Re-Evaluation of the Impact of Sewage Disposal on Coastal Sediments of the Southern Corniche, Jeddah, Saudi Arabia

The southern corniche area of Jeddah receives through Al-Kumra effluent the equivalent of 300,000 m3 of semi-treated sewage. Before 2001, the sewage was directly dumped from an outlet situatedat about 1 m above the sea surface. Since 2001, the same volume of municipal wastewater is disposed from underwater diffuser situated at about 3 km south of the old effluent. In order to study the environmental consequences of the dumping site transfer from a sheltered to an open sea area, the region was revisited and sediment samples were collected from the same stations sampled prior to the transfer of the effluent. Samples were analysed for their grain size distribution and their content of organic carbon, Al, Fe, Mn, Cu, Zn, Cr, Cd and Pb. Results were compared to those obtained in a revious study carried out in 1999. The study showed that despite the very pronounced dilutioneffect, the impact of the effluent is measurable and extends, in situ, north and south directions along the entire study area. The impact is very pronounced in the coastal area as shown by the excessivedevelopment of algal production which extends further southward and by the destruction of the mangrove stand. Sediments are becoming enriched in heavy metals where concentrations of Al, Fe, Mn, Cu, Zn and Cr are almost doubled. The present study is the first of its kind to be carried out after the effluent transfer. The authors therefore believe that the system did not yet reach a steady state and will continue to change and develop for several years.