Nutrients monitoring on the Bui multipurpose dam project in the Savannah region of Ghana

Abstract

Monitoring the nutrient levels of the dam water on the Bui hydropower project (Ghana) is vital for understanding its ecological health. The purpose of this study is to evaluate current (2021) nutrient levels and examine the irrigational water quality. The novelty of this research lies in the combination of nutrient analysis and irrigational water quality index (IWQI) as tool to understand the ecological health of the dam water. Bui dam water is slightly acidic (pH of 6.6) which partly influences nutrient bioavailability in the dam water. The composition of water in terms of ion dominance follow the order of ${Ca}^{2+}>{Na}^{+}>{Mg}^{2+}>K^{+}$ and that of anions followed the order of ${HCO}_3^{-}>{Cl}^{-}>{SO}_4^{2-}>{NO}_3^{-}$, with signatures of Ca²⁺- Mg²⁺- HCO₃^– water type. Pearson’s correlation plot shows pH, TDS, and EC influences sulphate distribution in the dam. EC mean level of 78.06 µS/cm is below acceptable ranges (150 and 500 µS/cm) known to sustain freshwater fish species (e.g., Alestidae, Anabantidae and Bagridae family) present in the Bui dam. Historical nitrate, phosphate and sulphate measured ${2.01mgL}^{-1}$, ${0.16mgL}^{-1}$ and ${20.96mgL}^{-1}$ as against ${0.79mgL}^{-1}$, ${0.60mgL}^{-1}$ and ${2.22mgL}^{-1}$ caused by the impoundment. The nutrient decrease shows improved water quality over time. The spatial plot shows low phosphate levels in the northwestern and southeastern part of the dam indicating rapid uptake and sediment trapping. IWQI shows the water has no toxicity risk for any plant. This study provides a basis for further monitoring to ensure the observed nutrient decrease is not altered by human-induced activities. Strengthening management policies is therefore encouraged to sustain the dam’s ecological health.