Are source groups always appropriate when sediment fingerprinting? The direct comparison of source and sediment samples as a methodological step

The classification of sediment source groups is often the least thoroughly considered part of a sediment fingerprinting methodology; however, the use of inappropriate source groups can be the cause of significant uncertainty. In many catchments, source groups based on land use or geology are a poor fit for their geomorphological processes and the nature of the tracers used. Against this context, this study directly compared the average percentage difference in the standardised concentrations of all tracers between a sediment sample and each individual source sample, to map the similarity between the properties of sources and sediment in 3 study catchments. The environmental significance of individual tracers and their similarity between individual samples were also examined in order to identify functionally important source groups. In the River Nene, UK, the mean percentage differences between source and sediment tracer concentrations were primarily controlled by the presence of distinctive ironstone and urban sources, which had very dissimilar properties to the target sediment. However, a generally consistent trend of certain source samples having more similar properties to multiple target sediment samples than others was also found; a finding that could not be identified when using conventional source groups. In the Sywell reservoir catchment, UK, sediment originated from throughout its catchment, apart from in the case of damaged road verges, and there was little indication of any major change in sediment sources through recent time. In the Vuvu catchment, South Africa, there was a larger contribution from distal igneous sources during high‐flow events. The trialled method, however, provided little advantage over the standard fingerprinting approach in this case, due to the existing good fit between catchment geomorphology, the tracers used, and the geological source groups. The method trialled herein can provide distinct advantages over the conventional fingerprinting approach and, although it should not replace it, provides a useful supplement by permitting an assessment of whether potential source groupings make best environmental sense and providing increased resolution of sediment provenance.