Seasonal effects on surface water quality in the Awetu River, Ethiopia

Abstract

Understanding the impact of seasonal variation on surface water provides a better understanding of pollution dynamics and the implementation of sustainable water-use and management strategies. The objective of this study was to assess the impact of seasonal variation on surface water quality. Water samples were collected from 14 sampling locations from the upper to the lower stream of the Awetu River in Ethiopia in the dry and wet seasons. Temperature, turbidity, electrical conductivity (EC), dissolved oxygen (DO), pH, chemical oxygen demand (COD), biological oxygen demand (BOD), nitrates, phosphates, total dissolved solids (TDS), total suspended solids (TSS) and faecal coliforms (FC) were compared across the two seasons. Average values for temperature (24.24 °C, 22.18 °C), turbidity (47.09 NTU, 645.9 NTU), EC (164.9 S m⁻¹, 90.64 S m⁻¹), DO (3.44 mg l⁻¹, 5.49 mg l⁻¹), pH (6.99, 6.73), COD (913.21 mg l⁻¹, 732.7 mg l⁻¹), BOD₅ (726.67 mg l⁻¹, 546.2 mg l⁻¹), nitrates (0.066 mg l⁻¹, 0.053 mg l⁻¹), phosphates (0.356 mg l⁻¹, 0.584 mg l⁻¹), TDS (935 mg l⁻¹, 252.4 mg l⁻¹), TSS (161.51 mg l⁻¹, 271.14 mg l⁻¹), and FC (1 387.14 CFU ml⁻¹, 4 025 CFU ml⁻¹) were recorded in the dry and wet seasons, respectively. Temperature, EC, DO, pH, COD, BOD₅, TDS and nitrates recorded higher averages in the dry season, compared to the wet season; whereas higher levels were recorded for turbidity, phosphates, TSS and FC in the wet season, with concentrations in the desirable range for the latter three parameters. The findings of the study show that the river is less polluted in the wet season than in the dry season. Focusing on point source pollution management, prevention and control are important consideration in reducing high rates of point source pollution in the dry season. This study provides valuable data on the effects of season on surface water quality, with Awetu River as a case study, and further motivates stakeholders in updating their management strategies promoting improved water quality.