Distribution and Geochemistry of Trace Elements in Central Red Sea Coastal Sediments

Abstract

Fifty-one surficial sediment samples were collected from 21 stations situated in the nearshore area of the central Red Sea. Sediments were analysed for the major elements Ca, Mg, Al and Fe and the trace elements Mn, Cu, Zn, Ni, Cr, Co, Cd and Pb. The major grain-size classes gravel, sand and mud as well as organic carbon and carbonates were determined. Some samples were subjected to X-ray mineralogy. Sediments were generally coarse-grained but the fine fraction increased in the sheltered areas. The major mineralogical constituents of the sediments were carbonate minerals (calcite and aragonite) and detrital silicates (quartz and feldspars). Organic carbon was low (0.38%) in the northern part of the area but greatly increased in areas receiving direct sewage discharge (1-9.5%). Concentrations of trace elements were highly variable and appeared to be related to the grain size and the mineralogical composition. Generally, trace element concentrations were positively correlated with the mud and Al and Fe contents. In the polluted sites these regular associations were perturbed and trace elements were associated with organic matter. Element/Al ratios were used to group the sampling sites according to their degree of enrichment. The resulting order was different from that based on the absolute concentrations. The use of a combination of the element/Al ratio and the absolute concentration resulted in the distinction of highly and moderately contaminated and uncontaminated sites.