The intensity of human-induced impacts on the distribution and diversity of macroinvertebrates and water quality of Gbako River, North Central, Nigeria

Abstract

The intensity of human-induced impacts on the distribution and diversity of macroinvertebrates and water quality of Gbako River, North Central, Nigeria, was evaluated monthly for 6 months using modified kick sampling techniques. Four study stations were selected along the river course (upper reaches of less human impacts through mid-reaches with relative high human impacts to lower reaches of less human impacts), designated as Stations 1, 2, 3, and 4. Water temperature (23.10–30.00 °C), flow velocity (0.10–2.40 m/s), pH, conductivity (32.00–110.00 µS/cm), and alkalinity (7.50–10.50 mg/L) were similar in all the stations sampled. However, BOD (2.20–6.00 mg/L) and nitrates (0.50–1.67 mg/L) were significantly higher (p < 0.05) in Station 3. A total of 676 individuals from 41 invertebrate taxa in 27 families from nine orders were collected from the four stations during the study. Aquatic insects represented 85.4 % of the taxa and 76.6 % of all individuals collected. The rest of the fauna was composed of Mollusca, Crustacea, and Gastropoda. Ten macroinvertebrate taxa, Philaccolus, Pseudocloeon, Bugilliesia, Calopteryx, Coenagrion, Brachythemis leucostica, Gomphus, Hydrometra, Sphaerudx, and Potadoma species, were found in all the four sampled stations. The overall abundance of benthic invertebrates was not significantly different (P > 0.05) among the sampling stations. Stations 2 and 3 with higher human disturbance recorded lower richness when compared with the less disturbed stations (1 and 4). Furthermore, the marginally high nutrient levels (phosphate and nitrate) obtained at these stations are an indication that the water body is becoming stressed with organic input and increasing levels of anthropogenic activities. The CCA ordination revealed strong relationships between species abundances and measured environmental variables. The low relative abundance of Ephemeroptera–Plecoptera–Tricoptera (EPT) taxa indicated that the environmental conditions were relatively stressed, along the whole stations. However, the abundance of mayflies (Ephemeroptera), Coleoptera (Gyrinus, Dytiscus), and Anisoptera in all the sites studied is an indication that the sites are relatively free from gross pollution, especially at the upper reaches. Overall, relatively less human impacts in some of the study stations and the heterogeneous nature of the stations served as suitable habitat for a more diverse benthic fauna. This could be responsible for the high abundance (number of individuals) and diversity of benthic invertebrates that was recorded in this study. This study revealed that macroinvertebrate communities responded to changes in disturbance as well as water quality along the river stations.