Evaluating and improving 137cs technology for estimating soil erosion using measured soil loss during 1954-2015

Authors: Zhang, Xunchang

Submitted to: Earth-Science Reviews
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2023
Publication Date: 11/9/2023
Citation: Zhang, X.J. 2023. Evaluating and improving 137cs technology for estimating soil erosion using measured soil loss during 1954-2015. Earth-Science Reviews. 247. Article 104619. https://doi.org/10.1016/j.earscirev.2023.104619.
DOI: https://doi.org/10.1016/j.earscirev.2023.104619

Interpretive Summary: Soil erosion causes worldwide land degradation. Long-term monitoring soil erosion in soil erosion plots and small watersheds is costly. Mathematical equations using radionuclide cesium-137 from atomic bomb tests are developed to retrospectively estimate soil erosion since 1954. However, those models have not been validated due to the lack of long-term measured soil loss data. Using rare soil loss data measured at Coshocton, Ohio during 1954-2015, we found that all theoretical equations over-estimate soil erosion rates because a key assumption is invalid. A new equation is developed to include a loss of cesium-137 by suspended sediment in surface runoff. Simulated soil loss rates using the new equation agree well with measured rates. The new equation can be used to estimate average soil loss rates since 1954 with one-time field visit and sampling. The improved technique would be useful to erosion scientists and soil conservationists for readily estimating soil erosion rates since 1954 and for laying out soil conservation plans. USDA is an equal opportunity provider and employer.

Technical Abstract: Soil erosion causes worldwide land degradation. Long term monitoring of soil erosion is costly and labor intensive. Multiple models using Cs-137 fallout from atomic bomb tests are developed to retrospectively estimate average soil erosion since 1954. However, those models have not been rigorously validated due to the lack of compatible long-term measured soil loss data and thus their usefulness has been seriously challenged. Using 70 years of rare soil loss data measured in two small watersheds of <0.78 ha during 1954 and 2015, the author found that all theoretical models overestimate mean net soil erosion rates by at least 400%, and further confirmed that a key assumption of the homogeneous Cs-137 transfer from rainwater to soil during fallout is invalid and a critical process of the enhanced Cs-137 loss and redistribution during transfer is overlooked. The enhanced Cs-137 uptake by suspended sediment during transfer was responsible for about 7 times more enriched Cs-137 loss in sediment, to which Cs-137 inventory and erosion estimation are extremely sensitive. A new mass balance model is developed to include the dynamic uptake of Cs-137 by suspended sediment in surface runoff and losses of Cs-137 in both runoff solution and uptake by plants. The new model greatly improves mean soil erosion estimation. The finding of the enhanced radionuclide loss with suspended sediment during transfer is also valid to other cosmogenic continuous fallout radionuclides such as Pb-210 and Be-7, which have been widely used in soil erosion estimation. Taking into account the enhanced radionuclides loss by suspended sediment during fallout will substantially lower soil loss estimation by all fallout radionuclides. USDA is an equal opportunity provider and employer.