Assessing the ecological health of the upper and middle Awash River, Ethiopia, using benthic macroinvertebrates community structure and selected environmental variables.

Abstract

Research on the Awash River focused on the upper section, while the middle and lower regions received little attention. Thus, the goal of this study was to evaluate the impact of anthropogenic activities on the upper and middle Awash River. The study took place in nine sampling locations in dry and wet seasons from September 2021 to April 2022 using a multi-habitat sampling approach. We used macroinvertebrate metrics, environmental variables, and multivariate analysis to evaluate ecological health. The highest concentrations of NO3, soluble reactive phosphorus, and total phosphorus (0.50-0.93mg L-1) were recorded at the river-mouth of the upper Awash, while the locations below Metehara had the lowest levels of dissolved oxygen (1.81-2.33mg L-1). Redundancy analysis indicated that dissolved oxygen, NH3, temperature, NO2, pH, TSS, NO3, and TDS influenced macroinvertebrate distribution. The presence of the sensitive groups Caenidae, Hydropsychidae, Heptageniidae, and Aeshnidae at upstream sites indicated better ecological conditions. The middle and downstream sites supported moderately tolerant and tolerant taxa demonstrating water quality impairment. The lowest Ethiopian biotic score was recorded at the river-mouth of the upper Awash. The study sites below Metehara demonstrated severe ecological impairment since highly tolerant taxa were abundant and had strong correlations with temperature, TSS, and TDS levels. Pollutants from agricultural farms and domestic and industrial wastes from Addis Ababa, Metehara, and Merti towns most likely affect the impaired sites. This study demonstrated that the middle Awash experienced substantial ecological deterioration, indicating the need for restoration works to fit the water for socio-economic development.