Daya

The Arabic term 'Daya' indicates a shallow natural or sometimes artificial depression (usually <1.5 m deep) that contains water for at least some period of the year. These ponds or small lakes occur mainly in the lowland plains and are characterized by a certain morphological homogeneity and are very common in subhumid and humid areas of North Africa, especially where annual rainfall exceeds 20 cm. Water levels vary seasonally and inter-annually and are usually recharged during October-November each year. The occurrence of these water bodies, in the least dry areas (northwestern parts of the Maghrebian countries), is usually semipermanent (type 3), whereas in the arid areas their presence is less irregular and some dayas can remain dry for years, depending on rainfall (types 1 and 2). A typical daya completely loses its water by evaporation and drainage during the summer period, and the site can be distinguished in the dry landscape by an area of green vegetation (types 3 and 4). In certain formations in the less dry areas, the daya can persist the summer as a saline pool of smaller dimensions. They are frequently encountered in the northern parts of Morocco, Algeria, and Tunisia and in the south of Spain and Italy, but are infrequent in the east of North Africa (see Figure 1). The duration of inundation can vary from 9 to 3 months in a year according to rainfall and local climate. Dayas usually have silty clay bottom sediments derived from local soil erosion. Vegetation in and around a daya can vary from one formation to another not only according to water availability but also to disturbance. Isoetes velata, Ranuculus aquatilis, and Marsilea quadrifolia can be common in dayas type 3 and type 4. The Notostraca Triops concriformis mauritanicus and Lepidus apus can be characteristics of dayas in North Africa. Livestock can exert a very strong pressure on soils and vegetation around dayas leading to deforestation and silta-tion. Those dayas are prone to large water level

Figure 1 Distribution of ponds and lakes areas in North African Sahara and south of Spain regarding annual rainfall average. Dayas type 1 are ephemeral water body limited between Sahara and Atlas mountains. Dayas type 2 in the arid areas; dayas type 3 in subhumid and humid areas, and dayas type 4 in mountain areas.

Figure 1 Distribution of ponds and lakes areas in North African Sahara and south of Spain regarding annual rainfall average. Dayas type 1 are ephemeral water body limited between Sahara and Atlas mountains. Dayas type 2 in the arid areas; dayas type 3 in subhumid and humid areas, and dayas type 4 in mountain areas.

changes that they support only a few marginal plants. Generally, in the wet period, water within a daya is constantly turbid as a result of suspended sediments arising from silt inwash and wave disturbance. Nevertheless, they can be valuable sites for aquatic diversity and water birds. In the areas where the annual average of rains do not exceed 30 cm and where the period of dryness reaches 9-10 months, water can be stored as groundwater and the daya quickly becomes viable again even after a small rainfall (Figure 2).

Project Earth Conservation

Project Earth Conservation

Get All The Support And Guidance You Need To Be A Success At Helping Save The Earth. This Book Is One Of The Most Valuable Resources In The World When It Comes To How To Recycle to Create a Better Future for Our Children.

Get My Free Ebook


Post a comment