Of humic substances in peatlands

The presence of large proportions of nonhumified material of diverse origins and properties hampers the dissolution, fractionation, and estimation of humic substances in peatlands. No satisfactory methods exist for these purposes. Most studies of peat humus therefore focus on pyrophosphate extracts or humic acids obtained by sodium hydroxide extraction. 

Geochemistry of Humic Substances in Natural and Cultivated Peatlands... 

Humic substances in peatlands are often hypothesized to be precursors in the formation of coal. In Table 2 the elemental analyses of several Canadian peats are compared with those of different coals. The data on peats show that the carbon, sulfur, and nitrogen contents increase with increasing degree of decomposition and the oxygen content decreases. The sulfur con-... 

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. 

Elemental composition, functional group analyses, spectral properties, and characterization of acid hydrolyzates have shown that peatland humic acids are similar to those in mineral soils. NMR spectroscopy has revealed that peat fulvic acids are largely carbohydrate in nature while the residue of alkaline extraction is not all humin. It is suspected but not proven that humic substances in peatlands are more soluble, due to lack of clays and mineral elements, than those in mineral soils. 

There are several areas of research on humic substances in peatlands that should be pursued. Data on the chemistry of tropical and southern hemisphere peats are very scanty. We need to study the chemistry of the peatforming plants of these areas, as well as the more highly decomposed peats of tropical regions such as Malaysia and Indonesia. 

Peatlands, or organic soils, are water-logged deposits of partly decomposed plant debris. Ecological variation and diversity in extent of domination by water influence the degree of humification in peatlands. Humification in peatlands does not coincide with decomposition as well as in mineral soils. Measurement and extraction of peatland humus are hampered by the presence of large proportions of unhumified material. Therefore, most studies on the characterization of peatland humus have focused on humic acids, or on pyrophosphate extracts of the organic soils. Pyrophosphate extracts contain less unhumified materials than alkali extracts but are far less effective in extracting the peat humic substances. 

The free-standing water in peatlands does not transmit light well enough to support phytoplankton growth due to the presence of dissolved humic substances. Therefore in the aquatic phase of peatlands, light limitation and the acidity of the water favor detrital food chains based on bacteria to the near exclusion of autotrophic food chains based on phytoplanktons (Speigt and Blackith, 1983). Phytoplankton-based food chains are characteristic of many aquatic environments, such as lakes and oceans. 

Large samples of each type could be collected and analyzed in several different laboratories, utilizing the latest techniques for the various humic substances. The classification and analytical methods would be standardized. In this way the extensive reserves of organic matter contained in the world s peatlands could be adequately characterized as to chemical substances. 

In studies with insoluble peat humic acids, Szalay and Szilagyi (1968) found that these organic substances retained Cu, Zn, Mn and Mo so tenaciously that the symptoms of deficiency of these nutrients in plants growing on drained moor, or peatland soils, could well be caused by such retention. In addition, Co was also so strongly held that plants grown on such soils supplied inadequate amounts to meet the needs of animals fed on the plant material. 

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