黔中高原岩溶丘陵坡地土壤中的^137Cs分布

THE DISTRIBUTION OF ^(137)Cs IN HILLY UPLAND SOIL ON THE QIANZHONG KARST PLATEAU

黔中岩溶坡地土壤中137Cs的深度分布坡顶和坡底具有相同的趋势,次表层土壤中137Cs的比活度最大;坡中土壤中137Cs的含量先增加后陡然减少。岩溶坡地土壤中137Cs的比活度介于9.1 Bq/kg^56.9 Bq/kg之间,变化趋势顺坡降低,与土层厚度变化趋势相反;平均比活度为26.1 Bq/kg,远远大于本底值。岩溶坡地土壤中137Cs的面积活度介于144.7 Bq/m2~440.2 Bq/m2之间,顺坡变化趋势不明显;与本底值比较,流失比较大;可能的原因一是黔中岩溶坡地早期石漠化较严重,基岩无法吸附137Cs,导致核爆期间沉降的137Cs随水流失;二是岩溶坡地土壤中的137Cs随土壤颗粒发生了地下漏失。基于以上调查和目前的计算模型,认为用于调查均质土壤地区土壤侵蚀的137Cs法暂时不适合直接用于基岩型岩溶坡地土壤侵蚀速率的调查。

The concentrations of caesium-137 on the Wangjiazhai slope are estimated to be 9.1--56.9 Bq/kg, with an average of 26. 1 Bq/kg, which is much higher than the background value. The reason is that the bedrock was unable to absorb caesium-137, instead caesium-137 was absorbed by soil. The deepward diffusion of caesium-137 in upslope soil shows a similar trend with the toe of slope, and the concentrations of caesium-137 in second-layer soil are higher than those in other sites. The concentrations of caesium-137 in middle slope soil tend to increase first and then to decrease. It may be explained by two reasons., one is the leakage of soil particles measured at 〈 2 mm in diameter, and the other is the deposition of oil from upper slope on the middle slope. And the concentrations of caesium-137 show similar trends with soil depth from upslope to the toe of slope. The inventory of caesium-137 is 144.7--440.2 Bq/m^2 , as compared with the background value. It is said that the amount of erosion is bigger. And the reason seems to be that caesium-137 had flown to the lake when it fell out, because there was no soil on the early plateau surface , so caesium-137 is hardly absorbed. Cadesium-137 inventory trend is not significant from the upslope to the toe of slope. In a word, based on the present research methods and models, we can consider that the caesium-137 method which was used in homogeneous soil is not fit to trace soil erosion on karst slope temporarily.