Impact of Pollution on Aquatic Macroinvertebrate Abundance in the Okulu River Eleme, Rivers State, Nigeria

The Okulu River which flows from Oyigbo down to Eleme and empties into the mangrove swamp of Okrika in the Southern part of Rivers State is strategic and plays a significant role to the aquatic needs of the people in the state and its environs. However, the information on the quality of the river is scanty hence it became imperative to study the impact of pollution on aquatic macro invertebrate abundance in the Okulu River Eleme, Rivers State. Water and macro invertebrates were sampled at different stations along the river. Macro invertebrates were sampled using a modified Surber-type sampler, while water was sampled for physico-chemical parameters such as Electrical Conductivity (EC), Salinity, Dissolved Oxygen (DO), Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD), Total Dissolved Solid (TDS), Nitrate (NO3), Phosphate (PO4), Sulphate (SO4), Zinc (Zn), Lead (Pb), Cadmium (Cd) and Chromium (Cr). The Water Quality Index (WQI) was determined using Brown’s method. The findings revealed that the water quality of the Okulu River was unfit for domestic activities. Mean value of Temperature (27.25), Salinity (59.30), conductivity (769.47), pH (7.11), DO (6.36), COD (32.39), BOD (4.65), Zn (0.097), Pb (0.225), Cd (0.017), NO3 (0.49), SO4 (350) and PO4 (0.055) correlated with abundance of macro invertebrates. Macro invertebrate abundance across the different stations were in the order of S1 (3400)>S2 (2425)>S4 (1850)>S3 (1550). Dominance of macro invertebrates followed the order; Arthropoda (82.11%) > Mollusca (10.29%) > Annelida (7.5%). Specific parameters used for calculating the WQI such as EC, TDS and SO4 exceeded the WHO acceptable limit. It is therefore recommended that regulatory agencies should continue to enforce environmental standards on industries and other stakeholders whose activities may have an environmental impact on the aquatic ecosystem.