Soil erosion rates evaluation via 137Cs and RUSLE modeling in the Sigilil watershed (northeastern Tunisia)

Soil erosion is a natural phenomenon which causes many problems such as the reduction of soil fertility and silting of dams. In this study, the Cs-137 activities and the RUSLE model were used to quantify soil erosion rates in the Sgilil river watershed of northeastern Tunisia, and where 20% of the agricultural land is devoted to the cultivation of olive trees. In addition, the erosion dynamics and its spatial variation were inferred. The net erosion rates in the cultivated field based on the measured Cs-137 activities and using the Fallout Radionuclide Conversion Models range from 2.24 to 34.23 t ha(-1) yr(-1) when the Proportional Model is applied and from 1.49 to 30 t ha(-1) yr(-1) when the Mass Balance Model 2 is applied. The average erosion rates of the Sgilil river watershed estimated by the RUSLE model after multiplying five erosion factors for an average year (1990-2019) is 6 t ha(-1) yr(-1). Based on the RUSLE model results, around 52% of the watershed area falls within the slight erosion risk class (0-2 t ha(-1) yr(-1)) and 11% within the very severe erosion risk class (> 30 t ha(-1) yr(-1)). The center of the watershed, where the olive cultivated field is located belongs to a high to severe erosion risk class. Results attained through the isotopic approach and those found through the RUSLE modeling are in agreement.