Seasonal changes-facilitated release of phosphorus and tungsten from the Lake Taihu sediments through reductive dissolution of Fe/Mn (hydr)oxides and competitive adsorption with dissolved organic matter

The release of phosphorus (P) and tungsten (W) from sediments can contribute to eutrophication and heavy metal contamination in water bodies, respectively. This study simultaneously investigated the seasonal variation characteristics of P and W in sediments in Meiliang Bay, China. The results indicated that seasonal variations in pH, dissolved oxygen (DO), and temperature (T) at the sediment–water interface influenced the P and W composition as well as their release from sediments. The diffusion fluxes of soluble reactive phosphorus (SRP) and soluble W (except in winter) were 0.145–2.881 mg⋅m⁻²⋅d⁻¹ and 1.785–3.006 μg⋅m⁻²⋅d⁻¹, respectively, indicating that the sediments served as a source of P and W. In autumn, the diffusion fluxes of SRP (2.881 mg⋅m⁻²⋅d⁻¹) and soluble W (3.006 μg⋅m⁻²⋅d⁻¹) were significantly higher than in winter (0.147 mg⋅m⁻²⋅d⁻¹ and −0.048 μg⋅m⁻²⋅d⁻¹, respectively). The concentration of SRP and soluble W in winter (0.20 mg⋅L⁻¹ and 0.22 μg⋅L⁻¹, respectively) were significantly lower than in autumn (1.57 mg⋅L⁻¹ and 1.39 μg⋅L⁻¹, respectively). These results suggest that under high temperatures and cyanobacteria degradation, sediments release more SRP, soluble W, Fe(Ⅱ), Mn, and dissolved organic matter (DOM). The significant positive correlations among SRP, soluble W, Fe, Mn, and DOM and their consistent trends in the top 20 mm of the sediment indicate that the main processes causing the release of P and W from sediments are competitive adsorption by DOM and redox reactions of Fe (III)/Mn (IV) oxyhydroxides. This study is of great practical significance for simultaneously addressing lake eutrophication and heavy metal pollution.