Assessment of Transboundary Pollution Dynamics in the Komadugu-Yobe River System Shared by Nigeria and Niger Republic

The Komadugu-Yobe River, draining eastward through Jigawa, Yobe, and Borno states before crossing into Niger Republic and discharging into Lake Chad, is subject to transboundary pollution from agricultural chemicals, artisanal activities, and urban effluents in both riparian countries. This study assesses transboundary pollution dynamics in the Nigerian section of the Komadugu-Yobe River system using a longitudinal water quality monitoring approach combined with pollution source attribution analysis. Water quality monitoring was conducted at twelve stations spanning 480 kilometres of the main channel and three major tributaries over two full annual hydrological cycles. Parameters measured include nutrients, heavy metals, pesticide residues, and bacteriological indicators, allowing computation of longitudinal pollutant flux profiles and seasonal loading estimates. Pollution source attribution combines land use spatial analysis, industrial register data, and stable isotope analysis of nitrate to identify agricultural, urban wastewater, and natural background contributions to observed concentration profiles. Findings indicate progressive downstream deterioration in nutrient and pesticide parameters during dry season low flows, when dilution capacity is minimal and irrigated agriculture is most intensive. At the downstream border crossing, phosphate and organophosphate pesticide concentrations exceed agreed Komadugu-Yobe Water Charter quality thresholds in 6 of 24 monitoring periods. The study provides the first systematic transboundary pollution loading assessment for this river system and informs the Lake Chad Basin Commission's water quality monitoring framework. Recommendations address harmonised monitoring standards, Nigeria-Niger bilateral pollution notification protocols, and improved agricultural chemical management upstream. Keywords: transboundary pollution, Komadugu-Yobe River, water quality, Lake Chad Basin, agricultural pollution.