2.2 Generalities on coastal lagoons

Only one lagoon, El Mellah, is present on the Algerian coast. It is located near the city of El Kala, Wilaya El Tarf, and it communicates with the sea by a channel (ONDPA/SPA 2003).

Table I: General information of El Mellah lagoon

Morphological and bathymetric characteristics

Lagoon shape: The El Mellah lagoon has an ovoid form, 4.79 km long, from the discharge system of the Bouaroug Wadi to the beginning of the channel.
Containment: The El Mellah lagoon is a coastal lake measuring approximately 864 ha, communicating with the sea by a channel. The hydraulic exchange is regularized by the tides, the movements of the sea and the variations of the lake level related to atmospheric precipitations.

 

The channel in communication with the sea was artificially arranged, facing over the years serious difficulties due to the progressive stranding, at a point that the persons in charge of lake aquaculture management made a second opening to the sea, and chose a strategy of consolidation of the dune formed on the old opening which previously came in contact with the sea only after strong risings:
• Maximum width is 2 603 km in the Northern half;
• Minimal width is 0.620 km in the Southern half;

 

Figure 1. Map of the coastal lagoon of El Mellah

• The perimeter is 13.53 km and the length of the channel is 0.870 km;
• Its dispatcher is 15 meters approximately.
Bathymetry: Bathymetric measurements emphasize that the El Mellah lagoon is a not very deep lake:
• Maximum depth is 6.40 meters;
• Average depth is 2.7 meters.
Agricultural activity: The arable land surface borders 734 ha, which represents in absolute value 9 percent of the total surface of the catchment area. The breeding of bovine associated to groundnut culture is generally practiced.
Fishing activities: fishing activities are practised only in the peripheral belt of the lagoon down to 4 m depth, because captures are rare in the central part. The cause of this phenomenon is probably the lack of oxygen in these central zones.
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Port of El kala: The fishing port in El-Kala has the following characteristics:
Length of the quays 800 m
Width of the pass of entry 70 m
Full ground 1.1
Drawing from water 4 to 5
Plane surface of water 3.6 ha

Legal framework

At the international level: The site is classified as an integral reserve in the El Kala National park with itsprotection ensured by the law of the environment and a decree fixing the National Parks Statute-type. In addition, the national park is classified as a Reserve of Biosphere of the MAB Unesco Programme and a wetland of international importance according to the Ramsar Convention.
At the national level: The reinforcement of the legal framework was carried out by the development and the promulgation of Law n°01-11 from July 3 relative to fishing and aquaculture.
Relevant laws in force governing the exploitation of the lakes:
• Executive decree n° 03-280 of 23 August 2003 defining the mode of delivery and establishment of the domanial concession for the exploitation of the lakes Oubeira and Mellah.
• Executive decree n° 06-372 of 19 October 2006 fixing the book of the load-type for the exploitation of eel.
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• Executive decree n° 04-189 of 7 July 2004 fixing measurements of hygiene and 4
healthiness applicable to aquaculture and fishery products.
• Interministerial decree of 30 August 2009 laying down the procedure of the committee of follow-up and monitoring of the activities of exploitation of the lakes Oubeira and Mellah (MPRH, 2011).
Climatology: El Kala, one of the most sprinkled areas in Algeria, is located in the sub-wet bioclimatic stage and receives an annual average pluviometry of 910 mm and a maximum of 1.300 mm. The dominant winds from the northwest, with a mean velocity varying from 3.3 to 4.8 m/s, bring the most significant precipitations of the Atlantic. On the other hand, the Sirocco,
which blows mainly in summer coming from southeast, drains the atmosphere and strengthens forests fires when temperatures are too high. The main evaporation rate is 889 mm/year.
Hydrology: It is influenced on the one hand by the movements of marine water penetrating through the channel, the exchanges between the lake occuring in a slow peripheral clockwise rotation, and on the other hand by the direct freshwater contributions at the time of the rains and, finally, by the water carted by the Oued.

Physicochemical characteristics of the water column

Temperature: The lowest value is recorded in January and the highest in August; there are two periods, one cold and the other hot, with relative temperatures ranging between 11.8°C and 20°C in winter and 20°C and 36.6°C in summer. During the cold period, there is a decrease of 5°C from October to January followed by a phase of growth during which a profit of 5°C is noted from February to April. Water temperature increases by 10°C in 4 months (from May to August). The difference of the temperature between the hottest month (August) and the coldest month (January) is 20°C.
Salinity (‰): The study shows an existence of a decrease in water, from September to January (28.7 and 22.5 g/l) followed by a phase of stabilization from February to May. From June, salinity increases with values ranging between 27 and 37.9 g/L.
pH: The lagoon water is alkaline, generally with a pH near 8. The water alkalinity shows that the lagoon is prone to a strong photosynthetic activity.
Dissolved oxygen: The lowest contents ranging between 3.9 and 5.45 mg/l are recorded in November, the highest contents oxygen reach 13.55 and 12.25 mg/l in December. The highest values are recorded between February and May (10.95– 13.1-12.75–12.85) respectively in the channel, the tables, the middle and the mouth of the Oued Souk Erguibet.
Nitrates: The exogenic nutritive salt contributions are rather weak, hence the contributions in nutriments necessary to the primary production come from the regeneration of salts starting from the sediments. The maximum contents nitrates raised in the El Mellah lagoon are definitely lower than the value guides of 5 mg/l for water of excellent quality.
Orthophosphates (Po4): The concentrations in ortho phosphates present differences: the lowest values are lower than 2.5 micromoles L -1 and are recorded in the channel, and in the mouth of Oued Belaroug the contents of ortho phosphates are close to 3 micromoles L.
Chlorophyll a contents: The results of the proportioning of chlorophyl, obtained starting from water samples taken monthly on the level of various sites of study, show that the concentrations in this pigment vary from one site to another and from one month to another. In the channel, chlorophyll a content is between 0.013 and 25.09 mg m-3, rising in summer and autumn. In the central part of the lake, Chlorophyll contents do not exceed 5 mg m-3 except in November and August (more than 19 mg m-3). The highest Chlorophyll content is in the summer and autumn. At the mouth of the Reguibet Oued, Chlorophyll content is lower than 5 mg.m-3 and increases
from November to June. From July to October it ranges between 6 and 12 mg m-3.

Suspended matter (MES): The maximum contents of MES (close relations of 140 mg l-1) are 5
found in December, in the channel and in the centre. However, values over 70 mg l-1 can be found in the mouth of Oued El Mellah and Belaroug in November, December and August.
Bacteriological quality of the medium: A weak concentration of germs in the lagoon water would be the result of a weak bacteriological pollution or a strong capacity of self-purification of this water, owing to the fact that it maintains the exchanges with the sea by means of the channel.
Geomorphology of the site: On the geological level, the site is made of sand and of laguno marine clay of the Neopleistocene, results from the slope of silician deposits followed by successive depressions. With the old Neopleistocene, the sea penetrated largely in the depression of the Mellah.
The side located below the outfall of the lagoon consists of molasses calcareous navy and dunaire. The tertiary formations are represented by elements of the average Eocene (clays of numidie) and elements of the Miocene.
The soil pH is slightly acidic, the profiles are dominated by sand associates to coarse silts or clays, sometimes also with fine silts. Coarse sands are represented very little on the level of the profiles. In a general way, texture is sandy to sandy-muddy.