Anthropogenic and natural factors impacting microbiological and physicochemical surface water quality along an urban tropical wetland

Abstract

Monitoring microbial water quality is essential for understanding pollution dynamics and associated public health risks, particularly in rapidly urbanizing regions of developing countries. This study assessed seasonal variations in physicochemical conditions and microbiological indicators along the Lubigi wetland, a tropical riverine system receiving stormwater and wastewater from Kampala's urban infrastructure. Over a 17-month period, water samples were collected from six sites during dry and wet seasons and analyzed for Escherichia coli, faecal coliforms, heterotrophic plate counts (HPC), Enterococcus, and Salmonella species. Results showed that nitrogen compounds and pathogenic indicators were associated with stormwater runoff, whereas phosphorus, organic matter, and HPC were linked to wastewater effluent. During the dry season, E. coli concentrations declined significantly along the wetland, while Enterococcus decreased by 58.6% during the wet season. In contrast, faecal coliforms and HPC showed limited attenuation below 20% and persisted at high concentrations across both seasons. Overall, pollutant loads from the Nsooba channel and the Lubigi sewage treatment plant exceeded the wetland's natural treatment capacity, resulting in sustained microbiological contamination and increased risks to downstream water quality and public health. These findings underscore the need for improved urban water infrastructure and source-based pollution control rather than reliance on natural attenuation alone.