Assessment of nutrient dynamics and eutrophication risk of urban stressors on riverine water quality :A case of rivers Auji and Kisat, Kisumu, Kenya

Urban rivers play an important role in sustaining freshwater ecosystems and supporting human livelihoods. However, in developing countries, rapid urbanization and inadequate waste management have increased pollution pressures on many river systems. This study assessed the physico-chemical water quality characteristics of rivers Kisat and Auji located in Kisumu City, Kenya. Both rivers drain into Lake Victoria and are important components of the existing urban watershed. Water samples were collected from multiple sampling sites along the two rivers and analyzed for key physico-chemical variables including temperature, pH, dissolved oxygen, turbidity, electrical conductivity, nitrite, nitrate, total nitrogen, total phosphorus, soluble reactive phosphorus, total dissolved solids, oxidation reduction potential, ammonium, hardness and alkalinity. Statistical analyses including R-Studio, independent sample t-tests and Wilcoxon rank-sum tests were used to evaluate differences in water quality between the rivers. The results revealed significant differences in several parameters. River Auji exhibited significantly higher water temperatures and electrical conductivity indicating elevated levels of dissolved pollutants. In contrast, river Kisat showed significantly higher turbidity and nutrient concentrations, particularly nitrates and nitrites suggesting sediment loading and nutrient enrichment. Dissolved oxygen concentrations were significantly lower in river Auji an indication of substantial organic pollution and high biological oxygen demand. However, no significant difference was observed in pH and total nitrogen concentrations between the two rivers. The findings demonstrate that both rivers are affected by anthropogenic pollution associated with urbanization, wastewater discharge, urban agricultural runoffs and riparian environmental degradation. The deteriorating water quality of these rivers poses potential risks to aquatic ecosystems and contributes to nutrient loading in Lake Victoria. The study highlights the need for improved urban watershed management strategies including enhanced wastewater treatment, restoration of riparian buffers and strengthened water quality monitoring programs.