EVALUATION OF WATER QUALITY PARAMETERS AND EUTROPHICATION OF HAWASSA LAKE USING WATER QUALITY INDEX

Abstract

Lake Hawassa is one of the Major Ethiopian Rift Valley Lakes which has endorheic1 basin system and Hawassa Town established near to the Lake. The lake gave major recreational site for the town and nearby cities. It receives inflow from the only perennial River Tikurwuha and runoff from the remaining sub-catchment. Lake water quality is vital for the surrounding community for proper and safe use of the Lake. The surrounding community uses the water for multipurpose use, like irrigation, water supply, recreation and fish harvesting. The present study was designed to examine the physicochemical and biological water quality suitability for determine trophic state of the lake for a period of three months from June to August in the case of summer or rainy time, 2017/18. Water samples were collected from the lake on monthly basis and analyzed for all water quality parameters by standard methods. Data analysis was performed by spreadsheet. The overall water quality parameters analytical results have been observed as pH (8.9±0.12), TDS (422.2±21.43), Temp. (20.8±0.35), DO (5.2±0.26), Turbidity (6.6±0.1NTU), COD (173.6±45.2), BOD5 (45±5.3), NO3ˉ (6.25), PO4 3- (1.35±0.54), EC(812.8±21.5µS/cm), TA (332.818), Clˉ (31.5±2.9), Chll-a(1037.018µg/l), Secchi depth (0.934) and units are mg/l except specified. On average, the trophic state of the Lake Hawassa was under hypereutrophic stage as per the standard depending on the value of Secchi depth, chlorophyll a, phosphate, and nitrate amount. The current study showed the lake is unfit for any purpose as per WQI range. Since the analysis undertaken during summer time, the rain water may reduce the amount of contamination range of pollutant and it absolutely increases in winter time. There are a lot of problems seen on the lake like eutrophication around the lake shore, on the other side three of the sample site like referral hospital, Fiker recreational area, and Tikurwuha seen more contamination and minimum amount of dissolved oxygen. According to the result of physicochemical and biological parameter of the lake the lake needs to mitigation to control eutrophication. This study put some remedial measure to control expanded eutrophication by managing point and non-point source of wastewater generated from Hawassa town and agricultural area.