Evaluating sediment deposition prediction by three 137Cs erosion conversion models

Authors: Zhang, Xunchang; LIU, BAOYUAN - Beijing Normal University; WEI, XIN - Beijing Normal University; Garbrecht, Jurgen

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2018
Publication Date: 7/5/2018
Citation: Zhang, X.J., Liu, B., Wei, X., Garbrecht, J.D. 2018. Evaluating sediment deposition prediction by three 137Cs erosion conversion models. Soil Science Society of America Journal. doi:10.2136/sssaj2018.02.0080.
DOI: https://doi.org/10.2136/sssaj2018.02.0080

Interpretive Summary: Although the cesium-137 tracer has been widely used to estimate soil erosion in past decades, most cesium-137 mathematical models are not rigorously validated. The objective is to explicitly evaluate the sediment deposition components of three widely used cesium-137 models using 34 years of soil loss data from a plot (200 m long by 80 m wide). The average slope of the plot is approximately 4% in the upper section and 1% in the lower section. The primary soil is silt loam with 23% sand and 56% silt. Winter wheat was raised primarily under conventional tillage in the plot. Sediment load was measured with a pump sampler at the outlet. Bulk soil cores were taken in a 10-m grid to estimate cesium-137 inventory. The cesium-137 depth profiles were measured at eight locations to determine net deposition depth. The proportional model (PM) and two mass balance models (MBM1 and MBM2) were evaluated. The measured average deposition depth in the depositional area of the plot was 5.83 cm, and the predicted deposition depths in the area were 4.12, 2.02, and 1.64 cm for PM, MBM1, and MBM2. The results indicated that the simple PM appeared to predict deposition depths better than the two sophisticated mass balance models under the evaluation conditions. However, the true capability of the two mass balance models still needs to be further evaluated under more complex conditions that include the critical period of cesium-137 peak fallout in the 1950s and 1960s. This study provides useful information to soil conservationists and erosion scientists for more accurate estimation of soil erosion using the cesium-137 tracing technique.

Technical Abstract: Although the cesium-137 technique has been widely used to estimate soil redistribution in past decades, most cesium-137-conversion models are not rigorously validated. The objective is to explicitly evaluate the sediment deposition components of three widely used cesium-137 models using 34 years of soil loss data from a plot (200 m long by 80 m wide). The average slope of the plot is approximately 4% in the upper section and 1% in the lower section. The primary soil (fine, mixed, thermic, Udertic or Pachic Paleustoll) is silt loam with 23% sand and 56% silt. Winter wheat (Triticum aestivum L.) was raised primarily under conventional tillage. Sediment load was measured with a pump sampler at the outlet. Bulk soil cores were taken in a 10-m grid to estimate cesium-137 inventory. The cesium-137 depth profiles were measured at eight locations to determine net deposition depth. The proportional model (PM) and two mass balance models (MBM1 and MBM2) were evaluated. The measured average deposition depth in the depositional area of the lower section was 5.83 cm, and the predicted deposition depths in the area were 4.12, 2.02, and 1.64 cm for PM, MBM1, and MBM2. The results indicated that the simple PM appeared to predict deposition depths better than the two sophisticated mass balance models under the study conditions. However, the true capability of the two mass balance models still needs to be further evaluated under more complex conditions that include the critical period of cesium-137 peak fallout in the 1950s and 1960s.