Effect of human activities on the benthic macro-invertebrates assemblages in Nsooba stream, Lubigi catchment, Kampala

Abstract

Nsooba stream is threatened by unregulated human activities and major development projects which raises the nutrient loading concern to Lubigi wetland, a major filter of wastewater and flood control for various parts of Kampala City. Six sites were sampled along the stream for water quality, hydro-morphological, near-catchment activities, and benthic macro-invertebrate, twice in a period of one month (January 2019). Results indicated that water temperature and BOD significantly increased along the stream while dissolved oxygen reduced along the stream. Meanwhile, pH remained within the natural ranges along the stream. The stream depth and flow rate gently reduced along the stream, except for sites D and B which had a greater stream depth and flow rate respectively. The distribution of benthic macro-invertebrates varied with the water quality and near catchment activities along Nsooba stream. Only 2 families occurred at sites D and E which were mainly characterized by open area and large settlement respectively. The highest (15) families were recorded at site B followed by A, E, and D with families 8, 8, and 6 respectively corresponding to minimal settlements and well-developed natural grasses. Naididae and Chironomidae were the most abundant families at almost all the sites. Temperature and dissolved oxygen had a significant negative influence on the distribution of Culicidae, Coenagrionidae, Hydropsychidae and Thiaridae, Physidae, Ceratopogonidae, and Hirudinea. Depth had a positive significant influence on the distribution of Ceratapogonidae, Culicidae, Hyalellidae, Physidae, and Hirudinea respectively. Meanwhile, negatively affecting the distribution of Gomphidae. Generally, the current study revealed that unregulated human activities and development projects in the near catchment significantly affect stream health. The study recommends enforcing minimal distance from the stream channel to maintain vegetation development. The study also recommends the establishment of constructed wetlands to reduce wastes accumulation and filter the run-off into the stream.