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ARS Home » Pacific West Area » Tucson, Arizona » SWRC » Research » Publications at this Location » Publication #191747

Title: Multi-year tracking of sediment sources in a small agricultural watershed 1820

item Nearing, Mark
item Shipitalo, Martin

Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2006
Publication Date: 5/17/2006
Citation: Kimoto, A., Nearing, M.A., Shipitalo, M.J., Polyakov, V.O. 2006. Multi-year tracking of sediment sources in a small agricultural watershed. Earth Surface Processes and Landforms. 31:1763-1774.

Interpretive Summary: Data has been collected from soil erosion from plots and watersheds for nearly 100 years, but there has always been a fundamental issue that has never been answered: how can one track the redistribution of sediment within watersheds? We can physically measure what leaves a plot. We can measure net loss and gain at points through radioactive fallout of a Cesium isotope. But never have we been able to track how sediment generated from one part of the landscape moves with time through the watershed. As such, there are basic aspects of sediment and contaminant movement that we don’t understand (diffusive vs. longitudinal transport), and models that we cannot verify. Now, with this study, we have developed a multiple tracer technique that for the first time gives us a complete sediment balance as a function of landscape position. This data is unique in the world and an important advance for the science of soil erosion and conservation. The impact of the work will be better spatial information on soil erosion and contaminant transport which will reduce costs and improve effectiveness of conservation plans and programs.

Technical Abstract: A technique using rare earth element (REE) oxides was applied to a small agricultural watershed near Coshocton, OH, USA. The experiment consisted of tagging six morphological elements within the watershed with different oxides, and measuring sediment yield at the watershed outlet for nearly four years. The total mass of depletion of the oxides and the tracer enrichment ratio were computed to examine the applicability and accuracy of the REE technique for the experimental period. A minimum of approximately 91% of the mass of the applied oxides was still available on any individual morphological element at the end of experimental period. The tracer enrichment ratio varied from 0.4 to 2.3 during the experimental period, and it did not significantly decrease as a function of time. The proportion of the sediment yield from the lower channel to the sediment yield left the watershed was significantly greater as a function of the amount of sediment yield for a given storm, while that for the lower backslope was significantly less. The proportion of the sediment yield from the lower channel significantly decreased as a function of cumulative sediment yield, while the proportions for the shoulder and the upper backslope significantly increased. This study showed that the REE technique had a reasonable potential for studying sediment sources for a multi-year period of time with some significant limitations associated with a selective depletion of tracers and a contamination of downslope elements with tagged sediments from upslope elements.