Environmental conditions of two Red Sea coastal lagoons in Jeddah : 1. Hydrochemistry

Abstract EN

Arbaeen (AR) and Reayat Alshabab (RA) are two shallow lagoons in Jeddah lying on the Red Sea coast.

Salinity.

dissolved oxygen.

hydrogen sulphide (H2S) and Secchi transparency depth as well as bott om topography of the two lagoons are studied .

The results reveal that each lagoon is a fjord like estuary hosting a dammed hypolimnitic anoxia and hypersaline water behind the sill s covered by a surface brackish water.

This water.

augmented by entrained water.

is freely Ilowing outside the lagoon and is compensated by a countercurrent of Red Sea water at mid depth (2 rn).

The brackish water is a seawater mixed with non-saline water discharged from Jeddah sewage treatment plants.

Periodic inllow of Red Sea waters into the lagoons frequently occurs but it is not sufficient to repla ce all the old.

dense and euxinic resident waters and (0 stop the evasion of malodorous H2S-gas , source of people complaint.

The last problem can be panially solved (as short-term solution) by the application of artificial aerations of 'the hypersaline water layers.