Hydrochemical characterization and water quality indexing for sustainable agriculture: the case of Kibwe River, Karonga

While surface water is crucial for agricultural productivity, both natural and anthropogenic activities increasingly jeopardize its quality. This study provides an integrated hydrochemical characterization and water quality assessment to evaluate the suitability of the Kibwe River, located in Northern Malawi, for irrigation purposes. In accordance with standard American Public Health Association (APHA) protocols, 20 surface water samples were collected and analyzed for key physico-chemical parameters, including pH, electrical conductivity (EC), total dissolved solids (TDS), major cations (Na⁺, K⁺, Ca2⁺, Mg2⁺), and anions (Cl⁻, SO₄2⁻, NO₃⁻, PO₄3⁻, HCO₃⁻, CO₃2⁻). Essential metrics such as the sodium adsorption ratio (SAR), sodium percentage (Na%), permeability index (PI), magnesium adsorption ratio (MAR), Kelly’s ratio (KR), residual sodium carbonate (RSC), and potential salinity (PS) were employed to assess the quality of irrigation water. The water quality index (WQI) was calculated using 12 hydrochemical parameters to deliver a comprehensive quality assessment. The results indicate that all parameters were within the permitted range established by the Food and Agriculture Organization (FAO). All sampling locations exhibited excellent to good irrigation compatibility, as verified by SAR, Na%, MAR, and RSC values. The water was classified as excellent quality for irrigation, with a WQI value of 18.63. Statistically, Pearson’s correlation, Gibbs diagrams, and Stiff diagrams revealed significant connections among ionic constituents. It also demonstrated that both natural geochemical processes and anthropogenic factors influenced the river’s chemistry. This study emphasizes the necessity of regular hydrochemical monitoring to maintain agricultural productivity and offers critical baseline data for water resource management. It further underscores the appropriateness of Kibwe River water for irrigation and offers substantial guidance for regional irrigation strategies and environmental planning in similar agro-ecological zones.