Effects of Land-Use Patterns and Land Cover Change on Freshwater Quality in the Guma Dam Catchment in Freetown, Sierra Leone

Abstract

Rapid land-use and land-cover (LULC) change poses significant threats to freshwater resources, particularly in rapidly urbanizing catchments in Sub-Saharan Africa. This study assessed the effects of LULC dynamics on freshwater quality in the Guma (Mile-13) Dam catchment, Freetown, Sierra Leone, between 2004 and 2023. Landsat 7 ETM+ and Landsat 8 OLI imagery from 2004, 2013, and 2023 were analyzed using post-classification change detection to quantify transitions among vegetation, agriculture, settlements, bare land, and water bodies. Water quality was evaluated through monthly sampling at upstream, midstream, and downstream locations from January to June 2023, covering key physicochemical and microbial parameters. To quantitatively link land-use change and water quality, normalized land-use pressure indices were developed, and Pearson correlation analysis was applied. Results indicate substantial urban expansion within the catchment, with vegetation-to-settlement conversion increasing by 39.40 km2 and total settlement gain reaching 55.47 km2 between 2013 and 2023. Water quality parameters were generally within World Health Organization (WHO) guideline limits for physicochemical variables; however, elevated turbidity (up to 5.0 NTU), episodic increases in nitrate and phosphate concentrations, and persistent detection of Escherichia coli indicate pollution risks. Pearson correlation analysis revealed strong positive relationships between settlement expansion and turbidity (r = 0.91), phosphate (r = 0.75), and nitrate (r = 0.59), while vegetation cover showed an inverse relationship with water quality degradation. These findings demonstrate that rapid urban expansion and vegetation loss are key drivers of declining water quality in the Guma Dam catchment. The study underscores the need for integrated land-use planning, protection of vegetated buffers, sustainable urban development, and continuous water-quality monitoring to safeguard Freetown’s primary water supply.