M@ppemonde ()
Cartographie spatialisée des pertes en terre selon la méthode isotopique du Césium 137 dans le bassin versant de l’oued El Mssine (Tunisie nord-est)
Abstract
Isotopic tracer Cesium 137 to study the erosion-accumulation cycle was used in El Mssine basin. Following the spatiotemporal distribution of this tracer one comes to understand the causes of the soil particles displacement as well as those due to the different determining factors. The Cesium 137 becomes an efficient quantification tracer of the movement of soil particles. These Cesium 137 isotopic tracers constitute a very interesting alternative method capable of overcoming certain difficulties which accompanied the previous empirical and experimental methods requiring colossal work and continuous monitoring in the field terrain (Moukhchane et al., 1998, Sadiki, 2005; Bouhlassa et al., 2000; Nouira et al., 2003 et 2007; Al Katmour, 2004; Felah, 2010; Damnati et al., 2010 et 2012; Ben Mansour, 2012). It has shown an efficiency in the quantification of soil losses and in the dating of sediments (Sogon, 1999) and dating of flood deposits (Philippe et al., 2001). Taking this fact into consideration, our study aims to examine the soil movement in light of this approach by measuring Cesium 137. These results are averages 40-year periods and are far away to represented the dynamics of erosion at the interannual scale. This technique may allow a better situation of priority sectors intensely eroded as well as choose the appropriate management policy. This approach was preceded by a qualitative study in order to highlight the physico-human conditions that made of this basin a zone strongly eroded, with a specific loss around 34 t/ha/year and can reach 63 t/ha/year on the slopes most susceptible to erosion. A local database of Cesium 137 activity was established and compared with neighboring countries. About the cesium 137 activity obtained in the study basin are consisted between 739 Bq/m2 and 13 Bq/m2, which implies a considerable displacement of sediments.
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