Decomposition of humic acids by incubation in a soil water-extract under various conditions of oxygen availability

Summary Decomposition of humic acids suspended in a soil water-extract under various conditions of oxygen availability (aerobic, anaerobic, alternating aerobic/anaerobic) led to the formation of fulvic acids, lower molecular weight compounds, and humin, a more complex mixture of insoluble compounds. The transformation of humic acids and formation of new humic compounds were higher under aerobic conditions than under either anaerobic or alternating aerobic/anaerobic ones.Although subjected to decomposition under greatly differing conditions of oxygen availability, the residual humic acids showed essentially the same types of chemical alterations, an increase of functional groups containing oxygen and a decrease of hydrolysable ternary and quarternary fractions.