Geochemical background for the Saudi Red Sea coastal systems and its implication for future environmental monitoring and assessment

The present study aims at determining a geochemical background for the Red Sea to be a base for future environmental studies along the Saudi Red Sea coastal systems. Eighty-nine bottom sediment samples were collected from three coastal lagoons; Sharm Al-Kharar (47 samples) at the northern terminal of Wadi Rabigh, Al-Shuaiba Lagoon (22 samples) a fossil lagoon about 80 km south of Jeddah and Al-Mejarma Lagoon (20 samples) a back-barrier lagoon about 40 km south of Al-Shuaiba. The mud fraction (<0.063 mm) was analysed to determine the concentrations of Al, Fe, Mn, V, Cr, Ni, Cu and Zn. The sediments of Sharm Al-Kharar yielded higher elemental concentrations than the other two lagoons. Aluminium (Al) displays significant correlation (r > 0.8) with Fe, Mn, V, Cr, Ni and Zn indicating that these elements are closely associated with the detrital influx. The geochemical background was determined after eliminating the outlier values using the equation median ± 2MAD (median absolute deviation) and then calculated descriptive statistics. Minimum values define lower limit of the background, the 98 percentiles define the upper limit and the geometric rather than arithmetic mean was used to define the average value. The calculation of environmental assessment indices using upper continental crust or average shale as background yields low values compared to the values calculated using estimated mean in the present study.