Sediment Phosphorus Supply and Availability in the Algal-Dominated Zone of a Large Eutrophic Lake (Lake Taihu)

In this study, sediment internal phosphorus (P) and its supply ability were studied in the algal-dominated zone of Lake Taihu during the overwintering and recruitment period of algae. The results indicated that sediment P fluxes, P mobile fractions, and P supply kinetics showed dynamic changes from the overwinter to the algal recruitment period. P flux and the concentration of the diffusive gradient in thin film (DGT)-measured labile P increased from winter to summer. However, the highest P supply ability was found in spring sediments, as indicated by the ratios of DGT-P to porewater P, suggesting that spring sediments can supply more P for the growth of overwinter algae. Laboratory incubation experiments show that sediment with a higher mobile P content could release more soluble P under suitable conditions, thereby increasing the chlorophyll a (Chla) concentration. The growth of overwinter algae appeared to be more correlated with porewater P concentrations and the ratios of nitrogen to phosphorus than with the solid-phase mobile P fractions, as indicated by the Pearson correlation analysis. This study strengthens our understanding of the relationship between the availability of sediment P and algal recruitment from sediments.