Investigation of Nitrate and Phosphate Pollution in the Kaduna River from Agricultural Runoff, North West Nigeria

Intensive agricultural production in the Kaduna River basin generates nutrient-rich runoff containing nitrate and phosphate compounds that contribute to eutrophication, reduced dissolved oxygen levels, and declining aquatic biodiversity. This study investigates nitrate and phosphate concentrations in the Kaduna River at six sampling stations representing upstream reference conditions, mid-stream agricultural discharge zones, and downstream urban reaches in Kaduna State, North West Nigeria. Water samples are collected bimonthly over a twelve-month period and analysed spectrophotometrically using the cadmium reduction method for nitrate and the molybdate-ascorbic acid method for phosphate. Dissolved oxygen, pH, turbidity, and biochemical oxygen demand are measured simultaneously to provide a comprehensive picture of water quality status. Land use patterns around each sampling station are documented using satellite imagery to correlate nutrient loads with specific agricultural activities. The study applies correlation and regression analysis to assess relationships between crop cultivation seasons, fertiliser application calendars, and observed nutrient spikes. Results are expected to demonstrate peak nitrate concentrations coinciding with post-planting seasons when rainfall leaches recently applied nitrogenous fertilisers from cultivated fields. Recommendations are formulated for buffer zone establishment, fertiliser application best practices, and enhanced monitoring by the Kaduna State Environmental Protection Authority. Keywords: nitrate, phosphate, Kaduna River, agricultural runoff, eutrophication