In the Eastern Rif of N Morocco, soil conservation is seriously threatened by water erosion. Large areas of soil have reached an irreversible state of degradation. In this study, the 137 Cs technique was used to quantify erosion rates and identify the main factors involved in the erosion process based on a representative catchment of the Eastern Rif. To estimate erosion rates in terms of the main factors affecting soil losses, samples were collected taking into account the lithology, slope and land use

The soil in the Rif, Morocco, is at serious risk because increasing anthropogenic pressures are gradually transforming large natural areas into farmland. The distribution of magnetic minerals within the soil profi le can be used to assess soil development and degradation. The soils in the study area are severely eroded because of a combination of highly erodible soils, intense rainstorms and scarce vegetation cover. To sample of representative soil profi les, lithology, slope gradient and land use were considered. The ranges of magnetic susceptibility in the soil profi les distinguished between two primary soil groups. Magnetic susceptibility varied in the soil profi le and along the soil toposequence, and the variations were related to the differences in the original magnetic composition and the infl uence of main erosion factors. Lithology is the main factor contributing to the variation in magnetic susceptibility. The magnetic susceptibility values in soils on Tertiary marls (χ = 13·5 × 10 −8 m 3 kg) differed significantly from those on Quaternary terraces (χ = 122·1 × 10 −8 m 3 kg −1). Slope affected the distribution of magnetic susceptibility because of the continuous loss of topsoil in some parts of the slope and the deposition of eroded soil in others. Elimination of the natural vegetation cover and a shift to cultivated land for cereals has had a negative impact on soil development and, on similar slopes and substrates, magnetic susceptibility decreased signifi cantly in cultivated soils. The soils on steep slopes that had natural vegetation cover retained the magnetic minerals better than did those on gentler slopes that were under cultivation. Grazing, clearing and, especially, tilling has weakened the soil and made it much more vulnerable to erosion. An analysis of the main factors causing erosion will help to promote rational use of the land and to establish conservation strategies in such fragile agroecosystems.

The Mediterranean Basin is an acknowledged hotspot for biodiversity, yet historical processes that shaped this biodiversity in North Africa remain poorly understood. This study aimed to elucidate the phylogeographic pattern of an endemic species of Mediterranean areas of North Africa, the Greater Egyptian Jerboa, Jaculus orientalis. The extent of phylogeographic patterns and molecular genetic diversity (mitochondrial cytochrome b gene) were addressed in a survey of 45 jerboas from 24 localities. Our phylogeographical analyses show a strong genetic subdivision into three areas along a west-east axis, corresponding to (1) Morocco and western Algeria; (2) eastern Algeria, Tunisia and western Libya; (3) eastern Libya and Egypt. Demographic analyses revealed different modalities of population expansion since the last glacial age depending on geographic areas. The dating using relaxed molecular clock analyses revealed that most splits occurred during the Quaternary (<1 million of years ago). Finally, we discussed the relative roles of geological and climatic change in generating this pattern of genetic structure observed for the Greater Egyptian Jerboa and other vegetal and animal species in North Africa.

The purpose of this study is to understand and quantify the relationships between current Cs inventories and the soil properties and the physiographic characteristics. A total of 36 cores were taken in seven transects with different slopes, lithology and land use. The analysis focused on theCs mass activity as well as inventories and its relationship with soil properties as grain size and organic matter. The mass activity of Cs and the inventories varied between 3.6 and 63.7 Bq kg and between 521.7 and 3304.4 Bq m, respectively. At uncultivated soils, high concentrations of Cs are located in the top 10 cm and decreased exponentially in depth. Cultivated soils record disturbed and heterogeneousCs profiles with values of mass activity and inventories up to 38.7 Bq kg and 2510.8 Bq m, respectively. The Cs inventories were significantly higher in uncultivated soils (mean: 2086.9 Bq m) compared to cultivated soils (mean: 1397.1 Bq m). The Cs mass activity showed a significant positive correlation with organic matter, silt and clay, but it was negatively correlated with sand and pH respectively. High levels ofCs were found at altitudes between 500 m and 640 m a.s.l, and at slopes from 8° to 11°, as well as in dense scrub land and Fersialitic soils. A principal component analysis showed that more than 86.7% of the variance in Cs mass activity was explained by the organic matter content and the land use. The results of this study provide insights into the effects of soil properties and physiographic factors on the behaviour ofCs in soils of Mediterranean environments of North Africa and strengthen the reliability of this radioisotope as an erosion tracer.

RÉSUMÉLe présent travail a pour objectif d'étudier l'érosion hydrique dans les deux bassins de Beni alaham et Al azhar situés au moyen Atlas, et de les hiérarchiser en parcelle selon le degré érosif à l'aide De l'approche PAP/CAR qui portait surtout sur l'intégration des facteurs influençant l'érosion hydrique, tels que la pente topographique qui traduit la morphologie et l'inclinaison des terres, le réseau hydrographique, le type de sol et le matériel lithologique, le type de couverture végétale qui traduit les systèmes d'exploitation agricole, et enfin, sur les mesures et structures anti-érosives existantes.Le travail a été réalisé à travers les trois étapes de la méthode tels que: L'approche prédictive qui se base sur l'analyse des facteurs naturels (pente, couvert végétal et lithologie) et le traitement des bases de données des cartes élaborées qui donnent des idées sur l'état de la dégradation des sols.L'approche descriptive se base sur la cartographie de différents formes et processus de perte en sol qui se manifeste sur la zone d'étude.L'approche d'intégration qui permet la combinaison de deux approches précédentes, son but c'est de fournir un produit cartographique très précis qui reflète la réalité de l'état de dégradation du sol et l'évolution future de l'érosion. RESUMENEl presente trabajo tiene por objetivo estudiar la erosión hídrica en las dos cuencas de Beni Alaham y Al Azhar situadas en el Atlas Medio, estableciendo jerarquias de parcelas según el grado erosivo con la ayuda de la aproximación PAP/CAR que permite, sobre todo, calibrar la integración de los factores que influyen en la erosión hídrica, tales como : la pendiente topográfica derivada de la morfología y la inclinación de las pendientes, la red hidrográfica, el tipo de suelo y el material litológico, la tipología de la cobertura vegetal que se relacionan con los sistemas de explotación agrícola, y en especial, sobre las medidas y estructuras antierosivas existentes.El trabajo ha estado realizado a través de tres etapas del método apuntado, éstas son: La aproximación predictiva que se basa en el análisis de factores naturales (pendiente, cobertera vegetal y litología) y el tratamiento de la base de datos especificadas en los mapas elaborados, los cuales muestran los resultados del estado de degradación de los suelos.La aproximación desctriptiva se basa en la cartografía de las diferentes formas y procesos de pérdida de suelo, manifestadas en la zona de esudio.La aproximación de integración que permite la combinación de las dos fases precedentes cuyo objetivo es conseguir un producto cartográfico muy preciso que refleje la realidad del estado de degración del suelo y la evolución de la erosión futura.Palabras clave: PAP/CAR, SIG, erosión hídrica, situaciones erosivas, formas de erosión.