The Water Quality Status of Washa and Borale Reservoirs Using both Water Quality Parameters and Macroinvertebrates in Ethiopian Central Highlands

Abstract

Washa and Borale reservoirs are important in regulating climatic and ecological conditions and providing various economic services. However, water quality and/or ecological health status of reservoirs has not yet been properly assessed in Ethiopia. Therefore, the main purpose of this study was to assess the water quality status of the Washa and Borale reservoirs/ wetlands located in North Shewa Zone of Ethiopian Central Highlands. Their water quality status was assessed using water physicochemical parameters and macroinvertebrates in December 2020 and November 2021. The results recorded from Washa Reservoir showed that the concentration of nitrate, phosphate, ammonia and silica on average was 69 µg/L, 53.52 µg/L, 188.86 µg/L and 14 µg/L, respectively. Similarly, the concentration of nitrate, phosphate, ammonia and silica obtained from Borale Reservoir on average was 43.5 µg/L, 32.6 µg/L, 50.0 µg/L and 109.8 µg/L, respectively. The concentration of ammonia was found to be high in both reservoirs indicating the presence of organic contamination. The total number of macroinvertebrates collected from Washa and Borale reservoirs were 519 and 789, respectively. Eight families belonging to three orders were recorded in Washa Reservoir whereas seven families belonging to four orders were recorded in Borale Reservoir. Order Hemiptera was represented by 5 families, Coleptera by two and Ephemeroptera by one in Washa Reservoir. Similarly, Hemiptera was represented by four families compared to other orders in Borale Reservoir. High dominance of tolerant macroinvertebrate families and absence of sensitive families indicated ecological instability and pollution in Borale Reservoir. Besides, ecological disturbance and pollution are observed in Washa Reservoir. Hence, human interference and cattle drinking should be regulated before both reservoirs are impaired permanently. Keywords: Central Ethiopia, Evaluation, Wetlands, Water parameters, Water pollution