Influence of the humification process on the properties of peat humic acids

Abstract

Influence of the humification process on the properties of peat humic acids Comparative and complex characterisation of peat humic acids (HAs) isolated from peat profiles of different origin in Latvia was conducted. Elemental and functional analysis of the isolated HAs was made and their acidity and molecular weight were estimated. Spectral characterisation included UV-Vis, IR, electron spin resonance and fluorescence spectra. Structural characterisation of HAs was by both 1H and13C nuclear magnetic resonance spectra. Properties of HAs isolated from the Latvian peat were compared with HA from other sources (soil, water, coal and synthetic humic substances). Major properties of peat HAs depended on their origin, indicating the importance of humification processes. HAs isolated from peat of more recent origin were more similar to soil Has, while there was a greater degree of humification in part from older sources.

The Molecular Composition of Humic Acids in Permafrost Peats in the European Arctic as Paleorecord of the Environmental Conditions of the Holocene

“…Similar results were obtained for cryosolic peat soils of the Arctic [40]. E 4 /E 6 decreased in buried horizons, which was indirectly indicative of reduced size of HA molecules [38,43]. The E 4 /E 6 ratio was inversely related to the degree of condensation of the aromatic network in HAs so that a low ratio would reflect a high degree of aromatic condensation and the presence of relatively low proportions of aliphatic fragments [8].…”

“…The x(H):x(C) ratio of HA characterizes the degrees of condensation and maturity, and is related to climatic parameters of its formation period [37][38][39]. There is a clear distinction of HAs extracted from the STL of oligotrophic and mesoeutrophic peat characterized by the highest values of x(H):x(C) (0.99-1.…”

Stability and biodegradability of organic matter from Arctic soils of Western Siberia: insights from <sup>13</sup>C-NMR spectroscopy and elemental analysis

“…Namely, H / C from humic acids has been used as an index of molecular complexity, as higher degree of conjugation implies a lower hydrogenation of the carbon chains (Andersson et al, 2012) and it has been found to decrease with humification (Zaccone et al, 2007). The optical index E4 / E6, being proportional to the average molecular weight of humic compounds (Chen et al, 1977), has also been used to trace humification (Dziadowiec et al, 1994;Hugelius et al, 2012;Šīre and Klavinš, 2010), during which an increase in the average molecular weight occurs due to condensation and polymerisation processes (McDonald et al, 2004). Similarly, C / N has been used as a measure of decomposition degree in peat soils (Kuhry and Vitt, 1996) and, moreover, has been found to be directly related to SOM lability, as it determines the stoichiometric availability of nitrogen to soil microorganisms (Andersson et al, 2012;Zaccone et al, 2007).…”

Potential of Baltic Region Peat in High Added-value Products and Environmentally Friendly Applications - A Review

“…And the highest content of FA can usually be found in the upper layers of peat of raised bogs. And Sire and Klavins [83] hypothesized that the topmost peat layers are subjected to periodic drying and wetting, which can increase aerobic decomposition and oxidation. As a result, the elemental composition of peat HAs does not regularly change with the depth in the peat layer [83].…”