MOLECULAR WEIGHT COMPOSITION OF HUMIC ACIDS IN URBAN SOILS (THE NORTHERN ADMINISTRATIVE DISTRICT OF MOSCOW CITY TAKEN AS AN EXAMPLE)

The article provides research results and comparative analysis of humic acids in sod-podzolic soil of the Experimental Forest of the Russian State Agrarian University (protected area) and urban soils located in the Timiryazev district of Moscow. Humic acids of the zonal sod-podzolic soil of the Experimental Forest include four fractions with varying molecular weight: the 1^st fraction – ≥ 23 440 unified atomic mass units (amu), the 2^nd one – 13 340 amu, the 3^rd one – 5 500 amu and the 4^th one – 2 460 amu. The fraction with a molecular weight of 5 500 amu and a relative content of 38 % dominates among them, while the share of low-molecular fractions (< 20 000 amu) accounts for 70 % of the total mass of humic acids. When weight-average molecular mass of humic acids is 17 530 amu, the average molecular mass of the low-molecular fractions is 9 960 amu. Humic acids of urbanozems differ in molecular weight composition from humic acids of sod-podzolic soil. In most cases it consists of 5–6, less commonly of 3, fractions with molecular weight from 1 780 to ≥ 23 440 amu. The share of medium- and high-molecular fractions fluctuates from 31–37 % to 47–50 % of the total mass of humic acids. The characteristic feature of humic acids of urbanozems is the presence in their composition of low-molecular fractions with such molecular weights, which are not found in humic acids of sod-podzolic soil. Thus, humic acids of urbanozems are characterized by higher weight-average molecular mass ranging from 17 680 to 19 980 amu, as well as by higher weigh-average molecular mass of the low-molecular fractions which vary from 10 680 to 13 650 amu.

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