Koka Reservoir in the Ethiopian Rift Valley (altitude about 1600 m) appears to be similar to natural lakes in the region. Its water is turbid because of suspended inorganic material. At the time of measurement it was supersaturated with oxygen to a depth of about 8 m, and displayed a pronounced conductivity stratification, due probably to the incomplete mixing of two inflows. The phytoplankton was dominated by Microcystis. The zooplankton was of low diversity but abundant. There was a large population of benthic invertebrates.Finchaa Reservoir in west central Ethiopia (altitude about 2200 m) is very different. It covers the former Ch'omen Swamp and so contains many floating islands and large quantities of decomposing vegetation, causing undersaturation with oxygen even at the surface. The water is somewhat turbid owing to the presence of organic debris, of low conductivity, slightly acidic, and apparently calcium-dominated. A species of Microcystis was the most abundant phytoplankter. The zooplankton was sparse and of very low diversity. There were almost no benthic invertebrates.
In the course of study of the cyanobacterial flora of Ethiopian soil crusts, we isolated a distinctive strain most closely resembling Chroococcidiopsis kashayi, and at first considered it to be a new Chroococcidiopsis species. However, when placed in nitrogen-free medium for an extended time period this strain developed heterocytes, and consequently was placed in the genus Nostoc. It is morphologically distinct from all other Nostoc species due to its consistent formation of microscopic few-celled colonies lacking clear filamentous organization, which release smaller colonies from the mother colony, leaving behind a persistent thin firm sheath that resembles cell wall material in the light microscope. Analysis of 16S rRNA and 16S-23S ITS sequence data confirmed its uniqueness among numerous strains of soil Nostoc. We are describing it as Nostoc oromo, named for the nationality of the people from the region of its origin.
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