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Title: Evaluation of 137 C's conversion models parameter sensitivity for erosion estimation

Author
item Zhang, Xunchang
item ZHANG, GUANHUI - Beijing Normal University
item WEI, XIN - Beijing Normal University
item GUAN, YINGHUI - Northwest Agricultural & Forestry University

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/2014
Publication Date: 2/20/2015
Citation: Zhang, X.J., Zhang, G., Wei, X., Guan, Y. 2015. Evaluation of 137 C's conversion models parameter sensitivity for erosion estimation. Journal of Environmental Quality. 44:789-802.

Interpretive Summary: The cesium-137 technique has been widely used to provide soil redistribution estimates since 1970s. However, most cesium-137 conversion models remain theoretical and largely unvalidated. The objectives are to validate the three widely used conversion models using long-term measured soil loss data and to evaluate the potential of using a geo-statistical tool like Kriging to improve soil redistribution estimation. Soil loss data measured from an 80-m wide by 200-m long plot were used. The plot slope gradually declined from about 5% in the top to 1% in the bottom. Wheat was grown under the conventional tillage for most years since 1978. Soil samples in a 10-m grid were taken from the plot to estimate 137Cs distribution. Soil redistribution rates were estimated using three conversion models and further smoothed using an ordinary Kriging. Compared with the measured soil loss, the relative errors of the mean net erosion estimates over the entire plot with (without) Kriging were -17 (28), 106 (141), and 100% (133%) for the proportional model (PM), simplified mass balance model (MBM1), and improved mass balance model (MBM2), respectively. The smallest error with the simplest PM indicated that PM performed the best in the simple case of this study, and that Kriging as a geo-statistical tool substantially improved estimates of mean soil redistribution. The findings would be useful to soil conservationists, engineers, and scientists who use the cesium-137 technique for estimating long-term soil redistribution rates over a landscape.

Technical Abstract: The Cesium-137 technique has been widely used to provide soil redistribution estimates since 1970s. However, most Cesium-137 conversion models remain theoretical and largely unvalidated. The objectives are to validate the three widely used conversion models using long-term measured soil loss data and to evaluate the potential of using Kriging to improve soil redistribution estimation. Soil loss data measured from an 80-m wide by 200-m long plot were used. The plot slope gradually declined from about 5% in the top to 1% in the bottom. Wheat was grown under the conventional tillage for most years since 1978. Soil samples in a 10-m grid were taken from the plot to estimate Cesium-137 distribution. Soil redistribution rates were estimated using three conversion models and further smoothed using an ordinary Kriging. Compared with the measured soil loss, the relative errors of the mean net erosion estimates over the entire plot with (without) Kriging were -17 (28), 106 (141), and 100% (133%) for the proportional model (PM), simplified mass balance model (MBM1), and improved mass balance model (MBM2), respectively. Compared with PM, MBM1 and MBM2 overestimated soil loss rates in eroding areas but underestimated deposition rates in depositional areas. Results indicated that the simplest PM performed the best in the simple case of this study, and that Kriging substantially improved estimates of mean soil redistribution. However, the full potential of the complex MBM2 needs to be further evaluated in more complex conditions in which loss of the newly deposited Cesium-137 existed.