Evaluation of the correlation between Caesium-137 inventory, magnetic susceptibility, and organic matter content to assess soil erosion status in two agricultural fields within El Hachef watershed of northwest Morocco

Abstract

<h2>Abstract</h2> Soil erosion by water threatens soil stability in Northwest Morocco. Various techniques have been used to study the phenomenon. This study applies an approach based on measurements of Caesium-137 (¹³⁷Cs), <i>in situ</i> magnetic susceptibility, and organic matter at two agricultural sites located in El Hachef watershed (Tangier-Tetouan-Al Hoceima region) to evaluate the correlations between these techniques in evaluating the status of soil erosion. Measurements of magnetic susceptibility, ¹³⁷Cs, and organic matter were taken along two parallel transects in Field 1 and a single transect in Field 2. A stable reference site near the studied fields was selected and sampled to represent the initial ¹³⁷Cs stock in the area. Soil stability in the two agro-systems is evaluated and compared with the reference site. In the reference site, the mean ¹³⁷Cs activity is 1707 Bq/m², magnetic susceptibility is 0.296∗10⁻³ SI, and organic matter content is 8.15 %. In Field 1, ¹³⁷Cs activities range from 135 to 1586 Bq/m², magnetic susceptibility measurements range from 0.009∗10⁻³ SI to 0.169∗10⁻³ SI, and organic matter content varies between 4.41 % and 7.74 %. In Field 2, ¹³⁷Cs activities range from 88 to 1558 Bq/m², magnetic susceptibility measurements range from 0.021∗10⁻³ SI to 0.165∗10⁻³ SI, and organic matter content varies from 3.81 % to 7.22 %. The results show that the areal activities of ¹³⁷Cs and magnetic susceptibility measurements are highly correlated (around 80 %) and the correlation factors for these parameters with the organic matter are over 70 % and 60 %, respectively. Estimated erosion rates based on Mass Balance Model 2 are 28.4 t/ha/yr in Field 1 and 42.7 t/ha/yr in Field 2. The multidisciplinary approach highlights the complementarity nature of the measured parameters in documenting soil movements.