Fractionation and transport of compost-derived dissolved organic matter fractions in saturated red soil and black soil columns

The fractionation and transport of compost-derived dissolved organic matter (DOM_C) could affect the transport and fate of nutrients and DOM-associated pollutants in the soil environment. In this study, the humic acid fraction of DOM_C (HA_C) and fulvic acid fraction of DOM_C (FA_C) were selected to investigate the fractionation and transport of DOM_C in repacked soil columns of a red soil and a black soil under different KCl concentrations. The effluent DOM_C fractions were monitored by ultraviolet (UV)-visible (Vis) light and fluorescence spectroscopy. The results showed that the molecular weight (MW) of the effluent DOM approached that of the influent DOM_C fractions with the injection of DOM_C fractions. Three-dimensional fluorescence excitation emission matrices (3D-EEMs) coupled with parallel factor analysis resolved three fluorescent components, that is, low MW UV humic-like substances (C1), high MW UV humic-like substances (C2), and protein-like substances (C3). The mobility of HA_C and FA_C decreased with increasing KCl concentrations (1 mM–50 mM), implying that electrostatic interaction was an important mechanism for the retention of DOM_C in soil columns. The fact that the mobility of DOM_C fractions in the black soil was greater than that in the red soil could be attributed to the high free Fe oxide content in the red soil. The retained DOM_C fractions did not entirely desorb by the background electrolyte solution, suggesting that a part of the DOM_C fractions retained in soil columns was strongly bound. These results are helpful in understanding the fractionation and transport of DOM_C in soil environments.