THE ASSESSMENT OF THE SEDIMENT QUALITY OF THE BENIN RIVER STRETCH: AN INDEX ANALYSIS APPROACH

Sediment is an integral part of the aquatic ecosystem that acts as contamination sink and a home to bottom dwellers. The need to evaluate the contamination status before the seaport development using different pollution indices prompted this study. Four stations were studied from Ajoki to opposite Young Town. Sediment samples from the van-veen grab were analyzed using standard laboratory procedures, quality assurance and quality control measures. The results showed the sediment to be slightly acidic. The mean concentrations of all physicochemical parameters except organic carbon and organic matter differed significantly (P< 0.01) across the stations. A posteriori Duncan Multiple Range test revealed that station 4 differed significantly from other stations while among heavy metals, Cadmium, Nickel and Vanadium showed significant variations (P<0.05) caused by station 2. Cadmium and copper were above DPR (Department of Petroleum Resources) intervention limit. The high sorption capacity (KD>6kg/l) implied low mobility of heavy metals in the water with Fe and Ni being the least and highest adsorbed metal respectively. The heavy metal contamination in the sediment was evaluated by applying the Enrichment Factor (EF), Contamination Factor (CF), Geo-accumulation Index (Igeo) and potential ecological risk index (PERI). Contamination factor ranged from moderate contamination (Cadmium) to very high contamination (Vanadium) showing anthropogenic sources (EF>1). Potential ecological index showed that sediment was severely impacted (RI≥600=Severe). This stretch of the Benin River sediment is contaminated with cadmium and vanadium from anthropogenic sources. Continuous monitoring of this sediment stretch during the Seaport development activities and operational stage is paramount to prevent further degradation.