Abstract

This study was aimed at relating the zooplankton fauna of Opa reservoir catchment area (Rivers Obudu, Opa and Esinmirin) to their physico-chemical water parameters and some aspects of their hydrology. Basin perimeter, basin width, total length, number of streams, river order and discharge showed significant positive correlation with species occurrence, while compactness ratio showed significant positive correlation with abundance. Conductivity, total dissolved solids, biological oxygen demand (BOD₅) and major ions were generally higher in the dry season than in the rainy season. On the other hand, flow velocity, discharge, total suspended solids, apparent colour, true colour, turbidity, dissolved oxygen (DO), DO saturation, phosphate and organic matter were higher in the rainy season than in the dry season. Cluster analysis indicated a strong relationship among some physico-chemical water parameters. pH, Na⁺, Mg²⁺, SO₄^2-, DO, DO saturation, BOD₅, Cu, Mn, Cr, Co, Pb, As and PO₄^3- all showed significant correlation (p < 0.05) with zooplankton occurrence and/or abundance.

Key words: Abundance, basin, hydrology, rivers, water parameters, species occurrence