Env Exp Biol (2013) 11: 91–98

Algal biomass and nutrient enrichment in the Angereb reservoir, Gondar, Ethiopia

Abstract

Nutrient enrichment leads to eutrophication in various types of water bodies. This phenomenon is characterized by the presence of large biomass of algae and water weeds, which can decrease water quality in the domestic water supply system. Eutrophication is an anthropogenic factor, and is considered as a global aquatic pollution problem. The aim of this investigation was to assess the trophic status of water in the Angereb reservoir, which is source for domestic water supply in Gondar, Ethiopia. A systematic approach was used to select sampling sites from which sediment, soil and water samples were collected. The trophic status of Angereb reservoir water was mesotrophic (4.2 µg L^–1 of chlorophyll a). Nitrogen and phosphorus were main factors causing eutrophication and algal blooms in the reservoir. Dissolved oxygen, pH and temperature of the reservoir were found at a level that was not harmful to aquatic biota. Additionally, the turbidity level was high. Sediments and soils of all selected sub watersheds contained significant amounts of total nitrogen and total phosphorus, leading to nutrient enrichment of the reservoir water. Particularly, the Angereb and Defecha sub watersheds were identified as the main sources of nutrient input to the reservoir. Appropriate soil and water conservation measures are required to reduce the input of nutrients to the Angereb reservoir. In addition, bio-manipulation techniques should be undertaken to impede further growth of algae.