Quality Assessment of Deposited Surface Sediment in Badagry Creek Ecosystem, Southwest Nigeria

Abstract

Aims: Sediment quality of Badagry creek under diffuse sources of suspected contamination was assessed for ecosystem health, using their particles sizes, organic carbon and metal distribution characterization. Study Design:  Stratified random sampling. Place and Duration of Study: Three (3) sampling stations were established in upper, middle and lower zones of Badagry creek, Nigeria and sampled bi-monthly from November, 2011 to September, 2013 between the hours of 9.00 am and 12.00 noon. Methodology: Sediment samples were collected using a Van-Veen grab in the selected study stations and conveyed to the laboratory for preparation, digestion and analysis using standard methods. Samples were analysed using different mesh sizes sieves, titration method and Atomic Absorption Spectrophotometer for particle size, organic carbon and metals, respectively. Sediment quality guidelines for marine and estuarine sediments and metals sediment quality criteria for marine sediments from Romanian national waters were used in describing the possible contamination levels of elements. Results: Sand dominated the sediment particle sizes. The mean values for the upper, middle and lower zones respectively were 2.72, 2.20 and 2.93% for organic carbon, 5185.30, 4097.10 and 4475.50 mg/kg for Fe, 10.63, 6.94 and 7.26 mg/kg for Cu, 39.47, 35.16 and 33.7 9 mg/kg for Pb, 27.47, 6.45 and 6.45 mg/kg for Zn, 116.37, 96.31 and 96.31 mg/kg for Cr and 0.02, 0.08 and 0.32 mg/kg for Cd. Seasonal variations were organic carbon 2.45 ± 0.91%; 2.78 ± 0.83%, Fe 4406.76 ± 676.64 mg/kg; 3182.99 ± 1736.65 mg/kg, Cu 8.40 ± 4.13 mg/kg; 8.16 ± 4.04 mg/kg, Pb 29.29 ± 16.78 mg/kg, Zn 29.35 ± 12.09 mg/kg; 12.22 ± 3.79 mg/kg, Cr 92.29 ± 89.64 mg/kg; 109.35 ± 77.84 mg/kg and Cd 0.09 ± 0.09 mg/kg; 0.01 ± 0.09 mg/kg for dry and wet seasons, respectively.  Significant differences (P < 0.05) were observed in silt and Zn among zones and seasons. While sand and Fe differed significantly among zones, Pb and Cd differed significantly between seasons. The metals mean concentrations decreased in the order; Fe>Cr>Pb>Zn>Cu>Cd, and except for Cr and Pb, were below their corresponding effect range level (ERL) values in the sediment quality guidelines, indicating toxic effect on aquatic organisms will rarely occur from these metals. Conclusion: Cr and Pb could possibly have adverse effects on aquatic organisms in the study area. Regular sediment quality monitoring is recommended.