Megene

This term is used in the Maghreb countries for describing a small lake in mountain areas. A typical example is Megene Chitane in North Tunisia, a small, usually clear, soft water lake located on the north slope of Chitane Mountain at 150 m altitude, overlooking the Mediterranean Sea to the north. The site is protected and was declared a nature reserve in 1993. The outflow is ephemeral and maximum water depth is normally ~1.2m. The catchment includes cork oak with fairly undisturbed scrub understorey. A perimeter fence some 50-100 m from the lake shores protects the catchment within the vicinity of the lake. Upslope from the lake, subsistence farming is practised on a small area of valley mire. Water flowing through the mire is currently being exploited for crop irrigation. A small aquifer supplies two small freshwater springs that feeds the upper mire bog and eventually the lake. The sandstone aquifer and the valley mire confers acidity to the lake as they are both acidic. The lake water is only slightly acidic, which is most unusual for North African lakes, because nearly all of them nearly possess alkaline water (Figure 3). In 1998, the underwater lake sediment was observed to be covered everywhere with desiccation fissures marking the earlier loss of surface water (Elkhiati et al., 2002). Loss of standing water probably resulted from overexploitation of the lake's natural acid spring water supply. Nevertheless, the lake still supports many aquatic plants, including Nymphaea alba, Juncus heterophyl-lus, and the rare Isoetes velata. The littoral zone is covered with terrestrial vegetation (Cotula coronopi-folia and some grasses). Fish were introduced by Forestry authorities but these seem to have been lost following the mid-1990s desiccation period.

Shallow Lakes Ecosystem
Figure 3 Megene Chitane in Northern Tunisia, a shallow and relatively undisturbed upland lake showing a late spring abundance of aquatic plants. The lake is unusual because the water is slightly acidic (photo April 1997).

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