Abstract
A study was conducted to determine the downstream impact of Bahir Dar Tannery wastewater on the head of Blue Nile River using macroinvertebrates as bioindicators. Four sampling sites (one upstream and three downstream) were selected along the river and samples were collected from October to March, 2010/11. Macroinvertebrates were collected using standard dip net based on the Rapid Bioassessment Protocols for use in streams and wadeable rivers and identified to the family level. A total of 9,162 individuals belonging to 28 families were collected during the study period. Results of analysis of variance (ANOVA) showed that, there was significant difference in macroinvertebrate metrics among sampling sites. Percent Ephemeroptera Plecoptera Trichoptera (EPT) Index, Shannon Diversity Index and Benthic Macroinvertebrate Index were higher and percent Diptera, Chironomidae and Hilsenhoff Family level biotic index were lower at the reference site. The categorization of sites based on Benthic macroinvertebrate index value indicated that the site just below the effluent discharge and 200 m from it were severely to slightly, the last downstream site moderately to less and the reference or upstream site very little to none impacted. The water quality at these sites was also very poor to poor, fair to good and very good to excellent, respectively. The most impacted sites ranked last in all sensitive metrics while the reference ranked first in sensitive metrics indicating the severe impact of the effluent on downstream sites. The result gave the trends of pollution of the river by the effluent and the urgent need for measures to be taken. Key words: Tannery effluent, macroinvertebrates, bioindicators, Blue Nile River.
Highlights
Rapid population growth, urbanization and industrial development have been adversely degrading the environment (Mason, 1990) by their effect through loss of biodiversity and pollution from wastes
In Ethiopia too, industries are increasing in number turning out wastes which are peculiar in terms of type, volume and pollution strength depending on the type of industry, raw materials used and process and technological variations applied to the process
Tannery wastewater is highly polluted in terms of biological oxygen demand (BOD), chemical oxygen demand (COD), suspended solids (SS), Nitrogen, conductivity, sulphate, sulphide and chromium (Mondal et al, 2005)
Summary
Urbanization and industrial development have been adversely degrading the environment (Mason, 1990) by their effect through loss of biodiversity and pollution from wastes. Industrialization, like other human activities that impact on the environment, often results in pollution and degradation. It carries inevitable costs and problems in terms of pollution of the air, water resources and general degradation of the natural environment (Suflita et al, 1983). As compared to other industries, leather tanning is one of the most polluting activities (Khan et al, 1999) as it consumes huge amount of water in several stages, generating an enormous sum of liquid effluents (Farenzena et al, 2005) which are hazardous for the environment to which they are discharged. Tannery wastewater is highly polluted in terms of biological oxygen demand (BOD), chemical oxygen demand (COD), suspended solids (SS), Nitrogen, conductivity, sulphate, sulphide and chromium (Mondal et al, 2005)
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