It's sedimentary, my dear Watson : implications of watershed processes on the sediment fingerprinting approach

Abstract

The sediment source fingerprinting approach is based on the assumption that the potential sources of sediment within a watershed can be linked to in-stream sediment by using the inherent physical or biogeochemical characteristics of the sediment (i.e., sediment properties) as fingerprints. At present, one of the main limitations of the sediment source fingerprinting approach is the ability to link sediment back to their sources due to the nonconservative nature of many sediment properties. Ideally, sediment properties do not change as the sediment (i.e., transported unconsolidated soil or rock particles) move through a watershed allowing for a direct comparison between sources and sediment. However, sediment collected downslope or downstream from its source is often found to have a finer grain-size distribution and a higher organic matter content as compared to the source material as the smaller and less dense particles are preferentially mobilized and transported.Accounting for changes in both particle size distribution and organic matter content are important as many fingerprint concentrations are correlated with both properties, but it is unclear as to what is the best approach to account for these changes. In an effort to provide a more reliable and robust link between sources and sediment, a series of experimental and observational studies were conducted to investigate the factors that control particle size and organic matter selectivity and their subsequent effect on a broad suite of geochemical fingerprints. These studies investigated particle selectivity at the landscape scale, represented by a sequence of hillslope, riparian and fluvial environments. Processes within each of these three environments were found to preferentially mobilize and transport fine-grained and organic-rich particles. Many commonly used particle size and organic matter correction ii factors assume that the relation between both particle size and fingerprint concentrations are similar for all fingerprints. However, this research has demonstrated that these relations are fingerprint specific in terms of the magnitude, direction and linearity which suggests that the use of correction factors needs to be given careful consideration. In addition, a watershedscale application of the sediment fingerprinting approach found that the scale of observation and the geomorphic connectivity of the watershed influenced the apportionment results.Overall, this research can be used to guide sampling design and protocols, fingerprint selection, data correction factors and the interpretation of apportionment results.iii