摘要
讨论了国内有关湖泊沉积137Cs断代资料解译的一些问题。一些高寒地区的湖泊,上世纪60年代主核爆期以后,入湖泥沙的137Cs含量变化不大,因此沉积剖面137Cs浓度达峰值后无明显降低趋势。一些浅水湖泊,由于人类活动扰动湖底表层泥沙,剖面表层泥沙的137Cs浓度比较均一。根据核尘埃沉降监测资料,中国湖泊沉积应存在明显的1963年137Cs蓄积峰,不应存在所谓的1974年137Cs次蓄积峰,可能存在不很明显的1986年次蓄积峰。沉积剖面中137Cs浓度的深度变化,不仅和137Cs大气沉降通量变化有关,也和流域内近几十年来的环境变化有关,1963年以后的137Cs次蓄积峰的确定要慎重。黔中红枫湖沉积物137Cs面积活度高于滇西湖泊,主要是由于石漠化严重的喀斯特山地,裸岩面积大,裸岩坡地几无土壤吸附137Cs尘埃,核爆期间137Cs降尘随降雨径流直接流失进入湖泊比例高的缘故,不是青藏高原的大气污染物散落屏蔽效应的结果。
Caesium-137(137Cs)is a man-made fallout radionuclide with a half-life of 30.2 years that is present in the global environment,primarily as a reult of the atmospheric of nuclear weapons in the late 1950s and early 1960s.137Cs aerosols produced by weapons testing were transferred into the stratosphere and the associated fall- out was globally distributed. The temporal patterm of annual fallout was broadly similar across the globe and closely related to the intensity of weapons testing.Significant fallout was first recorded in the mid 1950s, maxi- mum fallout occurred in the early 1960s ,and fallout declined rapidly through the mid and late 1960s and early 1970s as a result of the nuclear test ban treaty imposed in 1963,The expected137Cs depth profile,characterized by a single well-defined peak in137Cs activity for 1963,has been documented for many lakes in China,However, non-standard137Cs depth distribution profiles with no single peak have been reported for several lakes in China. Those non-standard137depth distribution profiles are discussed in thid paper. In the lakes of high and cold re- gions137Cs is evenly distributed in the upper layer of deposit profiles, because137Cs concentrations of delivering sediment into the lakes have had little changes since the nuclear weapon testing period in the middle of 1960s. 137Cs even depth distribution shapes in profiles also occur in some shallow lakes ,where the mud layers on the lake bottom are often disturbed by human activities.According to the monitoring data on137Cs precipitation in Tokyo, the 1963’s137Cs peak should be clear and the so called“1974’s137Cs peak”should not exist in the pro- files of some lakes.137Cs concentration changes in lake deposits are related not only to137Cs deposition flux fluc- tuations from the atmosphere,but also to the changes of137Cs concentrations and activities delivering into the lake with sediments and runoffs. The higher137Cs inventory occurring in the Hongfeng Lake of the middle Guizhou than those in the lakes of the western Yunnan is not caued by the shelter effects of Tibet Plateau on movement and precipitaion of atmosphere aerosols.There is little soil exist to adsorb the precipitated137Cs fallout on the bare limestone slopes,which occupies most of the Hongfeng Lake catchment,so the proportion of137Cs amount delivering into the lake from the catchment to the total precipitated137Cs within the catchment is much higher than the lakes in the western Yunnan,the catchments of which are not located in limestone regions.
出处
《山地学报》
CSCD
北大核心
2005年第3期294-299,共6页
Mountain Research
基金
国家自然科学基金委员会(40271015)
科技部(2003CB415202
2004CB720200)
国际原子能机构(12300/RO)资助。~~
关键词
湖泊沉积
^137CS
深度分布
解译
<Keyword>137Cs
lake deposit
depth distribution
interpretation
