BIOLOGICAL AND PHYSICOCHEMICAL WATER QUALITY PROFILE OF LAKE ADDELE, EASTERN HARARGHE DISTRICT OROMIYA, ETHIOPIA

Abstract

Freshwater ecosystems harbour a considerable proportion of Earth’s biodiversity, even though they cover < 2 % of the land surface. Lakes are one of humanity’s most important resources,where they are viewed as highly productive biological systems.The availability of good quality water is the major factor for preventing diseases and improving quality of life. In the present study the physicochemical parameters and the occurrence of three heavy metals in the tissues of fish specimens, Catfish (Clarias garpiens) and Tilapia (Oreochromis niloticus) and in the water samples as well as benthic macro-invertbrates were investigated. The water, fishes and Benthic macro invertbrateMIs samples were collected from Lake Addele at three selected sampling sites namely, in the road side, middle part and slant part (the hilly side) of the lake. The concentrations of selected heavy metals such as zinc (Zn), cadmium (Cd) and lead (Pb) in water samples and their accumulations in the edible tissues of fish samples were determined using Flame Atomic Absorption Spectrophotometery.The phosphate and nitrate were determined using UV specrophoto meter.The BMIs were identified by referring the standard species identification key for invertebrates. The results revealed that the dissolved heavy metals concentration in water samples were in the range of 4.10 to 5.62 mg/L for zinc (Zn), 0.096 mg/L 0.17 to for cadmium (Cd), 1.43 to 2.84 mg/L for lead (Pb) in both dry and wet seasons.The highest concentration of zinc, cadmium and lead in water samples were recorded during the dry season. The concentration of the same heavy metals in fish samples ranged between 0.03 to 0.082 mg/L for cadmium (Cd), 0.20 to 2.2 mg/L for lead (Pb) and 0.024 to 3.43 mg/L for zinc (Zn) in both fish species. Among the detected metals, zinc (Zn) showed the maximum bioaccumulation in fish samples.The measured values of physicochemical parameters of water samples ranged with respect to temperature from 1922.8oC, pH 8.16-8.72, biological oxgen demand (BOD) 15- 24 mg/L, the chemical oxgen demand (COD) 130- 190 mg/L, dissolved oxgen (DO) 2.26 - 5.76 mgL, electrical conductivity (EC) 279 - 639μs/cm, nitrate 2.86 - 5.09 mg/L and phosphate 0.211 - 1.35 mg/L. The results of diversity of BMIs, the Shannon Weaver index (H) values ranged from 0.469 - 0.491, the taxa richness (E) values ranged from 0.1262 - 0.1322,and the taxa evenness Hmax values ranged 3.71 - 3.91 during the dry and wet seasons. The concentrations of the studied heavy metals in water and fish samples were above the recommended limit by WHO and FAO. Thus, regular monitoring of the lake is needed by using essential biological and physico-chemical parameters.