Development of a multimetric index for assessing the ecological integrity of some selected rivers and streams in the north-eastern part of Lake Tana sub-basin, Ethiopia

Abstract

A multimetric index was developed using benthic macroinvertebrates to assess the ecological health of selected rivers and streams in the north-eastern part of Lake Tana subbasin, Ethiopia. One-time extensive sampling was carried out during the post-rainy season (November–December) of 2016. Macroinvertebrates were collected using a Surber sampler and a D-frame net at twenty sites. Based on the measured physico-chemical variables, sampling sites were clustered into references (n = 8) and test sites (n = 4). Approximately thirty potential candidate metrics were tested, and five metrics were selected as core metrics: number of Ephemeroptera Plecoptera Trichoptera taxa, percentage of Ephemeroptera individuals, percentage of EPT individuals, percentage that were shredders, and the percentage that were filter-feeders. These metrics were scored on a continuous scale from 0 to 10. To develop Lake Tana subbasin multimetric index (LTSBMI), scores were added and scaled to produce a score from 0 to 100. The final index was divided into five water quality classes: 'very good', 'good', 'fair', 'poor' and 'very poor'. The LTSBMI was effective in discriminating sites with different levels of impacts, but should be checked to other localities. The current LTSBMI could be used for ecosystem health assessment and monitoring in different Aftropical river systems with similar agroecology.