ABSTRACT
Freshwater ecosystems and biodiversity are threatened by many environmental stressors, particularly those derived from intensive human activities. In this study, the physico-chemical condition and zooplankton community structure, as well as their relation to water quality in Ovia River, Iguoriakhi, Ovia Southwest, Edo State, Nigeria was assessed. Three sampling stations were selected along the course of the river from upstream (station 1) to downstream (station 3) associated with various anthropogenic activities. Water and Zooplankton samples were collected and analysed for six months seasonally from September to November 2021 (wet season) and December to February 2021 (dry season) using standard methods. Of the sixteen parameters, turbidity (17.82 ± 2.44NTU) and pH (5.99 ± 0.28) exceeded the stipulated World Health Organization (WHO)/Nigerian Industrial Standard (NIS) guidelines. The results of PCA analysis revealed that electrical conductivity (EC), turbidity (turb.), total dissolved solids (TDS) biochemical oxygen demand (BOD5), Sulphate (SO4) and Chloride were the main environmental factors affecting the zooplankton community structure in the Ovia River. The physico-chemical parameters varied spatially; however, these variations were not significant (P > 0.05). Six parameters significantly (P < 0.05) varied seasonally. We recorded a total of 1972 individuals in three taxonomic groups of zoobenthos belonging to 33 taxa in this study. Cladocera (n=21), Copepod (n=6), Rotifers (n=6). Cluster analysis classified similar zooplankton community structure stations into 2 clusters. Cluster 1 comprising station 1 only, and Cluster 2 made up of stations 2 and 3 were more similar than cluster 1. The multivariate canonical correspondence analysis revealed a strong association between the zoobenthos assemblage and physico-chemical variables. We observed differential responses of zoobenthos to environmental parameters with taxa such as Bosmina longirostris and Alona gutata showing positive associations with electrical conductivity, turbidity, total dissolved solids, and sulphate. These taxa have been suggested as bioindicator organisms of poor water quality. Alona cambouei, Mesocyclops decipiens, Diaphanosoma sarsi and Lecane sp. associated weakly with BOD5. Overall, the study revealed further insights into the responses of zoobenthos communities to pollution, and their potential use as indicators organisms in freshwater ecosystem.
