Benthic macroinvertebrates based new biotic score “ETHbios” for assessing ecological conditions of highland streams and rivers in Ethiopia

The study describes the development of a macroinvertebrate based biotic score system (ETHbios) for assessing the ecological status of rivers in the Ethiopian highlands. The ETHbios is basically developed on the principle of the BMWP approach (version of the South African Scoring System) but excludes taxa that don't occur in Ethiopia and includes some of Ethiopian fauna. Macroinvertebrates were collected from 104 sites distributed in a total area about 98,000 square kilometers in the upper Awash, Rift-Valley, Wabi-Shebele and Genale basins. A sensitivity score was assigned to 59 taxa based on guide score, taxon distribution across river quality classes, reference score and autecological knowledge. To define the ranges of the five river quality classes (high, good, moderate, poor and bad), the ETHbios values of sites were correlated with the corresponding ecological status of the sites derived by the Ethiopian Multimetric Index. The validation procedure was done by comparing the ETHbios with selected environmental parameters (conductivity, dissolved oxygen, biological oxygen demand and total phosphorus); the analysis showed significantly high correlations (r > 0.5; p < 0.05). ETHbios can be considered as rapid, inexpensive but scientifically sound monitoring method that can be used to evaluate the ecological conditions of running waters in the highlands of Ethiopia.