Assessment of water quality for irrigation in the Keta wetland using ionic ratios and irrigation indices

Coastal wetlands provide rich ecosystems that support both biodiversity and human communities, with approximately 40 % of the global human population depending on their water resources for irrigation and other duties. The study’s main objective was to assess the quality of water resources in the Keta Wetland Complex (KWC) for irrigation for the betterment of local populations who primarily rely on these resources for agricultural purposes. Physicochemical parameters (Electrical Conductivity (EC), Total Dissolved Solids (TDS), pH, alkalinity, and Total Hardness (TH) and major ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, NO₃⁻, Cl⁻, HCO₃⁻, and SO₄²-) were conjunctively investigated for the study. For both groundwater (GW) and surface water (SW) sources, the most prevalent cation and anion were the ions Na⁺ and Cl⁻, indicating the influence of salinity. Seawater intrusion and geological processes were found as the major causes of elevated levels of TDS, TH, EC and some major ions in water samples. In contrast, NO₃⁻ and Cl⁻ contents in water samples were attributable to anthropogenic pollution, though Cl⁻ had other contributing sources. Powerful conventional tools such as the Gibbs diagram, CAI-1 and CAI-2 chloroalkaline indices, and ionic ratios of Ca²⁺ + Mg²⁺ versus HCO₃⁻ + SO₄²- and Na⁺ versus Cl⁻ unveiled weathering, evaporation, and ion exchange processes as well as sea intrusion. Widely recognized metrics and ratios such as cation ratio of structural stability (CROSS), residual sodium carbonate (RSC), Kelly's ratio (KR), magnesium hazard or ratio (MH), permeability index (PI), salinity hazard (SH/EC), sodium adsorption ratio (SAR), and soluble sodium percentage (%Na) revealed water suitability challenges for irrigation. The United States Salinity (USSL) diagram classified a few of the water sources (3.27 % GW and 27.77 % SW) respectively as unsuitable for irrigation due to high salinity levels. Principal Component Analysis (PCA) highlighted potential contamination processes and sources, including salt intrusion, evaporite dissolution, mineral weathering, and human activities. The Geographic Information System mapping tool was effectively utilised to show spatial trends and identify areas of concern. The study provides current information on the quality of water in the Keta Wetland Complex and would inform pragmatic management measures.