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.
