GEOCHEMISTRY FEATURES OF Pb-210 IN THE ESTUARY OF THE CHANGJIANG RIVER AND ITS ADJACENT SHELF

Pb-210 atmospheric flux of 2.06dpm/cm²·year has been determined by means ofmeasuring the soil sample from the area near the East China Sea continental shelf.The result agrees with the value prodicted from the model. After the Pb-210 activities in the sediments have been determined from more thantwenty columns in the estuary of the Changj:iang River and its adjacent shelf, it isfound that both virtical and horizontal distibutions of Pb-210 follow certain laws. The virtical distribution of Pb-210 in the estuary of the Changjiang River andits adjacent shelf can be divided into two typc;s and sis forms. The normal type coast-sts of three-region,two region and one regin forms, and the abnormal type consistsof parallel, upside-down and disorder forms.The normal virtical distribution of Pb-210 reflects the enviromental condition of steady-sate deposits and from the gradi-eat of Pb-210 profile, the sedimentary accumulation can be calculated.The abnormalvertical distribution of Pb-210 ref lects the enviromental condition of unsteady-state de-posits, some sudden events,such as resuspension, reworking and sliding, may takeplace in this area. The horizontal distribution of Pb-210 in the estuary of the Changjiang Riverand its adjacent shelf is quite different.Pb-210 activities of the surface layer in theinner-shelf mud deposit era almost two times smaller than those of the offshore muddeposit and relict sand area.The sedimentary accumulation is the main controllingfactor to the Pb-210 distribution·There is a negative relationship between the se-dimentarp accumulation and horizontal distribution of Pb-210, and a positive rela-tioaship between the sedimentary accumulation and virtical depth of Pb-210 in sedi-meats as well as the total Pb-210 radioactive quantity. The total Pb-210 radioactive quantity in the inner-shelf mud deposit area is ashigh as 160dpm/cm², much higher than the predicted value of.60dpm/cm², while thevalue of the offshore mud deposit and relict sand area is 30dpm/cm² approximately,much less than the predicted one. The Pb-210 deposit flux in the inner-shelf muddeposit area is four times greater than the predicted one, whereas in the offshoremud deposit and relict sand.area is oaly 60%of the value predicted, From the factsdescribed above, it can be sees obviously that the Pb-210 has been intensely focusedin the inner-shelf mud deposit area, but is the offshore mud二deposit and_relict sandarea, the Pb-210 has been largely dispersed. Based upon these geochemistry charac-teristics of Pb-210, it can be predicted that most of the lead pollutants carried bythe Changjiang River are scavenged in the inner-shelf mud deposit area, only asmall part of them is darried into offshore and open sea.