[Systemic Characterization of Phosphorous in the Sediments of Retired Aquaculture Lakes in the Yangtze River Basin]

The study of phosphorus release from sediments in retired aquaculture lakes is a crucial aspect of phosphorus management in the Yangtze River Basin. In this research, Qinglan Lake(a retired aquaculture lake within the Poyang Lake area of the Yangtze River Basin)was selected as the study site. By analyzing the physicochemical properties, phosphorus speciation, and the composition of organophosphorus compounds in both surface and core sediment samples, this study investigates the occurrence characteristics of phosphorus in sediments from degraded lakes and assesses its impact on the overlying water quality.The results indicated that the average total phosphorus (TP) content in the surface sediments was 797.67 mg·kg^-1, exceeding the ecological risk threshold of 600 mg·kg^-1, which is associated with the lowest level of sediment-induced ecological risk. Inorganic phosphorus was the dominant phosphorus form in surface sediments, accounting for 89.15% of the total phosphorus. Among these, calcium-bound phosphorus (Ca-P) represented the largest fraction at 30.91%. Monoester phosphorus (Mono-P) was the predominant organic phosphorus fraction in surface sediments, constituting between 7.57% and 42.88% of the TP extracted by NaOH-EDTA. Aluminum-bound phosphorus (Al-P) was identified as the primary source of bioavailable phosphorus (BAP) in surface sediments, with some areas exhibiting mild to moderate pollution levels.Furthermore, using the diffusive gradients in thin films (DGT) technique, the sediment was confirmed as a significant source of endogenous phosphorus pollution in the lake, releasing approximately 313.50 kg annually. These findings provide valuable data and a scientific foundation for phosphorus pollution control in retired aquaculture lakes within the Yangtze River Basin.