Assessment of River Kaduna Self-Purification Efficiency Under Different Hydrological Conditions

Abstract

This study evaluates the self-purification efficiency of River Kaduna, Nigeria, under varying hydrological conditions, focusing on the impact of seasonal flow regimes on water quality and pollutant attenuation. The research aimed to assess the river's natural capacity to mitigate pollution through processes such as dilution, sedimentation, and biodegradation, while identifying key pollution sources. Water samples from seven locations along an 11 km urban stretch were analyzed for physico-chemical, biological, and heavy metal parameters during both dry (March- April) and wet (August-September) seasons. Results indicate partial self-purification, with net pollutant increases downstream due to overwhelming anthropogenic inputs. Industrial discharges were identified as the primary pollution source (60-70%), followed by agricultural runoff (20- 30%) and domestic sewage (10-20%). Pollutant removal efficiencies were largely negative, with BOD increasing by up to 450% in dry seasons and DO depleting by 75%. Statistical analysis confirmed that wet seasons enhance purification efficiency by 20-40% through dilution and dispersion. However, critical thresholds were frequently exceeded, underscoring the river's limited assimilative capacity and the urgent need for integrated pollution control measures.

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