无侵蚀非农耕地土壤^(137)Cs深度分布入渗过程模型

Penetration process model for ^(137)Cs depth distribution in uncultivated soil without erosion

在阐明土壤中137Cs扩散与迁移过程的基础上,建立了无侵蚀非农耕地土壤137Cs深度分布入渗过程模型,再现了重庆开县和陕北子长两个剖面137Cs深度分布的变化过程。重庆开县剖面137Cs深度分布(2004年)为指数衰减形态,表层土壤137Cs浓度最高,137Cs深度分布形态系数ho=0.0997cm?1,入渗系数D=0.8006cm2·a-1。陕北子长剖面137Cs深度分布(2001年)为非指数衰减形态,次表层土壤浓度最高,全剖面拟合的深度分布形态系数ho=0.0825cm?1,入渗系数D=1.24cm2·a-1。子长剖面137Cs深度分布为非指数衰减形态的原因主要是表层和次表层土壤随深度增加土壤孔隙度或水分入渗速率急剧降低,导致137Cs入渗速率随深度增加而降低,137Cs入渗系数(D)为负值。

Based on ^137Cs diffusion and migration processes in soil, a penetration process model is developed for ^137Cs depth distribution in uncultivated soil without erosion. By using the model, the changes of the ^137Cs depth distribution with time for the ^137Cs reference inventory profiles at Kaixian, Chongqing and Zichang, Shaanxi, are tentatively reconstructed. The ^137Cs depth distribution in the Kaixian profile （2004） has an exponential decrease shape with depth. The highest ^137Cs concentration occurs in the surface horizon, and the coefficient for ^137Cs depth distribution shape is h0 = 0.0997 cml, with the related depth moving coefficient D = 0.8006 cm^2·a^-1. The ^137Cs depth distribution in the Zichang profile （2001） has a non-exponential decrease shape with depth. The highest ^137Cs concentration occurs in the sub-surface horizon, and the coefficient for ^137Cs depth distribution shape of the whole profile is h0=0.0825 cm^-1, with the related depth moving coefficient D = 1.24 cm^2·a^-1. The higher ^137Cs concentration in the subsurface horizon than in the surface horizon, which is represented by the non-exponential decrease shape of ^137Cs depth distribution with a negative value of D, is probably attributed to the fact that either porosity or moisture penetration of soil decreases with the depth＇s increase in the surface and sub-surface horizons, thus leading to a sudden decline of the ^137Cs penetration rate.