Inhibited vertical mobility of biochar-derived dissolved organic matter under low-intensity rainfall: role of mineral retention

Abstract Biochar has great potential in the application areas of carbon sequestration and environmental remediation. A significant amount of dissolved organic matter (DOM) may be released from biochar, which is highly reactive and mobile. However, it is unknown how this highly reactive DOM migrates in soil column, especially in rainfall events. In this study, pristine and aged corn biochars were applied to simulated soil columns filled with hematite/quartz or montmorillonite/quartz (3:7, w:w), and the DOM vertical migration was investigated under high- and low-intensity rainfalls. Results showed that montmorillonite could significantly inhibit the migration of the DOM by over 80% compared to the pure quartz system and 50% compared to hematite/quartz system. Minerals, especially montmorillonite, mainly preferentially adsorbed humic-like substance of DOM compared to polycyclic aromatic-like substance. Notably, under the same cumulative rainfall amount, DOM concentration gradually increased with the number of rainfall events in low-intensity rainfalls, but decreased sharply in high-intensity rainfalls. The relatively higher DOM concentration is beneficial to DOM sorption on minerals. These findings demonstrated that low-intensity rainfall facilitated the DOM retention on minerals especially in montmorillonite-rich soils. Graphical Abstract