The temporal and spatial distributions of 210Po and 210Pb in the surface sediment of eastern tidal flat,Chongming,China

210Po and 210Pb are one pair of the most important radionuclides used in the study of marine environment and radioecology.Based on the analysis of activities of 210Po and 210Pb in surface sediments collected monthly (2010) eastern tidal flat of Chongming Island,the fluxes of 210Po and 210Pb in the atmospheric deposition and the discharge of the Changjiang River,the temporal and spatial distributions of 210Po and 210Pb and their impact factors were discussed.The results showed that the mean grain size of the surface sediments were similar in spring and summer,which were significantly lower than those in autumn and winter,and it exhibited decreasing trend with a landward and a northward all the year round.The activities of 210Po and 210Pb in the surface sediments ranged from 20.9 to 124 Bq/kg and 26.1 to 101 Bq/kg,respectively,which were higher than those of suspended particles in Xuliujing(the end number of fresh water input of Changjiang River).The average activity ratios of 210Po/210Pb in northern section,middle section and southern section in East Chongming tidal flat were 1.05,1.06 and 0.97,respectively.The sediments of the Chongming tidal flat were mainly controlled by the supply of the Changjiang River input.The activities of 210Po and 210Pb of surface sediment in East Chongming tidal flat decreased with the decreasing of tidal flat elevation.For the seasonal change,the activities of 210Po and 210Pb surface sediment in the East Chongming tidal flat showed high in summer and low in winter.