A study was carried out on four tributaries of Gilgel Gibe Reservoir to identify water physicochemical characteristics in different land use categories (farmland, naturally vegetated land, and settlement). Water samples were collected from 12 sampling sites along four permanent streams flowing into Gilgel Gibe Reservoir. Data sets were evaluated using nonparametric statistical techniques. Dissolved oxygen (DO), temperature, biochemical oxygen demand (BOD5), total phosphorus (TP), soluble reactive phosphorus (SRP), total nitrogen (TN), turbidity, total dissolved solids (TDS), and total suspended solids (TSS) spatially showed significant differences in the wet season and DO, temperature, and BOD5 varied significantly during the dry season. When excluding DO, electrical conductivity (EC), and TP during the wet and dry seasons, the remaining variables showed significant differences. During the wet season, concentrations of most water quality parameters were greatest in influents from agricultural land. Pollution and eutrophication risk is closely associated with drainage from agricultural land, requiring that emphasis and priorities be given to land use management and conservation.
Keywords: Land use; Pollutants; Tributary; Water quality; Watershed.