Development of ecoregion-specific biomonitoring tools for a tropical river: addressing water quality and ecological connectivity in highland-lowland systems.

The study aimed to develop multimetric indices (MMIs) for the Awash River, stratified by altitude, covering the upper (above 1500 m) and middle (1000-1500 m) sections to provide a framework for incorporating Ethiopian lowland rivers in biomonitoring. The core metrics selection process evaluated 52 metrics commonly used for tropical rivers. The criteria considered during the selection of the core metrics included the response to disturbance gradients, sensitivity score, regional significance, representation across sampling sites, coverage of various aspects of macroinvertebrate communities, and avoidance of redundancy within metric categories. The metrics that passed the screening methods and were included in the MMI-U for the upper Awash were: richness (#Ephemeroptera and Trichoptera (ET)), composition (%Diptera and Hemiptera), pollution tolerance (Ethiopian biotic score (ETHbios)), and functional feeding (%predator). For the MMI-M in the middle Awash, the selected metrics included: #Ephemeroptera, Odonata, and Trichoptera (EOT), %Chironomidae and Oligochaeta, ETHbios, and %predator. After standardising and summing the core metrics, the indices for the Awash River were calculated with values ranging from zero to ten, and five ecological state boundaries were subsequently determined as very good (8-10), good (6-8), moderate (4-6), poor (2-4), and very poor (0-2). To validate the effectiveness of the MMIs, an independent dataset was utilised, and the results demonstrated that the MMIs were robust for assessing ecological integrity. Furthermore, the development process of these MMIs can serve as a model for creating similar indices to evaluate the rivers that drain both the highland and lowland regions of Ethiopia.