Hydro-geochemical analysis and quality evaluation of surface water in the Mamu River basin, southeastern Nigeria

Mamu basin is a major tributary of Anambra drainage basin and a reservoir for wastewater from agricultural and runoff processes within the basin. Water quality of the Mamu basin was evaluated to determine its suitability for potable water and agrarian uses. This study utilized 24 water samples collected during the rainy and dry season from the upstream and downstream segments of the sub basins within River Mamu. Hdyro-geochemical analytical results were employed in the evaluation of several water quality criteria such as QWI, SAR, TH, SSP, MAR, PI, KR, Na% and %E of the water from the basin. The results suggested that the surface water is unfit for ingestion when compared with the WHO and Standard Organization of Nigeria (SON) standards. However, the QWI result showed that 66.7% of the water samples are good for consumption in the rainy season, while 75% of the samples are classified unfit for drinking in the dry season. Parameters such as Fe²⁺, Mn²⁺, TDS, temperature and total coliform (p < 0.001) exhibited temporal variation unlike pH, EC, Ce, Ca²⁺, Mg²⁺, Cl⁻, K + , NO₃, PO₄³⁻, Na⁺, HCO₃⁻, Zn²⁺, TSS, SO₄, DO, BOD and turbidity which showed no response to season. Based on the results of SAR, TH, SSP, PI, KR, Na% and US salinity plots, the surface water is suitable for irrigation. Conversely, the MAR and %E results pointed out that water treatment is vital before use. The basin water is associated with permanent hardness due to CaCl₂ coupled with the dominance of Mg²⁺ and SO₄²⁻. Gibbs plots and Stiff diagram showed that geology and dissolution process have an influence on the water chemistry via weathering and rock–mineral interactions, while chemical ratios and correlation coefficients (R²) point on anthropogenic activities.