Particle labeling for sediment source tracking on hillslopes

Soil erosion on hillslopes is a dynamic process, which evolves temporally and spatially. Sediment source tracking can be used to identify the areas within a watershed where erosion is greatest. This study evaluated three sediment source tracking techniques, rare earth element (REE) particle labeling, interrupted rills, and ground based LIDAR, on slope surfaces under simulated rainfall. Laboratory rainfall simulations were conducted sequentially on 24 hr intervals to measure the cumulative effects of rainfall erosivity. Two bare soil plots, plot 1 and plot 2, measuring 3.6 m in length and 0.75 m in width were divided into three equal source sections along the length of the plot. Various REE tracers were applied to different plot sections. As a result of high tracer enrichment in plot runoff, the REE technique overestimated plot sediment yield. However, trends in runoff tracer concentrations suggested that the top plot sections contributed most to sediment yield. The interrupted rill method was conducted in three phases, each with a different plot length, and relied on the assumption that each phase followed the same sedimentation process. The top section of plot 1 and the middle section of plot 2 were found to have the highest sediment displacements. The ground based LIDAR method also overestimated plot sediment yield. 3-D surfaces attained through this method suggested the bottom section of plot 1 and the top section of plot 2 had the highest sediment displacements. Data supports the theory that LIDAR performance increases with greater soil displacement. Further studies involving tracer enrichment, interrupted rill sedimentation processes, and LIDAR precision could increase these techniques’ effectiveness at predicting eroded sediment sources