Sebkha Oglet and Chott

These types of water bodies are typically ephemeral and usually possess brackish water. They occur in steppe or substep zones with arid climate and are typical in dryer parts of North Africa that receive seasonal runoff from higher ground. Their salinity is derived from soil-derived salts and evaporation; sodium and calcium with chloride and bicarbonate are usually the dominating ions controlling salinity, but sulfate can be locally important depending on hydrogeology. Both sebkhas and oglets exist as shallow basins often of large dimensions (10-30 km); the water is always shallow and is susceptible to wind effects, especially desiccation. They can be dry or very shallow in summer, but can offer useful habitats for birds, e.g., Sebkha Kelbia in Tunisia. The term sebkha is used in the South the term oglet in the East, for identical sites in the SMR.

Chotts are immense depressions (30-100 km or more) without defined outflow channel; some years they may remain dry, but when flooded following a wet period, they expand to a large expanse of silty water. By the late summer, open water will be extremely reduced or nonexistent and in some cases standing water exists for only a few days before it is removed by infiltration and evaporation. These formations when exposed are often largely covered by a steppe terrestrial vegetation (e.g., Salsolacees) on suitable ground. Elsewhere, the chott landscape is dominated by exposed alluvium (often sands and coarse gravels) with occasional local depressions with evaporites. In these areas a surface crust of gypso-halite-carbonates often rest on sands and silts. These hollows may be reflooded several times in a year depending on rainfall in the catchment area. Duration of immersion of more than 5 months would be

Figure 4 Chott Iriqi (southeast Morocco) - a site that is dry in summer (left) but is flooded in the winter period (right) where it supports abundant microinvertebrates and attracts flocks of flamingos.

Figure 4 Chott Iriqi (southeast Morocco) - a site that is dry in summer (left) but is flooded in the winter period (right) where it supports abundant microinvertebrates and attracts flocks of flamingos.

exceptional. A well-known example of a large chott is the Chott El Jerid in Tunisia, an interesting site that possesses occasional accumulations of marine molluscs (Cerastoderma). In southern Morocco, the Sebkha Zima (Chemaia) presents characteristics between a merja and a sebkha because of the absence of vegetation, but having an effluent drainage system in wet years. Located in south-east Morocco, Chott Iriqi is another interesting site for birds (Figure 4).

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