Seasonal Variation in Water Quality of Orle River Basin, South West, Nigeria

Abstract

The seasonal variation of water quality of Orle River and its tributatries in S.W. Nigeria was investigated forthnightly or two weekly interval for eight months from November 1987 to June 1988. A total number of 336 observations were taken in six study sites within the drainage basin. The rivers drain both basement complex and sedimentary rocks. This geological background and the anthropogenic nature of the environment are sufficient indication of pollutional stress on the rivers. The study reveal that the chemical indices of pollution such as Biochemical Oxygen Demand (BOD₅), and Dissolved Oxygen (DO) vary significantly between the seasons. Likewise, Biochemical Oxygen Demand (BOD₅), Dussolved Oxygen (DO) and Chemical Oxygen Demand (COD) show increase in the wet season and decrease in the dry season. On the other hand total hardness show increase in the dry season and decrease in the wet season. The rivers are considered to be more polluted in the wet season than in the dry season. Surface water quality has many effects on human use of water resources, water being a basic natural resource required by all human being and the modern technological society.

Keywords: water quality; river basin; wet and dry seasons; pollution