The Forms of Phosphorus in Sediments of Large Lakes (Poyang Lake) and Its Impact on Endogenous Release

The release and retention of phosphorus (P) in sediments play a crucial role in determining whole-system P dynamics and balance in eutrophic lakes. Using Poyang Lake (China’s largest freshwater lake) as a subject for a case study, we performed field investigations and collected data on specific P forms in the overlying water, interstitial water, and sediment phases. The vertical concentration variations of the aforementioned P forms in the columnar sediment of Poyang Lake reflect distinct surface enrichment characteristics, primarily attributed to external P inputs. The average flux of dissolved total P at the monitored sites was 0.49 mg/(m2·d), and the estimated P release from Poyang Lake to the overlying water was 447.13–587.7 t/a, which is comparable to the release from typical eutrophic lakes in China. Sediment P release serves as a significant P source for interstitial water and plays a crucial role in the upward release of dissolved IP (interstitial water) from the overlying water. Fe–P (accounting for 47.07% of TP) is the P form in Poyang Lake sediments that is most involved in the migration and transformation process, with a large amount of activated P being transformed into Fe–P and released into the overlying water.