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 (DOMC) could affect the transport and fate of nutrients and DOM-associated pollutants in the soil environment. In this study, the humic acid fraction of DOMC (HAC) and fulvic acid fraction of DOMC (FAC) were selected to investigate the fractionation and transport of DOMC in repacked soil columns of a red soil and a black soil under different KCl concentrations. The effluent DOMC 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 DOMC fractions with the injection of DOMC 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 HAC and FAC decreased with increasing KCl concentrations (1 mM-50 mM), implying that electrostatic interaction was an important mechanism for the retention of DOMC in soil columns. The fact that the mobility of DOMC 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 DOMC fractions did not entirely desorb by the background electrolyte solution, suggesting that a part of the DOMC fractions retained in soil columns was strongly bound. These results are helpful in understanding the fractionation and transport of DOMC in soil environments. In two soils, the fulvic acid fraction of DOMC (FAC) has a higher mobility than the humic acid fraction of DOMC (HAC).Free Al/Fe oxides inhibit the transport of compost-derived dissolved organic matter (DOMC) fractions.Increasing KCl concentration inhibits the transport of DOMC fractions.The fractionation of HAC is more remarkable than that of FAC.