Tracing hillslope sediment contributions to a lake shore using geochemical and fallout radionuclide fingerprints

Soil erosion and sediment redistribution in Mediterranean agroforestry landscapes are strongly influenced by land use and substrate variability, affecting sediment delivery to downstream sinks. Identifying the relative contributions of hillslope sediment sources to depositional environments is essential for understanding sediment transfer processes and source–sink connectivity. In this study, sediment fingerprinting techniques were applied to quantify hillslope sediment contributions recorded in a lake shore sediment core within the endorheic Estaña catchment (NE Spain). The closed hydrological setting and the presence of a lake acting as a natural sediment trap provide favourable conditions for tracing sediment provenance from adjacent slopes. A sediment core collected at the lower part of the hillslope in a lake shore, was analysed and compared with potential sediment sources representing different land uses and lithological units. Potential source materials and sediment core samples, analysed as a sequence of 5 cm depth intervals from the surface to depth, were characterised using a suite of geochemical elements (Mg, K, Na, Pb, Ba, Zn, Sr, Li, Mn, Co, Ni, Cu, Cr, Fe, Al and Ca) and fallout radionuclides (¹³⁷Cs and excess ²¹⁰Pb). The unmixing model FingerPro 2.0 was used to identify and estimate the relative contributions of the potential sources to the lake shore sediment core, allowing uncertainty to be explicitly assessed. Preliminary results reveal marked spatial variability in sediment source contributions linked to land use and lithology on the contributing hillslope, demonstrating the potential of combining geochemical and fallout radionuclide tracers to improve the robustness of sediment fingerprinting in small Mediterranean catchments. This approach provides valuable insights into hillslope to lake shore sediment connectivity and contributes to a better understanding of sediment source dynamics and temporal shifts in dominant sediment sources under changing environmental conditions.