PHYSICOCHEMICAL AND BIOLOGICAL WATER QUALITY ASSESSMENT OF LAKE HAWASSA FOR MULTIPLE DESIGNATED WATER USES

Abstract

Lake Hawassa is one of the Major Ethiopian Rift Valley Lakes which is situated in southernregional state, which has a closed basin system and receives water from only Tikurwuha Riverand runoff from the catchment. Quality of the lake water is vital for the surrounding communityfor proper and safe use of the lake. The present study was designed to examine thephysicochemical and biological water quality suitability for multiple purposes and to determinetrophic state index of the lake for a period of three months from December to February,2011/12. Water samples were collected from the lake on monthly basis and analyzed for allwater quality parameters by using standard methods. Data analysis was performed bydescriptive, multivariate analysis (MANOVA) and Tukey-Kramer test. The overall waterquality parameters analytical results have been observed as pH (7.5), TDS (450.1), temp.(21.23°C), DO (17.85), turbidity (8.44 NTU), COD (48.73), BOD5 (117), Fˉ (12.8), NO3ˉ (5.27),PO43- (1.12), NO2ˉ (0.04), TN (5.42), TP (0.37), Clˉ (30.84), Mn (0.09), Zn(0.19), Na+(331),Chlorophyll-a(25.45μg/L), TC(11,883MPN/100ml) and FC (99.67MPN/100ml) and units forothers in mg/L. On the other hand, the value of indices for irrigation water quality was SAR(12.2-16), SSP (83.77-84.34%), MAR (93.83-95.37%) and KR (5.71-7.18). The values of thewhole analyzed parameters have shown significant variation in site (P<0.05). As irrigation waterquality mainly focuses on the indices of SAR and EC/TDS, the lake water is in good conditionfor the purpose. The values of trace heavy metals were under permissible limits for multipleaspects. On average, the trophic state index of the Lake Hawassa was hypereutrophic(TSI = 72.6), as Carlson value category. In general, the lake water is not suitable for drinking,recreational and irrigation of some raw consuming crops but it is suitable for aquatic life.