Assessing anthropogenic impacts using benthic macroinvertebrate as bio-indicators in central highland streams of Ethiopia

Abstract

Biological indicators particularly those using macroinvertebrate communities are increasingly used to assess the effects of human driven stressors on stream water and habitat quality.  The goal of this study was to establish relationships between benthic macroinvertebrate and common stressor types (siltation, agriculture and paper mill waste) in central highlands of Ethiopia. For analysis environmental variables and benthic invertebrate taxa were collected from four streams from November, 2011 to June, 2012. There was a significant difference in conductivity, dissolved oxygen, total phosphorus and five days biological oxygen demand between paper mill waste and other stressor types. In siltation sites, most environmental parameters were not significantly different (p > 0.05) from reference and agricultural sites.  Sensitive taxa such as Perlidae, Lepidostomatidae, Scirtidae and Philopotamidae were represented in the reference site. Paper mill waste was the worst stressor for deterioration of water quality and cause significant reduction of benthic invertebrate diversity directly by intoxication and indirectly by changing water quality parameters. Agriculture and siltation stressed sites showed major difference in abundance than richness of benthic invertebrates. Of 39 benthic macroinvertebrate metrics tested, five metrics representing richness, composition and sensitivity were identified as useful to discriminate stressor groups. These metrics are taxa richness, EPT (Ephemeroptera, Plecoptera and Tricoptera), % Oligochaeta & Chironomidae, % EPT-BCH (EPT without Baetidae, Caenidae and Hydropschidae and ASPT (Average Score Per Taxa). Among others % EPT-BCH was found effective to separate the effect of siltation from agriculture and reference sites. This study showed that benthic macroinvertebrate metrics were useful to assess the impact of different stressors in Ethiopian central highland stream and rivers.

Key Words: Benthic macroinvertebrate, Stressors, Pollution, Metrics, Highland streams