桂林西北郊光明山峰丛坡地土壤^(210)Pb与^(226)Ra分布与迁移规律研究

Distribution and migration of ^(210)Pb and ^(226)Ra in soil in of peak-cluster hillside of Guangming mountain,Guilin

利用单一^(210)Pb技术来估算岩溶区土壤侵蚀、水土流失和泥沙来源等还存在一定问题。岩溶区土层厚度不一,难以准确地确定支持性^(210)Pb放射比活度是制约该方法应用的一大关键问题。文章选取桂林西北郊光明山岩溶峰丛坡地的4个土壤剖面,测试了土壤剖面^(210)Pb与^(226)Ra放射性比活度,探讨其分布规律及影响因素,初步确定土壤中支持性^(210)Pb放射性比活度。测试结果表明4个土壤剖面中^(210)Pb垂向分布服从指数衰变规律,^(226)Ra放射性比活度随土壤深度增加基本不变。光明山峰丛山坡土壤中约95%的^(210)Pbex主要聚集在0~10 cm深度处,地表20~30 cm以下基本为支持性^(210)Pb。土壤中支持性^(210)Pb放射性比活度约为56.60±11.97 Bq·kg^(-1),与^(226)Ra放射性比活度值64.93±8.83 Bq·kg^(-1)在误差范围内一致。进一步研究发现,土壤剖面中^(210)Pb受研究区大气干湿沉降、植被覆盖类型、地形条件、土壤特性(特别是有机质)的影响。此外,研究区土壤剖面^(226)Ra的差异主要与土壤特性和植被类型有关。

There are still certain problems as to single ^(210)Pb technology used to estimate soil erosion,water and soil loss and sediment source,etc.of karst region.Due to different soil thicknesses,the difficulty in accurately determining the supported ^(210)Pb specific radioactivity is a key problem of this method.To solve this problem,four soil profiles of this study were selected on the hillside of karst peak-cluster.The distribution of ^(210)Pb and ^(226)Ra in the soil profile was analyzed;the specific radioactivity of supported ^(210)Pb was preliminarily determined;and the influencing factors of the distribution of ^(210)Pb and ^(226)Ra were discussed.The results demonstrate that the vertical distribution of ^(210)Pb in the four soil profiles shows exponential decay.The specific radioactivity of ^(226)Ra keeps stable with the distribution of soil depth,but its mean value varies greatly among different soil profiles.About 95% of ^(210)Pbex in soil of the hillside of Guangming mountain mainly concentrates at a depth of 0-10 cm.Below 20-30 cm from the surface is mainly supported ^(210)Pb.The specific radioactivity of supported ^(210)Pb in soil is about 56.60±11.97 Bq·kg^(-1),consistent with the value of ^(226)Ra 64.93±8.83 Bq·kg^(-1) within the error range.The further study shows that ^(210)Pb in the soil profile is affected by atmospheric deposition,vegetation cover type,topographic conditions,and soil characteristics(especially those of organic matter in the study area).In addition,the fluctuation of ^(226)Ra in the soil profile is mainly affected by soil characteristics and vegetation types.