Suspended sediment sources fingerprinting in the Ashebeka River catchment, Assela, Central Ethiopia

The Ashebeka River supplies drinking water to Assela City and its surrounding areas, yet rising pollutant loads threaten water quality, supply reliability, and treatment efficiency. This study, conducted in 2023, applied a sediment fingerprinting approach to quantify suspended sediment sources and inform the Water Safety Plan (WSP) implementation. Composite soil samples (n = 57) were collected across four sub-catchments: upper (UC), middle (MC), middle left (MLC), and lower (LC). In addition, 45 composite water samples were taken at the catchment outlet during the rainy season (June-August). Thirteen environmentally relevant geochemical tracers (Fe, Mn, Ni, Co, Cu, Zn, Cd, Hg, Pb, As, B, Se, Cr) were analyzed and screened for redundancy via variance and correlation analysis. Source apportionment employed discriminant function analysis (DFA) with non-parametric Kruskal-Wallis tests to accommodate non-normal data. Analytical recovery (82-105%) validated methodological robustness. Results revealed sediment contributions from the UC, MC, MLC, and LC sub-catchments were 22%, 45%, 19%, and 14%, respectively. The dominance of the MC reflects intensive cultivation on erosion prone slopes, marking it as a priority intervention area. Targeted soil conservation and agroforestry in the MC and LC are recommended to curb sediment influx and reduce downstream treatment costs. These findings equip government agencies, Assela City municipality, and stakeholders with quantitative evidence to prioritize hotspots and execute efficient catchment-scale water safety measures.