Spatial Variations in the Physico-chemical Variables and Macrobenthic Invertebrate Assemblage of a Tropical River in Nigeria

TL;DR

This study examined the spatial variations in physico-chemical variables and macrobenthic invertebrate assemblages in a Nigerian tropical river, revealing high biodiversity and indications of organic pollution despite overall water quality.

Contribution

It provides new insights into the spatial distribution of physico-chemical factors and invertebrate diversity in Ethiope River, Nigeria, highlighting pollution indicators and ecological health.

Findings

Physico-chemical variables showed no significant differences across stations.

Diptera was the dominant invertebrate group, comprising over half of the abundance.

Indicators of organic contamination were identified through invertebrate assemblages.

Abstract

The spatial variation in the physico-chemical variables and macrobenthic invertebrates assemblage of a stretch of Ethiope River, Nigeria were evaluated for 6 months at five study stations. The results showed that temperature, dissolved oxygen and bicarbonates were similar across the study stations. The highest values of conductivity and total dissolved solids were recorded at station 1. The physico-chemical variables showed no significant different (P < 0.05) in the study stations. The abundance of the macrobenthic invertebrates comprises 61 taxa in 34 families, and the highest and least values occurred at stations 3 and 1 respectively. The Diptera which accounted for 52.77% of the overall abundance was the dominant group encountered, while the Decapoda (10.97%) which was prevalent in station 1 and the Ephemeroptera (8.05%) which was common in stations 2, 3 and 4 constituted the subdominant group. Over 68% of the oligochaetes recorded were restricted to station 3 except Dero limnosa and Nais sp that occurred in all the study stations. The overall abundance of the macrobenthic invertebrates was not significantly different (p < 0.05) among the study stations. Based on the canonical correspondence analyses, total dissolved solids, biochemical oxygen demand, bicarbonates and pH influenced the macrobenthic invertebrate assemblage. The study stretch of Ethiope River was reasonably free from gross pollution as indicated by the presence of Ephemeroptera, Tricoptera, Odonata and Decapoda at the study sites. However, there were indications of organic contamination as shown by the preponderance of naidid oligochaetes and certain dipteran species including the chironomids. This study revealed a high diversity of macrobenthic invertebrates, and this was attributed to the relative spatial homogeneity of the physico-chemical variables recorded at the study stations.