Organic matter selective preservation

Lichtfouse E, Chenu C, Baudin F, Leblond C, DaSilva M, Behar F, Derenne S, Largeau C, Wehrung P, Albrecht P (1998a) A novel pathway of soil organic matter formation by selective preservation of resistant straight-chain biopolymers chemical and isotope evidence. Org Geochem 28 411-415... 

Hedges, J.I., J.A. Baldock, Y. Gelinas, C. Lee, M.L. Peterson, and S.G. Wakeham. 2001. Evidence for non-selective preservation of organic matter in sinking marine particles. Nature 409 801-804. 

Hedges, J.I., F.S. Hu, A.H. Devol, H.E. Hartnett, and R.G. Keil. 1999. Sedimentary organic matter preservation A test for selective oxic degradation. American Journal of Science 299 529-555. 

Environmental organic matter is a composite of humic and nonhumic substances, which is formed through operation and interactions of various biotic and abiotic processes. Humic substances are formed through both selected preservation (residue) and catalytic synthesis mechanisms. Both enzymatic and mineral catalyses contribute to the formation of humic substances in the environment. The relative importance of these catalytic reactions would depend on vegetation, microbial population and activity, enzymatic activity, mineralogical composition and surface chemistry of environmental particles, management practices, and environmental conditions. Selective preservation pathways would play a more important role in humification processes in poorly drained soils and lake sediments, compared with more aerated environmental conditions. 

Several studies have suggested that the extent of organic matter degradation may be imprinted on the relative distribution of amino acids. For example, the depth-dependant relative enrichment of certain amino acids in POM has been interpreted as enhanced preservation of particular proteins. Hecky et al. (1973) showed that diatom cell wall proteins were relatively enriched in serine and glycine Cowie and Hedges (1992) found that these amino acids were relatively unreactive in sinking POM and concluded that the observed pattern represented selective preservation of diatom cell wall material within POM. Glycine is enhanced in HMWDOM relative... 

The principal degradation mechanism of organic matter in the formation of peats (humic substances included) and leading to the formation of coal, therefore, appears to involve the preferential breakdown of labile biomolecules (carbohydrates, etc.), and the selective preservation of inert and relatively inert (i.e., somewhat degraded) biomolecules (Hatcher and Clifford, 1997). Melanoidin formation may also play some role in the... 

An example of this selective preservation is shown in Figure 6 with the NMR spectra of the algal sapropel from a near-surface and a 2.8 m interval. In the surface layers, the organic-rich sapropel is dominated by polysaccharides denoted by peaks at 72 and 106 ppm in the spectrum, and humin accounts for less than 20% of the organic matter. At depth, the polysaccharides and other labile substances are decomposed, and the sapropel contains mostly paraffinic macromolecular humin (approximately 70% of the organic matter). Hatcher et al. (1983b) have shown that the loss of labile... 

It is important to note that under the anaerobic conditions existing in the sapropel negligible amounts of humic acids are present. The humic acids that do exist account for less than 5% of the organic matter and are structurally unrelated to the humin. They are essentially polyuronic acids and are only called humic acids because they are operationally extracted as such (Hatcher et al., 1983b). Thus, it is unlikely that humic acids are intermediates in the formation of humin in this environment. Selective preservation is the simplest explanation for the existence of humin. 

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. 

Organic compounds and compound classes differ in their potential to be preserved in sediments and to survive early diagenesis. As a general mle, water-soluble organic compounds, or organic macromolecules, which are easily hydrolyzed to water-soluble monomers, have a low preservation potential. In contrast to this, compounds with a low solubility in water such as lipids and hydrolysis-resistant macromolecules are selectively enriched in the sedimentary organic matter. Table... 

What is meant with selective preservation of organic matter ... 

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