Humification process

Both and nmR showed the presence of aromatic and aliphatic components. In l C-NMR, resonances at =58 ppm indicate the presence of many OCH3 groups, such as those occurring in syringic, vanillic, and ferulic acids. Spectra clearly show the presence of palmitic and stearic acids by GC/MS, IR, and NMR data. The fulvic and humic acids are predominantly made up of phenolic and fatty acid units. These are highly aromatic because lignin residues have been incorporated in the humification process. 

J.C. Vedy and S. Bruckert, Seasonal evolution of soluble organic compounds in relation to different biochemical humification processes, Pedologie 20 (1970) 135-152. 

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. 

Haider, K. (1992). Problems related to the humification processes in soils of temperate climates. In Soil Biochemistry, Vol. 7, Stozky, G., and Bollag, J.-M., eds., Marcel Dekker, New York, pp. 55-94. 

Polak, J., Sulkowski, W. W., Bartoszek, M., and Papiez, W. (2005). Spectroscopic studies of the progress of humification processes in humic acid extracted from sewage sludge. J. Mol. Struct. 744-747, 983-989. 

Senesi, N., and Plaza, C. (2007). Role of humification processes in recycling organic wastes of various nature and sources as soil amendments. Clean Soil Air Water 35, 26 11. 

Hatcher P. G., Spiker E. C., and Orem W. H. (1986) Organic geochemical studies of the humification process in low-moor peat. In Peat and Water, Aspects of Water Retention and Dewatering in Peat (ed. C. H. Euchsman). Elsevier, London, pp. 195-213. 

Figure 23 Different humification processes operating in the transformation of litter to humic compounds (after Kogel-Knabner, 1993).

Kogel-Knabner I. (1993) Biodegradation and Humification Processes in Forest Soils. Dekker. 

V. R. Williams (1914), a well-known Russian investigator, also postulated the existence of two stages in the humification process, the first being the decomposition of the original plant residues to simpler compounds, and the second heing the synthesis of substances of a more complex nature. In contrast to the views of Maillard, both processes were believed to result from the enzymatic activity of microorganisms. 

The formation of humic substances in a peatland environment is a complex humification process which is principally due to certain enzymatic and microbial activities. These organic matter transformation processes are influenced by the nature of the peat-forming plants and certain physical and chemical properties within a particular peatland. In very acidic or low nutrient peatlands a very different microflora may exist than in a more eutrophic and less wet situation. In the former situation humification may be retarded and the peatland plants will be preserved and thus accumulate. On the other hand, in less acid environments with moderate amounts of nutrients and periodic water-table fluctuations humification proceeds relatively rapidly and leads to decomposed organic soils such is the case in drained and cultivated organic soils. 

In principle, this figure is valid for both lakes and running water. In clear lakes, the input of carbon via autochthonous production (and the humification process per se) is of greater significance than in rivers and bogs where allochthonous humic material predominates. 

Analysis of functional groups such as carboxyl, phenol, carbonyl, or meth-oxyl (Table 2) increases our understanding of the chemical structure of humic substances and can be used to explain the behavior of humic substances in various humification processes (Gjessing, 1976). Carboxyl and phenolic hydroxyl groups clearly predominate, although in some cases methoxyl groups are quantitatively important as well (Muenster, 1982). 

In conclusion, autochthonous humification processes in lakes must occur. The ratio of autochthonous to allochthonous input varies, of course, from lake to lake and depends on factors such as the specific ratio of watershed size to lake area, watershed structure, hydrologic input into the lake, productivity within a lake, and the relative sizes of pelagic and littoral zones of a lake. 

A third issue is that even though the soil is one source of stream humic substances, it is not necessary that soil and stream humic substances have the same composition. If they were of the same composition, then stream humic substances would be primarily humic acids, because the humic cidjo J fulvic acid ratio in soil is approximately 3 1. However, as previously dis- -cussed in this chapter, stream humic substances are approximately 90% fulvic acids. One may say that fulvic acids are leached from soils in preference to humic acids. This may be true, but no one has shown water leachates of soil to contain fulvic acid of the same composition as in the bulk soil. Beck et al. (1974) state that meteoric waters percolating through soil will selectively mobilize nonrepresentative fractions of the soil organic matter. It should be emphasized that even if stream humic substances are the same as soil humic substances, one can not infer that one is the source of the other, but that the same precursors and humification process are probably operable in both soil and stream environments. 

A third theory speculates that stream humic substances are soil fulvic acids leached from soil in the initial stages of humification and then modified, transformed, or aged by stream humification processes which result in humic substances unique to this aquatic environment. 

A fourth theory postulates that stream humic substances are formed by a unique stream humification process, whereby simple reactive moieties are polymerized and condensed into humic substances unique to the stream environment. 

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