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Title: A simple enrichment correction factor for improving erosion estimation by rare earth oxide tracers

Author
item Zhang, Xunchang
item LIU, GANG - Northwest Agricultural & Forestry University
item ZHENG, FENLI - Northwest Agricultural & Forestry University

Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/9/2017
Publication Date: 12/14/2017
Citation: Zhang, X.J., Liu, G., Zheng, F. 2017. A simple enrichment correction factor for improving erosion estimation by rare earth oxide tracers. Vadose Zone Journal. 16(12):1-10. doi:10.2136/vzj2017.03.0068.
DOI: https://doi.org/10.2136/vzj2017.03.0068

Interpretive Summary: Spatially distributed soil loss data are needed to better understanding soil erosion processes and validating distributed erosion models. Rare earth element (REE) oxides were used as sediment tracers to generate spatially distributed erosion patterns. However, a general concern exists regarding the accuracy of the technique due to preferential binding of tracers to fine soil particles as well preferential erosion of finer soil particles. The objective was to develop a simple enrichment correction factor to improve the accuracy of the technique without the need of measuring REE for multiple size classes. A coarse sandy soil, tagged with 8 REE oxides, was packed into 8 zones in a physical model of a small watershed to trace erosion from each zone. Three 30-min rains were simulated at the intensities of 1, 1.5, and 2 mm min-1, and runoff was collected every 2 min. Sediment was separated into 9 size classes, and REE in each class was extracted and analyzed. Results showed that both REE and clay + silt fraction (<0.05 mm) were enriched in sediment, resulting in consistent overestimation of soil loss. A simple enrichment correction factor, based on the enrichment of the <0.05-mm fraction, effectively corrected the overestimation, and reduced the event estimation error to <4.5%. The correction circumvents the need of measuring REE for multiple size classes, which is costly and time-consuming. Moreover, this study proved that REE tracers were conservative within each size class during erosion, scientifically underpinning the use of an enrichment correction factor and the tracing by multiple size classes. The correction factor should be further tested with different soils. The findings will be useful to erosion scientists and soil conservationists who are interested in using sediment tracers to fingerprint sediment sources and estimate spatial distribution of soil erosion for precision conservation planning.

Technical Abstract: Spatially distributed soil erosion data are needed to better understanding soil erosion processes and validating distributed erosion models. Rare earth element (REE) oxides were used to generate spatial erosion data. However, a general concern on the accuracy of the technique arose due to selective binding and erosion. The objective was to develop a simple enrichment correction factor to improve the accuracy of the technique without the need of measuring REE for multiple size classes. A coarse purple soil (2% clay and 20% silt), tagged with 8 REE oxides, was packed into 8 zones in a physical model of a small watershed to trace erosion from each zone. Three 30-min rains were simulated at the intensities of 1, 1.5, and 2 mm min-1, and runoff was collected every 2 min. Sediment was separated into 9 size classes, and REE in each class was extracted and analyzed. Results showed that both REE and clay+silt fraction (<0.05 mm) were enriched in sediment, resulting in consistent overestimation of soil loss. A simple enrichment correction factor, based on the enrichment of the <0.05-mm fraction, effectively corrected the overestimation, and reduced the event estimation error to <4.5%. The correction circumvents the need of measuring REE for multiple size classes, which is costly and time-consuming. Moreover, this study proved that REE tracers were conservative within each size class during erosion, scientifically underpinning the use of an enrichment correction factor and the tracing by multiple size classes. The correction factor should be further tested with different soils.