Estimates of soil erosion and deposition of cultivated soil of Nakhla watershed, Morocco, using 137 Cs technique and calibration models



Despite the effective threat of erosion, for soil preservation and productivity in Morocco, there is still only limited information on rates of soil loss involved. This study is aimed to establish long-term erosion rates on cultivated land in the Nakhla watershed located in the north of the country, using 137Cs technique. Two sampling strategies were adopted. The first is aimed at establishing areal estimates of erosion, whereas the second, based on a transect approach, intends to determine point erosion. Twenty-one cultivated sites and seven undisturbed sites apparently not affected by erosion or deposition were sampled to 35 cm depth. Nine cores were collected along the transect of 149 m length. The assessment of erosion rates with models va rying in complexity from the simple Proportional Model to more complex Mass Balance Models which attempts to include the processes controlling the redistribution of 137Cs in soil, enables us to demonstrate the significance of soil erosion problem on cultivated land. Erosion rates rises up to 50t ha-1 yr-1. The 137Cs derived erosion rates provide a reliable representation of water erosion pattern in the area, and indicate the importance of tillage process on the redistribution of 137Cs in soil. For aggrading sites a Constant Rate Supply (CRS) Model had been adapted and introduced to estimate easily the depositional rate.

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