干旱区生态环境知识资源中心

Nabkhas near Mopti in Mali, West Africa have formed as a result of continued cultivation coupled with grazing during periods of severe drought. Dune development at three investigated sites was initiated after the onset of drought conditions. The dunes have formed on deltaic soils which were previously cultivated. Although most of the dunes are at least partially vegetated, the interdune surfaces are generally devoid of vegetation, highly compacted and continually disturbed by animals. The dunes are elongate and average 0.57 m high, 3.45 m wide and 5.45 m long. They are strongly aligned ESE-WNW with stoss (windward) sides oriented towards the ESE. Dune sediments are sandier and better sorted than the parent deltaic soils but contain a high proportion of silt and clay thought to be transported onto the dunes as sand-sized aggregates.

The nabkhas have developed as a consequence of climatic and anthropogenic stresses on the arid ecosystem and are linked to desertification within the region. Ongoing disturbance from grazing and cultivation will cause further vegetation reduction and surface destabilization and may result in more widespread dune development.