Water quality and self-purification dynamics in a tropical urban river: the case of Ekulu River, Nigeria

Abstract

The Ekulu River in Enugu, Nigeria, is essential to agricultural and residential water needs. Hydraulic measurements and water quality assessments were undertaken in 2024 to determine the degree of pollution and self-purification capacity of the stream. The re-aeration coefficient (K₂) was estimated using ten empirical models, and the best model was determined using statistical methods. The average flow rate of the river was 0.742 m³ s⁻¹ and a mean velocity of 0.332 m s⁻¹. All locations have limited oxygen exchange capability as shown by the low to moderate re-aeration rates (0.059–0.203 hr⁻¹ indicative of weak re-aeration rates). The self-purification capacity values, which range from 1.386 to 1.862, show that the aquatic system under study has a moderately good natural purification capability. Biochemical Oxygen Demand (BOD) varied from 16.1 mg l⁻¹ to 64.5 mg l⁻¹, which is significantly higher than the permissible limit of 6 mg l⁻¹. Dissolved Oxygen (DO) ranged from 2.40 mg l⁻¹ to 5.40 mg l⁻¹, indicating moderate to severe oxygen deficit. pH fluctuated narrowly from 6.5 to 7.2 while staying within the permissible range of less than 8.5. Temperatures ranged from 20.2 °C to 22.0 °C. Overall, the findings point to substantial pollution, especially with regard to organic load and ionic content, which could harm aquatic health and water quality. Furthermore, the study encourages accountability, awareness and community action toward environmental conservation by disseminating the findings to stakeholders, including the public, businesses and government. Ultimately, it provides do-able tactics to enhance the river’s re-aeration potential, supporting long-term water quality control in Enugu State and elsewhere.