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 1st fraction - ≥ 23 440 unified atomic mass units (amu), the 2nd one - 13 340 amu, the 3rd one - 5 500 amu and the 4th 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...