Description précise du biotope B3, Al Arbaeen Lagoon, [i]Aphanius dispar[/i] a été observé sur toute la périphérie de l'"Inner sub-bassin" :
Al-Arbaeen Lagoon is a shallow (average depth about 4 m), tropical, anoxic, semienclosed
basin. It is situated on the Red Sea coast of Jeddah, Saudi Arabia. It is surrounded
by residential areas and is connected to the Red Sea through a mouth at its
northwestern end. The lagoon is characterized by a two-layer estuarine circulation system,
with restricted sub-surface sea water inflow and surface lagoon water outflow. The
lagoon basin is divided into three sub-basins (inner, middle, and outer) due to the construction
of concrete basements for two bridges cross the lagoon (Fig. 1). These structures act as sills
and therefore limit water exchange with the open sea to the upper 2 m
surface layer. The inner and middle sub-basins host stagnant water mass at greater
depths (greater than 2 m) until flushed completely or partially during particular hydrographic
events (El-Rayis et al., 1989). The lagoon is used as a dumping site for sewage
and wastewaters, mainly of domestic origin, discharged from Jeddah sewage treatment
plants. The limited circulation and the dumping of organic-rich wastes participate in
creation of anoxic conditions within the lagoon system. Under these conditions the water
body and sediments are enriched in organic matter, nutrient salts, heavy metals, and
hydrogen sulphide compared with the adjacent oxic Red Sea water (El-Rayis et al.,
1989; El-Rayis, 1990).
The input of anthropogenic waste into the relatively deep inner sub-basin (depth
range 2-8 m, average 4 m) far from communication with the sea, became inactive in October,
1990 (Ghazali, 1993). However, anoxia is still the main feature of the sub-basin.
On the other hand, wastewater is still discharged into the middle sub-basin (depth range
2-5 m, average 3 m), (El-Rayis et al., 1989; El-Rayis, 1990; Ghazali, 1993). Despite the
dilution by a limited influx of oxic Red Sea water into this sub-basin, high organic matter
input and hydrogen sulphide produced as a result of anaerobic oxidation of organic
matter are sufficient to maintain the anoxic environment (El-Rayis et al., 1989; El-
Rayis, 1990). In the outer sub-basin, the surface water flowing out as a top 2 m depth
surface layer mixes with materials discharged from a fish market and with the oxic Red
Sea water. Generally, this area is shallow (depth range 2-5 m, average 4 m) and relatively
sheltered and the texture of sediment, organic carbon content, and colour indicate
prevailing reducing conditions.
http://www.kau.edu.sa/Files/320/Researches/51280_21470.pdf