Abstract
Land degradation is one of the most important environmental threats facing the international community. In North Africa, many semiarid and arid regions are suffering significant land degradation, which can be an impediment to sustainable development. Therefore; land degradation is monitored in a regional context for a better understanding of its causes and consequences. One of the main consequences is a notable increase in sand encroachment with negative environmental implications. For this reason, the dynamics of sands between south-eastern Morocco and the wilaya of Nâama, south-western Algeria, was studied. Sand samples gathered from six distinctive areas were subjected to physicochemical, colorimetric (redness index), morphoscopic (circularity), and geochemical analysis, and studied statistically using an analysis of variance (ANOVA), wind direction data, ternary plots and a hierarchical cluster of trace elements (K, Rb, Fe, Ti, Ca and Sr). In all areas, a clear dominance of the sand fraction appeared showing percentages ranging from 89 to 96%. Sampled areas were all carbonated, and the pH was alkaline, with close values ranging from 8.4 to 9. The mean circularity values ranged from 0.67 in Merzouga (Morocco) to 0.80 in El Aguer (Algeria). The lowest value of the redness index was noted in Merzouga with a mean value of 4. The Algerian areas showed an almost similar redness index with a value of 6 but the highest value was noted in Saadana with a value of 11. Geochemical approaches, based on ternary plots and dendrogram cluster indicating the abundance of major elements (Fe, Ca and K), were used as indicators of wind transport. Results suggested the existence of a Regional Wind Action System (RWAS) implicated in the transport of sand from south-eastern Morocco and its redistribution towards south-western Algeria. Merzouga was connected to all areas but particularly to nearby Saadana and Kasdir in the Algerian territory.
Highlights
With an area of 20 million hectares (Houyou et al 2014), the Algerian steppe is one of the three main eco-climatic regions of the country and the largest area of rangeland of the North African countries
The Algerian south-western steppes have suffered from a decrease in rainfall and are under the threat of desertification, land degradation and increasing sand encroachment (Slimani et al 2010)
It is well accepted that sand encroachment is linked to driving forces like wind and results from a very active morphodynamic process (Slimani et al 2010; Ren et al 2014; Hamdan et al 2015)
Summary
With an area of 20 million hectares (Houyou et al 2014), the Algerian steppe is one of the three main eco-climatic regions of the country and the largest area of rangeland of the North African countries. The Algerian south-western steppes have suffered from a decrease in rainfall and are under the threat of desertification, land degradation and increasing sand encroachment (Slimani et al 2010). It is well accepted that sand encroachment is linked to driving forces like wind and results from a very active morphodynamic process (Slimani et al 2010; Ren et al 2014; Hamdan et al 2015). Several works monitoring desertification and land degradation have mainly focused on the study of sand encroachment (Bagnold 1941; Dubief 1952; Sharp 1966; Callot 1987; Mainguet 1992). Significant studies have been carried out using aerial photographs (Smith et al 1968) and Landsat images (Fryberger and Dean 1979) and, more recently, new approaches, including numerical modelling (Hersen 2004), field measurement (Hugenholtz et al 2012) and geochemical methods have proved
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