Assessment of particle size and organic matter correction factors in sediment source fingerprinting investigations: An example of two contrasting watersheds in Canada

This study investigated the conservative behaviour of geochemical fingerprints through the soil mobilization process. This was accomplished by comparing the concentrations of a broad suite of geochemical elements of soil mobilized by simulated rainfall from small plots to the source soil, in two contrasting agricultural regions in Canada. All samples were sieved to isolate the fine-grained fraction (<63 μm) prior to analysis in an effort to limit the differences in both particle size and organic matter content. Despite sieving the samples, there were still particle size and organic carbon content differences between the source soil and the mobilized soil. To account for these differences, particle size, and sometimes additional organic matter, correction factors are often applied to the source soil concentrations in an attempt to make the two sample types more directly comparable. The particle size and organic matter correction factors are typically based on the ratio of specific surface area (SSA), or soil organic carbon (SOC) content, between the eroded material and source material and the same correction factors are applied to all elements. It was demonstrated that for most geochemical elements the particle size correction factor resulted in an over-correction of the source soil relative to the mobilized soil and that using the organic matter correction factor in addition to the particle size correction exacerbated this over-correction. For most geochemical elements, the uncorrected source soil concentrations showed a smaller difference in concentrations relative to the mobilized soil as compared to the corrected source soil. In addition, it was found that the magnitude, direction and interaction of the relation of SSA and SOC on concentrations were generally both element and watershed specific. This study highlights some of the potential issues with applying correction factors to account for differences in particle size and organic matter content to a broad suite of geochemical fingerprints.