Applicability of rare earth element oxides as a sediment tracer for coarse-textured soils

A leaching experiment using a mixture of five REE oxides and gravelly, sandy loam soils was conducted to examine the applicability of the REE oxides as a sediment tracer for coarse-textured soils. The experiment showed little leaching of the oxides and an enrichment of various size classes of soil particles with the oxides, which reflected the strong binding capability of the REE oxides with the gravelly, sandy loam soils. It also showed that the REE oxides preferentially bound with small size classes of soil particles. The preferential binding of the REE oxides with fine materials will cause the overestimation of the soil loss from a given area (i.e., tagged with a given REE) if aggregates are broken down during sediment transport and clay materials are preferentially delivered, and if the soil loss is computed by analyzing the REE concentrations in the whole sediment. To address the non-uniform binding issue, the method based on measuring the REE concentrations for four particle size groups was tested. The potential error of the method was evaluated by comparing the soil loss that would be computed in the case that the particle size distribution was shifted to the smallest particle size class within a particle size group and in the case that no sediment sorting occurred. The result showed that the method would produce a potential error of approximately 4% in the estimation of the total soil loss when sediment sorting occurred. The non-uniform binding of the oxides does not preclude the use of the REE oxides on the coarse-textured soils in the presence of non-uniform binding of the oxides, but adjustments in the technique are required for an accurate estimation of soil loss using the REE technique.