Sectioning soil cores

Regardless of how the upper core is ultimately sectioned, the 15-120-cm depth cores are typically sectioned in 10-15-cm lengths for analysis. Techniques used to section soil cores are presented in Section 3.3.6. 

Another approach to improving agrochemical detection is to apply more of the active ingredient to increase the initial soil concentration. As mentioned previously, however, one must be careful not to exceed greatly the labeled application rate of the compound as questions may arise as to concentration effects on the observed dissipation. A more common and acceptable approach is to section the upper soil core into smaller depth increments, yielding increased residue concentrations as the total amount of soil mixed with the residues decreases in each processed sample (Table 1). 

Total soil weight per given depth per hectare assumes a bulk density of 1500 kg soil m. Calculations are based on a nominal application rate of 0.168kga.i.ha . Soil core sectioning techniques are discussed in Section 3. 

To investigate a vertical distribution of a chemical, a sediment column is divided into sections with appropriate thickness. The sediment column taken in a pipe should be refrigerated in an ice-cooled container, transported to the laboratory, and removed carefully on to a clean tray so that there is as little disturbance as possible to the soil core structure. In the case of a column in which there is little soil moisture and it tends to collapse, the soil should be pushed out to each required thickness and carved off. It is also possible to take a sediment column up to a 30-cm depth using a pipe that is connected to cylinders (5-cm height) with sealing tape. In this case, the sample in each 5-cm fraction can be obtained as it is, after removing the tape. 

Two soil sampling tubes were removed from each tank 2, 5, 9, 15, 27, 30, 43, and 58, and 72 days after the start of the experiment, then frozen and stored for later analyses. For analyses, the frozen soil cores were removed from the glass tubes (by brief immersion in hot water), then sectioned into four 1-cm cylinders representing 0-1, 1-2, 2-3, and 3-4 cm soil depths. Samples from each depth were shake-extracted with 100 ml ethyl acetate hexane overnight, and again with 100 ml methanol overnight. Extracts were filtered, concentrated to 20 ml and analyzed by LS and TLC as described below. 

Soil core data are available for only six of the pesticides discussed in this paper. The six pesticides are aldlcarb atrazlne 1,2-dibromo-3-chloropropane (DBCP) 1,2-dlchloropro-pane (DCP) 1,2-dlbromoethane (EDB) and slmazlne. Cores were always sampled at depths greater than one meter and the soil was characterized physically and chemically. The importance of soil core sampling in pesticide leaching assessments is presented in the Discussion section. 

In this section are more detailed discussions about soil sorption, volatility, soil core data and photolysis data and how they bear on leaching potential. 

At various times, soil core samples were taken, carefully sectioned, and analyzed for TCDD. 

Intact soil cores with little or no detectable soil compaction can be obtained by a PVC, acrylic, or aluminum cylinder (15 cm diameter) with sharpened lower edge that can be twisted through fibrous marsh soils to a depth of 60 cm. The top of the cylinder is sealed with a PVC cap or a stopper to provide suction, and the bottom of the cylinder after soil is extracted from soil is sealed with a rubber stopper. Soil cores can then be sectioned into desired depth increments, either in the field or in the laboratory. Surface detritus (distinguishable plant litter) is removed from the soil and saved for chemical analysis. Typically, soil cores are sectioned into 0-10,10-30, and 30-60 cm for routine characterization. Selecting soil depth increments should be based on site-specific conditions and soil profile characteristics. For routine monitoring of soil properties, typical root zone depth (0-10 and 10-30 cm) may be adequate to characterize the system. 

At each sampling point, soil cores were taken and sliced into vertical sections of 0.2 m, to allow for a depth-dependent analysis of texture, contents of stones, amounts of aluminium and iron oxides, and organic and inorganic carbon. Figure 1.2 gives the results from chemical analysis of selected soil properties. The parameters have a high variability, typical for anthropogenic sites. Physical characterisation comprised the analysis of bulk density and hydraulic properties like the capillary pressure-water saturation curve and the saturated hydraulic conductivity. 

As the plastic liners are removed from the probe, they are capped on both ends, the appropriate labels affixed, and promptly placed in a freezer (an in-field sectioning technique used for further partitioning of the 0-15-cm core is described later in this section). By convention, red plastic caps are placed on top of the core (i.e., the end that was closest to the soil surface) and black caps are placed on the bottom. Use of the two-color capping system is important when the cores are sectioned at a later time. This approach is referred to as zero-contamination sampling and is the industry standard in field soil dissipation. 

The Pebble Limited Partnership has provided drill core geology and rock chemistry, which were used to create a geologic and geochemical cross sections along the line of the 2007 soil traverse - a... 

Fig. 2. West to east plot of vanadium by enzyme leach in soils on top of a cross section showing vanadium in drill core. Dashed line shows the subcrop of Cretaceous, granitic rock of Pebble East beneath the Palaeozoic/Eocene volcanic and sedimentary rock cover.

Ultraclean ID-Tl-MS was employed to establish Pb concentrations in Vostok deep ice cores spanning the period 155,000 to 26,000 BP (62). Mechanical decontamination of the ice cores and appropriate analytical techniques afforded measurements with an uncertainty of 5% and 20% for outer and inner layers of the ice sections, respectively. Values ranging from 2-40 pg g were obtained, with higher concentrations during the ice age (Illinois) and the last glacial maximum, the major source of the metal being soil dust. 

In recent years geotextile wicks have replaced sand drains. Wicks consist of a thin corrugated core surrounded by a thin geotextile filter jacket. Typically, wicks are about 1/4 inch by 4 inches in cross section. They are placed by insertion into a similarly shaped mandrel (tube) whose bottom is closed with a plate to which the wick is attached. The mandrel is pushed or driven into the soil to the desired depth. When it is withdrawn, the bottom plate stays in place, holding the wick in place. 

Thirteen core samples were used from the earlier study of the environmental impact of phosphogypsum production (/). The sample identifications are the same as in that work A through I each represents an individual stockpile, and 1,2, and 3 represent different cores on the same stockpile. Five additional core samples were obtained for this study. The new samples were taken only through a short section approximately 3 m above and 3 m below the interface with the ground surface. The samples contained phosphogypsum or soil. The sample identifications are the same as before A, B, F, and H refer to the same stockpile as in Ref / 1 and 2 refer to different cores on the same stockpile, but the samples are differentiated from the former samples by -2, for example, F2-2. All sample depths are measured from the tops of the stockpiles of phosphogypsum. 

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