ABSTRACT

 Aquatic macroinvertebrates can be used to monitor aquatic environments because they are in constant contact with the surrounding aquatic environment. They are useful for such task due to their visibility to the naked eyes, ease of identification, rapid life cycle, and position in the food chain. Macroinvertebrate fauna of Ossah River in Ossah Ibeku, Umuahia, Nigeria was studied in 3 stations to evaluate the composition, abundance and distribution in relation to the environmental conditions and anthropogenic impacts. Macroinvertebrate fauna was sampled between January and June 2018 using the modified kick sampling method and disturbing aquatic macrophytes against the current with a sweep net. A total of 119 macroinvertebrate individuals comprising of ten (10) taxonomic groups and twenty (20) taxa was recorded. Percentage composition of taxa showed that n on-biting mid ge, chironomid had the hi ghest abundance (39.5%) followed by May fly nymph, (Cleon sp) 16% and Backswimmer, Notenecta spp. (7.6%) while the least were leech (Hirudo medicinalis), scud (Gummarus pulex), horsefly larvae (Tabunus sp.) water scorpion (Ranatara linearis) and water strider (Gerris sp. ),which contributed 0.8%. For spatial distribution, station 2 recorded the highest number of individuals (57) followed by station3, (37individual) and the least is station | (25individuals) . Diversity assessment recorded higher Shannon wiener diversity index (H) in station 2 (2.968) than in station 1 and 3 . Margalef species richness was higher in station 2 (2.968) followed by station 3 (2.769) and the least in station 1 (2.796). Evenness index was higher in station 1 (0.6843) followed by station 3 (0.5491) and the least was in station 2 (0.4285). The diversity indices which were a reflection of the species composition, abundance and distribution were equally high. Most of the pollution indicators were witnessed more in stations 1 and 2, which felt most anthropogenic impacts including effluents.