Spatial scale matters: broader landscape patterns better predict water quality in an Afro-tropical river system

We investigated how landscape patterns influence water quality across the Lower Niger River Basin, Nigeria, using multi-scale spatial analysis, contributing to Sustainable Development Goal 6 (Clean Water and Sanitation). Land use composition and configuration metrics were quantified within 5 km and 10 km buffer zones, and their effects on water quality were examined using stepwise multiple linear regression. Results showed that cropland fragmentation was the most significant driver of water quality degradation, strongly associated with elevated biochemical oxygen demand (BOD) and nitrite concentrations, particularly at the 10 km scale, indicating cumulative watershed effects. Urban-related metrics exhibited localized impacts, with built-up patch density influencing total dissolved solids (TDS) and BOD at the 5 km scale. Forest cover was generally linked to improved water quality, although fragmentation reduced its buffering capacity. Overall, configuration metrics outperformed composition metrics in explaining water quality variation, highlighting the importance of spatial arrangement in addition to land cover extent. These findings demonstrate that landscape fragmentation from agriculture and urban expansion exerts strong, scale-dependent effects on water quality. Integrating landscape configuration into watershed management can support evidence-based strategies for improving water quality and achieving SDG 6 in rapidly changing Afro-tropical river systems.