Caesium-137 re-sampling approach and excess Lead-210 sediment dating to assess the impacts of climate change and agricultural practices on soil erosion and sedimentation in Northwest Morocco

摘要

This study aims to evaluate changes in soil erosion and sedimentation processes in the Northwest region of Morocco based on the use of fallout radionuclide techniques. The Caesium-137 technique was combined with the re-sampling approach to assess soil erosion rates associated with two periods (1954-2000/2001 and 1954-2017/2018) in four agricultural fields located in El Hachef and Raouz watersheds, and excess Lead-210 was used to estimate the temporal variation of the sedimentation rate in a water reservoir named "9th of April 1947", located in this region, downstream from El Hachef watershed. The results show that the net soil erosion rates had decreased in the two study fields of El Hachef watershed, from 26.3 to 20.2 t ha(-1) year(-1) and from 50.8 to 42.7 t ha(-1) year(-1), respectively, and in one field of Raouz watershed, from 19.4 to 16.1 t ha(-1) year(-1), due to some beneficial changes in land use consisting of more frequent fallow periods combined with natural vegetation and crop rotation practice. However, in one of the two fields of the Raouz watershed, where agricultural practices were not changed, the net soil erosion rate increased from 4.5 to 5.7 t ha(-1) year(-1) between the two periods, which could be due to climate change impact on soil erosion in this area. Taking into account the relative uncertainties on the Cs-137 inventories and the period elapsed between the two sampling campaigns, the results obtained by the re-sampling Cs-137 method can be considered statistically significant in particular for fields with high changes in soil erosion rates. The results also indicate an increase of the sedimentation from 18.9 t ha(-1) year(-1) in 1950 to 79.8 t ha(-1) year(-1) in 2015 in the downstream water reservoir, which can be attributed to the combined impacts of both climate change and agriculture practices in the region.