MOLECULAR-MASS DISTRIBUTION OF HUMIC ACIDS OF PERMAFROST PEAT MOUNDS FROM THE EUROPEAN NORTHEAST OF RUSSIA

Abstract

The relevance of the research is caused by the polydispersity of humic acids and their insufficient study in peat soils of cryolithozone. The main aim of the research is to study the molecular mass distribution of humic acids in soils of mounds peatlands. Objects of the research are humic acid preparations isolated from two permafrost peats – from dry cryogenic soil of mounds (Hemic Folic Cryic Histosols, plot 2014-1) and soil from bare peat spots (Hemic Folic Cryic Histosols (Turbic), plot 2014-2), over the entire depth of peat deposits. Methods: elemental composition, liquid gel chromatography. Results. The authors have studied the molecular-mass distribution of humic acid preparations isolated from the hilly peatlands of the European North-East of Russia. The patterns of its changes along the profile are revealed. It was shown that the proportion of the low molecular weight fraction of humic acids in peat dominates and statistically significantly exceeds the mass fractions of the middle and high molecular weight fractions. The profile distribution of the number average molecular weights of humic acids of the two plots has a bimodal character, with maximum values in the upper and lower parts of the profile. High values in the upper part of the profile are associated with the presence of long unbranched carbon chains of paraffin fragments and fragments of oligo- and polysaccharides, leading to increase in the linear dimensions of humic acid molecules. The degradation of paraffin and carbohydrate fragments down the peat profile, leads to decrease in molecular wights of humic acids. The correlation dependences between the ratio x(H):x(C) and high molecular weight fractions of humic acids were established. The increase in molecular weights in the lower part of the profile is caused by coagulation of dispersed humic acids on peat mineral matrix. Cryogenic processes on the border of permafrost lead to significant transformation of humic acid structure with splitting off the least condensed molecular fragments. This is clearly reflected in decrease of molecular weights and polydispersity index of humic acids.

Keywords

• tundra zone
• peat mounds
• humic acids
• molecular weight distribution
• gel chromatography