Impacts of Koka Hydropower Dam on Benthic Macroinvertebrate Assemblages in the Awash River, Ethiopia

Macroinvertebrate distribution and community structure in lotic water are influenced by a range of natural environmental variables and other anthropogenic factors, particularly related to the construction of dams. Hydropower dams can alter natural flow regimes, sediment transportation, hydrochemical water quality, channel morphology, water temperature, and nutrient cycles and physically obstruct the dispersal and the migration of macroinvertebrates and fish communities. The objective of this study was to evaluate the impacts of the Koka Hydropower Dam on benthic macroinvertebrate assemblage structures. Environmental, hydromorphological, and macroinvertebrate community data were collected along the course of the Awash River in the upper Awash basin. A total of 2305 macroinvertebrates assigned to 11 orders and 41 families were collected from 15 sites in the upstream, midstream, and downstream reaches. Ephemeroptera (32.2%), Diptera (24.6%), and Trichoptera (20.2%) represented 77% of the total abundances.The canonical correspondence analyses, multivariate test, showed that river velocity and phosphate concentration explained the majority of the variation (60%) in macroinvertebrate community structure among the three reaches possibly due to the dam’s impact in addition to other forms of impairment differences between reaches. The water quality categories of the river reach based on the Shannon diversity index at upstream, midstream, and downstream locations were high, moderate, and low, respectively. Based on the macroinvertebrate family-level information, this study found that the water quality degradation was most severe in the downstream reach. Overall, detection of the specific impacts of the dam is complicated by nutrient pollution in the river.