ABSTRACT

The effect of point and non-point sources discharge. on the water quality and riparian vegetation of Aba River was investigated. The studies on water quality were carried out at six regular sampling stations. Station I was located upstream beyond all possible source of pollution as control. Stations 2 — 5 were located downstream as the river traverses the urban and industrial area,, representing the effluent receiving stations. Station 6 was located downstream at the outskirt of the town and designated as attenuated station. Sampling programme and technique were such that spatial and temporal variations in the physico-chemical factors might be revealed. Physico-chemical parameters used in assessing water quality such as temperature, pH, turbidity, dissolved oxygen, BOD5, nutrients and trace metals etc were investigated. Plant communities adjoining the river were enumerated and identified from which data on type and abundance of plant species were collected. The physico-chemical parameters of the effluent receiving stations were significantly (P < o. o 5) higher than the non-effluent receiving stations with the exception of pH and dissolved oxygen. All the measured water quality parameters were significantly (P < 0. 0 5) higher during the rains with the exception of dissolved oxygen and temperature. Among the water quality parameters evaluated, pH, turbidity, BOD, lead, Iron, chromium, cadmium and manganese concentrations exceeded the internationally recommended water quality criteria for drinking purpose, domestic use and aquatic life. A Principal Component Analysis employed showed that dissolved solid, cadmium, manganese, turbidity, and hardness contributed substantially to the discrimination among the stations as demonstrated on Principal Component 1, whereas pH, suspended solid, temperature, dominated PC2. A total of six phytoplankton families were recorded, the blue green alga comprising about 70% of the algal population especially in the downstream stations. The species diversity ranged from 0.91 to 1.3, and was higher at the non-effluent receiving stations than effluent receiving stations. Marked differences were observed in the composition and abundance of plant species occurring in the area studied. The plant species in the effluent receiving area were mostly members of the hemicrytophyte as against phanerophyte in the non-effluent receiving area. Species richness indices showed gradual progression in community stability as the distance from the effluent receiving area increases. Similarity index showed that the variation in species composition became wider as the distance between the communities being compared increase. The study revealed that Aba River is under pollution stress due to effluents from point and non-point sources discharges.