Investigating Long-Term Trends in Surface Water Quality in the Kaduna River Basin Under Land Use Change Pressures

This study investigates long-term trends in surface water quality in the Kaduna River Basin, North West Nigeria, over a fifteen-year period, analysing how progressive land use changes including agricultural expansion, urban growth, and deforestation in the catchment have influenced water quality parameters at multiple monitoring stations. Understanding the cumulative impact of land use change on river water quality is critical for managing Nigeria's major water supply catchments, yet multi-year, multi-station trend analyses in Nigerian river basins remain rare due to data continuity limitations. Archived water quality monitoring data from the Kaduna State Water Board and the Lower Benue River Basin Development Authority were compiled for nine monitoring stations on the main river and three major tributaries for the period 2008 to 2023, with data gap-filling and quality screening applied before trend analysis. Mann-Kendall trend tests were applied to annual median values of turbidity, total dissolved solids, nitrate, total phosphorus, biochemical oxygen demand, and faecal coliform. Concurrent land cover change analysis used multi-temporal Landsat imagery to quantify agricultural expansion and forest loss in sub-catchments draining to each monitoring station. Results reveal statistically significant increasing trends in turbidity, total phosphorus, and biochemical oxygen demand at seven of nine stations, with trend magnitude correlated with the rate of forest loss in each station's contributing catchment. Faecal coliform shows increasing trends at urban-influenced stations. Nitrate increases are detected downstream of major agricultural expansion areas. The study provides evidence-based support for catchment protection policies. Keywords: water quality trends, land use change, Kaduna River, Mann-Kendall, catchment management.