应用137Cs示踪技术估算土壤侵蚀的若干问题探讨

[目的]探讨用~(137)Cs示踪技术估算土壤侵蚀量方法(以下简称"~(137)Cs示踪方法")所存在的几个关键问题,促进该方法的标准化和系统化。[方法]对大量已发表的相关文献进行分析,根据作者的研究经验,归纳出~(137)Cs示踪方法在实践应用中所存在的核心问题。[结果]~(137)Cs示踪方法中关于~(137)Cs在空间是均匀分布的假设存在不合理性,不能直接用于定量估算单钻点取样的土壤侵蚀量。~(137)Cs活度的空间变化存在随机性的成分。敏感度和不确定性分析结果证明~(137)Cs活度的空间随机变化量是~(137)Cs示踪方法不确性的最大来源。[结论]可以用多钻点样本平均值来减少~(137)Cs随机变化量所引起的侵蚀估算误差。以统计学为基础的试验设计和采取独立样本的办法可以消除该误差。虽然~(137)Cs模型已被广泛应用,但由于缺乏长期观测资料诸多模型还处在理论研究阶段,没有得到严格的验证和评判。因为不同模型估算的侵蚀量差别甚大,模型验证和筛选对该方法的成功运用至关重要。

Several Key Issues on Using 137Cs Method for Soil Erosion Estimation

[Objective] This work was to examine several key issues of using the ¹³⁷Cs method to estimate soil erosion rates in order to improve and standardize the method.[Methods] Based on the comprehensive review and synthesis of a large body of published literature and extensive long-term research experience, several key issues in the application of the ¹³⁷Cs method were generalized.[Results] The core assumption that spatial distribution of ¹³⁷Cs inventories is uniform is invalid, and that the ¹³⁷Cs method cannot be used to estimate quantitative soil erosion rates using a single soil core sample. The author emphasized that there existed a random component in ¹³⁷Cs spatial variation, and showed that this spatial random component was the largest uncertainty contributor of the ¹³⁷Cs method using the previous results from a sensitivity and uncertainty analysis.[Conclusion] The erosion estimation error resulting from spatial random variation can be filtered out by using a mean ¹³⁷Cs inventory of multiple independent soil cores or samples. The spatial random component can be removed using appropriate sampling designs for taking independent samples based on geo-statistical properties. Although the ¹³⁷Cs erosion models have been widely used in the literature, none of them has been vigorously tested and validated due to the lack of measured long-term soil loss data, and most models still remain theoretical. Because extremely large differences exist between model estimates, model validation and evaluation are utterly important for successful application and acceptance of the ¹³⁷Cs method.