Impact of rubber effluent discharges on the water quality and macroinvertebrate community assemblages in a forest stream in the Niger Delta.

The ecological impact of rubber effluent on macroinvertebrate communities of the Adofi River, Niger Delta area of Nigeria were evaluated for a 6 month-period as part of a study to understand pollution processes in the river that may lead to improved regulation and policy development. Three sampling stations, each 25 m long were selected along 7 km stretch of the stream. Station 1, located upstream of the outfall from the rubber processing plant, station 2, immediately downstream of the effluent discharge point and station 3, 3 km downstream were sampled monthly. The rubber effluent impacted negatively on the sediment and water chemistry by elevating the levels of some heavy metals (Ni, Pb, and Zn), chemical parameters as biochemical oxygen demand (BOD5), chemical oxygen demand (COD), conductivity and the amount of nutrients at the discharged site. A combined total of 87 macroinvertebrate taxa were recorded from the three stations of the river. The abundance and community structure showed variation between the effluent impacted site and the reference sites as most sensitive macroinvertebrate taxa were completely missing from the effluent impacted site. The preponderance of oligochaetes and some dipteran taxa associated with low dissolved oxygen levels in the impacted site bears credence to the fact that the chemical components of the rubber effluent waste water were lethal to some aquatic forms. Based on canonical correspondence analysis results, conductivity, BOD, phosphate and nitrate were strongly associated with the impacted station. At station 3, a community similar to the upstream reference station was found. Results illustrate the need for careful consideration of the water quality and indicator organisms in restoration. Mitigation procedures suggested for the rubber effluent included, for example, the decolourization of the highly coloured effluent and biodegradation prior to discharge, were recommended.