Site selection organic matter

Soil properties A Soil texture (sand, silt, clay), organic matter/carbon content, and pH Stones, roots, and hardpans must be largely absent to allow representative sampling of soil profile Soil properties should appear uniform over test site Soil texture data should be available at time of site selection. Soil properties must match study purpose. This can be realistic use conditions, realistic worst-case or worst-case in terms of agrochemical mobility and persistence Must ensure that the majority of samples can be taken from the deepest sampling horizon. Information about sub-soils can be obtained from soil maps, test coring and on-site interviews... 

To assess the influence of some soil physico-chemical characteristics, viz., pH, organic matter, clay content, etc., and exchangeable cations, on the spatial variation and vertical distribution of the solid-phase Al species in the profile of Delhi soils at selected sites. 

In addition to their use in the functional speciation role, selective extraction methods have been used to target element species in soil, or elements bound to, or associated with, particular soil phases or compounds. Examples include the use of extractants to release, for determination, metals on exchange sites, or metals bound or associated with soil iron or manganese oxyhydroxides or with soil organic matter. Most of these extractants are, however, less specific than intended and may extract species from other phases. Such extractants, however, are commonly, and conveniently, designated by their target species, e.g. extractable metal species or carbonate-bound species, but should more strictly be regarded as examples of speciation in which the species are operationally defined, i.e. by the method used to isolate them. 

Kd,Za was reduced by half. Removing amorphous hydrous oxides reduced Kd cu 100-fold and Kd zn by 20-fold as compared to natural soil. The metal sorption sites in the amorphous hydrous oxides and organic matter were more selective for Cu than for Zn. 

In operationally defined speciation the physical or chemical fractionation procedure applied to the sample defines the fraction isolated for measurement. Selective extraction procedures are used to isolate fractions of elements, such as exchangeable, reducible, oxidizable, and residual. These fractions are often equated with the metals associated, bound or adsorbed in the exchangeable sites, in the iron-manganese oxyhydroxides, organic matter/sulfides, and silicate phases, respectively. Although this is often a convenient concept, it should be emphasized that the reagents used may not be that selective to regard the fractions as defined by the operational procedures. 

A comparison of organic matter (OM) components in cores from Dabob Bay (oxic bottom waters) and Saanich Inlet (anoxic bottom waters) indicates that 02 availability ultimately has little or no independent effect on OM preservation in these environments (Cowie Hedges, 1992). Comparative analyses of organic compounds in sediment traps and bottom sediments from Saanich Inlet indicates that the anoxic benthic interface is an important site of diagenesis, and that selective removal takes place at both compound-class and molecular levels (Cowie etal., 1992). Preferential loss of marine organic material is indicated by the calculated delta-C-13 value and biochemical composition of the substrate. 

Hence, for the evaluation of the proposed Elbe marker compounds the quantitative and spatial distribution as illustrated for selected substances in Fig. 1 and 2 are the most important criteria. The quantitative evaluation of the molecular markers has to consider the accumulation rates of organic matter at the different sampling sites. Thus, in order to avoid misinterpretation all quantitative data presented in Fig.l and 2 are normalized to TOC content (given in pg/kg TOC). 

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