a) and permeability (b) of the fractured and intact core samples (after Liu arui Liu, 2001a).

Overlying water incubations with intact cores ... 

The goal of this paper is to provide an overview of coupled hydrological and geochemical processes observed in large intact cores of Hanford sediments. A multiple nonreactive tracer technique will be utilized to quantify physical hydrology under saturated and unsaturated conditions. Adsorption isotherms will quantify the sorption of SrEDTA and U(VI) under kinetic and equilibrium... 

Transport experiments were conducted on the intact cores at a variety of water contents using saturated and unsaturated flow experimental techniques (24, 25, 38). The intact cores were epoxied into PVC pipe and enqtlaced into fabricated Plexiglas endcaps. The cores were hydraulically connected to a membrane inside the endplate to facilitate either saturated or imsaturated flow. Under saturated conditions, influent solution was ponded (1-2 cm) at the upper boundary to facilitate delivery into the cores, and efiluent was collected in a high-capacity fraction collector. Under unsaturated conditions, a vatmum-... 

Figure L Air-rotary coring apparatus for obtaining intact cores of the Plio-Pleistocene Unit, White Bluffs, Hanford Reservation. Diamond-bit core barrel (10-inch diameter) was attached to a track-mounted hydraulic motor. The entire apparatus was affixed to a backhoe bucket in order to obtain cores at any...

Figure 2. Excavation of the intact Hanford formation cores from the surrounding sediments. The annulus created by the coring apparatus was filled with foam or wax, and the surrounding material was car lly excavated, revealing the intact core.

Figure 3. Oat / iV/ge National Laboratory unsaturatedflow facility. The intact cores are contained in large polyvinyl chloride pipes, and a filter membrane was c ed to the sediments within a fabricated acrylic endcap at the lower boundary. Tension was maintained through the large white vacuum chambers, which also housed a fraction collector for samples of column effluent. Influent was delivered by a multi-channel pump at the upper boundary. Tensiometers, visible in the side of...

Uranium transport throu the undisturbed, unsaturated Plio-Pleistocene core resulted in similar retardation (R = 3.1) (Figure 6c) to that observed in the repacked sediments (Figure 6b). This is surprising considering the longer residence time in die intact core (280 h) versus the shorter residence time (2 h) and observed geochemical nonequilibrium in the repacked sediments. The... 

Figure 6. Coupled hydrology and geochemistry of the adsorption and displacement of U(VI) through the Plio-Pleistocene Unit, (a) Equilibrium adsorption isotherm showing both Freundlich and linear fits, (b) Observed (points) and modeled (lines) of the displacement of nonreactive tracer Br and U through repacked sediments, (c) Observed (points) and modeled (lines) of the displacement of multiple nonreactive tracers through the intact core, under saturated and unsaturated conditions. The displacement of U occurred under...

Chehroudi, B., Chen, S.-H., and Bracco, F.V. (1985) On the intact core of full-cone sprays. SAE Paper 850126. 

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