Sedimentological Characteristics of ^239+240Pu and ¹³⁷Cs in the Sedimentary Deposits of Poyang Lake

The spatial and vertical distribution of 239+240Pu and 137Cs in sediments of Poyang Lake was studied to assess the dynamics of disposition and the pollution status. The activities of 239+240Pu and 137Cs in surface sediments ranged from 0.005 to 0.616 Bq/kg and from 0.70 to 5.82 Bq/kg, respectively. The inventories of 239+240Pu in sediment cores of PYA and PYB were determined to be 75.2 and 19.9 Bq/m2, respectively. In sediment core PYA, the activity of 239+240Pu ranged from 0.043 to 0.485 Bq/kg, while that for 137Cs ranged from 0.39 to 6.80 Bq/kg. An accumulation peak along with two secondary peaks was observed in sediment core PYA, suggesting a correlation between the timing of these subpeaks and flood events in Poyang Lake. By employing 239+240Pu, the average deposition rate for core PYA was calculated as 0.79 cm/year from 1954 to 1998 and as 0.44 cm/year from 1998 to 2022. The results also suggested that the deposition rate of Poyang Lake has been impacted by human activities, such as the construction of water conservancy projects around Poyang Lake and the commissioning of the Three Gorges Dam Project.