Assessment of Anwai river water quality using the weighted arithmetic water quality index (WQI) in Delta State, Nigeria

Abstract

The weighted arithmetic water quality index method was used to assess the water quality of anthropogenically-laden Anwai-river within the Asaba-capital territory of Delta State, Nigeria, in Stations 1(Otulu), 2(Isele- asagba) and 3(Anwai-Asaba) using pH, electrical conductivity (EC), total dissolved solids (TDS), biochemical oxygen demand (BOD), dissolved oxygen (DO), turbidity, phosphates, nitrates, total hardness (TH) and coliforms, to determine its water quality status and its suitability for humans and aquatic biota. Aside from TDS, turbidity, and TH, other parameters such as pH (5.3-8.2), DO (2.0-2.8 mg/L), BOD (1.02-2.4 mg/L), EC (110-113 µS/cm), turbidity(2.3-5.2 NTU), TDS (8.0-16.0 mg/L), TH (30-62 mg/L), phosphates (0.13-0.28 mg/L), nitrates (0.05-0.27 mg/L) and Coliform (25.75-45.5 cfu/ml) indicated non-significant variableness (p>0.05) between Stations. Water depth, TDS, turbidity, TH, phosphate, nitrate and total coliform were significant contributors to the Anwai-river's water quality by Principal component analysis (PCA). The first principal component (PC1) exhibited 94.1% variance and a 0.1860 loading factor, while the second showed 5.9% variance and 0.0117 loading factor implying depth, flooding, excessive human activities and sewage disposal as important contaminants. Although the individual physiochemical-based water qualities were below the WHO recommended drinking water values translated into poor water quality by the weighted arithmetic water quality index at the three Stations; 86.83, 75.02 and 81.27 in Station's 1, 2 and 3 respectively, correspondingly poor to very poor based on Water quality index. The water of Anwai-river is a serious health threat to humans and aquatic organisms and thus, it should not be utilized untreated.