Impact of Urban Effluents on the Macroinvertebrates of a Creek in Accra, Ghana

Abstract

The impact of effluents on the macroinvertebrate communities of an urban creek in Accra was studied. Five study stations were selected along the reaches of the creek. Water and benthic samples were collected and analyzed between September 2005 and February 2006. The study showed that the effluent discharges caused a significant increase in BOD, COD and NH3 at the stations that received the effluents. The high levels of total and faecal coliforms at the midstream sections of the creek (626.0 x 10⁴ cfu/100 ml and 75.30 x 10⁴ cfu/100 ml, respectively) indicated increased pollution levels compared to the reference stations (446.0 x 10³ cfu/100 ml and 133.0 x 10³ cfu/100 ml). The Nima Creek showed characteristics of a disturbed urban creek. A total of 19 macroinvertebrate taxa, comprising a total of 11,613 individuals, were collected. Estimated Shannon-Weiner Diversity Index (H´) was low at the midstream section of the creek, H’= 1.14, where the effluents were concentrated than at the upstream H’=1.44 or downstream H’= 1.38 sections of the creek. Chironomini and Physa were the most abundant taxa within the creek, dominated by the genus Chironomus, which is known to be tolerant to pollution, which confirmed the polluted state of the creek. Rigorous and regular assessment and monitoring of effluents from waste treatment plants and other sources that discharge into the creek, with the aim of complying with the Environmental Protection Agency (EPA) guidelines are some of the mitigative measures suggested to protect life in the creek.