Does salinity have an influence on the diversity and structure of the wintering waterbirds of the Saharan wetlands in Algeria?

Study Extent

The eco-complex of the Oued Righ Valley wetlands in the Algerian Sahara is one of the most important wetland complexes in Algeria. This Saharan depression constitutes a wintering area that is favorable for the aquatic avifauna of the western Palearctic and a migratory stopover during the great crossing of the Sahara to reach the sub-Sahelian wetlands (Isenmann and Moali, 2000). The Oued Righ Valley includes several wetlands, three of which are classified as RAMSAR sites: Chott Merouane, Oued Kherouf and Chott Sidi Slimane. This valley in south-eastern Algeria occupies an area of 11,738 km 2 (Khechana et al., 2010). As part of the whole of the lower Sahara basin, it is a vast depression elongated between 32° 54 N and 34° 9 N. Like all Saharan regions, this depression is characterized by an arid continental climate. The average annual rainfall is low and irregular, about 80 mm, so it does not have a role in the direct recharge of aquifers and wetlands (Habes et al., 2016). The water comes from runoff, and surplus irrigation water arises not only from the drainage of palm groves but also from groundwater (Khechana and Derradji, 2014). Our study focused on six wetlands: Chott Merouane (sometimes designated on maps as Chott Felrhir) and Oued Kherouf - both of which have been classified as Ramsar sites since 2 February 2001 - , Lake of Sidi khelil, Chott Tendla, Lake of Ayata (fig. 2) and Lake of Merdjadja.

Sampling

The field study was conducted during two wintering periods (2017-2018 and 2018- 2019). Thirty-three visits totaling approximately 230 hours were made. Counts were carried out by direct observation of different waterbird species using a telescope (KITE SP 82 ED) and binoculars. An exhaustive count of individuals was carried out when the distance was less than about 200 m and the number of individuals was less than 200. When the group was greater than 200 individuals or if it was at a remote distance, we proceeded by dividing the visual field into several bands, counting the number of birds in an average band and reported as many times as bands (Blondel, 1975; Tamisier and Dehorter, 1999). All wetlands except Chott Merouane were fully studied. In Chott Merouane, which is very large, we established three stations, covering a total area of about 1,500 hectares.

Quality Control

To calculate wetland salinity, we chose the direct method using a portable optical refractometer with a measuring range of 0-100‰. We analysed a total of eleven stations on the six wetlands and classified these according to the categorization of the salinity of Mediterranean wetlands proposed by Farinha et al. (1996): freshwater < 0.5 ‰, Oligohaline (0.5-5 ‰), Mesohaline (5-18‰), Polyhaline (18-30‰), Euhaline (30-40‰) and Hyperhaline > 40‰.

Method steps

1. The salinity was determined during the wintering periods in 11 stations of the Oued Righ wetland complex (table 3). To measure the salinity of stations, we employed the direct method, using a portable optical refractometer with automatic temperature compensation (ATC) from AUTOUTLET with a measuring range from 0 to 100‰. To determine the affinities and intersite variations according to the different degrees of salinity we carried out a factor analysis of correspondences (AFC). The significance level for statistical analysis is p-value < 0.001. To determine the affinities and inter-site variations according to the different salinity levels during the monitoring periods, a correspondence factorial analysis was carried out using XLstat version 2016 software. The significance level for statistical analysis was p-value< 0.001.

1. Accipitriformes
   rank: order
2. Accipitridae
   rank: family
3. Anseriformes
   rank: order
4. Anatidae
   rank: family
5. Charadriiformes
   rank: order
6. Recurvirostridae
   rank: family
7. Charadridae
   rank: family
8. Scolopacidae
   rank: family
9. Laridae
   rank: family
10. Ciconiiformes
    rank: order
11. Ciconiidae
    rank: family
12. Gruiformes
    rank: order
13. Rallidae
    rank: family
14. Passeriformes
    rank: order
15. Hirundinidea
    rank: family
16. Pelecaniformes
    rank: order
17. Ardeidae
    rank: family
18. Threskiornithidae
    rank: family
19. Phoenicopteriformes
    rank: order
20. Phoenicopteridae
    rank: family
21. Podicipediformes
    rank: order
22. Podicipedidae
    rank: family
23. Suliformes
    rank: order
24. Phalacrocoracidae
    rank: family

The eco-complex of the Oued Righ Valley wetlands in the Algerian Sahara is one of the most important wetland complexes in Algeria. This Saharan depression constitutes a wintering area that is favorable for the aquatic avifauna of the western Palearctic and a migratory stopover during the great crossing of the Sahara to reach the sub-Sahelian wetlands.