Tuesday, 23 December 2014

Sebkhets of the Sahara

Geography Lessons from Ospreys #438

Location: Assouerd Province, Western Sahara

Dama Gazelles (Image: W.A.Z.A. Conservation)
The western coastal margin of the Sahara Desert is a region with almost no rainfall. To our eyes, it appears desolate and lifeless – and yet there IS wildlife here.

Among the dunes and wind-scoured rocky plains, isolated pockets of hardy vegetation grow, flower and set seed. The seeds attract sand grouse and roving bands of migrant finches. Dainty gazelles known as “Mhorro” (Nanger dama mhorr) which are critically endangered elsewhere in the Sahel, still graze there, and the almost-mythical white antelopes (Addax nasomaculatus) - one of the rarest hoofed animals in the world and until recently thought to be extinct in the wild, are also to be found... if you know where to look.

The reason for all this is the presence of sebkhets.

A sebkhet is (in this context) a low-lying area where groundwater from aquifers below the desert seeps to the surface. They can be brackish or can contain fresh water, depending on the local geology. The mendicant camel-drivers have always known about them and some of the larger, more permanent ones have Arabic names. Others are smaller: they can last for only a few years or even months, before the desert wind covers them with sand again and exposes some other sebkhet elsewhere.

Addax nasomaculatus (Image: wildaddax.org)
Ground-reflectance images from satellites, together with LIDAR measurements, have enabled scientists to map the distribution and extent of the desert sebkhets. There are many more of these features than was originally thought, and it is now clear that they are the secret of how large grazing mammals have been able to survive in a place where none should be. At the Parc National de Safia, a closed reserve as been established where the Mhorro and Addax are protected. Their numbers and gene pool have been bolstered with captive-bred animals from European zoos, and the last count was up 23% overall since the project started.

In UV's area, there is a permanent sebkhet and several small un-named ones. Perhaps it isn't such a dull place for an osprey after all!


Directory of African Wetlands, R. H. Hughes, J. S. Hughes, G. M. Bernacsek
Antelopes: West and Central Africa – action plan, R. East, ed. (WWF)

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