Impacts of the Koka hydropower dam on macroinvertebrate assemblages in the Awash River Basin in Ethiopia

The Koka hydropower dam is one of the oldest large dams in Ethiopia. Damming is one of the anthropogenic activities impacting the distribution of aquatic life forms. However, to date, little attention has been focused on the dam’s impacts on the river macroinvertebrate assemblages in Ethiopia. The objective of this study was, therefore, to assess the impacts of the Koka hydropower dam on macroinvertebrate assemblages in the Awash River basin in Ethiopia. In the three river reaches on the Awash River (upstream near the source of the river, midstream above the dam, and downstream below the dam), a total of 15 sites were selected for sampling. The statistical analysis tested the null hypothesis that there are no differences in macroinvertebrate assemblage patterns or a range of univariate metrics between the three river reaches. Additional analyses involved the identification of taxa responsible for significant differences in macroinvertebrate structure (e.g., percentage similarity) and an exploration of the variables that structure macroinvertebrates (e.g., canonical correspondence analysis). In the upstream, midstream, and downstream reaches of the Awash River, we recorded a total of 73 taxa belonging to 43 families and 12 orders. Trichoptera was the dominant order in the upstream river reach, whereas Diptera dominated the midstream and downstream river reaches. The diversity of macroinvertebrates decreased from upstream to midstream and downstream. The three river reaches differed significantly in Shannon and Simpson diversity indices, % EPT, EPT taxa abundance, total taxa richness, evenness index, % collectors, and % scrapers. In this study, we observed that macroinvertebrate assemblage differences and spatial patterns were significantly associated with values of river flow changes (velocity), phosphate concentration, and substrate index. The findings of this study have broad implications for the assessment of the impacts of dam construction on the rivers of the studied region in the future.