Factors influencing heavy metal concentrations in the bottom sediments of the Al-Kharrar Lagoon and Salman Bay, eastern Red Sea coast, Saudi Arabia

Abstract

The Al-Kharrar Lagoon (KL) and Salman Bay (SB) are located on the eastern Red Sea coast, Saudi Arabia. The concentrations of heavy metals such as Fe, Mn, Zn, Cu, Ni, Pb, Co, and Cd in their bottom sediments were measured and correlated with the surface water temperature, salinity, pH and dissolved oxygen (DO), organic carbon (OC), carbonates, and sediment grain size. The highest concentration of metals in the KL is mostly attributed to influx of siliciclastics from wadies to the center and south-eastern parts of the lagoon where metals were directly correlated with salinity, pH, and mud. At the inlet stations, the metals were the lowest indicating that the KL acts as a buffer zone, preventing metals from dispersion into the Red Sea waters. But also, the enrichment factor (EF), there, for Mn, Zn, Cu, Co, and Ni, was the highest due likely to the effectiveness of biosorption by mucus algae that proliferate on coral debris and sand grains. The metals had no relationships with the OC, but with mud and Fe-Mn oxides due possibly to the presence of high DO. The brine waters of SB showed inverse relationships with the metals that ascribed probably to the occurrence of many soluble salts preventing precipitation of heavy metals into the sediments. Normalizing the heavy metals with Fe and the world average shale indicated that the bottom sediments of the KL and SB were uncontaminated and mainly influenced by natural sources.