River Water Quality Assessment Using Physicochemical And Benthic Macroinvertabrate Metrics: The Case Of Gilgel Gibe River, Jimma Zone, Oromia National Regional State, Ethiopia

Abstract

The objective of the study was to assess river water quality using physico-chemical and biometrics by means of benthic macroinvertebrate metrics. The study was conducted on the Gilgel Gibe river which covers the area lying between 1678m at Asendabo SS to 1775m at Dedo SS. The Gilgel Gibe river crosses a wide area of farmlands, especially at Dedo sampling sites and is mostly exposed to frequent agricultural runoff from both the left and right side of the river. The samples were collected along the flow of the river from 15 sampling sites (six from Asendabo and nine from Dedo). Two wetland sites were selected as the reference following USEPA protocol, 2002. Physicochemical parameters listed below were analyzed on site by employing HQ40d multi Prob analyzer. Benthic macroinvertabrate metrics were sampled from shallow riffle areas of the river and were identified to the family level following the standard methods in the laboratory. SPPSS version 16, Cannoco and Arc GIS softwares were employed for statistical analysis and mapping of the sampling points. The water samples were analyzed for dissolved oxygen (DO), water Temperature, ambient air temperature, pH, Electrical conductivity (EC), Alkalinity, Chloride, Nitrate (NO3 - ), Phosphate , total suspended solid (TSS), Turbidity and flow rate. Accordingly; DO (5.18 to 7 mg/l), water temperature (19.1 to 23.9 oC), ambient air temperature (14 to 29.34 oC), pH (7.37 to 8.44), EC (70.4 to 86.9 μs/cm), Alkalinity (30 to 38 mg/l), Chloride (1.999 to 2.999 mg/l), NO 3 (0.41 to 0.9575 mg/l), phosphate (0.093 to 0.178 mg/l), TSS (113.33 to 700 mg/l) , Turbidity (64.2 to 290 NTU) and the flow rate (0.2 to 0.5 m/s) average values were recorded. In this study the canonical correspondence analysis (CCA) based on the invertebrates assemblages PCA axis 1 explained 25.5% and PCA axis 2 explained 17% of the variability among sites. Following careful analysis, the findings of the study depicts that almost all the parameters on the range of standard values kept for surface water by USEPA. The study was conducted from August 2016 to December 2016.