Between January and June, 2022 some physico-chemical and biological conditions of Upper River Benue were assessed at five selected sites on monthly basis between 6:00 – 10:00a.m. A total of 9.849 ×104 organisms/L was recorded for zooplankton abundance. Rotifera was observed to have a total abundance of 39.9%, followed by Cladocera contributed a total of 33.45%, while the least was Decapoda gave 1.37%. The higher number of taxa (25) was recorded at site V. The abundance of individuals was highest at site IV. Twenty-seven species (27) species of zooplankton were identified during the study period ranging from elven Rotifera, nine Cladocera, five Copepoda, one Ostracoda and one Decapoda. The order of dominance of the zooplankton of Upper River Benue is Rotifera>Cladocera>Copepoda>Ostracoda>Decapoda with Brachionus caudate, Bosmina longirostis and daphnia being the most dominant (6.94%) of the total zooplankton of Upper River Benue. The physico-chemical parameters results revealed that temperature, pH, electrical conductivity, transparency, dissolved oxygen, free CO2, alkalinity were within recommended acceptable limit except ammonia, phosphorus and nitrogen were higher than recommended acceptable limit. However, no significant difference was found between the seasons in terms physico-chemical paraneters and zooplankton distribution (P>0.05). The study showed the reservoir to be eutrophic with moderate water quality, high ecological and pass chemical status, with diverse assemblages of zooplankton. It was recommended that there should be continuous monitoring of the biological and physico-chemical status of the river to ascertain the long-term impact of anthropogenic inputs to take remedial measures so as to ensure the health of aquatic life.
Keywords: physicochemical parameters, zooplankton and upper
