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SOIL & WATER MANAGEMENT & CONSERVATION

Tracing Sediment Movement on a Semiarid Watershed using Rare Earth Elements

^a USDA-ARS, South West Watershed Research Center, 2000 E. Allen Rd., Tucson, AZ 85719
^b Pima County Regional Flood Control, 97 E Congress, Tucson AZ 85701

^* Corresponding author (viktor.polyakov{at}ars.usda.gov).

A multi-tracer method employing rare earth elements (REE) was used to determine sediment yield and to track sediment movement in a small semiarid watershed. A 0.33-ha watershed near Tombstone, AZ was divided into five morphological units, each tagged with one of five REE oxides. Relative contribution of each unit to the total sediment yield was determined by collecting runoff and sediment, and the spatial redistribution of sediment was determined from sampling the soil surface. Average sediment yield was 1.0 Mg ha^–1 yr^–1 from the entire watershed, but varied between 0.1 Mg ha^–1 yr^–1 from the upper slope to 5.0 Mg ha^–1 yr^–1 from the lower channel. Little re-deposition occurred in the channels indicating an effective transport system. The erosion pattern and rates were in agreement with the current morphology of the watershed, which has a well-developed channel network.

Abbreviations: DEM, digital elevation model • ICP–MS, Inductively Coupled Plasma Mass Spectrometer • LC, lower channel • LS, lower slope • MS, middle slope • REE, rare earth element • RHEM, Rangeland Hydrology and Erosion Model • RTK GPS, real time kinematic global positioning system • UC, upper channel • US, upper slope • USLE, Universal Soil Loss Equation • USDA-ARS, United States Department of Agriculture-Agricultural Research Service • WEPP, water erosion prediction project • WGEW, Walnut Gulch Experimental Watershed