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Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 9/1/2014 Publication Date: 11/21/2014 Citation: Zhang, X.J. 2014. New insights on using fallout radionuclides to estimate soil redistribution rates. Soil Science Society of America Journal. 79:1-8. Interpretive Summary: The fallout radionuclides such as 137Cs have been widely accepted and used in the past 40 years to provide quantitative soil redistribution estimates at a point scale. Recently their usefulness has been questioned by a few researchers challenging the validity of the key assumption that the spatial distribution of fallout radionuclides in soil is initially uniform. The objective of this work is to reconcile the opposing opinions by examining the assumption and by developing a new concept for correctly interpreting soil redistribution rates estimated with the tracing technique. This review shows that the key assumption is invalid, and therefore soil redistribution rate estimated for a sampling point is not the true erosion rate but a pseudo value because random spatial variation of the radionuclide inventory at the point is erroneously attributed to an effect of soil redistribution. Fortunately, such spatial variations at points are typically random in nature, and thus can be resolved statistically by increasing independent sample number and by interpreting soil redistribution rate in terms of mean value for a uniform area or slope position as the random spatial errors of the radionuclide inventories tend to cancel each other out. The new concept will help soil erosion researchers make more accurate soil redistribution estimates using the fallout radionuclides technique. Technical Abstract: The fallout radionuclides such as 137Cs have been widely accepted and used in the past 40 years to provide quantitative soil redistribution estimates at a point scale. Recently their usefulness has been questioned by a few researchers challenging the validity of the key assumption that the spatial distribution of fallout radionuclides in soil is initially uniform. The objective of this work is to reconcile the opposing opinions by examining the assumption and by developing a new concept for correctly interpreting soil redistribution rates estimated with the tracing technique. This review shows that the key assumption is invalid, and therefore soil redistribution rate estimated for a sampling point is not the true erosion rate but a pseudo value because random spatial variation of the radionuclide inventory at the point is erroneously attributed to an effect of soil redistribution. Fortunately, such spatial variations at points are typically random in nature, and thus can be resolved statistically by increasing independent sample number and by interpreting soil redistribution rate in terms of mean value for a uniform area or slope position as the random spatial errors of the radionuclide inventories tend to cancel each other out. |
