Eutrophication of Ethiopian water bodies: a serious threat to water quality, biodiversity and public health

Abstract

Freshwater ecosystems provide several ecological and economic services. However, these ecosystems in Ethiopia are deteriorating, because of economic growth, unwise use and pollution (eutrophication). This paper reviews existing trends of eutrophication in Ethiopian water bodies, identifies principal sources of nutrient pollution, highlights major consequences, and proposes measures to control eutrophication. The trophic state of all major Ethiopian lakes considered in the current assessment ranges from eutrophic to hypereutrophic. A major cause of eutrophication is the use of chemical fertilisers that has grown > 186 times between the 1970s and 2012. Similarly, the large livestock population has contributed to the increase in nitrogen and phosphorus accumulated in the soil, which is often washed into aquatic ecosystems. Urbanisation and industrial effluents and associated wastewaters are the other causes of eutrophication. The major consequences include shifts to bloom-forming cyanobacteria, prolific growth of water hyacinth, hypoxia, fish kills and health risks. To control eutrophication and avoid its devastating consequences, raising public awareness, creating buffer strips, development of chemical fertiliser use guidelines based on plant removal rates and soil types, wastewater treatments, issuance of policy on Water Quality Guidelines, and the establishment of a National Aquatic Ecosystem Monitoring Program are recommended.

Keywords: algal blooms, bloom-forming cyanobacteria, chemical fertilisers, economic growth, industrialisation, urbanisation, water hyacinth