Physico-chemical and biological evaluation of Blue Nile River at Lake Tana, Ethiopia, in relation to discharge of tannery effluent

Pollution of aquatic ecosystems with waste-water coming from tanneries is a serious challenge worldwide. The purpose of this study was to assess the water quality of Blue Nile River at a tannery in Bahir Dar, Ethiopia, using physicochemical and biological attributes. Four sampling sites were selected along the river based on the degree of degradation and major land-use types. Phyisco-chemical data, water samples, and chironomid larvae were collected monthly from March-May, 2016. Two liters of water were collected from each site and stored in the icebox and transported to Bahir Dar University. Water samples were analyzed for nutrients following standard procedures. Chironomid larvae were collected using a D- Frame net of 500 µm mesh size. One-way ANOVA was used to compare variations in all measured parameters among the sampling sites. Low dissolved oxygen (2.8 mg/l) was recorded at the site where the tannery meets the river. Moreover, the concentration of soluble reactive phosphorus, SRP (25.5±14.3 μg/l) and conductivity (1907.3±39.5 µS/cm) were low in the most upstream site of the river. A total of six Chironomid genera belonging to the subfamilies Chironominae and Tanypodinae were identified. The genus Chironomus dominated the impacted sites that had low dissolved oxygen levels. The other five genera were not found in those impacted sites. The result of this study indicated that the tannery effluent had impact on chironomid distribution as well as on river water quality.