Fingerprinting fluvial sediments deposited over the last 100 years: a practical examination of the accuracy and uncertainty in the Nene basin, United Kingdom

In recent years, sediment fingerprinting and the use of tracers to infer sediment provenance have gained widespread adoption in geomorphological research. In the published literature a wide variety of tracers have been employed when using sedimentary deposits to determine the effects on sediment source inputs of changing land use practice and changing weather and climate. Fingerprinting deposited sediments can also provide an indication of the natural sediment sources in a catchment, which would represent a state that catchment remediation might ideally seek to achieve. However, a number of recent publications have highlighted uncertainties associated with tracer behaviour during sediment erosion, transport and deposition and also associated with post-depositional alteration, raising concerns about uncertainties associated with tracer selection and modelling. This paper aims to explore these uncertainties using a comparison of fingerprinting results obtained using lithogenic radionuclide, geochemical, and mineral magnetic tracers in a range of depositional environments located in the Nene basin, United Kingdom. Specifically, tracing was undertaken on cores taken from a floodplain lake (1 core), reservoir (1 core) and floodplain (4 cores). Tracer groups were investigated both alone and in combination to determine the differences between their sediment provenance predictions. Average differences between the tracer group provenance predictions were lowest in the reservoir core at 19% and highest in some floodplain cores, with differences in excess of 50%. Factors of organic enrichment, changes in particle size distribution and indicators of the chemical alteration of the sediment were investigated using a correlation analysis to try to determine potential reasons for the observed inconsistencies between tracer groups. The inconsistencies were clearly attributable to the selective deposition of the fine particle size fractions, organic enrichment and to post-depositional chemical transformation. The relative importance of these potential controls on tracer stability varied significantly between cores. The in situ growth of bacterial magnetite appeared to be an important process in relation to the use of magnetic signatures in the reservoir core while the selective deposition of fine particle size fractions was a dominant factor in two of the four measured floodplain cores. The post-depositional dissolution of tracers was determined to be an important process in almost all cores investigated.