Abandonment of agricultural land is widespread in many developed countries. These surfaces are projected to increase significantly worldwide during the 21 th century. Identifying potential relationships between land abandonment and soil erosion dynamics over the long term (100 years) is therefore essential for predicting the environmental consequences of this extensive land use change. Accordingly, sediment cores were collected in two highland catchments of central France in order to reconstruct the change of sediment delivery during the last century. The results showed a substantial decline (71-78%) of rural population in both sites since 1900. This decrease occurred simultaneously with a sharp decline (85-95%) of the surface of arable land: previously cultivated areas were mainly converted into forests as the result of natural and anthropogenic processes. Consequently, sediment deliveries significantly decreased (75-99%) in both catchments. These trends were nevertheless interrupted by the implementation of afforestation works between 1945 and 1970 in one of the catchments. During these works, erosion rates increased threefold because of extensive soil disturbance, and sediment delivery stabilized only 15 years after the onset of these management operations. Overall, this study demonstrates the long-term effect of land abandonment on soil erosion, which supplements the more widely reported acceleration trend of soil erosion because of agricultural intensification.

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Long term records are needed to investigate the impact of extreme events in the current framework of global change. Sedimentary reconstruction with a high resolution remains difficult without conducting expensive, destructive and/or time-consuming analyses. In this study, ultra-high resolution CT-scan profiles (0.6 mm resolution) were used for investigating their potential for detecting flood deposits induced by heavy rainfall events. This method was applied to a sediment core -covering a 120-yr period -collected in a pond draining a small forested catchment (French Massif Central -Central France). Between 1960 and 2017, 28 layers were deposited. Seventy-fixe percent of these deposits were correlated to the occurrence of heavy rainfall (>50 mm) recorded during 1 or 2 consecutive days. The remainder of the deposits detected with the CT-scan (n=5) were not correlated to weather events. They mainly occurred in response to landscape management operations (e.g. afforestation works posterior to the major 1999 storm). This period was indeed characterized by an increase in the delivery of 137 Cs-enriched sediment, demonstrating a greater topsoil contribution to sediment during major forest management operations. The intensity of detritical layers has significantly decreased throughout time after a major land use change that took place in 1948 and land abandonment.The frequency of heavy rainfall and associated detritical deposits has nevertheless increased by 60 and 75% respectively between the 1960-2017 period. These results outline the potential of CT-scan for reconstructing long-term flood deposits associated with heavy precipitation.