Physico-chemical and Biological Water Quality of Fincha, Tamsa’a and Dogaja Rivers in Didessa headwaters (Blue Nile sub-catchment) south West Ethiopia

Abstract

All living organisms on the earth need water for their survival and growth. Nowadays, due to anthropogenic and natural activities rivers were highly polluted with different harmful contaminants. Physico-chemical and biological water quality of Fincha, Tamsa’a and Dogaja Rivers, located in the head water of Didessa basin (Blue Nile sub-catchment) have been assessed in one wet and one dry season between October 2018-March 2019.Water pH, EC, water T and (DO) were measured in-situ using a multiprobe meter while water samples were analyzed for BOD5 , TSS, NO3, NH3 and PO4 in the laboratory following standard procedures. Macroinvertebrates samples were collected using kick net, preserved in 75% alcohol and identified in laboratory following standard keys. The chemical and ecological water quality was assessed at18 sampling locations using the ASPT-ETHbios, which is based on macroinvertebrate. All Significant variations in the median values of physicochemical parameters and nutrients among the three river groups were tested using KruskalWallis followed by Mann-Whitney pair wise post-hoc tests due to lack of homoscedasticity and normality of the data. Normality and homoscedasticity of the data were tested using Shapiro-Wilk and Leven statistics respectively. Benferroni p values corrected for multiple testing were used to evaluate significance of pair wise comparisons for the Mann-Whitney post-hoc tests. Spearman’s correlation coefficient was used to test the possible correlations among the measured parameters. Statistical analyses were run in PAST version 3.08 and SPSS version 16.Accordinglymedian water T of the rivers varied from 19.45 o C -24.65 °C, average DO varied from 6.60 mg/L-7.18 mg/L, average EC varied from 56.35 µS/cm-89.69 µS/cm, pH values varied from 7.56-8.37, TSS values for the rivers varied from 0.006 mg/L-0.009 mg/L and BOD5 values varied from 1.55 mg/L-2.06 mg/L. Whereas the median values of NH 3, NO 3 -and PO 4 3-varied from 0.08 mg/L-0.12 mg/L, 3.25 mg/L- 4.20 mg/L and 0.78 mg/L-0.93 mg/L respectively. Tamsa’a and Dogaja Rivers are relatively more polluted than Fincha River due to urbanization and disposal of wastes by the nearby communities. The community, concerned administrative and/or non governmental bodies should support by fund and by preparing suitable waste disposal areas.