Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 4, 2004
Publication Date: November 1, 2004
Citation: Polyakov, V.O., Nearing, M.A., Shipitalo, M.J. 2004. Tracking sediment redistribution in a small watershed. Earth Surface Processes and Landforms. 29:1275-1291. 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 new method is used to track erosion, translocation, and re-deposition of sediment in a small watershed, thus allowing for the first time a complete, spatially distributed, sediment balance to be made as a function of landscape position. A 0.68 ha watershed in Coshocton, OH was divided into six morphological units, each tagged with one of six rare earth element oxides. Sediment translocation was evaluated by collecting runoff and by spatially sampling the soil surface. Average measured erosion rate was 6.1 t ha-1, but varied between 40.4 t ha-1 of loss from the lower channels to 24.1 t ha-1 of gain on the toeslope. With this technique it was possible for the first time to itemize the sediment budget for landscape elements into three components: 1) the soil from the element that left the watershed with runoff, 2) soil from the element that was re-deposited on lower positions, with the spatial distribution of that deposition, and 3) soil originating from the upper positions and deposited on the element, with quantification of relative source areas. The results are incongruous with the current morphology of the watershed, suggesting that diffusion type erosion must also play a major role in defining the evolution of this landscape. Judging from the deposition patterns, a significant part of the sediment diffusion apparently occurred due to water erosion, rather than to tillage erosion alone.