Potential use of Rare Earth Oxides as Tracers for Soil Erosion and Aggregation Studies

Most existing soil loss data are spatially‐averaged, though various tracing techniques have been used for obtaining spatially‐distributed data. Spatially‐distributed soil erosion data are needed for validating physically‐based erosion prediction models and for better understanding soil erosion dynamics. The objectives of this study were to evaluate the feasibility of using rare earth element (REE) oxides directly as tracers for soil erosion studies by examining their binding ability with soil materials, and also to test a quick acid‐extraction procedure. Five REE oxide powders were directly mixed with a Miami silt loam soil (fine‐loamy, mixed, mesic Typic Hapludalfs) and then leached with deionized water in a soil box to evaluate the mobility of REEs. Following leaching, soil samples were sectioned in 25‐mm increments and analyzed for REEs. The REE‐tagged soil was wet sieved to obtain REE concentrations in each aggregate size group. A simple acid‐leaching method was used to extract REEs from all soil samples. The extracts were analyzed by Inductively Coupled Plasma‐Mass Spectrometry (ICP‐MS) techniques. The data indicated that the maximum coefficient of variation of the proposed procedure was <10% for all REEs. The REE oxides were uniformly incorporated into soil aggregates of different sizes (>53 μm) and were bound with silt‐size particles. This finding shows that the direct use of REE oxides is feasible, which should be superior to other REE‐tagged particulate tracers because it eliminates the need of tagging exotic particles with REEs. Also, direct mixing of a trace amount of REEs does not substantially alter physicochemical properties of soil particles and aggregates. This work has shown that REE oxides have a great potential for tracing soil erosion and aggregation.