SCIENTIA GEOGRAPHICA SINICA ›› 2014, Vol. 34 ›› Issue (1): 97-102.doi: 10.13249/j.cnki.sgs.2014.01.97

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Distribution Characteristics of 239+240Pu and 137Cs in Subaqueous Delta at the Changjiang River Estuary and the Environmental Significance

Li-guo CAO(), Shao-ming PAN(), Xu-ying LIU, Yi-hong XU, Wei XU   

  1. Ministry of Education Key Laboratory for Coastal and Island Development, School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing, Jiangsu 210023, China
  • Received:2013-03-20 Revised:2013-05-16 Online:2014-01-10 Published:2013-08-16

Abstract:

The sediment core SC07 was collected in the subaqueous delta at the Changjiang River estuary. Radioisotopes of 239+240Pu and 137Cs were analyzed focusing on discussing the distribution characteristics of activity profile, then the difference between 239+240Pu and 137Cs profiles were obtained. Results displayed that, there were the same cumulative peaks of 1963 and 1958 both in 239+240Pu activity profile and in 137Cs profile. The 239+240Pu activity profile showed a good agreement with the 137Cs profile (R2=0.765), that is to say, they can convey the same information about sedimentation processes. The start layer of 239+240Pu activity was corresponding to 1948 while 137Cs was corresponding to 1954, which showed the more measurement sensitivity of 239+240Pu. 137Cs/239+240Pu activity ratio was quite different after moratorium on nuclear testing, which really did good to dating for the sediments. Moreover, the 137Cs/239+240Pu activity ratio played an important role in distinguishing nuclide source in the environment. Meanwhile, it has been seen that 137Cs/239+240Pu activity ratio of the sediments core was lower than the global average, indicating that 239+240Pu activity concentrations were partly from close-in fallout. 239+240Pu activity in the sediment core was between 0.072-0.716 mBq/g and 137Cs was between 0.390-16.210 mBq/g. 239+240Pu atmospheric fallout mainly concentrated in the 63-111 cm, while the 239+240Pu activity between 0-45 cm decreased obviously. There were one peak (71 cm) and two sub-peaks (63 cm and 99 cm) in the vertical profiles of 239+240Pu. It needs to be mentioned that the peak at 71 cm was corresponding to the year 1963. The cumulative sub-peak at 63 cm may be caused by China's nuclear test that happed during the 1970s-1980s. Also, the cumulative peak (73 cm) in the vertical profiles of 137Cs was corresponding to the year 1963, which was nearly the same with vertical profiles of 239+240Pu. Because of the extremely complicated dynamic action of Changjiang River estuary area, the existence of cumulative peak of 1986 the vertical profiles of 137Cs was still needs further research. In a word, it has been suggested that the radionuclide 137Cs, 239+240Pu and the activity ratio were useful tools in studying the material source, evolution of the delta, as well as the deposition rate.

Key words: 239+240Pu activity, 137Cs activity, sediment core, the subaqueous delta at the Changjiang River estuary

CLC Number: 

  • P73