The Geobiology of Bacteria Within the Extreme Conditions of Sidi El Hani Wetland, Eastern Tunisia: Environmental and Astrobiological Significance

Study Area

The sebkha of Sidi El Hani is a NW-SE lengthened depression in the Sahel area in Tunisia) with a relatively small drainage basin. It is by no means communicating with the sea. But it contains huge quantities of salt spanned on tens of kilometres. It is fed by temporary (Oued Maktaa) and (Fig: 1) and permanent (Oued Chrita) hydrologic networks. It represents the basal part of the endorheic system Sidi El Hani-Chrita-Mechertat (Ben Jmaa, 2008). Moreover, eventhough it has always been treated as a single unit, the sebkha of Sidi El Hani as such is actually made up of three communicated playas; from north to the south one finds: the playas of Sidi El Hani (sensu stricto), the playa of Souassi and the playa of Dkhila. Administratively, it stretches on four governmental subdivisions (Fig: 1). Its northeasternmost belongs to Sousse state; its northwesternmost is distant 13 km of Kairouan center; a minor part of Sidi El Hani playa is located in Mounastir state. The Mahdia state includes the southeasternmost of Dkhila sebkha (i.e. the southeasternmost of Sidi El Hani saline environment). This administrative subdivision and its large geographic extension are handicaps to create a clear database about the sebkha; thus, the dispersed and incomplete data are hard to collect. Topographically, Sidi El Hani playa is limited by various hills that barely reach more than 100m of altitude. Westward, one finds the undulation of Aïn El Ksar, Aïn Tarfaïa and El Guessaat; southward, the undulation of Bou Thadi and Eljem and towards the East the Zarmdine anticline. The basin of Sidi El Hani is an eastern diverticulum, of the Kairouan plain, which penetrates toward a coastal folded upland. This topographic contrast helps to create a developed hydrological network within the 3300 km² of its hydrological basin, on which many dams are constructed (Fig: 1). The three components of sebkha Sidi El Hani have different orientations. Sidi El Hani (sensu stricto) and Dkhila playas are oriented N 170; the playa of Souassi is oriented N 90. The bottom of the playa of Sidi El Hani (sensu stricto) hangs slightly towards the East and that of Souassi towards the North. The surface of Sidi El Hani playa is approximately 370 Km² and its average depth of water is 0.4m; but it can reach in some locations 0.8m. The principal highest point, which is located in North East of the depression, can reach 33m of altitude.

Figure 1.

Administrative location and topography of Sidi El Hani playa

(Leduc et al., 2004; Ben Jmaa, 2008)