Land Use Effects on Water Chemistry in Lagos Lagoon, Nigeria (West Africa)

Abstract

Understanding the effects of changes in land use patterns in the catchment area on water quality is crucial for effectively protecting aquatic resources. As transition zones between freshwater and the marine realm, Lagoon systems are especially vulnerable to anthropogenic influence due to their limited water exchange and challenging salinity regimes. To assess the environmental consequences of land use changes on water quality parameters under subtropical African conditions, 12 sites in Lagos Lagoon were sampled monthly over an entire year, covering the wet and dry seasons. The relationships between land use patterns and water quality were studied by combining seasonal water analysis results with GIS mapping based on satellite images. The results of the monthly water analysis showed a large degree of seasonality effects on almost all parameters but also some site-specific features pointing to local dominance of catchment area-related impacts. To unravel them, correlations between water parameters and land use patterns were analyzed based on a rough but robust classification. The land use forms were divided into five categories: waterbody, bare land, forest, urban area, and wetland. Independent of the restricted range of land use pattern variability covered by this study, several significant correlations between land use form and water quality parameters were found. Most of them are exclusively restricted to either the wet or dry season. Consistent season-independent significant correlations were found between the percentage of urban area and dissolved oxygen concentration. For wetlands, such consistent and significant correlations were found with nitrate, chemical oxygen demand, and turbidity. The findings provide first insights into the impact of land use changes on lagoon water quality under subtropical biodiversity of these systems and aquatic resources in general.