桂林西北郊光明山峰丛坡地土壤210Pb与226Ra分布与迁移规律研究

利用单一210Pb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210Pb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210Pb与226Ra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210Pb放射性比活度。测试结果表明4个土壤剖面中210Pb垂向分布服从指数衰变规律， 226Ra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210Pbex主要聚集在0~10 cm深度处，地表20~30 cm以下基本为支持性210Pb。土壤中支持性210Pb放射性比活度约为56.60±11.97 Bq?kg-1，与226Ra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210Pb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226Ra的差异主要与土壤特性和植被类型有关。 

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

There are still certain problems as to single 210Pb 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 210Pb 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 210Pb and 226Ra in the soil profile was analyzed； the specific radioactivity of supported 210Pb was preliminarily determined； and the influencing factors of the distribution of 210Pb and 226Ra were discussed . The results demonstrate that the vertical distribution of 210Pb in the four soil profiles shows exponential decay. The specific radioactivity of 226Ra keeps stable with the distribution of soil depth， but its mean value varies greatly among different soil profiles. About 95% of 210Pbex 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 210Pb. The specific radioactivity of supported 210Pb in soil is about 56.60±11.97 Bq?kg-1， consistent with the value of 226Ra 64.93±8.83 Bq?kg-1 within the error range. The further study shows that 210Pb 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 226Ra in the soil profile is mainly affected by soil characteristics and vegetation types.