Influence of Urban Pressure on the Ecological Status of Showunga River, MizanAman Town, Bench Maji Zone, Southern Ethiopia

Abstract

Background: Urbanization is one of the main causes for ecological problems due to the introduction of pollutants into water bodies. Degradation of water resources with pollutant effluent occurs by altering attributes that influence ecological integrity of surface water resource such as water quality, habitat structure, energy source and biotic interactions. Showunga River crosses Mizan-Aman town and has long been used for a variety of purposes including source of public water supply, small scale irrigation, recreation, bathing, washing, animal watering, and sand and stone dredging. Objective: The main objective of this study is to assess the influences of urban pressure on the ecological status of Showunga River. Method: A total of eleven samples were collected along Showunga River by following the standard methods of American Public Health Association procedures in April 2019 using cross sectional study design. The assessment involved on-site measurements and collection of water samples, laboratory analysis of water samples and macroinvertebrates identification to the level of family using microscope. Kruskal-Wallis multiple comparison test, Pearson correlations, Excel, SPSS version 24, PAST version 3.18 and STATISTICA® software package were performed. Results: The result clearly shows that upstream sites have oxygen level of 7 mgLˉ¹, while turbidity, BOD, nitrate, phosphate, and chloride concentrations was elevated at midstream sites where main human activity is undertaken. Macroinvertebrate assemblages were compromised in the mid-stream sites where diversity of sensitive taxa was diminished due to anthropogenic disturbances. However, downstream sites showed a gradient of recovery where the most downstream site, S11, was found to have better macroinvertebrate diversity with improved water quality than midstream sites. Conclusion: Physicochemical and biological data revealed that much influence of urban pressure at the midstream sites (waste water discharge, coffee processing, sand and stone deranging are main ecological deteriorated), thus necessitated a need for mitigation measure to save the Showunga River.