Accumulation and composition characteristics of organic phosphorus in sediments from the Yangtze River–connected lakes, China

Purpose Lying in the flood basin of the Yangtze River, Lake Poyang (PY) and Lake Dongting (DT) have suffered from strong hydrological alternations due to the operation of The Three Gorges Dam. Yet, it is still unclear whether the changes in the hydrological regime significantly affect the accumulation and composition of phosphorus (P), especially organic P (OP), and how this influence threatens its water quality. Methods Sediment P pools were determined (inorganic P, OP, NaOH-EDTA P, and total P), and P species were characterized by 31 P NMR spectroscopy. Results and discussion Compared with other lakes, the Yangtze River–connected Lakes (RC) sediments have low OP content but accounted for a higher proportion of total P (TP) (22.3–53.7%, with an average proportion of 36.8 ± 9.0%). Urban rivers into the lake and incoming water from the Yangtze River contributed to the accumulation of sediment OP, and the short hydraulic residence time constrained the retention of sediment OP. Monoester P (mono-P) and diester P (di-P) were the main components of sediment OP. The contents of mono-P and di-P in sediments of RC were lower (23.5 ± 16.2 mg kg −1 , 4.8 ± 3.0 mg kg −1 ) than expected. Both lakes show opposite distribution trends of labile OP components with sediment elevation. The frequent dry–wet alternation of sediments due to water fluctuation in the RC enhanced the degradation of mono-P and di-P. Conclusion The impact of sediment OP on the overlying waters of RC was limited. However, repeated exposure to sediments caused by water level fluctuations promotes the degradation of OP components and aggravates the risk of P release to the overlying water.