How do drying-wetting cycles influence availability of heavy metals in sediment? A perspective from DOM molecular composition

Investigating the influence mechanism of drying-wetting cycles on the availability and mobility of heavy metals in sediment from the perspective of the molecular composition of dissolved organic matter (DOM) may gain a new understanding, but little current information exists. Here, we used spectral technologies, high-resolution mass spectrometry, and elemental stoichiometry method to trace the change rules of the molecular composition of DOM in the riparian sediment of the river. Results showed that the drying-wetting cycles could benefit the degradation of labile fractions (e.g., proteins, aliphatics, and lipids) of DOM and retain the fractions with high aromaticity and molecular size (e.g., lignin). The decrease in the availability of Cd after drying-wetting alternation processes was highly related to these changes in DOM composition. However, the availability of Zn and Cu remained almost unchanged, which probably resulted from the release and depletion of N and S in sediment derived DOM under drying-wetting alternation conditions. As for Cr, its exchangeable fraction was unchanged during the drying-wetting alternation process, likely due to its high stability in the sediment. These results have implications on the environmental geochemical cycling of heavy metals in the riparian sediment with frequent drying-wetting alternation.

Automated summary

This study investigates the influence of drying-wetting cycles on the availability and mobility of heavy metals in sediment, focusing on the molecular composition of dissolved organic matter (DOM). The results show that drying-wetting cycles can promote the degradation of labile fractions of DOM and retain fractions with high aromaticity and molecular size. The decrease in the availability of Cd is closely related to changes in DOM composition, while Zn and Cu availability remains almost unchanged. These findings have implications for the environmental geochemical cycling of heavy metals in riparian sediment.