Physicochemical Assessment of Surface Waters along an Urbanisation Gradient in Lagos and Epe Lagoons, Nigeria

Abstract

Rapid urbanisation and population growth in coastal cities have resulted in increased discharge of domestic waste, industrial effluents, and surface runoff into adjacent water bodies, leading to significant alterations in water quality. Assessing seasonal and spatial variations in physicochemical parameters is essential for understanding the extent of anthropogenic impacts on lagoon ecosystems. This study assessed the physicochemical characteristics of surface waters along an urbanisation gradient in the Lagos–Epe Lagoon system, Nigeria. Surface water samples were collected from three sites representing varying degrees of anthropogenic influence: Makoko (highly urbanised), Ikorodu (moderately urbanised), and Epe (less urbanised). Sampling was conducted across four seasonal cycles (March, May, August, and November) to capture dry, wet, and post-wet season conditions. Key physicochemical parameters, including pH, temperature, dissolved oxygen, total dissolved solids, and electrical conductivity, were analysed using standard methods. Results revealed clear spatial and seasonal variations across the lagoon sites. Higher pH, temperature, total dissolved solids, and electrical conductivity values were consistently recorded at Makoko and Ikorodu compared to Epe, indicating stronger anthropogenic influence in the more urbanised areas. Dissolved oxygen concentrations showed moderate seasonal variation, with generally higher values observed during the wet and post-wet seasons. Seasonal trends indicated decreasing surface water temperatures and increasing dissolved oxygen from the dry to wet seasons, while total dissolved solids and electrical conductivity increased toward the later sampling periods. Overall, the findings demonstrate that surface water quality within the Lagos–Epe Lagoon system is strongly influenced by both urbanisation intensity and seasonal hydrological conditions. Continuous monitoring and site-specific management strategies are recommended to mitigate the impacts of urban pressures and ensure the sustainability of lagoon ecosystems. This study underscores the importance of routine physicochemical monitoring as a baseline for understanding lagoon water quality dynamics and supporting effective environmental management. The results provide valuable baseline data that can inform future studies, including assessments of benthic waters and contaminant distribution within the lagoon ecosystem.