Seasonal Groundwater Quality and Hydrogeochemical Assessment in Idemili South and Nnewi North, Anambra State, Nigeria

Abstract

Understanding seasonal variations in groundwater chemistry is crucial for sustainable water resource management and agricultural planning. This study presents a comprehensive assessment of groundwater quality and hydrogeochemical processes in Idemili South and Nnewi North of Anambra State, Southeastern, Nigeria, across dry and rainy seasons. A total of 48 groundwater samples were analysed for major cations (Ca²⁺, Mg²⁺, Na⁺, K⁺), anions (HCO₃⁻, Cl⁻, SO₄²⁻), pH, electrical conductivity (EC), total dissolved solids (TDS), and minor constituents (NO₃⁻, Fe). Hydrochemical facies were characterized using Piper, Durov, Schoeller, ionic plots, and Stiff diagrams, and irrigation suitability was evaluated using Wilcox diagrams. Pearson correlation analyses elucidated interrelationships among water quality parameters, revealing the dominant geochemical controls. Results indicate that dry season groundwater is slightly acidic (mean pH 5.65) with low to moderate mineralization (mean TDS 162.2 mg/L), dominated by Na⁺ and HCO₃⁻ due to carbonate dissolution, silicate weathering, and ion exchange. Na-Cl waters exhibited medium to high salinity hazards, whereas most waters were suitable for irrigation based on low sodium adsorption ratios (SAR). During the rainy season, increased recharge led to higher TDS (mean 226.6 mg/L) and greater hydrochemical diversity, including Ca-HCO₃ and Na-SO₄ water types. Strong correlations among Ca²⁺, HCO₃⁻, and TDS indicate enhanced carbonate dissolution, while Na⁺ and SO₄²⁻ reflect silicate weathering and sulphate mineral contributions. Notably, Na-Cl and Na-SO₄ waters pose significant salinity risks for irrigation. These findings provide critical insights into seasonal hydrogeochemical dynamics, guiding sustainable groundwater utilization and agricultural water management in regions with variable hydrological conditions.