Sediment composition and metal concentrations in mangrove leaves from the Saudi coast of the Arabian Gulf

Abstract

Samples of sediment and mangrove leaves were collected from Tarut Bay and Gurmah Island on the Saudi coast of the Arabian Gulf. The sediment and mangrove leaf samples were wet-digested. Concentrations of 20 elements were determined in the aliquot samples of sediment and leaves using an inductively coupled argon plasma analyzer. Inter-station differences in metal concentrations in the sediment samples were significant ( P < 0.05). Sediment samples from Gurmah Island contained relatively higher concentrations of Cd, Co, Cr, Ni, V, Mn and Ti than those found in the samples collected from Tarut Bay. Concentrations of Ba, Cu, Pb and Zn in the sediments from both areas (Gurman Island and Tarut Bay) were comparable. Phosphorus was higher in the samples from Tarut Bay compared with those collected from Gurmah Island. Concentrations of Cu, Zn and P were probably influenced by agricultural drainage from the Qateef Oasis and discharges of municipal wasterwater into Tarut Bay. Inter-station differences in metal concentrations in the mangrove leaves were also significant ( P < 0.05). Correlation analyses of the analytical data revealed that, except for Mn ( r = 0.36) and Ni ( r = 0.31), no metal in the sediment was significantly ( P < 0.05) associated with its respective concentration in the leaves. The fixation of metals as non-bioavailable forms in the sediments or the physiological adaptation of mangrove plants to avoid metal accumulation may be responsible for the above lack of correlation. The results of this study suggest that nitric acid extractable fraction of metals was a poor indicator of metal bioavailability to mangroves in the Arabian Gulf.