Use of caesium-137 re-sampling and excess lead-210 techniques to assess changes in soil redistribution rates within an agricultural field in Nakhla watershed

The Nakhla watershed was one of the most affected areas by water erosion in Northwest Morocco. This phenomenon caused the sedimentation of the Nakhla dam, an important water reservoir that contributed to water supply in the region. The motivation behind our investigation is to know the evolution of the situation in this watershed. The objective of this study is to use fallout Caesium-137 and excess Lead-210 to assess changes in soil redistribution rates during the last century and the impact of recent soil conservation practices within an agricultural field in the Nakhla watershed. The Caesium-137 technique, which has proved its efficiency in estimating erosion rates over the last 50–60 years, was associated with the re-sampling approach in the current study to reveal the response of soil redistribution rates to land use change over the last fifteen years within an upland agricultural field in Northwest Morocco under Mediterranean conditions. The excess Lead-210 was used to generate data on soil movement over a longer time window of 100 years. Subsequently, the combined use of Caesium-137 re-sampling with excess Lead-210 techniques allowed for the estimation of soil erosion rates over three periods: 1954–2002, 1954–2017 and 1917–2017. Quantification of water erosion with excess Lead-210 indicated a rate of 27 t ha−1 yr−1. Based on Caesium-137 measurements, the comparative analysis of the soil redistribution estimates over two periods (1954–2002 and 1954–2017) shows that soil loss rates have significantly decreased from 36 t ha−1 yr−1 to 29 t ha−1 yr−1 during the period between the two sampling campaigns (2002–2017) due to the beneficial impact of agricultural practices. This decrease is consistent with the available records of sediment yield in the Nakhla dam during these periods. The main findings show that the sustainable agricultural practices and the implemented soil erosion control strategy, based on more frequent fallow with natural vegetation and olive plantations, were effective in reducing soil erosion in the investigated area.