Spatial and Seasonal Water Quality and Heavy Metal Pollution for Irrigation Use in Awash River, Ethiopia

Irrigation water quality impacts the agro-ecosystem, human health, and the overall well-being of the environment. The purpose of this study was to investigate upstream municipal and industrial pollution impacts on irrigated farming and ecosystem health. The suitability indices and Heavy Metal Pollution Index methods have been used to identify the contamination extent and corresponding spatial and seasonal variability. Samples were collected twice per annum, i.e., during the low-flow season and high-flow season (rainy season) in the 2022/23 year. Results showed that during the low-flow season, the salinity hazard was 0.7 dS/m to 2.5 dS/m and medium to high. Sodicity hazards were obtained below <10 for the low-flow season, and for the rainy season, medium (16.63), high (18-26), and very high (>26). The toxic level of chloride for low-flow season showed slight to moderate at 3.6 mg/L and 6.07 mg/L, and toxicity was severe at Deho (14.6 mg/L), slight to moderate at Ambash (4 mg/L), Ertaale Lake (5 mg/L), and Gewanie (4.6 mg/L) in high-flow seasons. No heavy metal contamination was observed for low-flow periods except at Werer Research, which had a Heavy Metal Pollution Index (HPI) > 100. But, during the rainy season, Kesem Dam, Sedi Weir, WARC Pumping, WARC Offtake, and Ambash had a HPI > 100, which implied contamination by metals. Cadmium (Cd) was at moderate to ecological risk at low flow in sites Kesem factory, WARC Offtake, Ertaale, Meteka, and Gewanie, whereas Sedi Weir (Cd and Hg) and WARC Offtake (Cd) were at moderate risk during high flow. To conclude, metal pollution is a serious concern that needs upstream quality monitoring.