Deciphering human and climatic controls on soil erosion in intensively cultivated landscapes after 1950 (Loire Valley, France)

International audience ; Intensification of agricultural practices during the second half of the 20 th century has accelerated of soil erosion around the world. Although this phenomenon has been widely investigated through a combination of monitoring or modelling at short timescales (<10 years), few records are available for reconstructing the trajectory of soil erosion during longer periods (i.e. the 20 th century). Analysis of sediment deposits in reservoirs provides a valuable tool for reconstructing these trends and for identifying the driving factors that may have disturbed the sediment cascade after 1950. Accordingly, sediment cores (n=5) were collected in a reservoir located at the outlet of an intensively cultivated lowland catchment (24.5 km²) representative of those found in central France. Natural (excess lead-210) and artificial radionuclides (caesium-137, americium-241) enable dating of these sedimentary sequences. The corresponding sediment accumulation and erosion rates were calculated for the 1928-2017 period. In addition, daily rainfall records, land use change and agricultural field patterns were reconstructed for the period comprised between 1950 and 2017, based on weather records, digitalized aerial images (n=10) and agricultural census data (n=6). Results showed substantial acceleration of erosion rates after 1928 (+500%). This increase occurred simultaneously with major landscape changes that led to an increase in plot size (+465%) and decrease of the surface occupied by grassland and fallow land (-93%). Both parameters correlated strongly with the erosion rates reconstructed in this catchment (r=0.87 and r=0.95 for the plot size and grassland/fallow land surfaces, respectively). In addition, spectral analyses of daily rainfall records and mass accumulation rates, estimated with high temporal resolution from the sediment core tomography scanner data, showed concomitant short (i.e., 1 year) and long-term (i.e., 16 years) cycles between mass accumulation rates and rainfall. Overall, this ...