运用β多样性的测度方法探讨不同人为干扰强度对米槠林乔木层的影响

定量转换模型的选用是137Cs技术测量土壤侵蚀速率的一个关键,从最初的经验公式到现在的理论模型,形成了定量转换模型的两大主要类型。对常用模型建立的原理、适用范围和不足之处进行了分析。其中的质量平衡模型(包括不同的版本)因基于137Cs沉降、吸附、再分布等物理过程和相对精确而受到众多研究者的青睐。其局限性表现在:为方便计算而过度简化与实际过程或为充分考虑实际过程而过多引入无法准确测定的参数。剖面分布模型和扩散迁移模型与质量平衡模型有相似的缺点。由于各模型的假设原理和计算公式不尽相同,使用相同137Cs损失值估算出来的侵蚀速率差值甚至可以超过一个数量级。现有理论模型的完善和操作性较强的模型开发将是137Cs技术发展的主要方向之一。

Discussion on Several Models Used in Converting 137Cs Measurement to Soil Erosion Rates

The choice of a quantitative conversion model is a key to the()~(137)Cs measurement to estimate soil erosion rate.Two main kinds of models including preliminary empirical equations and recent theoretical models have been established. The ranges and limitations of the common models are discussed respectively to the mass-balance model.Great attention is paid for its precision and basis of physical-chemical processes.At the same time,there are also several limitations with them.Firstly,for the convenience of computation,the processes are simplified.Secondly,in order to improve the processes related to the()~(137)Cs precipitation and erosion,many parameters which can not be measured accurately are incorporated.The profile-distribution model and the diffusion and migration model have the same situations.The results from the same reduction of()~(137)Cs may differ remarkably between different models for their different theories and expressions.So,improving the existing models and developing more reasonable models are still one of the main tasks for the()~(137)Cs technology.