Seasonal variations in cadmium mobility in sediment-water systems of algae- and macrophyte-dominated zones in Lake Taihu

Variations in trophic status affect water quality and sediment geochemistry, thereby influencing cadmium (Cd) mobility and its release into the water column. This study conducted seasonal sampling in algae- and macrophyte-dominated zones of Lake Taihu, China, using high-resolution dialysis and multispectral techniques to simultaneously monitor Cd, manganese (Mn), ferrous iron (Fe(II)), and dissolved organic matter (DOM) in sediment pore water. A sudden Cd release was observed in April in eutrophic, algae-dominated sediments, attributed to Cd complexation with tyrosine. Redundancy analysis (RDA) confirmed tyrosine as a key factor driving this Cd release. Multispectral analysis further showed that Cd was stably bound to functional groups in tyrosine-like substances, including aromatic C–H (630 cm⁻¹), alcoholic C–O (1150 cm⁻¹), phenolic O–H (1350 cm⁻¹), alkene C=C (1630 cm⁻¹), and aliphatic −COOH (3320 cm⁻¹). In summer and autumn, Cd mobility in algae-dominated areas was mainly regulated by cyanobacterial uptake and redox reactions involving iron–manganese oxides. In macrophyte zones, DOM influenced soluble Cd in winter, while lower Cd levels in summer and autumn likely resulted from adsorption onto iron–manganese oxide–rich sediments, enhanced by photochemical processes and rhizosphere oxidation. Overall, Cd contamination in algae-dominated systems warrants greater attention.