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

Abstract 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.