Geochemical Evaluation of Surface Sediments in Niger Delta Mangrove, Nigeria

Abstract

Mangrove surface sediments from Choba, Ogbogoro and Isaka along the New Calabar and Bonny rivers respectively in Niger Delta, Nigeria were sampled and analyzed to evaluate their geochemical compositions, inter-element relationships and potential ecological impact. Results show that the highest mean concentrations in parts per million (ppm) of Pb, Zn, Cu, Ni, Cr, Y, Nb, Th and Sc in Choba sediments were 36.2, 65.2, 19.6, 47.4, 121.6, 21.4, 23.0, 13.8 and 16.8; As, V, Sr, Zr, TS and F in Ogbogoro sediments were 6.4, 192.3, 70.0, 273.4, 14627.0 and 104.8 while Br, I and Cl in Isaka sediments were 27.4, 41.4 and 4189.6 respectively. Box plot of the elements show contrasting concentrations in different sampling locations. Compared to the upper continental crust (UCC), As and Ni are higher in Choba, Ogbogoro and Isaka. The abundance of Pb was found to be higher in Choba and Ogbogoro. Though Th and Sc are more concentrated in Choba and Ogbogoro relative to the UCC, they were found to be lower in Isaka. However, Zn, Cu, Cr, V, Sr and Zr concentrations in the UCC were found to be higher than the mean concentrations of these elements in Choba, Ogbogoro and Isaka mangrove sediments. Most of the trace elements correlated positively and strongly with Fe₂O_3. This implies that Fe₂O₃ is important in controlling metal concentrations in the area. The concentrations of As and Zn were either equal to or below the low effect level (LEL) and interim sediment quality guideline (ISQG). Pb, Cu and Ni were found to be higher than LEL and ISQG in Choba while Cr concentrations in Choba, Ogbogoro and Isaka all exceeded the LEL, ISQG and severe effect level (SEL) values but below probable effect level (PEL) value; thus indicating potentials for moderate to severe ecological harm.

Keywords: Mangrove sediments, Geochemistry, Heavy metals, Sediment quality, Niger delta