Several key issues on using 137Cs method for soil erosion estimation

Authors: Zhang, Xunchang

Submitted to: Grazinglands Research Laboratory Miscellaneous Publication
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2017
Publication Date: 10/30/2017
Citation: Zhang, X.J. 2017. Several key issues on using 137Cs method for soil erosion estimation. Bulletin of Soil and Water Conservation. 37(5):342-346.

Interpretive Summary: This work was to examine several key issues of using the fallout radionuclide cesium-137 to estimate soil erosion rates in order to improve and standardize the erosion estimation method. Based on the comprehensive review and synthesis of a large body of published literature and the author’s extensive research experience, several key issues in the application of the cesium-137 method were generalized. The results show that the core assumption that spatial distribution of cesium-137 inventories is uniform is invalid, and that the cesium-137 method cannot be used to estimate quantitative soil erosion rates using a single soil core. The author emphasized that there existed a random component in cesium-137 spatial variation, and showed that this spatial random component was the largest uncertainty contributor of the cesium-137 method using the previous results from a sensitivity and uncertainty analysis. The erosion estimation error resulting from spatial random variation can be filtered out by using a mean cesium-137 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 cesium-137 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 cesium-137 method. This work will provide useful insights into the cesium-137 erosion estimation method, which can be used by erosion scientists and soil conservationists to improve the estimation accuracy of the cesium-137 method.

Technical Abstract: This work was to examine several key issues of using the cesium-137 method to estimate soil erosion rates in order to improve and standardize the method. Based on the comprehensive review and synthesis of a large body of published literature and the author’s extensive research experience, several key issues in the application of the cesium-137 method were generalized. The results show that the core assumption that spatial distribution of cesium-137 inventories is uniform is invalid, and that the cesium-137 method cannot be used to estimate quantitative soil erosion rates using a single soil core. The author emphasized that there existed a random component in cesium-137 spatial variation, and showed that this spatial random component was the largest uncertainty contributor of the cesium-137 method using the previous results from a sensitivity and uncertainty analysis. The erosion estimation error resulting from spatial random variation can be filtered out by using a mean cesium-137 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 cesium-137 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 cesium-137 method.