Assessment of water quality degradation in the Upper Awash River, Ethiopia using integrated pollution indices and multivariate statistical methods

Abstract Despite increasing pollution pressures from urbanization and agriculture in the Upper Awash River basin, comprehensive index-based evaluations integrating multiple pollution indices and multivariate statistical methods remain limited. This study addresses this gap by utilizing water quality indices and multivariate statistical methods to assess water quality degradation and its implications in the Upper Awash River. Thirteen parameters were examined by collecting water samples from five sampling sites from May to October 2021. Our findings showed that most parameters in the Upper Awash River basin exhibited spatial variation with the level of human activity. BOD ranged from 15 to 128 mg/L, turbidity ranged from 22 to 381 NTU and phosphate ranged from 0.9 to 3.9 mg/L. The value calculated for the comprehensive pollution index (CPI) ranged from 0.93 to 18.74 and exceeded pollution thresholds (> 2.01) at all sites except the reference point. The river’s water quality varied from marginal to poor for irrigation with the mean CCME-WQI value of 48.6 (range: 41–60), with turbidity, phosphate, and ammonium identified as the key parameters impacting the index. The principal component analysis identified two primary pollutants including organic pollution and nutrient enrichment with 92.4% of the total variance explained. This shows the significant effect of wastewater effluent and agricultural runoff on the receiving streams in the Upper Awash River, a pattern consistent with trends documented in other rapidly developing regions worldwide. This was supported by the existing strong correlations between BOD and TDS and turbidity representing multiple wastewater sources in the system, while correlations between phosphate and nitrogen represent pollutants from shared agricultural sites. Our findings provide essential evidence on the degradation of the Upper Awash River. We recommend that wastewater treatment facilities minimize discharges of poorly treated wastewater into water bodies. In addition, the agricultural sector should improve the fertilizer management practices for the ongoing agricultural production system.