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Title: Understanding erosion process using rare earth element tracers in a preformed interrill-rill system

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

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2017
Publication Date: 1/12/2018
Citation: Zhang, X.J., Liu, G. 2018. Understanding erosion process using rare earth element tracers in a preformed interrill-rill system. Science of the Total Environment. https://doi.org/10.1016/j.scitotenv.2017.12.345.
DOI: https://doi.org/10.1016/j.scitotenv.2017.12.345

Interpretive Summary: Tracking sediment source and movement is essential to fully understanding soil erosion processes. The objectives of this study were to identify dominant erosion process and to characterize the effects of upslope interrill erosion on downslope interrill and rill erosion in a preformed interrill-rill system. A coarse textured soil with 2% clay and 20% silt was packed into a scaled small watershed, which was divided into eight geomorphic units and was tagged with eight different tracers. Three 30-min rains were made at a sequential intensity of 60, 90, and 120 mm h-1, and runoff and sediment were collected every 2 min at the outlet. Tracer concentration in sediment was measured and used to estimate source contributions after corrected for enrichment of fine particles in sediment. Results showed that interrill erosion rate and sediment concentration increased with downslope distance, indicating that sediment transport might have controlled interrill erosion rate. In contrast, rill erosion rate was largely limited by rill detachment process. Rill erosion contributed most soil loss; however, the proportion decreased from 78 to 61% as intensity increased and rill network matured over three rains. Interrill erosion was more sensitive than rill erosion to rainfall intensity increases. The former was mostly affected by intensity in this experimental setup, while the latter was controlled by flow discharge, slope steepness, and rill network evolution stage. The greatest sediment concentration occurred in the stage of the fastest rill development. The increased sediment delivery from interrill areas appeared to suppress rill detachment by concentrated flow. The findings will be useful to erosion scientists and modelers who are interested in understanding erosion processes and improving erosion prediction tools.

Technical Abstract: Tracking sediment source and movement is essential to fully understanding soil erosion processes. The objectives of this study were to identify dominant erosion process and to characterize the effects of upslope interrill erosion on downslope interrill and rill erosion in a preformed interrill-rill system. A coarse textured soil with 2% clay and 20% silt was packed into a scaled small watershed, which was divided into eight geomorphic units and was tagged with eight rare earth element (REE) oxides. Three 30-min rains were made at a sequential intensity of 60, 90, and 120 mm h-1, and runoff and sediment were collected every 2 min at the outlet. REE concentration in sediment was measured and used to estimate source contributions after corrected for enrichment of fine particles in sediment. Results showed that interrill erosion rate and sediment concentration increased with downslope distance, indicating that sediment transport might have controlled interrill erosion rate. In contrast, rill erosion rate was largely limited by rill detachment process. Rill erosion contributed more soil loss than interrill erosion; however, the rill proportion decreased from 78 to 61% as intensity increased and rill network matured over three rains. Interrill erosion was more sensitive than rill erosion to rainfall intensity increases. The former was mostly affected by intensity in this experimental setup, while the latter was controlled by flow discharge, gradient, and rill network evolution stage. The greatest sediment concentration and delivery rate occurred in the stage of the fastest rill development. The increased sediment delivery from interrill areas appeared to suppress rill detachment by concentrated flow.