Water quality index: Application in the Warri River, Nigeria

The seasonal variations in the water quality indices of dissolved oxygen, biological oxygen demand (BOD), turbidity, total solids, nitrates, phosphates, hydrogen-ion concentration (pH), temperature and faecal coliforms of the Warri River at five sampling points were investigated from July 1981 to July 1982.

With respect to nitrate and phosphate levels, the waters are oligotrophic and therefore excellent throughout the period of investigation. Water quality indices for hydrogen-ion concentration (pH) and temperature also showed that the waters were medium to good from month to month. However, water quality indices for dissolved oxygen, turbidity and total solids revealed a seasonal effect on these parameters, although the waters were generally medium to good. With respect to faecal coliforms, however, there was a longitudinal gradient whereby the waters deteriorated from Udu Bridge (near the source) to Warri, where they are very polluted as a result of indiscriminate disposal of human wastes into the river.

The application of the weighted mean index to all nine parameters showed the Warri River waters to be medium to good. The immediate source of pollution in the Warri River is sewage, rather than industrial.