Evaluation of the Effect of Domestic Sewage Discharge on Macrobenthic Fauna of Kuramo Creek, Lagos

Untreated domestic sewage discharge into urban coastal creeks degrades aquatic habitats through nutrient enrichment, hypoxia, and pathogen contamination. This study evaluated the effect of domestic sewage on macrobenthic fauna in Kuramo Creek, Lagos State, South West Nigeria. Sediment samples were collected from five stations along an established sewage input gradient using an Ekman grab sampler during two seasonal surveys. Macrobenthic invertebrates were extracted using a 500-micrometer mesh sieve, identified to family level, and counted. Biotic indices including the Shannon diversity index, AMBI (AZTI Marine Biotic Index), and the Benthic Opportunistic Polychaetes and Amphipods index were applied to assess ecological status. Sediment organic content and porewater sulfide concentrations were measured. Total coliform bacteria counts were recorded at each station. A total of 29 macrobenthic families were identified across all stations. The sewage-proximate station was dominated by polychaetes of the family Capitellidae and by Tubificid oligochaetes, typical indicators of severe organic enrichment. AMBI scores classified the most impacted station as being in bad ecological status. Shannon diversity declined from 2.84 at the reference station to 0.46 at the most polluted station. Sediment organic matter and porewater sulfide levels were highest at the sewage-proximate stations. Coliform counts exceeded acceptable bathing water standards at three stations. The study recommends construction of sewage interception systems along Kuramo Creek and establishment of buffer zones to reduce direct sewage ingress. Keywords: macrobenthos, domestic sewage, Kuramo Creek, biotic index, Lagos.