Assessment of nutrients and metals in sediments of Ogba river, Southern Nigeria

Abstract

This study assesses the concentrations of nutrients and metals in river bed sediments of Ogba River, a fourth-order river in Southern Nigeria. Most rivers in this region are exposed to untreated industrial and domestic wastewater discharge, including atmospheric deposition from crude oil exploration activities. River bed sediment samples were collected from four sites located downstream of an urban sewage discharge and agro-allied industry wastewater release point. The results showed statistically significant differences in sediment particle size distribution, nutrient and metal concentrations across the sites. The sediment particle size distribution was dominated by sand (92%), with mean pH range of between 5.1 and 6.0. Concentrations of metals and nutrients were highest in sediments of Site 2 located in close proximity to refuse dump sites and arable land use. Total organic carbon (TOC) and nitrate (NO₃^--N) were negatively correlated with sand but positively related to clay (P<0.01). No significant relationship was found between metals except for Ni and cadmium (Cd), and Fe and Ni. In addition, no significant relationship was found between TOC and metals (Fe, Zn, Cu, Cd, Pb and Ni), suggesting that in this fluvial system TOC may not be effective in the complexation of metals.

Key Words: Sediment, metals, nutrients, freshwater, Nigeria