Effect of Season on the Concentration of Nutrients in the Three Highland Lakes of Ethiopia

摘要

Water resource contamination is still a major concern in several regions of developing countries especially in sub-Saharan countries in which polluted waters pose serious risks to human health and the environment. The research was aimed to evaluate the current water quality status of highland Lakes (Ardibo, Logo and Tana) of Ethiopia in different season and to identify potential pollution sources sites. Physico-chemical water quality parameters have been determined by taking duplicate samples from three sampling sites of each lake and the results were compared with WHO and FAO standards. The result of the study indicates nutrients concentration to be Alkalinity (428, 269.945, 109.935 mg/L), calcium (31.542, 46.873, 77.12 mg/L), chloride (89.165, 77.5, 40.125 mg/L), magnesium (94. 755, 93.165, 39.396 mg/L), NH3 (0.418, 0.184, 0.6493 mg/L), NH4 (0.433,0.145, 0.753 mg/L), potassium (1.299,19.325, 6.547 mg/L), sodium (22.489,39.5, 10.671 mg/L) and sulphate (2, 2.075, 1.479 mg/L) in Lake Logo, Ardibo and Tana, respectively. The concentration of Calcium and NH4 were significantly more abundant in rainy season than dry season (p<0.01) and the concentration of Chloride, magnesium, Potassium, Sodium and Sulphate were significantly more abundant in dry season than rainy season in lake Ardibo (p<0.01). The concentration of NH4 were significantly more abundant in rainy season than dry season and the concentration of magnesium were significantly more abundant in dry season than rainy season in lake Tana (p<0.01) and also the concentration of alkalinity, magnesium, and sulphate were significantly more abundant in dry season than rainy season in Lake Logo and the concentration of NH3 and Potassium were significantly more abundant in rainy season than dry season (p<0.01). The concentration of NH3 and NH4 were 0.6088 mg/l, 0.679 mg/l in rainy season and 0.6897 mg/l, 0.8083 mg/l in dry season respectively in Lake Tana. As the result shown that the concentration is higher in rainy season and the main reason for these results were the storm water and sediment load from different catchment of the lake released in the form of run off and soil erosion. The farmers use fertilizer to increase their crop production since NH4 and NH3 are directly released in to the lake in the form of runoff hence the concentration of these nutrients increase in rainy season. .