广西平果龙何屯岩溶洼地剖面土壤^(137)Cs和^(210)Pb比活度分布的影响因素研究

A study on the influencing factors for distribution of ^(137)Cs and ^(210)Pb specific radioactivity in Longhetun karst depression area in Pingguo,Guangxi

^(137)Cs和^(210)Pb技术广泛应用于土壤侵蚀研究,但由于岩溶区的特殊性,如地表地下双层结构的存在,土壤形成慢,土层薄且不连续,易被侵蚀等特点,一定程度上限制了^(137)Cs和^(210)Pb技术在岩溶区的应用。文章选取广西平果果化石漠化综合治理示范区龙何屯洼地剖面,沿剖面采集土壤样品,进行^(137)Cs和^(210)Pb放射性比活度研究,得到以下认识:(1)土壤表层及整个土壤剖面^(137)Cs和^(210)Pb放射性比活度正相关,主要是人类活动及土壤迁移引起的土壤再分配导致的;(2)石穴地的137Cs和^(210)Pb放射性比活度均为最大,除受到邻近裸岩影响还与石穴地良好的集水集土条件有关;(3)洼地底部及沟底^(137)Cs和^(210)Pb放射性比活度相对偏小,主要是坡面长期受到地表径流侵蚀影响,土壤和泥沙在此沉积导致的;(4)退耕还林之后土壤得到很好的保护,并能拦截一定量上游带来的土壤,但由于岩溶环境的特殊性,地下漏失无法避免。

^137Cs and ^210Pb radiometric techniques have been widely used in soil erosion research. However, due to the special characteristics of karst area, such as dual layered structure of surface and subsurface, slowness of soil formation, thin and discontinuous layer and the erodibility of the soil and so on, the applications of ^137Cs and ^210Pb radiometric techniques to the karst area are limited. In this study, the Longhetun de pression profiles in Guohua karst ecological experimental site, Pingguo, Guangxi was chosen as an example. Soil samples along the selected profiles were collect and the specific radioactivities of ^137Cs and ^210Pb were an- alysed. The results showed that, （1） positive correlation of ^137Cs and ^210Pb was found both on the surface and at depths along soil profiles; this phenomenon was largely caused by human activity and soil migration, which also caused the migration of soil composition at depth. （2） Because of the enrichment of ^137Cs and ^210Pb in the adjacent bare rock, the maximum values of ^137Cs and ^210Pb specific radioactivity were found in rock cavities which are good spaces for water accumulation. （3） The ^137Cs and ^210Pb specific radioaetivities were relative low at the bottoms of karst depression and karst valley, for perennial runoff causes the soil ero sion to happen mainly on the slope and the soil deposition happen at the bottoms. （4） The soil has been well protected in the area after the previous farmlands were returned to forestlands; and the soil from the up- stream can be preserved by forest, but the underground leakage cannot be avoided due to the particularity of karst environment.