SEASONAL ASSESSMENT OF WATER QUALITY OF RIVER OSUN USING WATER QUALITY INDEX

Abstract

This paper considered Fourteen (14) water parameters for the Osun river quality assessment and water quality index (WQI) tool to classify it and to see if it required treatment before usage. Samples from three different points were collected in November, 2022, April and July 2023 representing dry and wet seasons, respectively, and in accordance with American Public Health Association, APHA (Publications on standard methods for the examination of water and wastewater, pp 123–189, 2005) standard procedures. Most of the parameters were within maximum permissible limits of the World Health Organization (WHO), Food and Agriculture Organization (FAO) and Nigeria Standards for Agricultural use water with the exception of total dissolved solid, turbidity, electrical conductivity and total coliform in both seasons. The water quality of the river is generally poor with exception at a few sampling stations during the dry season. The average pH values were found to be within the permissible limit and fall within the standard expected. In this study, EC (in μS/cm) values varied from 115 to 232 μS/cm with a mean value of 156.44 μS/cm in the dry season and varied from 228 to 367μS/cm with a mean value of 281.5556 μS/cm in the wet season. EC values of all the water samples recorded are below 750 μS/cm, which is in compliance with both WHO value and FAO regulation and thus indicate good quality of irrigation water. The box and whisker plots of the water revealed that pH, acidity, EC, TA, Ca, Mg, Cl, carbonates, phosphates and nitrates have almost the same trend. These parameters do not vary significantly along the sampling stations at different sampling locations within the study area. The magnesium hazard values of all the samples during the sampling periods have values below the permissible limit and, therefore, considered suitable for irrigation purpose. Overall, the water of Osun River is good for industrial and agricultural purposes.