High-frequency spatial sediment source fingerprinting using in situ absorbance data

Sediment fingerprinting is a commonly applied approach to quantify catchment suspended sediment (SS) source contributions. However, due to the high workloads and costs involved in SS sampling and laboratory analyses, traditional procedures often result in a limited number of samples and sampling campaigns, which can hamper the capacity to capture the intra- and inter-storm variations in SS source activation and deactivation. A better understanding of the temporal dynamics in source contributions is needed, however, to improve the understanding of dynamic sediment generation and delivery processes for selecting management practices. In recognition of the extant need to improve high-frequency source estimates and to permit long duration measurement campaigns, the work reported herein presents a sediment fingerprinting procedure using UV-Vis absorbance spectra measured in situ with submersible spectrophotometer probes to estimate spatial SS source contributions based on a confluence-based monitoring strategy. The high-frequency (5-minute intervals) measurements were used to fingerprint SS sources during seven selected periods with varying hydrological conditions. Source apportionment estimates (MixSIAR model) were validated using an independent sediment budget. The results showed a mean deviation of 9.4 ± 6.0 %, compared with the sediment budget, for the seven periods combined (n=7,282 time steps). The most accurate results (mean absolute error of 5.3 ± 4.3 %) were obtained for the period covering the July 2021 flood event in central Europe (return period for the monitored catchment >20 years). Overall, modelled variations in SS source contributions mostly followed the sediment budget dynamics. This novel work highlights the potential for using spectrophotometer absorbance data for high- frequency and long-term sediment fingerprinting purposes. We argue that the presented method can lead to new opportunities to improve our understanding of SS sources and their dynamics.