Benthic Macroinvertebrates as Indicators of Water Quality and Ecological Health in a Tropical Lake, Southern Nigeria

Abstract

This study assesses the community structure and diversity of benthic macroinvertebrates in Ozomu Lake, Southern Nigeria, to evaluate the water quality and ecological health. Sampling was conducted twice monthly from March to August 2020, at three stations using bottom sediment grabs and bank-root zone sampling. A total of 23 taxa and 427 individuals were recorded. Diptera (25%) and Odonata (22%) were the most abundant, followed by Coleoptera (18%) and Ephemeroptera (12%). In terms of diversity, the stations were ranked as follows: Station 2, Station 1, and Station 3. The Shannon-Wiener index indicated that Station 2 had the highest species diversity (2.896), followed by Station 1 (2.828) and Station 3 (2.472). Pielou’s Evenness index revealed that Station 2 had the most even distribution of species (0.7871), while Station 1 had the lowest (0.6235). Pollution-sensitive taxa at station 1 comprised 40.8% of the benthic fauna (58 individuals), indicating relatively good water quality. Moderately tolerant taxa represented 28.9% (41 individuals), while pollution-tolerant taxa accounted for 30.3%. Station 2 recorded similar results for pollution-sensitive taxa at 40.3% (52 individuals). However, moderately tolerant taxa dominated this station, making up 41.1% (53 individuals), with pollution-tolerant taxa at only 18.6%, suggesting lower environmental stress. Pollution-tolerant taxa predominated at 40.4% at station 3 (65 individuals), indicating greater environmental disturbance. Moderately tolerant taxa constituted 33.5%, while pollution-sensitive taxa were reduced to 26.1%, reflecting the most stressed environment among the stations. Overall, the lake’s ecological health appears stable, but localized stressors may require targeted management.