Lütschine fan delta response to climate variability and land use in the Bernese Alps during the last 2400 years

Despite important progress in Holocene palaeoclimate and palaeoenvironmental studies in the Alps during recent years, the knowledge of Alpine river dynamics and their chronology is still limited. To address the influence of external factors, such as climatic variability and land use, on aggradation and floods, we focused our research on the Late Holocene sedimentary and geomorphologic history of the Lütschine fan delta. Morphological mapping, sedimentology, geochemistry, palynology, historical maps, building inventories and 14C-dating techniques provided valuable data for the reconstruction of palaeofloods, wetland environments, and anthropogenic impact. The sedimentological findings showed a general agreement between geochemical and pollen changes and δ14C anomalies from 2400 to 850 yr cal. BP. Furthermore, the coarse-grained layers, deposited during palaeofloods about 400 yr cal. BC and 100, 700, 1100, 1550, and 1830 AD, correlate with positive radiocarbon anomalies, suggesting that aggradation in the Lütschine fan delta during the focused period was triggered by solar forcing. According to our pollen data and the traced correlations, the Lütschine river floods occurred during cold and wet periods. The return interval of recorded flooding events during the last 2400 years varies between 300 and 600 years. With regard to the last millennium, anthropogenic impacts, such as woodland clearance for grazing and agriculture and river diversion, have changed the sedimentary and geomorphic pattern on the Lütschine fan delta, reducing wetland environments.