  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.
