DISTRIBUTION AND SPECIATION OF PHOSPHORUS IN SEDIMENTS OF OVIA RIVER IN BENIN-CITY NIGERIA

ABSTRACT

The distribution and speciation of phosphorus in sediments of Ovia River in Benin City, Nigeria were investigated by analysing sediment and water samples collected during a study period of three months (November 2021 – January 2022). The overlying water's phosphorus concentration, temperature, and pH were measured using standard methods. Extraction for the different species of phosphorus was carried out using the modified William’s protocol adopted by the Standards, Measurements, and Testing Programme (SMT) of the European Commission, and the analysis was done with a UV-Vis spectrophotometer. The pH values obtained were mostly within the limit of 6.5 – 8.5 recommended by the National Environmental Standards Regulations Enforcement Agency (NESREA), except for the values obtained for S1 (6.20) and S3 (8.51) in November, and S1 (5.21) in December. The temperature of the water with a range of 20 – 33 °C was observed to decrease with a corresponding increase in phosphorus content in water (water-P) across the study period from November to January. This was attributed to the harmattan or dry season in Nigeria. The concentration values of water-P with a range of 64 - 281 µg/L were observed to be below 3.5 mg/L (3500 μg/L) which is the recommended permissible limit for phosphorus in domestic water by NESREA. Results showed that the concentrations of total phosphorus (TP) in sediments were from 377 – 2811 µg/g. The concentrations of TP and the different forms of phosphorus varied across the study period in the sediments, displaying an increasing trend from November to January. The monitoring and maintenance of phosphorus levels in water bodies are important in the mitigation of eutrophication of water bodies.