Validating a Basic Assumption of Using Cesium‐137 Method to Assess Soil Loss in a Small Agricultural Catchment

Abstract

AbstractAlthough the fallout radionuclide 137Cs technique has been widely used to provide soil redistribution estimates in recent decades, some researchers have recently challenged the usefulness of this technique. Thus, it is necessary to evaluate the usefulness of the 137Cs technique to study soil redistribution, especially in areas that suffer from severe soil erosion and where the 137Cs inventory distributions vary. This study analyses the abundance of 137Cs deposited in sediment trapped by a check dam over 31 years in a small agriculture catchment in the Loess Plateau, which has experienced some of the most extensive agricultural soil erosion in the world. The 137Cs inventory and soil loss were evaluated, and the results indicated that the sediment deposition rate behind the check dam was approximately 38 cm/year. The specific soil erosion rate of the catchment is estimated to be 178 t ha−1 year−1. A geochemical properties fingerprinting method indicated that the ratio of the inter‐gully erosion from cropland to gully erosion was 0·46:0·54 during the investigated period of 31‐year period. Our results suggest that the 137Cs technique cannot be directly used in the study catchment. Gully erosion is the main type of soil erosion that occurs in the loess catchment, and the amount of gully erosion changes from year to year. Therefore, the abundance of 137Cs cannot be used to estimate soil redistribution where gully erosion is severe. However, after calibration, the inter‐gully soil loss was consistently related to 137Cs abundance, which means that the 137Cs technique can be used at the plot or slope scale on the Loess Plateau. Our results also reveal the particle‐size selectivity of soil detachment and sediment deposition during runoff‐erosion events. The average 137Cs content of the fine group couplets is 63% greater than the 137Cs content of the coarse group. When the studied section spans more than 15 years, the 137Cs inventory is consistent (R2 = 0·95, p < 0·01) with soil loss, which means that the selectivity may be offset over a long period. Our results confirm that the 137Cs method requires careful planning when applied at the catchment scale. Copyright © 2017 John Wiley & Sons, Ltd.