The diversity and abundance of benthic macro-invertebrates along Namanve stream, Kampala industrial and business park- Namanve

Abstract

Increasing urban development has taken a toll on the fresh water ecosystems in their proximity, thus contributing to their deterioration, destruction and loss. However, biomonitoring of fresh water sources and ecosystems is vital for informing their management approaches to ensure their sustainability and provision of cleaner and healthier water. Namanve stream like other urban streams is negatively affected by pollution from human activities, like industrialization, sewage disposal, and road construction. This study therefore investigated: a) the diversity and abundance of the benthic macro-invertebrates; b) the variation of water physico-chemistry (pH, temperature, dissolved oxygen, turbidity, water flow velocity, stream dimensions (depth and width), nutrients (Total Phosphorus and Total Nitrogen) along Namanve stream; c) the effects of the water physico-chemical parameters on the benthic macro-invertebrates. Five sites i.e., A-E, were sampled for benthic macro-invertebrates and physico-chemical parameters in triplicates, while observing the human activities associated with the sites. The stream physical attributes and physico-chemical parameters varied significantly in all sites (p < 0.05), for example stream depth and width increased downstream i.e., (0.5 ± 0.0 to 1.4 ± 0.0 m) and (2.3 ± 0.0 to 12.0 ± 0.0 m), respectively. Dissolved oxygen decreased downstream with the highest being (3.85 ± 0.4 mg/L), pH decreased downstream (7.5 ± 0.0-6.4 ± 0.1), as well as temperature with the highest being (27.1 ± 0.0 °C) and the lowest being (24.2 ± 0.9 °C). Ten macro-invertebrate orders were identified, where the Diptera were dominant and widely distributed compared to the Ephemeroptera. Species belonging to Ephemeroptera are sensitive to low dissolved oxygen levels and this was evident by their absence at sites D and E (downstream) where low oxygen levels were observed. Increased turbidity levels at the same sites, as well contributed to absence of sensitive benthic macro-invertebrates due to presence of organic matter that uses up oxygen during its decomposition. This study therefore recommends strengthening and implementation of the environmental policies, for example leaving natural vegetation buffer (stretch) from the streams and rivers to ensure that wastes are not directly deposited in to the water, as well as setting up waste recycling plants and points prior to setting up physical infrastructure like industries.