Spatial Distribution Of Lead、Radio-cesium And Plutonium In Typical Lake Sediments And Their Application For Recent Chronology

Lakes(reservoirs) sediment is an important boarding for watershed erosion and environmental pollutants, and the integrity of the continuity of deposition and its profile make it the indicator to reveal the climate and environment change, which was important archives to study of environmental change in the past. 210Pb、137Cs and Pu isotope as a tracer element has been widely used in all kinds of sedimentary environment of modern sedimentary inference, the estimation of sediment deposition rate and environmental quality change process of tracer, etc. The plutonium and radio-cesium can provide significant recent chronology data for these environmental researches due to their exclusively characteristic.In the paper, Fuxian lake and Dianchi lake, the typical representative of Yunnan-Guizhou plateau, as well as Chaohu lake and Jingpo lake,were selectively studied as spatial distribution of environment radiation nuclide 210Pb、137Cs and Pu, in combination with special peak 137 Cs and Pu and determine sedimentary differentiation of and pollution, and discussed the related species in lake sedimentary and migration.The results help to understand the source and sediment dating of artificial radionuclide 137 cs and Pu isotopes in plateau lakes. The main conclusions are as follows.1、230+240Pu activity in Fuxian lake sediment column core is the accumulation of single peak distribution obviously and 240Pu/239 Pu characteristic value was 0.186 ±0.008 on average. Both Pu isotopes show that the core sediments from the global atmospheric precipitation. Because of strong interference, 137 Cs distribution was in disorder, which can’t provide chronology characteristic. The result show Pu is 137 Cs can provide more reliable for dating information Fuxian lake.2、The distribution of 137 Cs and 239+240Pu in Dianchi column core is consistent, presenting the accumulation of all present a single peak. Combined with the feature of 240Pu/239 Pu value indicates that the core sediments radionuclide stems mainly from the global atmospheric precipitation; The accumulation of 137 Cs and 239+240Pu main peak at the same time marked in 1964 and the average sediment rate was 0.190 ±0.024 g/cm2/a, consistent with 210 Pbex rate of 0.183±0.024g/cm2/a. 210 Pbex distribution in line with the good relationship with index, indicating relatively stable sedimentary environment.3、From study of lakes, anthropogenic factorlake and eutrophication degree were the main factors for 137 Cs migration and redistribution and may lead to 137 Cs overall distribution disorders and Dianchi lake sediment column 137 Cs constantly high specific activity, as well as the reason of higher proportion of 137 Cs and 239 + 240 Pu in the surface sediment.4、137Cs activity in Chaohu lake and Jingbo lake sediment column in the core were showing typical unimodal distribution, showing that global atmospheric sedimentation is the only source, corresponding to accumulation peak of the year for 1964. Chaohu lake sediment 210 Pbex activity exponentially with the increase of physical depth is reduced, the overall stable sedimentary environment.5、According to 137 Cs main label position, we can calculate the Chaohu C4 and C14 column sediment deposition rate to an average of 0.218 g and 0.264 g/cm2/a, and 210 Pbex calculated respectively were 0.230 g/cm2/a and 0.253 g/cm2/a. Lake sediments of chaohu lake sediment core number results show the sediment accumulation rate of regional differences.