Submitted to: European Journal of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2006
Publication Date: 6/1/2006
Citation: Lei, T.W., Zhang, Q.W., Zhao, J., Nearing, M.A. 2006. Tracing sediment dynamics and sources in eroding rills with rare earth elements. European J. of Soil Sci. 57(3): 287-294. Interpretive Summary: Rates of soil erosion are quite variable from place to place in the field. In order to most effectively develop plans for conserving soil we need to know where on the field the erosion is most critical. Some of our models of soil erosion give conservation planners estimates of this variability (of where the greatest erosion occurs in the field), but data to verify such models is severely limited. The purpose of this study was to develop a method whereby sediment particles could be tracked so that we can identify where the particles originate, how far they move, and which ones leave the field. Thus we developed a method using special chemicals called Rare Earth Elements, which bind strongly to soil and sediment particles and can be measured in sediment and soil samples. This kind of data is unique in the world and an important advance for the science of soil erosion and conservation. The Rare Earth Element technique has been applied previously on plots and small watersheds. In this study we applied the method to individual rills in order to help understand the basic processes of soil erosion. This will help us to develop better technologies for both predicting soil erosion and for developing measures to control erosion in order to protect this valuable resource for use by future generations to produce food and fiber.
Technical Abstract: Eroding rills evolve morphologically in time and space. Most current studies on rill erosion use spatially-averaged soil erosion data, providing little information on soil erosion dynamics. A method is proposed to use rare earth elements (REE) to trace sediment distribution in eroding rills. Laboratory flume simulation experiments were conducted at three flow rates (2, 4 and 8 litre minute-1 and five slope gradients (5, 10, 15, 20 and 25 degrees) with three replicates of each treatment. The rills, of 8 m length, were subdivided into 10 equal segments of 0.8 m length and 0.1 m width, with a different REE element applied to each segment. We derived computational formulae for estimating the distribution of eroded amounts along the rills. The actual erosion distribution along rills was then estimated with the data from the experiments. The precision of the REE for tracing rill erosion was analyzed. The results showed that sediment concentration increased with rill length, but the increased rate (the slope of the curve) flattened gradually. Sediment yields increase with slope gradients and flow rates, but the slope gradients had a greater effect on sediment concentration than flow rates, and greater flow rates caused more rill erosion and soil loss under the same slope gradient. The results also demonstrated the feasibility of using REE to trace the dynamic processes of rill erosion.