EVALUATION OF SEDIMENT QUALITY OF OGBA RIVER, BENIN CITY

ABSTRACT

River sediments are potential sources of heavy metal pollution in aquatic environment globally. The physico-chemical parameters and some trace metal contents of Ogba River in Benin City, Nigeria were investigated seasonally in August and September, 2021 and January 2022. Four stations were studied from upstream to downstream using standard methods. A total of 10 physico-chemical characteristics and trace metal were examined. The sediment samples were collected from four different stations using flat hand shovel and Vanveen grab sampler. The results reveal that only copper varied significantly (p < 0.05) across the sampled stations. Seasonal variability of sediment physico-chemical characteristics shows that 5 parameters differ significantly (p<0.001) between the dry and wet season. Of all the 5 heavymetals analysed, only copper (Cu) with mean concentration of 29.43mg/kg is slightly above the United State Environmental Protection Agency sediment quality guideline (moderately polluted). Furthermore, Cu levels (21.59 – 36.72 mg/kg) across the stations exceeded the PEL guideline. Sediment physico-chemical parameters namely, nitrate, cadmium, chromium, lead and zinc correlate with one another. Contamination factor (CF) and contamination degree across the stations indicate low degree of contamination across the stations. The pollution load index values were below 1, suggestive of no pollution across the sites. The Geoaccumulation index (Igeo) showed no pollution with respect to all the heavy metals across the sites. As anthropogenic activities continue to increase in Ogba River catchment, sustainable approach must be adopted to reduce the potential ecological risk of metal pollution in the river sediment.