Abundance and Distribution of Benthic Macroinvertebrates and Plankton in the Okulu Aleto River, Eleme, Rivers State, Nigeria

Abstract

Freshwater ecosystems in the Niger Delta region are increasingly threatened by industrial pollution, which can disrupt aquatic biodiversity and ecosystem functions. This study aimed to assess the abundance and distribution of benthic macroinvertebrates and plankton in the Okulu Aleto River, Eleme, Rivers State, Nigeria, to evaluate the ecological impacts of varying pollution levels. Using an experimental research design, samples were collected from six strategically selected locations including: upstream, midstream, downstream, effluent discharge site, and two control sites, representing a gradient of anthropogenic influence. Stratified random sampling was employed to ensure representative spatial coverage. Key results showed a complete absence of plankton and benthic macroinvertebrates in the effluentimpacted site, while control sites recorded the highest taxa richness (up to six taxa) and organism counts (up to 18 individuals). Diversity indices, including Shannon’s index and Simpson’s diversity, were highest at control and composite stations (Shannon’s H up to 1.61, Simpson’s 1-D up to 0.82) and lowest downstream and at effluent sites, indicating reduced ecological health in polluted areas. Elevated physicochemical parameters such as electrical conductivity (up to 17,070 µS/cm) and biochemical oxygen demand correlated with diminished biodiversity. The findings conclude that industrial effluents significantly degrade aquatic biodiversity and water quality, emphasizing the need for continuous monitoring and pollution control to protect riverine ecosystems in the Niger Delta.